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......---. - --- ----------- Energy Principles in Architectural Design 4 Legal Notice: This report was prepared as the result of work sponsored by the California Energy Commission. It does not necessarily represent the views of the Energy Commission, its employees, or the State of California. The Commission, the State of California, its employees, contractors, and subcontractors make no warranty, express or implied, and assume no legal liability for the information in this report; nor does any party represent that the use of this information will not infringe upon privately owned rights. , Energy Principles in Architectural Design Written and Illustrated by Edward Dean Shelley Dean and Fuller, Architects Architecture, Planning, Energy Consulting Oakland/Berkeley, California California Energy Commission In cooperation with The California Board of Architectural Examiners This book was prepared under a contract from the California Energy Commission, Conservation Division, 1111 Howe Avenue, Sacramento, California, 95825. First Printing: 1981, by the California Energy Commission. All rights reserved. Foreword This text was developed for the California Board of Architectural Examiners for use as a study guide by applicants for the California license to practice architecture. The intent of this book is to provide a foundation of basic information pertaining to design and energy use in buildings. The idea is that the reader will be able both to seek out more detailed texts in the various topic areas and to become aware of potential applications of new research and product development in the coming years. In accordance with this objective, the emphasis is on prin- ciples and concepts rather than applications of particular solutions. Energy is clearly an area of emerging possibilities in building design, and solutions that are appropriate or workable now are likely to be less attractive than future alternatives. We hope that the notion of this conceptual approach to energy and building design will encourage some architects to undertake the difficult reading in more technical texts and journals, and ultimately to make the kinds of needed contributions in this field that only architects can provide. v Acknowledgments To Hal Levin, member of the California Board of Architectural Examiners, whose personal energy and commitment to energyresponsive design led to the development of this book. To Sung Chough, D.C. Berkeley, for helping with some of the illustrations. To Eugene Mallette and Jose Martinez of the California Energy Commission for their timely support. VI To the members of AlA, CALBO, who reviewed the original manuscript and provided helpful suggestions. To Edward Allen, whose recent book, How Buildings Work, provided the excellent model for explaining technical concepts in a thoroughly understandable man~ nero To my associates, family and friends for their support and encouragement. Contents Foreword Acknowledgments 1. Fundamentals of Energy and Building Materials v VI Introduction 1 Energy Use and Power Demand Energy Transfer Mechanisms Energy Storage in Building Materials 2 6 20 2. Site Planning and Site Design Energy Energy Energy Energy Impacts Impacts Impacts Impacts of Landforms and Topography of Vegetation of Wind and Ventilation of Sun 24 25 26 27 3. Building Envelope Design General Passive Passive Passive Design Considerations Systems: Heating Systems: Cooling Systems: Lighting 31 38 49 50 4. Building Active Systems Design Heating Systems Cooling Systems HVAC Systems Lighting Systems Bibliography Index 59 64 66 71 73 83 1. Fundamentals of Energy and Building Materials In trod uction I I 1 I I I Before considering the technical aspects of energy use in buildings, it is important to understand that the demand for energy in buildings is not due to the characteristic design of the building envelope or the use of mechanical systems per se, but the users' subjective requirements for personal comfort. People control their thermal and lighting environments to suit their needs based on patterns of culture, geographic region, age and personal life style. Given a particular set of these social factors, variation in personal comfort requirements still occurs because of individual differences in activity and personal preference. The level of energy use in any building ultimately depends on the choices made by the people who occupy and operate it. TT nderstanding these variations iil user demand is important since the acceptable range of comfort variables establishes a certain design performance specification for the building. Often the designer can include a certain flexibility and local control of energy systems that allow for these variations, and which as a result help reduce overall energy consumption levels. Conditions that yield a comfortable environment involve a combination of several related variables that could be modified separately to maintain comfort.1-3 Thermal comfort, for example, depends primarily on air temperature, humidity, air movement 2-82231 1 and the temperature of the surfaces surrounding the person. The perceived comfort range of indoor air temperature can be enlarged by providing warm surfaces that reduce a person's heat loss to the surrounding environment. That is, people will find that they are comfortable at lower air temperatures if the surrounding surfaces are warmer. Likewise, for conditions of high air temperature people may feel comfortable if they are near cool surfaces. This expansion of the comfort zone, the range of temperature and humidity that most people experience as a comfortable condition, usually results in lower energy comsumption in the building. From an energy point of view, the building should generally be thought of as' a passive moderator of energy flows, designed to achieve the most comfortable conditions, both thermally and visually, for the particular user group and building program. This important point having been mentioned first, the remaining sections of this chapter treat the basic technical concepts of energy and building materials. Energy Use and Power Demand Energy is defined as the "capacity to do work", while power is the rate at which energy is used. For most building design applications, both energy use and power demand should be considered from the beginning of the design process. Energy appears in several forms-heat, light, electrical, mechanical etc., -and can be transferred or stored. Heat ~I 2 Heat energy can be stored in a material or transferred to another material by a variety of methods. The basic driving force behind all the mechanisms of heat transfer from one material to another is the temperature difference between the two. It should be remembered that temperature is not the measure of heat content of a material but, relative to a second object's temperature, is a measure of heat flow from one to the other. The units of temperature are either degrees Fahrenheit (OF) or degrees Centigrade (Dc) .. Heat will not spontaneously transfer from one material to another at higher temperature, so the direction of heat flow is always from the material at the higher temperature to the material at the lower temperature. In order to transfer heat to a material at a higher temperature, as in the case of a refrigeration machine or room air conditioner, energy from an external source must be applied. The units of measurement of heat energy are commonly the Btu and the kilojoule (metric). One Btu is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. (The kilojoule is approximately the same quantity of heat energy as the Btu: 1 kj = 0.95 Btu.) In one hour, for example, a 60-watt light bulb releases approximately 200 Btu of heat energy. Light Light has always been regarded as a principal element of architectural design, from both a visual and spatial point of view, and from a concern for user needs and user comfort. The need for energy conservation and control of peak electric power demand in buildings now requires a more careful consideration of the functional requirements of lighting, especially as daylighting techniques are integrated into lighting design. One major requirement is simply the amount of light available for a given visual task. Light energy is measured in lumens. One lumen is defined as the amount of light energy from a source of intensity one candela (1 candlepower), incident on a unit area at a unit distance from the source. The footcandle and the lux (metric) are measures of illumination. One footcandle is the amount of illumination provided by one lumen 1 footcandle 60 wntts j! of light energy incident on a onesquare-foot surface. One lux is equivalent to one lumen per square meter. (One footcandle is about the same as 10 lux, so the number of lux equivalent to a certain footcandle level can be determined by multiplying by 10. Therefore 50 fc is approximately 500 lux.) Visual comfort is a primary condition of the success of any lighting scheme designed to minimize electrical demand.4 The factors that determine visual comfort include not only the amount of light energy available for a specific visual task, but also the direction of the light relative to the eye, the brightness of objects surrounding the task object and within the field of view, and the surface reflectance and light-diffusing characteristics of the task object. 5 A good lighting design optimizes these factors for visual comfort, and can be expected to result in maximum energy conser- 100 footcandles 10,000 footcandles 3 vation as well. On the other hand, failure to control glare and other uncomfortable conditions can result in higher energy consumption levels than expected, since the user is likely to overcome light imbalances by using available electrical light sources. In short, energy conservation through efficient lighting design involves much more than simply prescribing "task lighting" or limiting the amount of light available per task. Indeed, these simplistic approaches are likely to be counterproductive in the absence of a total design approach. Power Energy Equivalences Energy Equivalences 1 Btu=0.293 watt-hr and Energy-Rate Equivalences Energy-Rate Equivalences 1 watt = 3.413 Btu/hr 3413 Btu = 1 kilowatt-hr 1 kilowatt = 3413 Btu/hr 100,000 Btu = 1 therm 1 horsepower = 3/4 Kw 1015 Btu = 1 quad 1 ton of refrigeration = 12,000 Btu/hr 4 The concept of the power demand of a building is an extremely important aspect of energyefficient design. Load management aspects of building design become more significant for larger buildings, and for utility service areas with "inverted" rate structures where the building owner is billed at successively higher rates for higher levels of peak electrical power demand. In these instances design strategies should have the objective of reducing both the energy consumption over the annual operation cycle of the building and the peak p0wer demand under peak load conditions. Power differs from energy in that power is the rate at which energy is used. In the metric system, the unit of power is the watt, and 1000 watts is equal to one kilowatt. The common unit of power in the English (American). system is the horsepower. One horsepower is equal to about 3/4 of a kilowatt. Design strategies that minimize electric power demand in buildings, and that avoid unnecessary use of electric power for heating and cooling in spite of the advantages of smaller initial costs or simpler installation of equipment, will provide a more energyefficient overall building stock. In the first place, utilizing "high quality" energy (electricity) for a "low quality" energy application (heating or cooling) is wasteful and inefficient. In addition, the "real" conversion efficiency of electric energy is low for these applications compared to alternative methods. Approximately twothirds of the energy used by a typical power plant to generate electricity for a modern California office building is lost as waste heat.5.7 Therefore, only one-third of the original energy available goes to heat and illuminate the building. This is a "real" efficiency of only about 33 percent. (This "typical" power plant is a weighted average of hydro, fossil, nuclear and geothermal power plants in California and represents the average conversion factor adopted by the California Energy Commission as part of the State Energy Conservation Standards. 7) Finally, the design effect of unnecessary electric power demand creates a supply problem that must be met, if possible, by capital investment in new power plants with the concomitant economic, social and environmental impacts. The advantage of initial cost savings by using electric heating should always be weighed against the serious disadvantages of higher operating cost, low conversion efficiency, and increased demand for capital investment in new power plants by California utilities. J I J,. I 5 Energy Transfer Mechanisms The Nature of Solar Energy mdicmt heat ~ I ,,-t '" ',i ;1 'j , 0.1 0.5 1.0 '-' 5.0 10 r-adio wO,ves-0 1 50 100 \Ncwe \enqth (millionths of'd mete-f) \/Isible radiant light heC1t }E->\ , ~, I I " " .", .. " ....' ' ' /' cI?ti1ysky , ...... . I ~ 0,1 1.0 . - .. ...I 10.0 Wavelength (m'dlionths ofa meter) The Solar Spectrum 6 I 100 The sun is an efficient source of heat and illumination for buildings, and is the single most important natural element to consider in building design. The problem for designers is that the amount of heat and light from the sun is much larger than necessary for comfortable conditions. In the past, the simple solution has been to exclude the solar input as much as possible and to rely on building systems for control of heating, ventilation and illumination. Now greater skill is demanded of the designer to utilize this free energy as much as possible. Solar energy arrives at the earth's surface at the rate of about 200 Btu/hr per square foot of surface perpendicular to the direction of the sun. This is equal to about 60 watts per square foot. This sunlight is in the form of radiant energy in a range of "wavelengths". That portion of the sunlight visible to the human eye is short-wave radiant energy. Thermal radiation (known as radiant heat) is long-wave radiant energy. About half of the energy in sunlight is visible light (short-wave radiant energy). This light energy amounts to about 7500 lumens at the earth's surface on a clear day. The ratio or the number of lumens produced by a light source to the power output in watts, a ratio known as the "efficacy" of the light source, is a measure of the efficiency of that source. For sunlight, the lumen/watt ratio is approximately 7500/60 = 120.8 By comparison, a 40-watt incandescent lamp produces about 480 lumens for an efficacy of 12, while a 40-watt fluorescent lamp can produce about 2640 lumens for an efficacy of 66. This means that fluorescent lamps are about five times as energy-efficient as incandescent lamps-that is, onefifth of the power wattage is required to provide the same bright- \\\ 11//// \\ \' \\",11//// cc-- [@:: ~s~ 1//1/ II / (III \\ \ \ \ \ \ \ ~ / /// 450 Iumens/ 40 ~ I WC1ttS 2640 lumens/4O worts ~// 5000 I! \ \\ \ \~, lumens/4O WC\tts ness level. Yet fluorescent lamps are only about half as efficient as the sun. The implication for designers is that daylighting, if properly done, will not only reduce electric energy consumption for lighting, but should minimize loads on air-conditioning equipment. In fact, in many situations the air conditioning load from daylighting should be less than that from a comparable fluorescent lighting system. Solar energy should therefore be thought of as both a heat source and a light source for buildings, although a variable one. When solar energy strikes building surfaces, certain energy flows and transformations occur. Energy flows in the environment involve a complex set of energy transfer mechanisms that interact to produce a given set of environmental conditions. The designer's task is to control and plan the combination of these interactions in order to produce a set of conditions that requires the least amount of outside energy for comfort. In order to manage this combinant energy flow, it is necessary to understand the characteristics of each of the individual heat transfer mechanisms, namely, radiation, convection, conduction and evaporation. 7 Thermal Radiation Absorptance and Reflectance of Common Ground Materials (expressed as fraction of total incident solar energy) 0.6 0.2 0.4 0.9-0.8 0.3 0.1 Reflectance 0.1-0.2 0.8 0.7 0.9 Absorptance .:;:.l;: 8 Thermal radiation is radiant heat, emitted by all warmed materials. The higher the temperature of a material, the more radiant heat is emitted. The warmth felt from an asphalt parking lot on a sunny day, from an ordinary campfire and so-called "body heat" are all examples of thermal radiation. The amount of thermal radiation given off by a normally clothed person at rest is about 200 Btu/hr, or the equivalent of the heat radiated by a 60-watt bulb. Thermal radiation is like light energy: incident radiant energy can be absorbed, reflected or transmitted by a material. The three material properties associated with these processes are, respectively, absorptance, reflectance and transmittance. The absorptance is the fraction of incident energy that is captured and causes a temperature increase of the material. The reflectance is the fraction that is deflected at the surface of the material and causes no change in temperature. The transmittance is the fraction that passes through the material and has no effect on the material. The sum of these fractions must equal 1.0 since all the incident energy must be absorbed, reflected or transmitted. An important fact is that these fractions can have different values for different wavelenths of radiant energy. Whitepainted surfaces, for instance, have a very low absorptance of short-wave solar energy but a very high absorptance of long- . wave radiant heat. By definition opaque materials have a transmittance equal to zero, so any energy not reflected is absorbed. The accompanying table lists some common ground and building materials and gives their absorptance and reflectance characteristics for solar energy. Ground materials near buildings with a high absorptance for solar energy and a relatively low thermal capacity, such as black asphalt, will cause heat to accumu- I I 1 ) late around buildings. On the other hand, material such as grassy soil and plants, which have some reflective characteristics and a higher thermal capacity, will keep air temperatures down around buildings and provide some additional free humidity. An additional property of construction materials, known as emittance, is a measure of the ability of a material to radiate heat. For a specific wavelength of radiant energy the emittance is equal to the absorptance. The second table lists the absorptance, emittance and reflectance values for some common building materials for both short-wave solar energy (primarily visible light) and long-wave radiant heat. Some important facts about energy flow in buildings can be observed. Note, for instance, that most opaque building materials are absorptive. of solar energy unless deliberately light- or white-colored. In the latter case they become quite reflective of the sun's energy. This characteristic is desirable for building walls and roofs in the desert and valley regions of Black-painted Walls orptance) 0.85 0.50 0.90 0.80 0.10 0.45 0.40 0.05 00.90 .90 .10 .95 .20 0.10 0.20 0.60 0.15 0.50 0.90 0.55 Reflectance Reflectance Emittance Energy Characteristics Solar Energy i I ~ ~\\!/ ~ \ l// ~~_! ·"~~~UJ··· ~ // ~ ~ -./'" It;" high emmc:mce >.~ : high emittcmce ~ // ,/ ,/ // ~.~~~ low eml\rance Radiant Heo.t high absorptqnce low obsorptance Sola, Energy Heat ofRadiant the Surfaces of Common Building Materials 9 block California, but not necessarily in the coastal areas and other climatic regions where significant heating may be required. In these regions the material on the surface of the south wall should have a dark-colored surface for maximum solar absorption in winter. Another feature is that whitepainted surfaces and black-painted surfaces have the same emittance values for long-wave radiant heat. Therefore, the interior surfaces of masswall passive systems (described in chapter 4) can be painted white without suppressing the radiation of heat. Likewise, in a hot climate where heating is not a maj"or concern, a white roof has the double advantage of having a high reflectance of the short-wave sunlight and, during the night when the sky is clear and relatively cold, of having a high emittance (0.9) of the long-wave radiant heat built up internally during the day. The latter process is known as nocturnal radiation cooling. A further observation in this regard is that the emittance of po- lished metal surfaces remains low for both solar energy and radiant heat. Such materials used on roofs, for instance, tend to suppress radiant heat loss to the sky, an important concern in areas of clear, cold winter climate conditions. Glass is a material that is generally highly transmissive of short-wave solar radiation (visible light), although absorption and reflection also take place to a small degree. However, glass has a remarkable property relative to long-wave thermal radiation-that the transmittance for thermal radiation is zero and the absorption is practically equal to one. This characteristic is illustrated in the accompanying figure which shows the transmittance of glass for different wavelengths of radiant energy, and the wavelength spectrum of both incident solar energy and a hypothetical warmed building mass. The radiant heat emitted by the mass has wavelengths in the region where glass has zero transmittance. The phenomenon experienced as a re- 1~11111111111111111 10 ~ll ~IIIIIIII~IIII ~IIIIII!II! I1III1 , I I visible I( >',I rod iant hear ~light Jj;-' 16 Il 10 • 3> (j) oc £ E <f) c .~ L 0 .6 t- .7 .'5 A· o.~ 0.2 100 0./ o .£ .J 0.1 I 1.0 II 10 I 100 Wave\en~th (millionths a a meter) I ..". I 11 Hem-Absorbing 61055 Heat-Absorbing 61055 V::! Interior Clear 61055 Reflective GI055 Reflective 6\055 '!:! 12 Interior Clear 61055 suIt of this property of glass is commonly called the greenhouse effect. Short-wave solar energy is transmitted by glass and absorbed by a building's internal mass, which results in a temperature increase of the mass. The warmed mass then emits radiant heat that is not transmitted outwardly by the glass. As a consequence of this "heat trapping", the air in the building increases in temperature. The greenhouse effect is probably the most significant factor pertaining to energy consumption in buildings. In residential buildings, small non-residential buildings and in the perimeter zones of larger buildings in climates that require heating, sensible allowance of solar gain through design can greatly reduce the usual need for the consumption of energy for heating. Similarly, prevention of solar gain through architectural design during the cooling season can reduce the standard need for energy consumption for cooling in larger buildings. Other than clear glass, there are two principal types of glass that are commonly used in buildingsreflective glass and heat-absorbing glass. Heat-absorbing glass is more accurately described as lightabsorbing glass and appears gray or tinted. The absorbed sunlight heats the glass which then radiates thermal energy inside and outside the building. This reradiated thermal energy contributes significantly to solar heat gain. The effect can be mitigated, and a high performance glazing system can be obtained by adding an inner lite of clear glass. This double-glazed system, a type of insulating glass, reduces the heat gain by preventing ready transfer of the re-radiated thermal energy to the occupied space, and by reducing conduction heat gain. In general, the effectiveness of heatabsorbing glass is inferior to reflective glass for the purpose of shading solar radiation. Reflective glass typically appears to have a silvered or bronz- ed reflective quality and is highly effective in reducing solar gain. For the same reason involving the case of heat-absorbing glass, adding an inner lite of clear glass increases the energy performance of this glass system. In both cases, the effectiveness in blocking solar heat gain applies as well in winter as in summer. If solar heat can be used in the building during the heating season, in smaller buildings in most areas of the state, use of these treated glasses will have a disadvantageous effect over the course of the year. Other options, such as external shading devices with clear glass, will yield better overall performance in terms of energy consumption. For buildings and climates where some heating is required, the use of clear glazing on the south side of.buildings is preferable where solar control can be easily designed. Unprotected eastand west-facing glass should be avoided. If necessary, reflective glass would be a better choice than clear glass if overheating is to be prevented. Buildings with high internal loads may require no heating, even in cooler California climates. In such cases single lites of either heat-absorbing or reflective glass would be preferable to clear glazing for all glass areas. The ability of a particular type of glass to reduce the amount of solar energy transmitted is characterized by a quantity called the shading coefficient. The shading coefficient is defined as the ratio of the amount of solar energy . transmitted by a given type of glass to that transmitted by ordinary lI8-inch clear unshaded double-strength glass. The definition of the shading coefficient has been extended to include the reduction in solar transmission caused by various shading devices. The accompanying table lists typical values for the shading coefficient of some sample window systems. More complete listings are available in several reference manuals. 9-11 1.0 0.45 0.56 015 Shading Coefficients of Some Typical Window Systems Window System Shading Coefficient 1/8" DS Clear Unshaded Glass 1.00 w Inside dark roller shade completely drawn 0.80 Yi Inside dark venetian blind fully drawn 0.75 Yi Inside medium venetian blind fully drawn 0.65 Yi Dark-colored drapes fully drawn 0.58 Yi Average tree casting shade Yi Inside white venetian blind fully drawn 0.56 Yi Inside white roller shade fully drawn 0.41 Yi Light-colored drapes fully drawn 0.40 Yi Outside vertical fixed fins on east/west sides 0.31 Yi Outside canvas awning 0.25 Yi Overhang, continuous on south side 0.25 Yi Dense tree casting shade Yi Outside venetian blind Yi Outside moveable horizontal or vertical louvers 0.60-0.50 0.25-0.20 0.15 0.15-0.10 -.,,I Unshaded 1/4" Heat-Absorbing Glass (gray or other tints) 0.70~0.50 Unshaded 1/4" Reflective Glass 0.60-0.40 Unshaded Clear Glass Block 0.65 13 rr-rr •.•••.•---------------------- _ In general, one of the principal considerations in building design with regard to thermal radiation is its overall effect on user comfort. An environment that has a high level of radiant heat flow can achieve thermal comfort conditions at lower air temperatures, thereby allowing significant savings in winter fuel consumption. One of the major advantages of passive solar designs is the characteristic high levels of thermal radiation from solar-heated building surfaces. Well-insulated walls also actually increase the radiant environment by keeping the inside surfaces at a higher temperature. On the other hand, large areas of glass, can cause thermal discomfort in cold, cloudy or night condi- tions, and will result in higher levels of fuel consumption because of excessive radiant heat flow from the user to the large cold surface. For this reason, thoughtful passive design incorporates methods of insulating the user from these glazed areas under these conditions. Under summer conditions, the high radiant energy environment produced by inadequate solar control in the design of the building is likely to make thermal comfort difficult to achieve, even at lower air temperatures. Chilled air from an air conditioning system will generally not be adequate to provide comfort conditions where sunlight is admitted to the workspace and there is a high level of radiant heat flow. Convection and Conduction Thermal convection is the process in which heat is transferred from a fluid-air, water, etc.-to a solid, or vice-versa, by the motion of the fluid as the fluid comes in contact with the solid surface. For the purposes of this discussion, convection is included in the description of the process of conduction. Thermal conduction is the process in which heat is transfered through a solid material because of a difference in temperature of the surfaces of the material. A physical characteristic of all materials is the insulating property known as resistance. The thermal resistance of a uniform material of a given thickness corresponds to its relative ability to resist heat conduction. The accompanying table gives values of the resistance for several types of building materials. More complete lists appear in other references.12-15 The thermal resistance of building materials varies considerably, as demonstrated in the table. The materials with the lowest resistance to heat flow (high conductivity) are metals and glass (in the absence of insulating air films). Masonry materials and plasters also have low thermal resistance. 14 06 20 Masonry Wood 09 6bs5 4.:) Air Spaces (Reflective) Thermal Resistance of Some Typical Building Materials Thermal Resistance (Btu/hr-sq. ft. - °F)-1 5-1/2" Fiberglass Insulation 19.0 2" Sprayed Polyurethane 12.5 3-1/2" Fiberglass Insulation 11.0 2" Preformed Roof Insulation 5.6 8" Concrete Block, 2-core with vermiculite 5.0 I" Preformed Roof Insulation 2.8 Metal Door 2.5 Y:{ Urethane Foam Core (1-3/4") Solid Wood Door (1-1/2 ") 2.0 Storm Window (4" gap) 1.8 Glass Block (8" x 8" 1.8 X 4") Glass, Double Lite (1/4" gap) 1.5 Wood, Soft (3/4") 0.9 Glass, Single Lite 0.9 -Particleboard (5/8") 0.8 Brick, Common (3") 0.6 Plywood (1/2") 0.6 Concrete, Sand and Gravel Agg. (6") 0.6 Gypsum Board (1/2") 0.5 15 ;:r""'-~~~~------------------ Ij I~I~ I ~I{ Surfaces on 1.4 2.2 1.7 1.4 1.7 Both 4.6 1.3 1.1 Reflective Sides 0.90.7 0.6 0.8 2.7 Reflective on One on Side Thermal Only Resistance of Typical Air Spaces in Walls and Roofs Winter Non-Reflective ~~__ Wood has a moderate insulating property, with a resistance (R-value) equal to about 1.0 per inch. The most significant insulating material is air, and therefore any materials or construction that incorporate layers or pockets of trapped air will have high resistance to conductive heat flow. Glass, for instance, achieves an R-value of about 1.0 because of air films that adhere naturally to the surface. Two panes of.glass increase the resistance almost 100% simply because of the addition of a layer of air between the panes. Care should be taken, however, to control the width of the air space. The resistance of the air space increases as the width increases, up to about l/2 inch. Beyond this width there is no appreciable increase in resistance to conductive heat flow because of convective loops that occur within the air space. Insulating materials also generally have a high resistance because of trapped air between particles or fibers of the material. The thermal resistance of air spaces in a construction depends on the emittance of the surface on either side. Surfaces with low emittance (high reflectance) on either side of an air space significantly reduce the heat transfer from one surface to another across the air space by suppressing the thermal radiation. Since air is a natural insulator, this reduction produces a substantial increase in the thermal resistance of the overall assembly. The accompanying table gives the resistance values for some typical air spaces in1walls and roofs. A more complete listing can be found in the'standard references.16 The thermal resistance of surface air films is small but contributes to the overall thermal resistance of the construction assembly. Generally, walls and roofs that are highly textured have a higher natural thermal resistance due to the thick surface 16 + , I + I T i' - , air films that result than walls and roofs with slick surfaces. The amount of heat transferred through a building material by conduction is inversely proportional to the total resistance of the material, and directly proportional to the surface area and the temperature difference between inside and outside surfaces. The inverse of the total resistance of a particular assembly of materials is known as the overall heat transfer coefficient or the U-value. Various energy insulation standards prescribe upper limits on the U-values for walls, roofs and floors. 17,18 It is interesting to compare the overall conductive characteristics of some typical assemblies of building envelope construction. If a surface area of 100 square feet is assumed for each sample construction in the accompanying figure, then the rate of conductive heat loss for each degree of temperature difference is as indicated. Note that a double-glazed window has a conductive heat loss less than that of a six-inch concrete wall of the same area. The addition of an insulating shutter reduces the heat loss of the double-glazed window to one-fifth of the unshuttered window, making the window system almost equivalent to a well-insulated frame wall. When located on the south side of buildings that require heating, such a window system becomes an effective passive solar heat collector. Thermal bridges in certain types of construction assemblies can contribute to conductive heat loss through the building envelope. Concrete block walls, for instance, contain many thermal bridges even when the block cores are filled with loose insulation material. One solution is· to apply sheets of rigid insulation to the outside of the block. Wood frame walls also have bridging through the stud, but the effect is not as serious since wood is a fairly efficient insulating material. Metal windows are another example where thermal bridging can cause significant 4--82231 Air Film R= 0.7 Insulation Plywood R ~11.0 R= 0.6 R- 0.2 Sheetrock R = 0. 5 - Stucco Air Film O.L R: Tota! R-VQlue= /3.2U-value = \lRTotal = 0. 08 5inglePane 6"Concre,te 120 67 DaublsRAre 60 TriplePcme 36 DJuble-Pane 't! Shutter IL R-l\WG\11 B R-I'3 W:\II 5 Heat (Btu/hr-·fL()SS byfooConduction ~. ft.) 17 Therma! Bridge ot Exterior Fireplace Thermo I Bridge Sources of Infiltration 18 heat loss. Some manufacturers include thermal breaks in their window product design in order to improve the window's performance. Other types of thermal bridging occur where the total building envelope contains gaps in the insulating enclosure. Construction details that maintain the thermal integrity of the enclosure should be specified wherever possible. Joints of floor and wall, or wall and roof, as well as corners, are common problem areas. Masonry fireplaces located on an exterior wall also create a location for heat loss. Wherever possible, fireplaces should be located away from the insulating envelope of the building enclosure. A form of convective heat loss and heat gain in most buildings (those that are unpressurized) is infiltration. Air infiltration in houses generally accounts for about one-third of the total heat loss. For houses that are not weatherstripped, or which have other significant sources of air leakage, the figure can be much higher. Weatherstripping is required on all windows and doors by current state energy insulation standards. Infiltration can be reduced by the addition of a storm window in winter-a common practice in colder climates. Many window manufacturers offer both single-pane and insulating (doublepane) glass storm windows as part of their standard product. Other sources of infiltration can be more insidious. In houses with ventilated crawl spaces, for instance, outside air can enter the house in large quantitites through holes drilled for plumbing and electrical lines. Where possible, these leakage points to the crawl space should be caulked. Winter Summer Combined Effects of Radiation, Convection and Conduction , " _Because of the greenhouse effect and the high conductive heat loss characteristic of glass, it is important to consider the net energy impact of all the heat transfer mechanisms. There are three basic glass types relative to energy flow characteristics: clear, heat-absorbing and reflecting. The accompanying figures are based on research by the National Bureau of Standards19 and indicates, for a given input of solar energy, the proportional approximate energy flows and transformations caused by the glazing system for both summer and winter conditions. As stated earlier, a certain amount of incident solar energy is absorbed by the glass and emitted in the form of long-wave thermal radiation. Note that although heat-absorbing glass is effective in absorbing a substantial amount of incident solar energy, most of the absorbed energy is actually radiated into the conditioned space as heat during the summer, rendering its performance in summer only slightly better (10%-20%) than clear glass of the same thickness. Reflective glass, on the other hand, reflects incident solar energy at the surface, thereby reducing both the transmitted and re-radiated portions of solar heat gam. Combining various types of glass in a double-glazed system can provide dramatic improvements in reducing conductive losses and gains and, by greatly reducing the re-radiant gain, can enhance solar protection during the cooling season without significantly affecting daylight levels. As the accompanying figure shows, utilizing an inboard lite of clear glass and an outboard lite of heat-absorbing glass or reflective glass, either fixed or as a "storm window", can essentially halve the total solar gain compared to the treated glass alone. At the same time, the transmitted daylight is reduced only 10%. 2.4-7 215 onduction +17 Net Gain- 167 Net 6ain 239 Clear 81ass --- 5ummer -.-- Winter 25' 107 107 -52. Conduc.tion Net 6Qin: 102 Ner Hecn- Absorbing 6ain: 213 61QSS Winter Summer 2.47 75 75 ~-.-:;'> -52.. Conduction NetGain: 47 +17 Net 6ain: 144 Reflective 61Q55 Summer 2-47 -Heat-Absorbing Gloss -·Clear Glass 900 93 +6 CondLiction !\Jet Go in- 104 19 r rr,r , -~ --- Evaporation couPling with the incident solar Evaporation involves the change of state of a given fluid, usually water, from a liquid to a vapor state. This change of state requires an energy input from some source of heat which is then "cooled" by the process. Evaporative cooling as part of the building energy system has great energy saving potential for buildings in most California climates, and should be considered among the alternatives in the system design. Some passive cooling systems can utilize evaporation to improve performance.20 Some roof pond designs for climates where little or no heating is required expose the water directly to outside air conditions. The combined effects of evaporation and night radiant cooling provide sensible cooling for the space. In climates where some heating capability is required of the design, the water is enclosed under plastic or glass. During the cooling season the enclosed roof pond is then shaded and flooded with water to provide the evaporative cooling. energy. Technically, the thermal mass is defined as the amount of heat required to raise the temperature of that material by 1 degree Fahrenheit. The accompanying table shows the thermal mass per cubic foot of various building materials. Water, by far, has the greatest thermal mass per unit volume, and therefore stores a certain quantity of heat at a given temperature using a smaller volume, compared to other materials. One important point should be kept in mind concerning the practical use of thermal mass-thermal mass is effective only if its temperature changes, increasing during the day and decreasing at night. The insulating properties of a material can effectively prevent heat storage in that part of a block of the material that is away from the surface exposed to incident energy. For instance, thickened floor slabs in residential construction have limited usefulness in the daily charge/discharge cycle since the most significant temperature variations due to absorbed incident energy occur in the top few inches only. Furthermore, there is a time delay associated with conduction through the material, so that for thicker material the heat that penetrates beyond the top few inches may reappear at the surface after the discharge mode and when the mass is again charging. Thus beyond a depth where this effect begins to happen, typically 4 inches for brick and adobe and 7 inches for concrete,21 added material actually decreases performance. Theoretically, therefore, a thin layer of mass applied to many building surfaces if preferable to a concentrated mass. The advantage of thermal mass in passive heating is that the incident solar energy is prevented from overheating the air, while large amounts of energy are captured and stored in the material. This stored energy is released by the thermal mass at a later time Energy Storage in Building Materials Thermal Mass Indirect Coupling (Solar to Room Ad") Direct Coupl ing (Solar to Room Air) 20 In those climates and buildingtypes where some heating is required and the greenhouse effect can effectively be utilized, thermal mass is an important feature necessary to temper the immediate effect of solar gain and extend its useful heating beyond the daylight hours. The thermal mass absorbs either directly incident solar energy because of its designed exposure to the sun, or reradiated heat after the incident solar energy is absorbed by some other building surface. In the first case the room air is said to be indirectly couPled with the incident energy via the thermal mass, while in the second case the room air is described as having direct Thermal Mass of Building Materials (Btu/ of per Cubic Foot) Air Wood 0.018 25 20 29 18 63 weight) 7.5 gal.) in the form of radiant (long-wave) heat energy as its temperature rises above that of the surrounding objects in the building interior. Thermal mass can also be utilized for passive cooling in buildings with low internal heat gains by tempering peak outdoor temperature swings through absorption of external heat gains. The accompanying figure provides a qualitative sketch of the effect of thermal mass on indoor air temperature for several types of residential construction. The heat gained by the mass during the day must be dissipated at night by ventilation or by radiation of heat to a clear night sky. This technique is utilized in some vernacular architecture in various hot arid regions of the world. On the other hand, in larger buildings with sig- . nificant internal heat gains from lights and people, the thermal mass of the building structure itself can be used to absorb this heat during the day while maintaining comfort conditions.22 The mass must then be,purged mechanically using naturally cool outdoor air at night or evaporatively cooled night air. This technique is discussed more extensively in a later section. It should be emphasized that the practicality of these mechanisms depends very much on the climatic characteristics of the region of the state in which the 11me Lag No 11me Log Outdoor Air Temperoture Light Wood-Frclme HOlASe Hou5e with M055 Bermed House with MeAse, 46 ?j)0 Time of DAy Indoor "ThmperCAture VClriatron <~\ ~~~f I ./111 ,1111 IIIMIIIIIIII~IIIIII\llllllil!IIIIIIIIIIIIIIWiIIIIIII 111~[[il~ I~ 21 building is being built, as well as on cost characteristics and the effect on the functional elements of the building. Since these techniques have the potential of greatly reducing operating and peak power demand cost, their application should receive appropriate engineering and architectural study. Combined Effects of Thermal Mass and Insulation In order to optimize the dynamic thermal performance of a building, the appropriate blend of insulating materials and energy storage materials should be used in the design of the building enclosure. The use of mass in conjunction with insulation has demonstrated a significant improvement in the overall performance. However, the relative effectiveness depends, on (1) the severity of the climate and the characteristic daily outdoor temperature swing, (2) the amount of internal heat gain and solar gains, and (3) the position of the mass in relation to the insulation in the wall or roof construction. The accompanying figure indicates the relative effects of insulation and mass on the transmission of external heat gains to the building interior. Insulation basically reduces the instantaneous energy transmission with- Incident Energy -Wall Exterior (; AM G PM Time of cay Insulation 22 GfWI bAM G A'v1 lime of MOS5 GAM Doy out affecting the time of peak heat gain. Mass, on the other hand, delays the energy gain and spreads the transmission over a longer period of time, thereby shifting and reducing the peak heat gain. The total amount of energy transmitted, however, is essentially the same except for some reductions due to the limited insulating property of the material and some extra losses due to the time delay of transmission. When considering the overall building performance during daily and seasonal variations, several conclusions can be drawn concerning the combined use of mass and insulation.23 In residential construction, where internal loads are minimal, mass combined with insulation effectively reduces the heating requirement compared to insulation alone. That is, adding mass to the building envelope permits reduction in the R-value of the insulation without changing the annual heating requirements. For less severe climates, the use of mass in conjunction with insulation is even more effective in reducing heating requirements. In more extreme climates adding mass to the building envelope (other than in direct passive systems) has less of an effect, and a high level of insulation is required. The location of the mass layer in the wall or roof affects both the heating and cooling requirements. Locating the mass adjacent to the conditioned space, with the insulation layer adjacent to the exterior, results in significant energy savings compared with the reverse location of the mass layer relative to the insulation layer. A sandwich-type construction where the insulation is located between two mass layers is also an effective arrangement. Utilizing mass in this type cf construction also can, by the various techniques described in other sections, effectively reduce cooling loads in almost all types of buildings in all geographic locations. Notes for Chapter 1 1. V. Olgyay and A. Olgyay, Design with Climate, Princeton University Press (1973) Princeton, N.]., pp 14-23. 2. E. Allen, How Buildings Work, Oxford University Press (New York) 1980, pp 46-49. 3. American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), ASHRAE Handbook of Fundamentals, ASHRAE (1977) New York, pp. 8.1-8.18. 4. R. Hopkinson, Architectural Physics: Lighting, Her Majesty's Stationery Office (London) 1963, pp. 18-25. 5. J. Kaufmann (ed.), IE.5. Lighting Handbook' The Standard Lighting Guide, Fifth Edition, Illuminating Engineering Society (New York) 1972, pp. 2-6 to 2-11 and 2-18 to 2-26. 6. General Services Administration, Energy Conservation Design Guidelines for New Office Buildings, U.S. Govt. Printing Office, Washington, D.C., 1975, pp. 1-2 to 1-3. 7. California Energy Commission, Energy Conservation Design Manual for New Nonresidential Buildings, Division 2, p. 5.1.3. 8. Hopkinson, p. 19. 9. V Olgyay and A. Olgyay, pp. 67-71. ..." I J I 18. California Energy Commission, Energy Conservation Design Manual for New Residential Buildings, pp. 4.1-4.4. 19. S. Hastings and R. Crenshaw, "Window Design Strategies to Conserve Energy", Building Science Series 104, National Bureau of Standards (1977) Washington, D.C. 20. California Energy Commission, Passive Solar Handbook for California, June 1980. 21. U.S. Department of Energy, Passive Solar Design Handbook, Vol. 2, U.S. Government Printing Office, Washington, D.C., 1980, pp. 180-181. 22. C. Barnaby, E. Dean, D. NaIl et aI., "Utilizing the Thermal Mass of Structural Systems in Buildings for Energy Conservation and Peak Power Reduction," June 1980, Report to Lawrence Berkeley Laboratory by Shelley, Dean and Fuller, Architects, 4331 Piedmont Avenue, Oakland, CA 94611 and Berkeley Solar Group, 3026 Shattuck Avenue, Berkeley, CA 94703. 23. S. Goodwin and M. Catani, "The Effect of Mass on, Heating and Cooling Loads and on Insulation Requirements of Buildings in Different Climates", ASHRAE Transactions, 85, 1979. 10. ASHRAE, pp. 26.30-26.37. 11. California Energy Commission,pp. A.1.18, Table 3. 12. ASHRAE, pp. 22.11-22.17. 13. California'Energy Commission, pp. A.l.20, Table 4. 14. B. Anderson, Solar Energy-Fundamentals in Building Design, McGraw-Hill Book Co. (1977) New York, p. 338. 15. E. Mazria, The Passive Solar Energy Book, Rodale Publishing (1979),Emmaus, Pennsylvania, , pp.352-357. 16. ASHRAE, pp. 22.18-22.25. 17. California Energy Commission, pp. 4.1.1-4.1.11. 23 2. Site Planning and Site Design Effects on energy use from design decisions related to site planning cannot be measured directly in the final design. Because of the close relationship between the microclimate of the site and the thermal and lighting loads experienced by buildings, it is important to consider ways of utilizing and designing microclimatic effects to minimize these loads. For both large-scale and smallscale planning, the site elements which can effectively be utilized are landforms, vegetation, wind and sun. These elements can be combined to provide buildings with optimal solar effect, wind protection, ventilating breezes and advantageous local temperature and humidity. 0--------, C'. •.•• ;, '-'f ••• ,) I (;1 i, I I .••.• 24 -------~ ,) -,:,1 , , .. , . Energy Impacts of Landforms and Topography Landforms can be altered to provide protection from winter winds and to create sunny enclosures. In some applications, landforms and earth berms can be integrated to a certain extent with the building itself for both wind and thermal protection. For large-scale planning in areas requiring heating, the designer should keep in mind that southfacing slopes have the most advantages in terms of solar exposure, protection from northern winter winds and isolation from cold air settlement and movement at the base of major landforms. At higher elevations frost is more likely to occur at these bases of landforms and in depressions of relatively flat terrain, In areas requiring cooling only, the north slope is obviously advantageous because of the reduction in intensity of solar radiation (Btu per square foot). Maximum solar radiation is collected by ground surfaces that are perpendicular to the. sun's direction. Slopes closest to this perpendicular direction will receive the most intense solar radiation. Surfaces sloping away from the sun's direction, such as north-facing slopes, receive the least intensity.l A site surface that is tilted 10 degrees toward the south will receive the same solar impact and have the same basic microclimate as a flat site 6 degrees in latitude closer to the equator, all other conditions being equal. 2 Landforms also affect winds and breezes on both a large and small scale. In general, wind speeds are higher at the crest of a hill than on the leeward slope, and increase through any openings in the landform. Because cold air flows downhill in a sheet on open slopes at night, cold air pools may form if the flow is blocked by dense trees or man-made structures. A landform that blocks cooling breezes and provides a south-sloping surface will create a sun pocket, which is desirable in colder California climates. The same considerations apply for small-scale planning and site design. Orientation in relation to wind and sun is important in most California climates and most types of buildings. In sum, the best sites for optimum energy conservation opportunities have the correct solar orientation, limited vegetation coverage for solar access, protection from winter winds and no land depressions that could function as cold air pockets. Energy Impacts of Vegetation I "I' i J Vegetation can be used to control both winds and breezes and the ground surface reflectance near buildings. These are the most important uses of vegetation in terms of energy conservation. Plant material should be carefully selected so that there is no present or possible future interference with solar energy utilization. The density and ultimate height of trees should be controlled in relation to the solar angles of incidence and the desired degree of seasonal solar utilization. The use of certain ground materials can provide beneficialfea' tures for the site. Placing shaded lawns and vegetation on the windward side of buildings can increase the cooling capacity of prevailing summer breezes for naturally ventilated buildings. Asphalt surfaces and other heat-absorbing 5-82231 1111\\\\ 1 ! surfaces should be on the leeward side of the buildings to avoid heating these cooling breezes. Protection from winter winds is effectively achieved by landscaping with dense evergreen bushes and trees. Most cold winds come from the north, so northside planting of evergreens is desired. Cooling summer breezes originate from the south, requiring an absence of obstructions in this direction for smaller buildings capable of utilizing natural ventilation. Moderate and deciduous planting on the south side of buildings is preferable so that light shading can be produced by the planting in summer while admitting sun in winter. In this regard, a deciduous tree is a natural solar control element, although care should be taken to choose a native species whose leaf period closely matches the building's cooling season. Vegetation can also significantly 25 affect airflow through naturally ventilated buildings. The placement and type of planting and the configuration of the building will determine the airflow pattern, although the precise effect is often difficult to predict. 3 Energy Impacts of Wind and Ventilation Wind Loco \ Wind 5eeed as 0 PercenT of til~ Prevailing c=J Less Thcm 50% c=J 50'(, - GO'/~ r;·;o.:.;~~ GO % ITIIITI! 70'(, - 80% ~ BO% -90% _ 90';' -/00% ~ 100% - /106/, l1li liD'/' - /2D% - 70 °10 \0 5 0 5 \0 Distance from Wind 26 15 20 25 Barrier Feet The direct interaction of winds with the building is an important consideration in site planning. The principal objectives in designing this interaction are to minimize air infiltration during the heating season and to maximize natural ventilation during the cooling season when outside air temperatures are moderate. Air infiltration occurs because uneven pressure distribution around the building envelope causes air in high pressure areas to move through the building toward negative pressure areas on the leeward side. Since infiltration accounts for 20% to 50% of the heating load in most houses, it is important to design for this air movement. One effective design strategy is to arrange the configuration of the building or the collection of buildings to minimize these pressure differences to the fullest extent. A second method to reduce pressure on the windward side is to install wind barriers at an appropriate distance from the building. Wind barriers can reduce the infiltration 25% to 60%, depending on their design.4 The effectiveness of the windbreak depends on both the type' of windbreak and its location. Dense trees are most effective at a distance of about 5 times their height, and some protection can still occur up to a distance of 25 times the height. Solid barriers such as walls and fences have an effective protection range up to 10 times the barrier height, with the optimum range occurring at 3 to 5 times the barrier height5• Porous barriers, such as slatted fences, are even more effective windbreaks since turbulent eddys are not created. If trees are used as windbreaks, dense shrubbery, a low fence or a wall should be added to provide protection near the ground. This combination achieves the largest overall reduction in infiltration. In large buildings, where the air pressure around the building is greater in some places, the stack effect can create serious air infiltration problems. Internal pressurizing using the HV AC system reduces the severity of this situation. Effective natural ventilation, on the other hand, generally requires pressure differences and openings for the prevailing summer breeze on both the windward and leeward sides of the building. In residential design the increase of summer cooling breezes is desirable. A height difference between the air inlet and outlet locations helps induce this ventilation. An alternative is to utilize the stack effect and a gravity ventilator. This approach is useful if the building has inadequate openings on the outlet side due to minimized window area or earth berming. If the building is to be sited at an angle to the direction of the prevailing cooling breezes, then openings on the opposite sides provide the best internal airflow patterns. If the siting is perpendicular to the prevailing direction, then openings should be located on adjacent walls. Better airflow patterns result if the outlet opening is larger than the inlet openmg. I '"\- I I -J&. I L . Two facts should be remembered, however, when using natural ventilation as a cooling method. First, natural ventilation is effective only when the outside air temperature is low enough to produce the sensation of cooling. Secondly, natural ventilation in large buildings can be counterproductive if used improperly by the building occupant, and the result is unnecessary cooling loads that must be removed by the building's active or passive cool- ing system. The tradeoffs are the psychological cooling effect of individual control and the simple amenity of having an openable window. Energy Impact of Sun Of all micro climatic factors, the sun is the most predictable, and therefore most within control of the designer. The great importance of both- passive and active solar utilization in smaller buildings in most areas of California, and the need for solar protection for larger buildings, require that all building designers understand and design for sun movement. This understanding should be applied at both the site planning stage and during the detailed building design stages. ~ ~ ~n __ Regment lOll of ~ir move greatest 11! 27 ~ l!! _ L4 Lower- Lati tudes /' 28 Sun movement varies with latitude, generally having a lower midday position at the higher latitudes. There is also a large degree of variation during the year, as illustrated in the accompanying figure. When the sun is imagined as an object moving on a hemisperical sky, it rises in the southeast region of the sky in the winter, achieves a fairly low sun angle at noon, and sets in the southwest. On March 21 and September 21, the vernal and autumnal equinoxes, the sun rises due east and sets due west. During the summer the sun rises in the northeast region of the sky and sets in the northwest. The highest sun angle at noon occurs on June 21. The southerly orientation is preferred because the solar exposure is greatest overall and, because of the geometry of sun movement, most easily controlled. The solar impact from the easterly and westerly directions is severe in most cases because of the nearly perpendicular incidence angle, but the westerly sun is most extreme since this impact occurs after the building has absorbed heat all day. Therefore, even though solar movement is symmetrical about the north-south direction, an asymmetry results from the cumulative effect of solar energy absorbed by the building. Thus the same building, even in the Higher Latitudes absence of climatic variation, would be expected to have different facade designs for each principal orientation. Each of these might also be adjusted according to site latitude. The site microclimate and the amount of internal heat gain are additional energy considerations in facade design; these factors are treated in the next chapter. Sun movement considerations have some influence on site planning and site design decisions. In most California climates, houses and small buildings can utilize solar energy in a direct (passive) manner. There is usually a period of time during the year when solar protection is also essential. Therefore in siting buildings or groups of buildings, care should be taken to avoid shading of the structure during the period when solar utilization is desired, and to provide shade when cooling is ne~ cessary. The type and location of trees and other vegetation should be planned with this objective in mind. The solar access problem is particularly important for designers to consider in buildings that can use solar energy. 6,7,8 Solar access for a project can be analyzed, optimized and recorded as part of a regular site analysis and planning procedure. A variety of methods have been developed: " --------- ,<J,. I 1. Special on-site devices9,10,l1 that can be moved from point to point allow the designer to survey existing objects relative to inscribed sun paths for the entire year. These are useful to provide a rapid but complete check for unforeseen site conditions. 2. Site models can be constructed and studied using a "heliodon", a device that accepts architectural models and duplicates sun positions. Accuracy of the method depends on accuracy of the model, but the technique is convenient for evaluation of alternative site planning schemes. These devices are available commercially or can be constructed. 3. A graphical method has been developed,12 but its use is limited by the availability of the graphical charts. 4. Sun angle charts 13,14can be used to determine sun angles for direct plotting of shadows from existing objects onto a site map. The same charts can be used in conjunction with a "shading mask", a drawing generated onsite by the user that locates the extent of all site objects casting shadows for a specific point on the site. The methodology is described in detail in an other reference.1S The latter technique is useful in lieu of one of the devices mentioned above. The usual procedure in analyzing solar access is to consider December 21 between 9 am and 3 pm in particular, and to check the same time period at the beginning and ending of the heating season. A "solar envelope" can then be effectively created for the site that describes the region within which solar access is guaranteed for any building. Conversely, given a proposed building location, the height limits of nearby objects can be determined, and a "solar interference boundary" map created that guarantees solar access for that particular plan. Such solar-related aspects of site planning are an essential part of any effective energy efficiency and adaptability in the future. 50 lor Access Not Considered 60% Solar Solar Access Considered 78%50lar 5ubdivi.sion Site Plan for .solar Orientation So lor Interference Boundary Map 29 ,~{ '~ Notes for Chapter 2 1. See also E. Mazria, The Passive Solar Energy Book, Rodale Publishing (Emmaus, Pennsylvania) 1979, pp. 13-15. 2. G. Robinette (ed.), Landscape Planning for Energy Conservation, Environmental Design Press (Reston, VA) 1978. 3. California Energy Commission, Passive Solar Handbook for California, CEC Publications Unit (1111 Howe Avenue, Sacramento, CA) 1980, pp. 70-74. 4. G. Robinette, Plants, People and Environmental Quality, U.S. Government Printing Office, Washington, D.C., Stock No. 2405-0479, 1972, p. 71. 5. Ibid, pp. 75-84, and California Energy Commission, p. 70. 6. R. Knowles, "Solar Access and Urban Form", AlA Journal, February 1980, pp. 42-49. 7. T. Holzberlein, "Don't Let the Trees Make a Monkey Out of You", Proceedings of the Fourth Passive Solar Conference, Kansas City, Mo., 1979, p. 416. 8. Robinette, Footnote 2. 9. The Solar Pathfinder™ utilizes reflected images of site obstructions from the surface of a transparent dome. A quick tracing on the sun path chart provides a permanent record of the full year's solar patterns. (Solar Pathways, Inc., 3710 Highway 82, Glenwood Springs, Colorado, 81601) 10. The Solar Site Selector™ is a vertically-read tripodmounted device that utilizes a transparent surface etched with the year's sunpaths. Objects are viewed directly with the image of the sunpaths superimposed. (Solar Site Selector, Dept SA 5, 105 Rockwood Drive, Grass Valley, CA 95945). 11. A similar device is included in the publication, Solar For Your Present Home, published by the California Energy Commission and available through the Publications Unit, 1111 Howe Avenue, Sacramento, CA 95825. 30 12. B. Givoni, Man, Climate and Architecture, Elsevier Publishing Co. (1969) New York, pp. 197-204 (contributed by M. Milne, School of Architecture, UCLA). 13. Sun Angle Calculator is a kit available from Libbey-Owens-Ford Co., Merchandising Dept. P-1, 811 Madison Avenue, Toledo, Ohio 43695. 14. E. Mazria, pp. 302-322, includes mylar sun charts .. 15. Ibid, pp. 325-327. 3. Building Envelope Design The design of the building envelope is of the utmost interest and importance to the architect. Building enclosure design affects the users' perceptions of view, light and space. It also determines the formal visual esthetics. Optimizing the energy performance of the building will affect all of these impressions since it will affect the characteristics of the envelope. This thermal and lighting optimization is an essential part of the considerations surrounding these aspects of the envelope design. General Design Considerations An energy-conscious approach to the design of a building involves all aspects of the building from the planning concepts and program through the details of the energy systems. A deliberate effort will include a set of strategies, each of which may require the coordinated consideration of aspects not usually dealt with simultaneously. For instance, strategies of building lighting system operation for minimal energy use depends on the building envelope configuration and the building program as applied to space organization. The choice of a structural system may depend on a cooling system operation strategy that takes advantage of cool nighttime temperatures and the thermal mass of the structure. Where choices are possible, aspects such as these should be designed simultaneously so that the building as a whole system achieves optimal energy efficiency. The design of the building envelope, as a building subsystem, should be coordinated in the same manner. Opportunities can be created for the efficient operation of lighting, cooling and heating systems through design of the building skin for daylighting, natural ventilation, and solar control. Standard systems can be greatly augmented, or in some cases replaced, by envelope design features that collect, store and dissipate thermal energy in a controlled manner. These passive heating and passive cooling systems are discussed in some detail in this chapter. The building envelope features that principally determine energy Planning Factoro r • User Needs Enerqy 5trcrregi8s . Program 'Site Conditions · LegQ I Rffl/mts. ·Budget Building Systems 31 efficiency of the final design are: (1) configuration and orientation, (2) materials, (3) openings, and (4) the building section (component assembly). For any particular building project (in the absence of unusual site constraints), the appropriate design for each of these envelope features largely depends on the characteristic building'-type (archetype), the site climate, the thermal impact of the internal load (heat generated by people, lights and various kinds of equipment), and the size of the potential lighting demand. The characteristic of internal loads in a building is the primary reason why large buildings have very different thermal characteristics when compared to small buildings such as residences, and why envelope design strategies for energy conservation are necessarily different. Internal heat gains effectively shorten the heating season and lengthen the cooling season for the building's energy systems. A large building with a relatively small perimeter (a "deep" floor plan) will have large internal loads because of the need for extensive artificial lighting and the large building population. For the resulting extended cooling season in these types of buildings, the envelope design will involve more extensive solar control, preventing the potential additional heat gains Intern a I Load Dominated Envelope Dominated Perimeter Core 44, 100~ (7T/.) Cor-e 27. 000 57)600 Toto! 57,600rp Toto I 32 13,500 ¢ (2.3%) tII Perimeter- 30,600 ¢ (5~/0) qr (4770) from the sun. On the other hand, residential envelope design will exhibit the need in most climates to admit the low-angle sun in winter. Configuration and Orientation Envelope configuration determines potential solar and daylight accessibility and influences the heat loss/heat gain characteristic of the building. The latter can be adjusted for a given configuration by changing the insulating value of the envelope material, but the accessibility features are purely a function of the building configuration. For this reason the amount of solar heat and daylight that can be used in a particular building should be evaluated, and the appropriate configuration determined within the context of the space planning program. Buildings with large internal loads, as noted above, can require cooling even when outside air temperatures are low; year-round cooling system operation would not be uncommon. Solar accessibility in these cases is not a consideration, but minimizing solar impact is a major concern. If large internal loads are caused by so-called process energyl-that is, energy used for purposes other than comfort heating, cooling and lighting-then the building envelope configuration is not a crucial factor. Variations in outside conditions affect the lighting, heating and cooling systems to a relatively small degree, and the effects are even smaller still if the building is well-insulated and protected from the sun. However, if the large internal gains are the result of general lighting requirements, then the internalload can be greatly reduced by utilizing a high perimeter configuration that places the largest amount of floor area within 15 feet of glazing in an exterior wall and provides manual or automatic light controls. Perimeter heat gains and losses can be increased in this case, but generally the saving in lighting energy and the reduction in peak power demand due to daylighting sufficiently offsets the increase in perimeter heating and cooling loads. These increases are most sensitive to the amount and type of glazing, as well as the extent of solar control features, and these require the appropriate design refinements. Orientation is a factor in buildings with large internal loads insofar as the solar impact is minimized. If the internal heat gain is produced primarily by sources other than lights, for example, then an orientation and configuration that results in a large amount of north-facing glass may allow excess internal heat to leak from the building, thereby augmenting the cooling process. If the large internal heat gain is produced by lights only, reduction of this heat gain through daylighting can create a heating demand. In this case a configuration favoring the southern orientation of major glass areas may be desirable since the greatest degree of control over sunlight is possible, and the potential exists for some perimeter space heating if required. Each building project of this scale should be carefully evaluated in the early stages of design in order to select the most appropriate design concept. Natural ventilation is another possible factor in determining configuration and orientation in larger buildings. In order that natural ventilation be a reliable method of providing adequate fresh outside air to all parts of the building, the building should be no wider than about 40 feet, and the floor space should offer no obstructions to the passage of air across the building width. Therefore the building configurations that allow major potential energy savings through natural ventilation by permitting the normal mechanical ventilation system to shut down for periods of time are similar to those required for good daylighting design. ,A building could be designed 6-82231 uo o Envelope Heat Saine, .-J 07 C Internal HeatGains CS o U il WWIIIIIR L 3 4- 5 8 9 /0 II 12 J Time of Day Lorge Building - No Doyllghting uo o --1 01 c o o Envelope Heot60ins U Internol Heo16oins 8 9 10 II /2. I 2- 2) 4- 5 Time of Day Lorge Building - With DC\ylighting 40 feet 40 feet 33 N 34 for partial natural ventilation in that the perimeter spaces would have operable sash, allowing local introduction of outside air, but the standard interior zones would be mechanically ventilated. Real energy savings would be achieved only if this local introduction of outside ventilating air resulted in the reduction of the space heating or cooling load, or if the building system responded by limiting the heating or cooling energy supply to that space. The building configuration would not have any particular resultant form in the case of this partial natural ventilation, since only the perimeter is affected. Buildings with small internal loads are known as envelopedominated buildings. Residences and small office buildings fall into this category. The principal energy feature of these types of buildings is their close link with the outside climate. Because of this, orientation is a major consideration. The utilization or control of solar energy as it directly affects the small building's thermal balance is often best achieved by arranging the building so that most of the facade has north/south exposure rather than an east/west exposure. The latter orientation for the small building would result in overheating in the warmer part of the year and a lack of balance between the desired solar gain and conductive heat loss in the colder part of the year. For the larger building, the east/west exposure produces a difficult solar control problem. The north/south exposure provides the greatest opportunity for sun control, particularly for the small building and the house where the sun should be admitted to the building for a period of time in winter for most California climates, but excluded for a portion of the other seasons. ("North/south" is meant as a general orientation, and studies show that a variation in orientation for small buildings of 150 or 200 from true south has little effect on thermal performance.2) Materials Choice of envelope materials has a great impact on the admittance of thermal energy and on indoor space conditions. As discussed in Chapter 1, materials have both insulating and storage characteristics that respectively reduce the quantity of heat flow and delay its transfer. A good envelope design will incorporate both features in the most feasible and most energy efficient combination.3 In conventional buildings, the use of significant mass in the building envelope is beneficial in cold climates where sunshine is available and in hot climates where diurnal temperature variations are large and clear skies prevail. In the former case the mass should be inboard from the insulating layer of the envelope. In both cases the properties of storage and re-release of energy by the mass help to temper indoor conditions. (See Chapter 1.) Taken to the extreme of an envelope with "unlimited" mass, primarily underground or bermed buildings, large energy savings are possible if properly detailed with regard to insulation and glazing.4•s The cost-effectiveness of such an approach varies greatly with the individual design. Various passive systems utilize glass, insulation and mass in order to collect solar energy, store it as heat and release the energy in a controlled manner for space heating purposes. These systems are discussed in detail below. Openings Openings in the building envelope should be designed to facilitate thermal balance, daylighting and ventilation (where appropriate). Windows typically perform these functions, utilizing a wide range of design alternatives. The amount of opening desirable relative to climate, internal load and building configuration should be studied in the early design stages to ensure adoption of a favorable design concept. ,\ Heat Loss Reduced ISF 25F 32F 43F 57 F 1emperoture Isotherms Two Weill Insulation Openings for natural ventilation are a real user amenity that can result in energy savings if, as noted above, it is coordinated with BVAC operation. Most California climates are suitable for naturally ventilated buildings for at least a portion of the year. At other times of the year, ventilation with outside air must be minimized to avoid unnecessary heating or cooling loads. Site problems associated with excessive acoustical or air pollution problems may preclude natural ventilation when climatic conditions are favorable. These factors should be considered as well. Detoils4 / / / / """'''"' ··f~ I c=7 Building Section/ Component Assembly The refined design of the building envelope should combine structural materials, openings and other components to provide the optimum balance of thermal factors and, in the case of larger buildings, to produce comfortable daylighting conditions. Such an integrated approach presents challenging design problems requiring creative solutions at a level not previously demanded of architects. Passive heating, cooling and daylighting subsystems are treated in the following sections. Another particularly important component assembly is the envelope solar control feature. In almost every California climate it is necessary to manage the amount of sunlight being admitted to the building. As discussed above, residential buildings and smaller non-residential buildings usually will benefit from the admittance of sunlight during the heating season when thermal losses can be offset by solar gains. Most climates in the state also require protection of openings from direct solar gain for an extended period of time. In buildings where there would ordinarily be a significant lighting demand, the solar control design must also maximize diffuse light penetration while minimizing both direct and contrast glare. The design of sun-shading 35 ~ c5unshade Designfor '---------' Energy Balance SolC1r Doyl ight Internal ~ HeL1t Hear 6ains 6ains~ Conductive Heat Loss or 00 in JfMAMJ BAM?>\ 3350 62'i;s:j 9 ~2 37 54- 6S7i~ 10 34- 53:~ II 3744 12. 39 47 I 2.. 40 50 .•~. ;:17: 42. 53'~CJ t(7; '3 41 55 :cd.?S: 40 53 't{;.7$: 4- 4-1 •.•. I 7? 62.1Cii .~-?7~ 5 PM 3£> 9:J ;flpc7~ Buildinq-IY~ CI imate,-IYpe. A1 Enerqy Balance i=blnt Temperature Attctchments Envelope Shape, 36 , 'j"' Planting features of the building envelope depends on the criteria established for the periods of time for solar admittance and solar exclusion, and on the solar angles associated with each facade orientation for those times. The criteria for shading will depend on characteristics of local climate, the size and use of the building, and any specific thermal characteristics that strongly affect the energy performance of the building. In the early stages of design, the architect must make a general assessment of these factors, particularly the climatic characteristics, and establish an initial set of criteria for sun-shading design. As the design is further refined and the energy performance profile is established, the sun-shade design can be modified as necessary. A specific design methodology for solar control is described in the classic reference of this field6• Sun-shading can be accomplished by modifying the shape of the building envelope, by adding attachments, overhangs and louvers and by utilizing trees or planting. In general, since the sun is at its highest position at noon, horizontal-type devices are most appropriate for facades with a southerly orientation. The low-angle sun in morning and late afternoon requires a vertical-type sun-shading feature for the east- and westfacing elevations. A combination of horizontal and vertical elements would be required for orientations between south and east or west. Reduction of solar gain can be accomplished by the properties of the glass material used, but external sun-shading techniques are much more effective in protecting envelope openings from solar gain. In addition, heat-absorbing and reflective glass reject winter sun, while external shading can be designed. to admit winter sun while excluding summer sun. The Olgyay methodology for analyzing the design of a sun control feature utilizes plan and section drawings and the concept of the shading mask. Model studies Horizontal 5hading for South Orientation 37 , !'/..~..,-~. are very useful also, particularly when used in conjunction with a heliodon device to duplicate actual solar positions. An added advantage of model techniques is that the effect on daylighting can be approximately observed. The day lighting aspect of sunshading features is best treated through light-colored elements that obstruct direct sun but allow the glazing to "see" as much sky as possible. Generally, this means a design that is relatively porous for diffuse light. The reference cited above includes examples of such design. Passive Systems: Heating The design of the building envelope (walls, roof, floor) to capture, store and release solar energy in a controlled manner to 'provide comfortable conditions for people in the enclosed environment is known as passive solar design. Specific envelope subsystems or component assemblies that perform this function are usually refered to as passive systems. Active systems, which are treated in the next chapter, are generally thought of as environmental control systems that are separable from the actual building enclosure and which require mechanical components to transfer and release energy. Passive solar design has become recognized as the most effective technique to produce building designs that demand a minimum of non-renewable energy for the least additional cost. Buildings that employ passive solar concepts appear to be reliable, eminently livable and generally more comfortable. The direct involvement with the building enclosure places these energy systems under the control of the architect, creating new opportunities for architecture, as well as new responsibilities. The apparent simplicity of passive systems belies the subtle com- 38 plexity of the energy flows described in Chapter 1, which must be controlled and directed for good performance and a sound design. Because passive systems are integral with the building envelope, the materials and components must be carefully designed and balanced to provide both environmental comfort requirements and basic architectural amenities. General concepts and guidelines about passive system design and performance in smaller buildings have been well-formulated.7-15 A sound design can usually be developed if these recommendations are followed. Even so, an evaluation of the anticipated energy performance is often useful so that appropriate design improvements can be made if necessary. A number of performance evaluation methods are available for the small building, including tabular methods,16 programmable hand calculator methods 17.18and computer programs.19 In spite of their present usefulness in guiding design decisions, these evaluation tools are likely to become a less critical step in ensuring good passive design as experience with passive systems increases. The design analysis required for the small building should ultimately involve no more effort than the usual structural calculations. For larger buildings, experience with passive systems is limited. In addition, passive systems are most Hfective in envelope-dominated buildings and have much less impact on buildings that have significant internal loads. When applied to larger buildings, passive systems must be designed in response to the internal loads as well as the external sources of energy. Interaction with the lighting systems (daylight controls) becomes an additional factor as well. The engineering involved in buildings of this type is understandably beyond the scope usually experienced in design, and the energy performance evaluation of the overall design is essential as an integral part of each step of the design process. Many of the subsystems utilized in larger buildings are conceptually the same as those developed for smaller buildings. There are significant differences, however, in the applications with regard to sun control, collector and storage sizes and user operation. Designers should take great care in adapting residential passive systems to larger buildings. The following sections elaborate on some of the architectural concepts of passive heating systems that may be integrated with the overall building design. Although applicable to some larger buildings if modified and. carefully evaluated, the emphasis is on their application to smaller buildings. Quantitative methods are not discussed; consult the references16,19 for further information on this topic. General Concepts There are three basic categories of passive heating systems: (1) direct systems, (2) indirect systems, and (3) isolated systems. In direct systems the incident solar energy is allowed to penetrate the building envelope through openings to the interior of the building, where it is absorbed by the thermal storage mass (floor or walls), converted to heat, and gradually dispersed throughout the space. If the mass is located in one area so that it receives direct sunlight from the fenestration, it is called a concentrated. mass system. If the mass is distributed throughout the building's interior surfaces so that most of these surfaces absorb heat energy primarily by reradiation from directly sunlit surfaces, then the system is known as a distributedmass system. Indirect systems usually contain the energy collecting, storage and controlled-release functions in the building envelope. The thermal . wall system combines the basic elements of glazing and mass on south-facing walls. The sunlight penetrates the glazing, is absorbed by the massive wall interposed between the glazing and the conditioned space, and is converted to heat. The heat is then gradually released to the space by radiation and convection. The roof-pond system utilizes mass and insulation on the building's roof and functions in much the same way as the thermal wall. Isolated systems involve intercepting solar energy before it strikes the conditioned space enclosure, and controlling the rate of heat transfer from the passive system to the space. The usual application of this type of system is the attached greenhouse of sunspace. In this application the building consists of two basic thermal zones separated either by a massive wall or by movable doors or louvers. Direct System Thermo I WC111 System Direct Systems The direct system is probably the most interesting to the designer who is required to utilize essentially conventional building materials and techniques. The envelope is generally lightweight and heavily insulated, punctured by predominantly south-facing openings, and contains a large amount of mass in the interior. Aside from the extra mass and insulation, the direct system is basically a conventional building .with desirable orientation and window locatio~. There are, however, both technical issues and architectural issues that require careful refinement of this basic concept. The major technical concerns are quantity, distribution, material and color of the thermal mass; the number, type and orientation of glazings; the effect of lightweight objects; and the degree of temperature variation in the spaces. Proper design of the thermal mass is essential. As illustrated in Chapter 1, the mass is effective only if its temperature changes, increasing during the day and decreasing at night. The comfort level is affected since this tem- Roof Pond System Sunspace 39 I \ I TI i / i /\ Sou t h 40 /\ 32 TILO° .\ \ ~ perature swing of the mass must not cause an excessive swing in air temperature. Overheating is a major problem in many passive solar buildings. Enough mass must be provided to absorb excess solar energy during the day without a large space temperature swing, or without causing the user to ventilate the space and consequently lose the heat that might be stored for nighttime demand. Ventilation should ideally be used as a means of controlling overheating only in the spring and fall, when the vented heat is not likely to be needed at night. Because of the ineffectiveness of increasing mass thickness beyond a certain poinFo, thermal mass should be added elsewhere in a manner that maximizes the mass surface area exposed to the interior. A rule of thumb is that the mass should have a surface area equal to three times the solar glazing area21. The absolute amount of glazing required depends on the climate and the amount of solar heating desired. Simple guidelines for a large number of specific locations are available22. Once the solar glazing area is established, the required amount of thermal mass can be determined. A rule of thumb is that a thermal mass of 3.0 X S pounds of masonry or 0.6 X S pounds of water is recommended for each square foot of solar glazing, where S is the desired solar savings in percent. Thus a building that is to be 70% solar should have either 210 pounds of masonry or 42 pounds of water per square foot of solar glazing. The most effective location for heat storage materials is directly in the sun, or at least in the same zone that experiences direct solar gain. Concentrated-mass systems are generally designed in this manner. Obtaining direct exposure to sunlight is more difficult in distributed-mass systems because of the large surface area involved. Although it may be desirable to locate thermal mass in other areas (for cooling purposes, for example), only that mass in the direct gain zone will act as part of the passive solar heating system. Distributed-mass systems perform better than concentrated mass systems23 and provide a more thermally uniform living environment. Studies24 have shown that the location of the distributed mass on north, south, east or west walls does not affect performance. Walls are preferred to the floor because of the shielding effect of furniture and because the floor tends to be cooler than the room. Carpets thermally isolate the floor from the space to an even greater degree. The performance of the distributed mass system is enhanced by using some light-diffusing glass since energy is distributed more uniformly to the mass surfaces and allows a minimum thickness for the largest surface area of mass. All glazings should be double. Objects of low thermal capacity such as light-weight interior partitions or furniture can impair performance of a direct gain building if they receive direct sunlight and are darker in color. If these objects are light-colored, they can help redistribute the energy to the more massive elements. Orientation of the major glazing elements is a sensitive factor only if it deviates greatly from true south. The guideline is that solar glazing should have a bearing between 20 degrees east and 32 degrees west of true south.25 If the designer adheres to this generalization, the decrease in performance compared to the "optimum" orientation will always be less than 10%. The optimum orientation varies with site climate, but under normal climate patterns is not more than 150 to the west of true south. The slightly western orientation is preferred since heat stored in the afternoon is released during the very late night hours when a major part of the heating load occurs. In many California coastal locations frequent morning fog conditions in winter push the optimum orientation of solar glazing to 30 degrees west of true south since the largest solar gains occur in the afternoon Where possible, glazing systems should incorporate insulating shutters that can be used at night to reduce overall demand. The performance of passive solar systems increases dramatically26 when some form of night insulation is integrated into the design. In view of these technical considerations, there are several major architectural issues that arise which influence the design of direct gain systems. The success of direct systems depends largely on the manner in which the extra mass is handled. In a concentrated-mass system a large block of heavy material is inside the occupied space, usually near windows for direct exposure to sunlight. For a residence this occurs in the major living areas, so the desirability of having such large mass elements present should be considered. In a distributed-mass system the walls and partitions must be fairly massive, and their placement for space planning must be coordinated with their relation to sunlight and airflow. There is, therefore, an inherent lessening of spatial flexibility. A major architectural problem with direct systems is the effect on visual comfort caused by the large amount of sunlight admitted to the interior of the space. Direct glare can make passive solar buildings decidedly unpleasant for living and working. The large quantities of direct sunlight can also cause fading of fabric and furnishings. It is therefore desirable to plan the living spaces so that direct sunlight can be controlled in the primary use locations' while still permitting the mass to receive direct sunlight. Skylights or clerestories combined with the use of higher spaces is one approach to a solution. (Higher spaces develop heat stratification, but a low-speed fan will eliminate this problem. There is 41 also an advantage to higher spaces in improving natural ventilation since a greater distance between inlet and outlet vents is possible, enhancing the stack effect.) In addition to the potential direct glare problem, there can also 'be a problem of contrast glare if light is admitted to the building only from the south. In order to balance the light and illuminate other interior surfaces so that contrast glare is reduced, some openings should be placed in walls of other orientations. Another potential problem in direct passive solar residences is acoustical privacy. Because of the desirability of exposing massive surfaces in the interior environment to direct sunlight, as well as providing maximum throughventilation for cooling, open plans are frequently developed. Requirements for acoustical isolation should be considered. Odors transporting between spaces is often observed in such circumstances. Indirect Systems l Day :!iiilll!llllllllllllliilllliiliiiliiiliir!lllllllllllilllll~IIII!II~IIIIIIIIII~lIlllllllilllllI 11111111!1~1,1111111 c· Night 42 In indirect systems, the sunlight is absorbed and stored by a mass of material that is placed between the solar glazing and the conditioned space. The space is therefore partially enclosed by the thermal mass so that a strong thermal coupling is achieved. Typical applications of this concept are thermal walls and roof ponds. The thermal wall is masonry wall or a water wall that is darkcolored on the exterior side to allow solar collection during the day. At the end of the day the heat will have been conducted to the inside face of the wall and will be radiated to the adjacent space. Often the wall is vented to the space at the top and bottom to create a thermo siphon loop from the wall's exterior face. This venting keeps the wall surface cooler, allowing more efficient heat collection. However, if the wall is vented, unwanted cooling of the room can occur at night when air in contact with the cold glass cools and falls, reversing the thermosiphon and releasing heat to the outside. This is prevented by utilizing backdraft dampers in the vents. Heat delivered by the thermosiphon vents can be up to 30% of the total heat delivered by the system in 24 hours27, but this occurs only during the daytime. Thermosiphon vents are therefore most useful in colder climates that require maximum daytime heating. Most California climates are mild enough to permit elimination of this feature without seriously affecting the overall system performance. Water walls have a much lower thermal lag than masonry walls because of the higher conductance of water. Thermosiphon convective loops are therefore not necessary for water walls. The greater thermal mass of an equivalent volume of water also permits a thinner wall. . The use of insulation at night enhances the efficiency of the thermal wall and should be considered as an integral part of the design. Overheating is prevented by shading the glass and venting the space between the glass and the massive wall. In many California climates where heating is required in the spring but cooling is necessary in the fall for the same solar position, the shading must be adjustable or removable. The thermal wall can be directly utilized for cooling in many climates as well by pulling cool night air past the wall with small fans. The chilled mass of the wall will then absorb heat from the room during the following day. The sizing of the thermal wall has obvious cost and seismic design implications. Not only is the wall relatively expensive, but the space which it occupies is valuable. Studies28 have shown that energy performance increases markedly with increasing thermal storage mass up to a point where the mass is sufficient to carry 1111111!1111111111!111'1~"II:':II)IIIII'~;!i'!I"II:1II~!j!~il~II~lllmi' ~~I.qhtInsulqtion Aids Healing Performance illll~IIIIIIII!IIII~lilli!11111111111~i~~li!llllllllil1IIIIIIIIIIillll!lilllllllilli! ~ ~~ I~ II ,IIIIII~I Night Cooling of Thermal Wall 43 The roof-pond system operates in two positions, with the insulation panels covering the roof ponds and with the panels removed. When heating is required the panels are removed during the day to allow absorption of solar energy. At night the panels are moved into place covering the ponds, causing the collected solar energy to be released primarily to the interior space as radiant heat. During the cooling season the panels are kept in place during the day, preventing the absorption of solar energy. The large thermal mass of the ponds keeps the metal ceiling of the space cool, thereby creating a good absorbing surface for internal radiant heat created by space heat gains. At night, the panels are removed to allow the absorbed radiant heat to be dissipated to a clear night sky. If additional cooling is required the ponds can be flooded to increase heat loss by evaporation. Roof ponds usually produce much smaller diurnal space temperature swings than other passive systems because of the large ratio of mass surface area to room volume. Typical average values are 5 of to 8 of in summer and winter, and 3 of to 6 of in spring and fall30• The thermal performance of roof ponds has been measured and computational methods have been developed31, 32. The performance of schematic designs can be estimated using these engineering design tools, and the design adjusted accordingly. Parametric studies33 of roof pond designs in several California locations indicate that the area of the roof pond should be at least 30% of the floor area, and ideally should equal the total conditioned floor space. Greater pond area enhances overall performance. In addition, the thickness of the pond should be at least 4 inches, with thermal performance improving as the thickness increases up to 12 inches. The corresponding roof dead load will be 20 lbs. per sq. ft. for a 4-inch thickness and Winter 'u- [by Winter Night ,.-----u Summer Day Summer- Night 65 lbs. per sq. ft. for a 12-inch thickness. The insulation panels in existing applications have been constructed of 1.5 to 3 inches of expanded foam, with a module width of 8 to 12 feet. Several variations are possible in the basic design of the roof pond system that allow either heating or cooling to be emphasized as appropriate to the climate. For example, in climates where cooling only is desired, fixed shading of the pond in lieu of the movable insulation components permits evaporative cooling of the structure all day. The shading should prevent the sun from striking the pond and warming it. If the climate requires some heating so that the movable insulation panel system is required, but cooling remains a major concern, the cooling operation can be augmented by flooding the ponds 45 Roof Pond RodlClnt Ceiling Panel 46 during the cooling season. The additional evaporative cooling can be increased by using fans to force air over the flooded ponds below the closed insulation. If the climate requires heating primarily, then the movable insulation panels can be designed to act as reflectors when retracted from the ponds, thereby increasing the amount of solar energy collected. Architectural constraints are considerable for roof-pond systems. Costs can be quite high unless the system is designed to utilize a few simple components to perform these complex functions on a daily basis. Seismic design is important in a structure of this type and consideration should be given to the bracing of the supporting walls and their connections to the roof system. Roof pond systems are more demanding in regard to roof configuration, as well as the structural and modular integration of components. There must be planned storage spaces for the retracted insulation panels. A major constraint is that the roof must be flat and the building generally is required to be one-story so that all spaces can be radiantly coupled to the ponds through the ceiling. Two- and three-story buildings are conceptually possible if the water from the ponds is circulated to the lower floors and used in fan coil units or radiant ceiling panels. An advantage of the roof-pond system compared to other passive types is that the interior spaces need not have a specific orientation and partition location is not restricted in any way. Therefore there is much more flexibility in space planning. The building itself can also assume any configuration within the modular constraints of the system. Isolated Systems As a general classification, isolated systems collect solar energy outside the conditioned space and transfer the heat by convection as conditions dictate, The convection process is usually by natural air movement controlled by user-operated dampers, but can incorporate small fans controlled by thermostats. The sunspace or attached greenhouse is the most common type of isolated system34, The sunspace is an unconditioned space that collects solar energy during the day and acts as a buffer space between the inside and outside environments at night. If mass is added to the sunspace, less solar energy is wasted when heat is vented during the day due to excessive temperatures in the sunspace. The excess heat will be absorbed by the mass rather than the air in the sunspace, and will be prevented from increasing the air temperature. When the heat is released later, the sunspace essentially remains at warmer temperatures into the night, making it a more effective buffer. Basic designs include: (1) placing the mass directly in the space in a variety of forms; (2) utilizing the mass of the floor and the earth beneath it, properly insulated from the surrounding ground; (3) making the boundary wall between the sunspace and the conditioned space a massive wall, obtaining some performance behavior similar to the thermal wall; (4) placing the mass inside the conditioned space. The latter type of design has architectural advantages to be discussed below, but results in larger temperature swings in the sunspace. Generally the sunspace glazing area should be 10% to 50% of the conditioned floor area served, with the ratio of the actual sunspace floor area to its glazing area equal to 0.6 to 1.635, Care should be taken not to overglaze, as excessive heat loss on winter nights and summer overheating can result. Shading of sunspace glazing 111111!lllllllillll~I'1111111111111111111111111111111111111111'1111111111III1IIII11111111 Direct Hoot Loss Over-heating and Glore Wi thout Sunspace Controlled Hoot Gain Buffer- SpClceReduced Meat L055 With SunspClce Moss in Sunspace /' /' / / // / I /' ------------ Moss in Floor 47 - Mass in Common Wall Mass in Cond itloned Space He<At 48 Delivery by Greenhouse Fans and venting techniques are an essential part of the design to manage the overheating problem. Insulating panels or shutters are desirable to reduce nighttime heat loss and maintain higher temperatures in the sunspace. Since the suns pace roof receives the major impact of summer sun and very little winter sun, it is usually glazed over only a small portion, if at all. The west wall of the sunspace should be unglazed and well-insulated. For maximum solar collection the south glazing is sometimes tilted at an angle that emphasizes perpendicular incidence of winter sun angles. This tilting also ininimizes the roof area and therefore helps prevent overheating. Vertical south glazing is frequently preferred, however, since interior shades and insulating panels are easier to operate, and there is more usable space for the occcupant. Sunspace heat can be delivered to adjacent spaces through openable windows and doors, vents or thermostatically-controlled low wattage greenhouse fans. The latter devices respond to both a threshold temperature of the sunspace and the air temperature of the conditioned space, operating when the suns pace temperature exceeds the predetermined setpoint and the interior space calls for heat. There is also radiant heat supply if the intermediate wall is a thermal wall. The principal architectural issue associated with the sunspace is defining the use of the space and its integration with the rest of the building activities. If the sunspace is to function as an adjunct living space, then excessive air temperatures must be controlled and visual accessibility is probably desired. Glass doors provide easy physical and visual accessibility and a means of controlling convective heat transfer. As a solarium, the sunspace has the same glare problems as a direct system. However, people generally accept, or even welcome, these conditions in this type of space. If the space is to function for plant growing, excessive heat and uneven light must be avoided during the day and excessive heat loss at night must be curtailed. Interior mass and double-glazing are therefore necessary, and insulating panels for night use are recommended if the growing season is to extend into winter. Translucent glass can be used to provide the even lighting needed for balanced plant growth. There are obviously many combinations of system-types possible. For a discussion of some of these possibilities, refer to the CalIfornia Passive Solar Handbook36• Passive Systems: Cooling Passive cooling systems involve the removal of heat energy from the occupied spaces by convection, radiation or evaporation. These mechanisms dissipate the energy to anyone of a number of possible heat sinks: the ground surrounding the building, the sky, the outside air, or mass within the building. As in the case of passive heating systems, the passive cooling systems can be classified as direct, indirect or isolated systems. Direct Systems Most California climates exhibit the characteristic that summer nighttime temperatures are low (55 OF to 65 OF frequently) even when daytime temperatures are quite high (85 OF to 100 OF). In such climates the use of night ventilation of the building's thermal mass can remove heat built up during the day and pre-chill the mass for the next day's cooling load. This direct system utilizes building envelope fenestration, and occasionally can be augmented by a house-venting fan if normal breezes are insufficient. The distributed-mass system works best for cooling since a greater surface area of mass is exposed to the chilled night air. An Insubting Shutters / Limited Roof 610zing / Double-Pane Diffusing 6lass Sunsp(x~ for Food Production-. important factor for successful performance is that windows and skylights be shaded so that the cooling load experienced during the day does not exceed the capacity of the thermal mass and prevent it from being chilled to a sufficiently low temperature at night. The architectural issues for direct systems involve spatial flexibility, acoustical privacy and odor propagation; these are discussed in the previous section on passive heating systems. 1111111111111111111111111111111111111111111111111111 Night Ventilation Indirect Systems Roof pond systems utilize a clear night sky as a radiant heat sink in order to cool the building structure. This system utilizes the same operation of components, phased differently on a daily basis, to achieve both heating in winter and cooling in summer. This operation is described in the discussion of roof pond systems in the previous section. Modification of the system to emphasize the cooling aspects is also treated. For information on thermal performance analysis and construction details, consult the California Passive Solar Handbook. 37 Night Radiation Isolated Systems In addition to night air, night sky and the building mass, the 49 Passive Systems: Lighting Earth-Sink Cooling ground itself can be used as a heat sink. The earth sink system utilizes· a network of noncorrosive air pipes under the ground, usually on the north side of the building, through which air is drawn into the building. Air passing through the buried pipe network is cooled since the ground temperature is stable at some conveniently low temperature (50 °-65 0). To provide cooling, the incoming cool air must be sufficient to balance the building's heat gains. Therefore the cooling load should be minimized by shading and by preventing infiltration. of warm outside air. In addition, the interior air that is exhausted so that the cooled air can be drawn into the building as makeup air should be vented near the top of the building to augment heat removal. This is usually done with a fan or gravity ventilator. A practical constraint on this system is the size of the site. The size of the earth sink field varies with the average cooling demand, the earth temperature and the soil conductivity. Other types of cooling techniques that do not involve the building envelope but contribute to energy conservation and reduction of peak power demand are discussed in the next chapter. 50 Natural lighting in buildings is a traditional architectural skill that is intrinsic to the making of space. Creation of a space means control of the light-control of openings, planes, textures, and colors. Control of light means control of the mood and the ambience. Well-lit spaces require sensitive integration of building elements to modify, filter, direct, screen, control or receive natural light. Designing with natural light means understanding and using its fundamental qualitative characteristics. In spite of its essential role in building design, natural lighting (or "day lighting") ceased to be a major consideration under the combined impacts of cheap electric energy, the invention of fluorescent lighting and air conditioning, and rising urban land costS.38 With the gradual disappearance of cheap energy and the need to consider the quantitative aspects of light, architects are turning their attention again to design for effective daylight. For the architectural profession it is a time of relearning old skills and development of related new methodologies and technologies. Referring to the natural lighting of buildings as a "passive system" is to emphasize the role of lighting based on a renewable energy source-a role that will assume greater importance as heating and cooling loads diminish as a percent of the overall building energy demand. There is also an implication of a new approach to daylighting through technology that will increase its efficiency in terms of distribution of light or the minimizing of the accompanying thermal loads. Although this is definitely part of the current trend, it is important to design for the qualitative as well as quantitative aspects of light, and for the user's role as well as the technology's role. In lighting more than in heating and cooling, the qualitative aspects and user response frequently govern the success or failure of a design in terms of energy savings. It is beyond the scope of this publication to treat completely the topic of good lighting design in architecture, and the reader is referenced to several books on the subject.39-44 The major points to be discussed here will simply be the lighting characteristics of the principal types of envelope openings, the impact of building configuration, and some new technologies for the distribution of daylight and the responsive control of electric lighting systems. General Concepts The importance of daylighting in saving energy and reducing peak power demand is treated in Chapter 1. As the design of larger buildings improves in thermal efficiency, the principal energy -consuming feature of new buildings will be the electric lighting systems. The demand for electric power in the middle of the day will then be determined primarily by the lighting load. Having adequate natural illumination without glare will allow great reductions in demand if the electric systems can respond in ways tolerable to the user. Therefore, three principal factors in any day lighting system are (1) adequate illumination, (2) glare control, and (3) responsive control systems for the electric lighting. Providing Adequate Illumination I J.. A major objective in any good daylighting system is to provide illumination at an adequate level over the largest possible area, and to make the most of the levels achhieved in terms of visual comfort and glare control. The amount of daylight illumination at any point in a space depends first of all on the amount of light available at the surface of the window. The light reaching the window has two sources: the sky and the surround. Direct:~:'L. .C!f1\gL::-r "... _'. '. .r-t Diffuse Skylight 51 Overcost Sky Clear Sky Sky Briqhtness Oisrribution5 ~ Maximize DGylight Aperture 50uth- FClcin9 Clerestories Exclude Sun/Admit Daylight 52 The sky is a source of reflected light from the sun. Different regions of the sky have different brightness levels, even on overcast days. Overcast skies vary in brightness by a ratio of three-toone, where the brightest region is at the zenith (directly overhead) and the dimmest region is at the horizon45• This condition remains constant all day and is independent of solar movement. Clear skies, by far the dominant condition in California, have a more pronounced variation (ten-to-one according to one model of sky brightness46), and a very different distribution of brightness. The brightest region is not surprisingly near the position of the sun, but the dimmest region of the sky is not at the horizon but rather in a region directly opposite the sun and at an angle of 900 from its position. The clear sky brightness distribution obviously varies during the day as the sun moves. The pronounced difference in light level from the morning to afternoon on a clear day for an eastfacing office illustrates this phenomenon. Another interesting consequence is that the northern sky is brighter on an overcast day than on a clear day. A basic guideline is that in order to maximize the daylight available at the surface of the window, the window should "see" as much sky as possible. That is, the window should sub tend the largest possible solid angle or aperture. The portion of sky "seen" should be the brightest portions on average over the day. If skies were predominantly overcast in a certain location, skylights might be the most effective in maximizing incident light from the sky. For most California locations where clear-sky conditions prevail, skylighting is still very effective, but the necessary solar control may substantially diminish the daylight levels because of the amount of sky blocked from view. South-facing clerestories or southfacing vertical glass in roof monitors may be the best solution, since the solar control can be designed to be out of view of the brightest portions of the sky while still providing shade from direct sun. The least desirable option for a building that requires heating in the absence of electric lamps is north-facing windows, clerestories or roof monitors. Because of the "dark spot" in the clear sky that generally remains in the northern sector as the sun makes its daily circuit, the north-facing glass "sees" the dimmest source of sky illumination. The result is a comparatively low level of illumination and an accompanying large heat loss. As pointed out in an earlier section of this chapter, for some buildings where heating is not a major issue (even without the contribution of electric lights) north-facing glass may actually provide a thermal balance as well as be a source of some daylight. The second source of light reaching the glass of a window is the surround. The surround is the field of view of non-sky objects outside the glass which reflect light toward it. This includes the ground around the building, nearby buildings, trees, and any screens and other intentionallydesigned sunlight reflectors. For overcast skies the surround is a dimmer source of illumination than the sky replaced by these obstructions, generally only about 10% of the sky illumination. However, clear skies produce just the reverse effect if the objects are illuminated from the brightest portion of the sky. Nearby walls of buildings or the ground below the glazing can be tremendous OverCQst Sky sources of illumination, brighter even than the sky. Care should be taken in these cases, and when light reflectors are used, that the quantity of light does not create glare problems or an imbalance of light which might result in the use of electric lights to correct the situation. A common device for daylighting interior spaces of large buildings is the atrium or courtyard. A window facing a courtyard space is basically surrounded by three obstructions to a complete view of the sky, with the lowest floor having the greatest obstruction of sky illumination. The smaller the courtyard, the smaller the portion of sky seen by the window. Courtyards should be as large as is practical and stepped back to increase the sky aperture of windows at the lowest level. For best day lighting, however, a "finger" scheme of building configuration is preferable to a courtyard scheme since a larger glazing area can achieve the maximum view of sky and consequently receive the highest level of sky illumination. Once the amount of light reaching the glazed openings in the building envelope has been maximized, the transmission of that light to locations in the space must be considered. Light quality and the direction of light relative to the activity locations become important architectural issues, but the distribution of the light and the illumination levels achieved at these locations are the major energy considerations. Cleo.r Sky Brightness of Surround 53 -- ~] ~j~11 ~j [101 ~.-.~~~.~.~.~~~~,....,-.~ .. ft Light Distributions "'.,' 54 .' Light from windows on one wall produces a distribution of light that drops off rapidly away from the glass surface. Under normal conditions a 50 footcandle level or higher is achieved only within 15 or 20 feet from the window.47 For a multistory building then, the maximum width for each floor should be about 40 feet for daylighting using sidelight only. For low-rise buildings that must be wider than 40 feet, top lighting using skylights or a courtyard scheme would be required to overcome the drop in the light distribution from windows. Because skylights "see" the brightest portions of the sky for the longest period of the day, light distribution in the space from skylights is significantly more uniform overall than from window sidelight. Major interior surfaces such as the walls and ceiling become secondary light sources in a space when washed with daylight, and have a major impact on the amount of light available away from the area near the window. Therefore the geometry of a room and the color of the walls affect daylight levels. Walls perpendicular to the window plane act as reflectors, and should be lightcolored; ceilings should always be white to reflect as much light downward as possible and to dispel any feeling of gloominess. Where possible, intermediate partitions should be glazed at least in the upper portion so that daylight can be shared with adjacent spaces. Design evaluation is possible utilizing a number of methods. The preferred method is through physical modeling of the space and direct observation or measurement. Light is scaleless, so an accurate study model placed in the sun will yield the exact distribution and quantity of light in the space for the given sky brightness conditions. For the model to be "accurate" for the daylighting studies, several requirements must be met, including accurate representation of the color and location of interior surfaces and the modeling of any external obstructions. The reader should refer to current publications48. 49 iri the area of physical modeling techniques for lighting design. Various calculation techniques50 and graphical methods51 are also available for design evaluation. The advantages of models are the accuracy obtained for relatively complex designs of openings and the effects of obstructions, the ease in studying alternatives, and the informing of the overall design concerning the qualitative aspects of the space. Glare Control Successful daylighting design requires consideration of user comfort, and therefore user response to designed lighting conditions. From an energy savings standpoint, a particular design succeeds if the user feels disposed to keep electric lamps turned off. Frequently, high daylight levels are achieved in a design, yet the light is so unbalanced or certain surfaces in the field of view are so bright that the user takes some action that reduces or eliminates the daylight conditions. There are many forms of glare that can create this problem. Bright sources of light in the field of view directly affect the ability to see. The best conditions for visual comfort occur when the visual task itself is somewhat brighter than the immediate surround. The glare effect of bright sources of light in the surround, known as disability glare, depends only on the intensity of the source. This intensity can be the same for a small source of high brightness or a large source of low brightness. Thus equal visual disability can be created by a small sunlit area on a neighboring building or by a large area of lowbrightness northern sky. In the first case, one common to urban locations, methods of reducing the intensity by screening the light without seriously decreasing the daylight level should be considered. In the second case, one not usually considered a potential problem by designers, the solution is to provide illumination of the interior surfaces adjacent to the window so that the "veil" of brightness from scattered light is overcome. Rather than have the user resort to electric lighting, a second daylight opening should be used to provide the proper balance. A simple solution in both cases would be to plan the space so that no one faces the daylight source, situated in his activities so the bright sources are out of the field of view and light is incident from the side. Another alternative is to make use of clerestory lighting that produces daylight penetration and good daylight levels while allowing the user to control glare at the window by using blinds or shades. Direct sunlight entering the space creates an obvious glare problem. Since control is necessary for thermal reasons, the best solution would either admit direct sun while diffusing the light without causing new disability glare' problems (for passive heating and lighting), or exclude direct sun while allowing diffuse sky light to penetrate. Sun shading design should incorporate these daylighting features in addition to direct sun control. A variation on clerestory lighting, known as the light shelf, can admit direct sun and bounce light deep into the space, diffusing it from the light shelf and the ceiling surface. This 55 system allows user control of glare at eye level, while still providing solar gain for heating and daylight penetratoin. Exterior devices that exclude direct sun but are very porous to diffuse light, such as the example in the accompanying figure, are preferred in cooling applications. Daylight Controls Winter 5un Summer Sun "Uqht Shelf" Concept No energy savings will result from daylighting unless electric lights are turned off or dimmed in response to available daylight levels. Light controls are therefore an essential part of any design. User control of on-off switches is the simplest approach, but frequently the least reliable. Photosensitive automatic on-off controls provide reliability and efficiency, but involve extra cost and risk user annoyance because of the sharp changes in light levels that occur during operation. Use of on-off controls shortens the life of fluorescent bulbs, but the savings in energy costs more than offset the added maintenance cost. The user acceptance problem can be mitigated by controlling individual fixtures rather than large areas of lights, and by using "multilevel" ballasts. Dimmable control systems, though more expensive than on-off controls, are more naturally linked with variation in daylight levels. Use of fluorescent ballasts that provide multilevel step dimming (in steps small enough to be regarded as essentially continuous dimming) is ultimately the best design solution52• Notes for Chapter 3 1. Division 2, ST20-1470(e), California Energy Conservation Standards for New Nonresidential Buildings. 2. U.S. Dept. of Energy, Passive .Solar Design Handbook, Vol. 2: Passive Solar Design Analysis, January 1980, p. 26. See also: Los Alamos Scientific Laboratory /Solar Energy Group, ERDA's Pacific Regional Solar Heating Handbook, 1976, p. 21. 56 ~ I ~- 3. S. Goodwin and M. Catani, op. cit., footnote 23, Chapter 1. 4. S. Campbell, The Underground House Book, Garden Way Publishing Co. (Charlotte, Vermont 05445) 1980. 5. Underground Space Center, Earth-Sheltered Housing Design: Guidelines, Examples and References, Van Nostrand Reinhold (New York) 1979. 6. A. Olgyay and V. Olgyay, Solar Control and Shading Devices, Princeton University Press (Princeton, N.].) Second Printing 1976. 7. U.S. Dept. of Energy, Passive Solar Design Handbook, Vol. 1: Passive Solar Design Concepts, January 1980. 8. California Energy Commission, Passive Solar Handbook for California CEC Publications Unit (1111 Howe Avenue, Sacramento, California 95826) 1980. 9. D. Watson, Designing & Building A Solar House, Garden Way Publishing Co., (Charlotte, Vermont 05445) 1977. 10. B Anderson, The Solar Home Book, Cheshire Books (Harrisville, NH) 1976. 11. E. Mazria, The Passive Solar Energy Book, Rodale Press (Emmaus, PA) 1979. 12. U.S. Dept. of HUD, Solar Dwelling Design Concepts, U.S. Government Printing Office (Washington, D.C.) Stock No. 023-000-00334-1, $2.30. 13. Sunset Books, Homeowner's Guide to Solar Heating, Lane Publishing Co. (Menlo Park, CA) 1979. 14. D. Wright, Natural Solar Architecture, A Passive Primer, Reinhold Publishing Co. (New York) 1978. 15. ]. Leckie et al., Other Homes and Garbage, Sierra Club Books (San Francisco, CA) 1975. 16. U.S. Dept of Energy, Passive Solar Design Handbook, Vol. 2: Passive Solar Design Analysis, January 1980. 17. D. Goldstein, M. Lokmanhekim and R. Clear, "Design Calculations for Passive Solar Buildings by a Programmable Hand Calculator", LBL-9371, Lawrence Berkeley Laboratory (Berkeley, CA 94720) August 1979. 18. Programs for programmable calculators include: • TEANET, Total Environmental Action, Inc., Church Hill, Harrisville, NH 04530. • PEG FIX and PEGFLOA T, Princeton Energy Group, 729 Alexander Road, Princeton, NJ 08540. • ST33, Solarcon, Inc., 607 Church Street, Ann Arbor, MI 48104. • SEEC VI, Solar Environmental Engineering Co., Inc., 2524 East Vine Drive, Fort Collins, CO 80522. 19. California Energy Commission, Passive Solar Handbook for California, CEC Publications Unit (1111 Howe Avenue, Sacramento, CA 95826) 1980. 20. U.S. Dept. of Energy, Vol 2, pp. 180-181. 21. Ibid., p. 49. 22. Ibid., pp. 20-29. 23. Ibid., pp. 66-76 and pp. 180-181. 24. W. Wray and]. Balcomb, "Sensitivity of Direct Gain Space Heating Performance to Fundamental Parameter Variations", Los Alamos Scientific Laboratory Report submitted to Solar Energy August 1978. 25. U.S. Dept. of Energy, Vol. 2, p.28. 26. Ibid., pp. 82-84. 27. California Energy Commission, p. 196. 28. U.S. Dept. of Energy, Vol. 2, pp. 89-97. 29. Ibid. 30. California Energy Commission, p. 231. 31. K. Haggard and P. Niles, "Modeling the Atascadero 57 House", in Proceedings of the Passive Solar Heating and Cooling Conference, Albuquerque, May 1976. 32. California Energy Commission, pp. 312-330. 33. Ibid., pp. 231-248. 34. See the California Passive Solar Handbook for a discussion of other, less common types. 35. California Energy Commission, pp. 284. 36. Ibid., pp. 299-303. 37. Ibid., pp. 233-258. 38. S. Selkowitz, "Effective Daylighting in Buildings", Parts 1 and 2, Lighting Design & Application, February and March 1979. 39. W. Lam, "Lighting for Architecture", Architectural Engineering/Environmental Control, R. Fisher (ed.), McGraw-Hill (New York) 1964, pp. 118-164 . 40. W. Lam, Perception and Lighting as Formgivers for Architecture, McGraw-Hill (New York) 1977. 41. R. Hopkinson and J. Kay, The Lighting of Buildings, Praeger (New York) 1969. 42. L. Larson, Lighting and Its Design, Whitney Library of Design (New York) 1964. 43. D. Phillips, Lighting in Architectural Design, McGraw-Hill (New York) 1964. 44. Progressive Architecture, Lighting Design Issue, 54:9, September 1973. 45. "Estimating Daylight in Buildings", Parts 1 and 2, Building Research Station Digest (Second Series), Her Majesty's Stationery Office (London) December 1963 and January 1964. 46. cm TechnicaLCommittee 4.2, "Standardization of Luminance Distribution in Clear Skies", cm Publication No. 22,Commission Internationale de l'Eclairage (Paris) 1973, p. 7. 47.D. Pritchard, Lighting, Environmental Physics Series, Second Edition, Longman Publishing Co. (New York) 1978, Chapter 6: 58 "Daylighting of Buildings". 48. B. Evans, "The Use of Models for Evaluation of Daylighting Design Alternatives", in Window Design Resource Package, Unit 8, Design Methods: Physical Models. 49. R. Hopkinson, Architectural Physics-Lighting, Her Majesty's Stationery Office (London) 1963, pp. 38-49. 50. Libbey-Owens-Ford Co., How to Predict Interior Daylight Illumination, LOF (Toledo, Ohio) 1976. 51. R. Hopkinson, op. cit., footnote 50, Chapter 3, pp. 50-84. 52. For further information see F. Rubinstein, "Strategies and Techniques for Lighting Control in Buildings", in Window Design Resource Package, Unit 10, Design Methods: SupPlementary Electric Lighting, Lawrence Berkeley .Laboratory, Berkeley, CA 94720, 1980. 4. Building Active System Design The mechanical energy system is the final major ingredient affecting the energy performance of the building. Whereas site and envelope design generally fall within the purview of the architect, the design of the mechanical energy system will likely be determined by the engineer. This is not to suggest that these tasks are independently carried out. It is of the utmost importance that architect and engineer work closely from the early stages of the design to develop appropriate interactive strategies to minimize energy consumption while providing environments that satisfy user needs and produce good architecture in every sense. The importance of the energy system increases with the size and complexity of the building. For residences and small buildings in certain California climates, perceptive design of site and envelope could alleviate the need for any mechanical energy system at all. For larger buildings where site and envelope are fixed by other considerations, careful design of the energy system features will be required to avoid unnecessary energy use. Heating Systems Heating systems can be characterized as warm-air or warm-water systems, or a combination of the two, depending on the medium of heat transport. In each case the fuel involved could be natural gas, solar, electricity, propane, wood (or some other similarly based organic material) or oil. The,heat energy can be produced by direct combustion or release in the building, or can be transported to the building as a by-product of some other process. In warm-air convective systems, the heated air must be delivered to each space, then returned to the heat source for reheating. This transport function can be done by direct natural convection, but is usually accomplished using ducts and fans. With the latter features, such heating systems are known as active systems. Warm-water systems, or "hydronic" systems, circulate heated water through pipes or tubing for either convective heating or radiant heating in the space. For the purpose of addressing some energy efficiency issues, three typical energy sources used in California are treated in the following sections. Heated Supply Air<2l~Combustion Burnem Fresh Return Air-qnd Air (;---' ~ Cutaway Exhaust 60S Supply ~ Vlew- Typica I fur-nace 59 Gas-fired Systems Supply Ducts Return Duct Combustion exhaust Gas-Fired Worm-Air Systern Reverse Return Expansion Tc:mk ~JL~. Combustion /'~Pump "" Boll e.r Convec,t"lve Warm-Water System Combustion Exhaust -- -. Expans"'onlank-Boiler Pump Radiant 60 Warm-Woter System Exh~u5t Gas-fired warm-air furnaces offer comparatively low first cost and use a relatively cheap fuel. There is some energy inefficiency intrinsic to its use of high quality energy (that is, a high temperature source of heat) for the low quality application of space heating. Continual on-off cycling of the system causes additional waste. A well insulated building envelope, and reduction of the heating load through passive solar means, will greatly reduce the onoff cycling and will increase the operating efficiency. An added disadvantage of forced-air furnace systems is that only air temperature is affected. Radiant heat and its role in human comfort are ignored. With some radiant heat component to the system, the same level of comfort could be achieved at lower thermostat setting, and hence at some savmgs m energy. To counteract drafts and to warm cold surfaces for comfort reasons, heat supply registers are usually placed near glass areas. For better efficiency, air returns can be placed high near southfacing glass areas in order to collect solar-heated air. This preheated air can then be distributed to the remainder of the house utilizing the furnace fan and supply registers away from the perimeter wall. With the furnace burner off, the forced air system can effectively augment passive heating of more conventional residences through distribution of the solar gams. Gas-fired warm water systems can be used in both convective and radiant applications. Any space warmed by the heating of its walls, floor or ceiling has a radiant heating system: As mentioned above, radiantly heated spaces are perceived to be more comfortable at lower air temperatures. While electrical radiant panels are usually installed in the ceiling, warm water radiant systems are typically floor installations. Warm water radiant sys- terns are, well suited to active solar heating. Electric Heating Systems I " Direct heating by electricity is known as electric resistance heating. The larger problems associated with electric resistance heating have been treated in Chapter 1. Because of these broader cost and efficiency issues, justification for its use on a cost-effective basis over gas-fired, solar or heat pump systems is required by the California Energy Standards for both residential and non-residential buildings. The heat pump is actually an electrically driven system that is an energy-efficient choice for both heating and cooling.4 The heat pump can either heat or cool using a standard mechanical refrigeration cycle. When air conditioning, the heat pump works basically the same way as a room air conditioning unit, removing heat from the room (the heat source) and transferring it outside the conditioned space (to the heat sink). The operation of the heat pump is more efficient if the heat sink is water or the ground rather than outside air. When heating, the heat pump works in reverse, taking heat energy from outside the conditioned space (even if the outside temperature is well below freezing) and transferring it into the room, which acts as the new heat sink. A heat pump can economically utilize the stored hot water of a small active solar system as the heat source in the cycle. Even if the solar storage is at a comparatively low temperature for heating, the solar energy collected by the system can be utilized to heat the space to the required temperature by the boosting action of the heat pump. This type of system is known as the solar-assisted heat Warm Airor Cool Air-Out Water Out Condenser- Cool Air- or Water In Compressor BasIc Re.friqerntion Cycle Warm Air to Hea r Sink r« Conc\enser Cool AI r from Heat Sink Compressor Air Summer Conditioner Coollnq or Hear- R.Jmp Cool Air tb Heat Source Evapomtor War-m Air from Heat Source pump. Active Solar Systems Active solar heating systems are ideally suited to providing the low-temperature heat energy re- Compressor Wi nter Heating Heat Pump- 61 r------------~~-l 5o\or Collector ~ I I I, : I II ~~~ I : J r I :~---------------~ LPump : Wo.rm Wo.ter 5toro.ge Compreocor Sobr-Assisted Hear Pump 6\ass Cover5 Distri butlon Auxiliary Water Wcoter 6.Jpply ..... :: ::::::::.,~. -storo.ge ..Auxiliary Spcoce Heater Active. 5010.r Heating Systems 62 He.Qter quired for space and water heating applications. The three main elements of a typical domestic solar heating system are the collector, the storage medium and the distribution system to the load. There are two basic types of collectors, the flat-Plate collector and the focusing collector. The focusing collector employs curved or multiple-point target reflectors or lenses to increase the intensity of solar radiation on a small area. Often a mechanism is employed to allow the collector/reflector to follow or track the sun's movement across the sky. In a flat-plate collector both direct beam and diffuse solar energy are absorbed by the absorber plate, and this energy is transferred to a fluid, usually air or an anti-freeze solution. Active solar systems therefore can be warm air or warm water heating systems, utilizing convective or radiant heat distribution, just as in conventional systems. Focusing collectors do not collect any more energy than a flatplate collector of the same basic area. Focusing collectors merely concentrate the energy, raising the temperature of the absorber higher than for a flat-plate collector. This higher temperature is necessary only in the case of solar cooling applications. Solar heating requires temperatures in the range of 90 of to 180 of, well within the range of standard flatplate collectors. Solar cooling requires temperatures of approximately 180 of to 230 of, difficult to achieve with regular flat-plate collectors. Heat storage is necessary if adequate heat is to be provided during those periods of little or no sunshine. The heated collection fluid is piped or ducted to the storage component where the heat is transferred to the storage medium, usually water for a liquid system or a rock-bed for an air system. Phase-change materials5 are also used as a storage medium in air systems, though passive ap- plications of these materials are more widespread. Since the thermal mass of a given volume of water is higher than that of masonry material,6 a smaller volume of water is required for storage of heat at a certain temperature as compared with the volume of rocks required for the same amount of energy. A general rule is to provide sufficient volume of storage medium for 11/2 days energy supply at the minimum required temperature. This is typically about 2 gallons of water or 2 cubic feet of stacked river rock, per square foot of collector. Accurate design and construction of rock-bed storage systems are described in detail in the references 7,8. The accompanying figures show schematic designs for solar warmair and warm-water space heating systems. Further details and a more complete description of active solar energy system design can be found in standard ref- HW Dis tri bullon Exr:msion lank Valves ~ Domestic HW ~ WcrtBr Supply "'\ Water Storc1ge Pumps liC1ry Heater 50br WC1rm-WC1terSystem erences9-10• The use of active solar heating systems involves aspects of lifecycle system cost since the initial cost is quite high, even though the fuel cost is zero. Therefore the extent and design of such systems are usually determined by economic constraints. In general, these systems provide heat energy to replace an equal amount that has leaked out of the structure by radiation, conduction and convection. Obviously the initial cost of the system can be minimized by reducing the heat loss characteristic of the building. Therefore economic application of active solar heating systems requires an energy-conserving building. It is generally cheaper to prevent the loss of 1 Btu, or to supply 1 Btu directly to the building from the sun, than it is to supply that Btu indirectly via an active solar heating system. Given a careful energy-conscious approach to the design of a building, there is still likely to be a heating load for small to mediumsized buildings in many California AuxillC1ry BackdlOft llimpBr5 Hwter Rockbed Storage Air Handling Unit " Motorized Domper5 Solar Warm-Air System locations. The characteristics of this heating load will depend on climatic and weather patterns for the site. Generally, the largest demand for space heating will occur in December and January, and the minimum demand will occur on the fringes of the heating season. If the active solar system is designed to meet the peak December space heating load, a large collection capacity is required. This capacity is essentially wasted at other times during the heating season, since only a small portion of the solar energy collected is used to offset the smaller heating load. The remaining energy collected must be dumped. 63 r r A 2DOO 5q ______ /(1500 5g A 1000 Scj Ft: 1500 ~.Ft Unused Energy Useful Energy .5ep~ oct-t:0y- [)e.c-Jan Feb Mar Apr May Energy Demond and Enerqy Supplied by Sok:\r, for Various Col rector Areas The most economic design (smallest initial cost per Btu used), therefore, is achieved by utilizing active solar to meet only the base space heating load for the heating season. The peak demand would be met in this case by a combination of the solar space heating system operating at full capacity and an auxiliary heating system. The usable heat provided by the active solar system per square foot of collector decreases as the size of the collector increases. A solar space heating system can be built up incrementally, so a practical strategy that responds to this performance characteristic of active solar heating systems is to provide an initial installation to meet the projected base load, along with space and flexibility to add to the system over time. Domestic water heating needs remain fairly constant over the entire year. Since this application of solar heating is generally the most cost-effective, every active solar system includes a basic capacity for this purpose. As described above, if a building has a demand for both space heating and cooling, a hybrid system of solar combined with heat pumps, the solar-assisted heat pump, may be a practical and economical use of the solar subsystem. Cooling Systems Water Distribution Piping Wetted Pods (Four Sides) Air In (FVurSides) ~I~ o Ai r D/suharge Fbd-lYpe Evopomtive 64 Cooler Cooling systems remove heat from a space to maintain comfortable air temperatures, and sometimes control air humidity as part of this process. The cooling can be done by radiant absorption, convection, and evaporation. Radiant absorption of heat is usually a characteristic mechanism of passive cooling systems (discussed in Chapter 3). Typical systems are roof ponds and massive walls. A technical term that describes the relative energy efficiency of electrically-driven cooling processes is the coefficient of perform- ance, or COP. The COP is defined as the rate of energy removal in Btu/hr divided by the power input in watts. Evaporative systems have a higher COP than standard air conditioners, and therefore are more energy-efficient. Because of the extra humidity introduced in such systems, evaporative coolers operate best in dry climates such as those common to most areas of California. Extra maintenance can be required because of deposits of lime on the copper screen or fungus growth on the fibrous pads. Regular cleaning or pad replacement will maintain the efficiency of the operation. Convective cooling is usually accomplished by passing room air over a cooling coil. The heat removed by the coil is transfered to a heat sink, usually outside air, by a mechanical refrigeration process. Mechanical refrigeration is described above in the section on heat pumps. In the figure accompanying that discussion, the three components are identified as the compressor, the condenser, and the evaporator. The compressor drives the cooling cycle, the condenser dumps the removed heat to the heat sink, and the evaporator absorbs heat from the room air. In large building applications the condenser is usually linked to a cooling tower, where the heat is transferred to the outside air. If the outside air is humid and warm, the efficiency of this heat transfer process is very low. In these large applications where the cooling coil is far from the main mechanical plant, the evaporator incorporates a piece of equipment know as the chiller. Reduction of the building's daytime cooling load not only results in lower operating cost, but can reduce the size of the chiller required thus saving on first cost. A technique of load management in larger buildings involves operating the chiller at night when the electrical demand on the utility is low, and storing the chilled water in insulated tanks for use during the following day. In addition to pos- Warm Air to Hea r Sink Condenser Cool Awfrom Heat Sink Compressor Air Summer Conditioner Coolinq or Heal' R..Jmp Worm Water from Condenser Cool Supply Air to~ Space Cooled Woter to Condenser Pump Evaporator Warm Return Air I L _ CondenreI! ~"t rr-om SpClce Compressor Coolinq lOwer Cycle rI ------------- - ------- If ~rr= Warm iD Heat Air 5ink ~ U":) Condenser Cool Air I I I 1 ~ from Heat SinK: J : +-- ' t ~ L_ - __ ! T~ f ---------- tJ Chilled SupplyW////A'.? Water Warm Return Wo.ter I i J ( Compressor Chilled Water System 65 Warm Air to Heat Sin k Conden'3er EVG1goro.tor Warm Return Air from SpAce -'~----"-----------l I I I I I t-Heat exchanger I Heat Source -1-11 i-5tron9-:Jolut,'on 50\ ution rWeo.k 111' I 1 I 6e-nemtor ~------------------j Absorption Refriqemtion Steam 5epo.rc\tor (I ~/ ((, '~ ) ;steom----? 2~O· Wo.ter-and ,steam E.\ectric 6enemtor Ener9t ion) SXstem -A Total ~genem I : sible rate benefits, this off-peak cooling has the advantage that the cooling tower is operating more efficiently because of lower outdoor air temperatures. The compressor is usually an electrically-driven machine. It can be replaced by a special device known as an absorption refrigeration machine that utilizes chemical processes driven by steam heat rather than electricity. Since high quality flat plate solar collectors and focusing collectors can produce the heat required to drive the absorption refrigeration process, these machines make active solar cooling technically feasible. The interesting concept is that solar heat is used to produce cooling. However the cost of this cooling equipment and the solar technology make such a system a relatively expensive one. Another application of absorptionmachines is in cogeneration systems, Large users of electricity who must also heat and cool a substantial building plant can utilize the waste heat from the process of generating electricity on-site. Heating is accomplished by direct use of the normally wasted heat by-product. Cooling is accomplished using the same waste heat and an absorption refrigeration installation. Again, a careful cost-benefit analysis must be done for a particular project to justify a cogeneration system because of the high initial cost. 11, 12 HVAC Systems The mechanical energy system of a building maintains a comfortable and healthy air environment by occasionally heating the air, by introducing fresh air and exhausting foul air, and by air conditioning. The latter involves cooling and humidity control. These HV AC systems vary greatly in their energy efficiency and can include features that improve their overall performance. The most wasteful systems, 66 now greatly restricted by the California Energy Conservation Standards, involve the simultaneous heating and cooling of a building zone. Systems which utilize methods of temperature and humidity control that feature simultaneous heating and cooling are the reheat system, the dualduct system and the multi zone system. The reheat system cools down air in the mechanical room to the temperature required by the zone with the greatest cooling load. Other spaces, requiring less cooling, are kept comfortable by heating the cooled air separately for each space using reheat coils. The result is efficient control over each zone's temperature conditions, but at the cost of energy expended both for cooling and heating. 0'0 • The dual-duct system separates the supply air stream into two parts. One portion of the air is heated, and perhaps humidified, while the other portion is cooled. The two air streams are ducted separately to each space, where they are mixed in the correct proportion to satisfy the space temperature and humidity requirements. Again, high quality air with precise control of air conditions is possible. The inherent excessive energy use involved in such a process is obvious. The multizone system is the same basic system as the dualduct system. In this case, however, the mixing of the heated and cooled air streams for each zone takes place at the air-handler, and a separate supply duct is routed to each individual zone. As with the dual-duct system, air is simul- '!. ~.o. ";. '.'~ Reheat 5:,istern 0 .~o~.~ ~-- ------ - - --O~.~ ---• :::::= ::::: =;+ Cooling Tower --------- --------- ---------\ , I I I I I I I I I I I 1\ I~Warm Refrigemtion Warer ~ ~ Cycle Cool Water Reheat CoiJ Return fan ~' Exhaust Air 67 Duo 1-Duct 5xstem Cooling Towet- Heoting Co,\ Ccoling Coil Hot All Duct Chilled Air Duct Circulation Loop Heo.1"Recovery Coil SY51e\" ~- '-S"-i ... " , Re.turn Fan •........ : .. ~::--~~. ... Exhaust Air Mu Itizone Cooling Tower Fresh Air ....•• ~ .... ....•. Exhaust Air 68 Retum Fan )~..... ~: S-X5tem l l taneously heated and cooled, resulting in excessive expenditure of energy. These three HVAC systems are severely restricted in their use in California because of these characteristics. Variable-air-volume (VA VJ sys- tems are not restricted by the energy standards. This type of HVAC system generally produces energy savings up to 30 percent for typical medium to large buildings. The efficiency results from supplying air to a zone only in the amount required to offset the specific zone load at a particular time. The effect is that the supply of cool air "follows" the load around the building from east to west during the course of the day. Although the VAV system is generally more efficient than constant volume systems, if the zone load does not vary very much during the day because the building is well insulated and well shaded, a constant volume system may be the better choice. Because of the architectural implications, the architect should consult with the mechanical engineer early in the design process concerning the best HVAC systems choice for the specific application. Several design features of normally standard energy systems can be utilized in some California climates to produce significant energy savings and reduction of peak power demand. In the following two subsystems, the basic concept is to take advantage of favorable climatic conditions to offset the usual need to cool the building during the day with electric or heat-driven cooling equipment. The economizer cycle, a feature now required by the California energy standards, is an operational mode where the system uses outside air directly for cooling the spaces when the outside air is sufficiently cool for that purpose. When the system begins to experience a demand for cooling, outside air dampers open to admit a small portion of cool outside air. As the demand for cooling increases, more and more outside air is admitted to meet the load. At some point the cooling load may increase so that all of the air moved through the system is outside air used for cooling. During this entire period of operation, the cooling coil is not used and there is no energy demand on the cooling equipment. As the outside air warms up, however, it will be insufficient to meet the cooling load. The outside air dampers will then close to their minimum setting, the cooling coil will come on, and most of the air will be recirculated. Most California climates have long periods during the year when outside air can be effectively used for cooling, thereby saving larger amounts of energy. The larger the building and the higher the internal loads, the more advantageous the use of the economizer cycle since the "cooling season" for these buildings will extend into the seasons when the outside air temperatures are relatively low. I I ;-----7Cooling Coil On Hooting Coil On ~ I I +-1 ,g fJ ~ I 1001-11: Airl'I~lyby wt5ide Jil "tIJtI ~~I ~I 07. fi)' Air Conditioning CMln Out5ide J\ir) , ~ fj)' . Outside Air Tempero.ture Heoting R~quiredI (Min. Outside Air) The Economizer Cycle 69 I© Heat 60ins Absorbed by MC1S5 during the Day 70 Moss RJrgE1d of Heat by Nightventilation Night ventilation is another operational mode that should be studied for possible cost-effective application in medium to larger buildings. This technique also utilizes the natural cooling potential of a great many local climates in California. A typical characteristic of these climates is that nighttime temperatures during the summer frequently drop to the range of 55 of to 65 of, low enough for cooling purposes, even when daytime temperatures reach 100 of. If the ventilating system is operated at night for a short period of time (to be determined from appropriate engineering studies), the mass of the building and its contents can be purged of the heat stored from the previous day and cooled to a sufficiently low temperature to minimize the impact of the loads from the following day. This use of the thermal mass of the building's structure and its contents to store "coolth" from the night air is, in a sense, a passive energy system for buildings of this size. Studies13 have shown that for most California climates the principal advantage of night ventilation is in the reduction of peak power demand during the day. Energy savings over the cooling season are minimal since the building fans must operate at night as well as during the day. However, the daytime load is so effectively shifted off-peak that it appears possible, in one type of design14 at least, to eliminate the need for a chiller. A second type of system design feature can often be used to recover heat energy that would normally be lost with the warm air exhausted from the building during the heating season. The same devices can be used to remove heat from incoming fresh air and transfer it to the cool air exhausted from the building during the cooling season. One type of heat exchange device is the thermal wheel. The thermal wheel is installed in the air intake and air exhaust ducts so I •..- I that half the wheel is located in the air stream giving up heat, and the other half is in the air stream absorbing the heat. The wheel rotates and the two air streams flow in the opposite direction through a large mesh in the wheel. The mesh absorbs heat in one air stream, then seconds later gives up this heat to the other air stream. Factors that should be considered in the use of thermal wheels are the need to locate exhaust air ducts near the fresh air intake ducts, potential air leakage from exhaust to incoming air streams, and the need for more frequent maintenance. Another type of design is known as the circulation loop heat recovery coil or the runaround cycle. In this system, a water coil is installed in both the exhaust air duct and the fresh air intake duct, and water is circulated from one coil to the other to transfer heat from one airstream to the other. The air leakage problem is overcome in this type of design. The heat pipe is a more exotic device. There are no mechanical parts, so heat is transferred from one airstream to the other solely by the movement of refrigerant sealed within long pipes. By capillary action, liquid refrigerant rapidly flows horizontally through a pipe toward one end, where heat entering the pipe vaporizes the refrigerant. The refrigerant vapor moves immediately to the other end of the pipe, where it gives up its heat and condenses back to liquid form. Effective heat transfer between air streams results when an assembly of heat pipes is installed in the system. When considering energy-saving devices or subsystems for use with the building's mechanical system, it is important to realize that the appropriate design approach is best determined by the coordinated efforts of architect and engineer from the early stages of the design process, and that all aspects of energy-related building design features should be considered as a whole system. Lighting Systems Interiors of buildings have been lighted by either an overall high level of general lighting, allowing indiscriminate location of work areas, or a task-oriented lighting system. The California energy standards require the latter approach to electric lighting systems and encourage the use of daylighting to offset much of this electric demand. Daylighting is treated in detail in Chapter 3, and several references on lighting design in architecture are cited.15 The concepts of good lighting design apply equally to electric lighting systems as to daylighting systems, and usually will result in lower energy use. The reader should consult these references for a complete treatment of this important topic. The actual lighting levels achieved by a system are of secondary importance to good lighting design. The ability to see well is a function of many design variables other than raw footcandle levels. With the previous approach of overall high levels of general lighting, problems resulting from bad lighting design could be overpowered by the high levels of illumination. Now, the taskoriented approach will require lighting design skills to overcome these problems without resorting to higher energy consumption. The type of task lighting used should be carefully considered. Using a low level of fluorescent lighting for general illumination, and providing convenience outlets for incandescent lamps for task lighting, may result in higher levels of energy consumption for lighting and cooling. This may occur because of the much lower efficiency of incandescent sources compared to fluorescent and others. In any case, operation of the task lighting will be the primary determinant of energy savings. Integration of good daylighting design is an important influence on 71 how efficient the operation is likely to be. This integration depends largely on the proper control of the electric lighting systems in response to available daylight. Multilevel step dimming systems are most likely to be adequately responsive to changes in daylight levels and to produce the least amount of annoyance to the user.16 (See chapter 3.) Finally, energy efficiency in lighting can be increased through the use of more efficient luminaires and light sources. Metalhalide and high-pressure sodium vapor sources have a very high efficacy, that is, a high light energy output per unit electrical input. Considerations other than efficacy are usually more important in the selection of a light source, however. Color, color rendition, starting and operating characteristics and cost are all factors to be considered. The metal-halide and sodium vapor luminaires can have some problems in this regard, and care must be taken in their use. Special features of a luminaire should also be considered. Aircooled and water-cooled luminaires have a higher efficiency since the bulbs operate at a lower temperature. ·In·addition, the heat generated by these luminaires can be removed so that the heat of light cooling load does not appear as an· immediate load on the cooling equipment. Other types of luminaires have specular reflectors that focus light and limit its concentration to a small area. Early discussions with the lighting engineer will allow development of a lighting design that best suits the particular application and incorporates the best features for energy conservation. Notes for Chapter 4 1. W. McGuinness, B. Stein and ]. Reynolds, Mechanical and Electrical EquiPment for Buildings, Sixth Edition, J. Wiley & Sons (New York) 1979. 2. Carrier Air Conditioning Co., Handbook of Air Conditioning Systems Design, McGraw-Hill 72 (New York) 1965. 3. American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), ASHRAE Handbook and Product Directory, 1977 Systems, ASHRAE (1973) New York. 4. ]. Sumner, An Introduction to Heat Pumps, Prism Press (London) 1976. 5. For a detailed discussion of these materials, see the series of articles in Solar Age, Vol. 5, No. 5, May 1980. 6. See the table on thermal mass of building materials in Chapter 1 of this book. 7. California Energy Commission, Passive Solar Handbook for California, CEC Publication Unit (1111 Howe Avenue, Sacramento, CA 95825) 1980, pp. 278-279, 295. 8. See also the set of articles in Solar Age, Vol. 3, no. 4, April 1978. 9. B. Anderson, Solar Energy, Fundamentals in Building Design, McGrawcHill(New York) 1977. 10. ]. Duffie and W. Beckman, Solar Energy Thermal Processes, John Wiley & Sons (New York) 1974. 11. Educational Facilities Laboratory, Total Energy, EFL Technical Report (New York, N.Y. 10022), 1973. 12. See also McGuinness and Stein, pp. 392-434. 13. C. Barnaby, E. Dean, D. NaIl et al., op. cit., footnote 22, Chapter 1. 14. Ibid, pp. 31-34 and 81-89. . 15. See footnotes 39-43, Chapter 3. 16. For a list of manufacturers who presently market lighting control systems which can be used in conjunction with natural light, see F. Rubinstein, "Strategies and Techniquesfor Lighting Control in Buildings", in Window Design Resource Package, Unit 10, Design Methods: SupPlementary Electric Lighting, Lawrence Berkeley Laboratory, Berkeley, CA 94720, June, 1980. lJ'" <lJ <:: if) <lJ E "2 •... <:: <:: 0P- >, (fJ Eif) 2 <lJ • ~ ~~ •... U <lJ OJ > <:: OJ if) '"d OJ '0 <:: ..c: ;:! bO (fJ <:: <:: P bO ;J -. bO <:: r> e<lJ '2 ,2: .iI n: '"'2 U u 15: 2;a ';:; '0 <lJ •... OJ bO OJ OJ Q) <lJ (fJ r.iI 'w ~ <lJ •... <:: if) • Bibliography • • • • • Fitch, ]. M., American Building 2: The Environmental Forces That Shaped It, Houghton-Mifflin (1972) Boston. A classic treatment of the strong but unnoticed role that has been played by energy management requirements and systems on the direction of modern architecture. Banham, R., The Architecture of the Well-Tempered Environment, University of Chicago Press (1969) Chicago. An historian's view of the impact of energy technology on architectural form and how integration of environmental concerns was achieved in many cases. Allen, E., How Buildings Work, Oxford University Press (1980) New York. A general introductory text to building technology, including a complete and insightful treatment of energy in buildings. Delightful to read. Heschong, L., Thermal Delight in Architecture, MIT Press (1979) Cambridge. This book explores the potential for using thermal qualities as an expressive element in building design. Olgyay, V., Design With Climate, Princeton University Press (1973) Princeton, N.J . The classic reference, originally published twenty years earlier. The text remains unchanged, and as such has become obsolete in many places. Givoni, B., Man, Climate and Architecture, Elsevier Publishing Co. (1976) New York. A technical treatment of climate, envelope design and the thermal performance of buildings. 73 '" <J) <J)<=: '" c.)U) E<J) >-. <=: 0p. ·5 <J) >, (f) EU) 1:1 <:: •:§;j0 v•u0• ·2 ~ u~ '"•• ~ ·cou 2 2: >-. <J) co > U) co ..c: -0 b.() ::J > Ui > b.() UJ P... b.() .:::: 0:: 1:1 P:1 <r: UJ <=: <=: <=:<=: <=: <J) co b.() co <J) >-. 0 co ·w ...., >-. <J) <=: 5iJ U) • • • CD 0 • Markus, T., and Morris, E., Buildings, Climate and Energy, Pitman Publishing (1980) London. Technical text on energy management in buildings from site considerations to mechanical systems. o 'Callaghan, P., Building for Energy Conservation, Pergamon Press (1978) Oxford. Technical text with emphasis on how to calculate the thermal performance of components and systems. Thorough and rigorous on fundamentals of heat transfer. Koenigsberger, 0., Ingersoll, T., Mayhew, A., and Szokolay, S., Manual of Tropical Housing and Building, Part L Climatic Design, Longmans Publishing (1973) London. Comprehensive book on climate-sensitive design with emphasis on principles and design techniques. Excellent resource for design in any climate. Collins; B., "Windows & People: A Literature Survey", NBS Building Science Series 70, U.S. Department of Commerce, National Bureau of Standards (June, 1975) Washington, D.C. A fairly comprehensive review of psychological reactions to environments with and without windows. Includes an extensive bibliography. Lawrence Berkeley Laboratory, Windows for Energy-Efficient Buildings, LBL (1979) Berkeley, California. An annual publication concerning research and development in the area of "windows" ,including topics pertaining to heating, cooling and daylighting. Valuable for new product information and window design ideas related to energy efficiency. Hastings, S., and Crenshaw, R., "Window Design Strategies to Conserve Energy", Building Science Series 104, National Bureau of Standards (1977) Washington, D.C . NBS publication concerning properties of glass, effects of shades and shutters, and other related topics. 74 I ! I E <l) I g I ~ C'V I ~ e Cl) ~ I v Goodwin, S., and Catani, M., "The Effect of Mass on Heating and Cooling Loads and on Insulation Requirements of Buildings in Different Climates" I ASHRAE Transactions, 85, 1979. Dexter, M., "Energy Conservation Design Guidelines: Including Mass and Insulation in Building Walls", ASHRAE Journal, March 1980, pp 35-38. ~ ~ ~ ro o r~"O ~ H I ~<l) E ....• :iJ b.() ro .0: .:::: :> .5 ::J (Ij ~ .f~ : <=: •••••• '"2 ......, VI;g ~ en (/) <l) P:) b.() ~U (/) "" <l) v C"C U '-"'V ;J P... ~ ~0 (l) -5 2 oe:: I I · .1. • • Dix, R., and Laran, Z., "Window Shades and Energy Conservation", Illinois Institute of Technology (1974) Chicago . Anderson, B., The Solar Home Book, Cheshire Books (1976) Harrisville, New Hampshire. ~ Q) I •• •• • A good not-too-technical introductory treatment of active and passive systems. I I .. I Anderson, B., Solar Energy-Fundamentals Hill Book Company (1977) New York. in Building Design, McGraw- " This hard-cover book includes similar information, but emphasizes active solar to a much greater extent. Not an active system design manual, but still fairly technical in its treatment. I Mazria, E., The Passive Solar Energy Book, Rodale Publishing (1979) Emmaus, Pennsylvania. ·1 • This book introduces a design methodology for passive solar and includes tables and calculation techniques for performance evaluation. Good graphics help explain concepts of sun movement. Sunset Magazine, Homeowner's Guide to Solar Heating, Lane Publishing Co. (1978) Menlo Park, California. I •• • A summary of active and passive solar design techniques, with many illustrations. I 75 c <1) c..? "@ ... <1) 00 "@ <:: w c "a 0- 0>. (f) E00 <1) • • •• • • Wright, D., Natural Solar Architecture, Van Nostrand Rheinhold Co. (1978) New York. Sketches and discussion on conceptual ideas and principles of passive solar design. Watson, D., Designing and Building a Solar House, Garden Way Publishing (1977) Charlotte, Vermont. A collection of concepts on solar design, with an emphasis on active systems. Watson, D., Energy Conservation Through Building Design, McGraw Hill (1979) New York. Leckie, ]., et aI, Other Homes and Garbage, Sierra Club Books (1975). A collection of ideas on decentralized applications of solar, wind, methane, water supply and agriculture. AlA Research Corporation, Solar Dwelling Design Concepts, U.S. Government Printing Office (1976) Washington, D.C. Stock No. 023-000-00334-1 Available through local U.S. Government bookstore. Though somewhat obsolete, this book provides a summary of design considerations for site and building design. Total Environmental Action, Inc. Solar Energy Home Design in Four Climates, Church Hill (1975) Harrisville, New Hampshire. The first chapters deal with siting and solar design procedures; the re- . maining portion applies the step-by-step process to four hypothetical solar homes in four different climates. Robinette, G., (ed.), Landscape Planning for Energy Conservation, Environmental Design Press (1978) Reston, Va. Site planning issues related to energy conservation are treated. Use of plant materials for wind protection is covered in some detail. 76 ~ • • v• • uc c;J .c c:a ~~ b() ... '"b() .•.. :> '" 00 '" "0 :> b() (Jj :> P;J tx. -.E "@ "a '" 1:: p:; <r:: b() ":::s ;3 <1) <1) u (f) u ... '" "0 I (f) "S <1) w'""00 "0 ~c <1) 00 0tiJ t:: <lJ rn E tiJ <: '2 <lJ I-. 0P- >, U1 rn E "0 1:1 <lJ • • U .•... I-. OJ <lJ <lJ OJ > "0 .•... t:: rn ..<:: OJ ::! > t:: <lJ b/) U1 > t:: b/) ;.:5 P-. (t:: Jj tiJ :i:J:) :s p:; "5 ;.a ~ '2 ~ 1: .5 '" U1 I-. U <lJ OJ OJ b/) b/) OJ ~"w"0u t:: 5;; I-. <lJ rn • •• •• Bainbridge, D., Corbett, ]., and Hofacre, ]., Village Homes' Solar House Designs, Rodale Press (1979) Emmaus, Pennsylvania. Primarily examples of passive solar house designs in Davis, California. Includes plans and photographs. Olgyay, A., and Olgyay, V., Solar Control and Shading Devices, Princeton University Press (1957, reprinted 1976) Princeton, N.]. This text is still the definitive source for a design methodology for solar control design. Half the book is comprised of photographs and commentary on many good, though dated, examples. Sun Protection, An International Architectural Survey, Praeger Publishers (1967) New York. Campbell, S., The Underground House Book, Garden Way Publishing (1980) Charlotte, Vermont. A comprehensive treatment of underground house design from site problems to detailing; examples are shown and discussed. Underground Space Center, University of Minnesota, Earth-Sheltered Housing Design, Van Nostrand Reinhold Co. (1979) New York. Similar topics, more technical and manual-like than the previous work. Wells, M., Underground Designs, Malcolm Wells (1977) Box 1149, Brewster, Mass. 02631. Sketches of design concepts of underground shelter by the architect. California Energy Commission, Passive Solar Handbook for California, June, 1980. Available through the CEC Publications Unit, 1111 Howe Avenue, Sacramento, California 95825. A compendium of passive design techniques, with abundant architectural detail drawings for each type of system. Beyond some introductory conceptual material, the major emphasis in addition to architectural detailing is quantitative evaluation utilizing CALP AS and CALPOND computer programs. The handbook is especially useful in conjunction with these programs. 77 v OJ f'ito: I 0'5'20p, v '"§I I:: UJ to: I I • I I I I v I I I •... to: UJ ..<:: to: bI) ;:J to: bI) P... "" to: .2:: bI) p::, I ~ E:t3 0 U.S. Department of Energy, Passive Solar Design Handbook (Vol. I and Il), U.S. Government Printing Office (1980) Washington, D.C. Available through National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161. This technical publication contains both descriptions and calculation methods for the various passive systems. Volume II is particularly valuable for the tables and data that permit reasonable assessment of performance for a large number of U.S. locations. American Society of Heating, Refrigerating and Air Conditioning Engineers, ASHRAE Handbook of Fundamentals, ASHRAE (1977) New York. The standard technical reference of the field. California Energy Commission, Energy Conservation Design Manual for New Nonresidential Buildings, CEC (1977) Publications Unit, 1111 Howe Avenue, Sacramento, CA 95825. This publication explains the California nonresidential energy standards and the methods of compliance. California Energy Commi.3sion, Energy Conservation Design Manual for New Residential Buildings, CEC (1978) Publications Unit. This publication explains the California residential energy standards and the methods of compliance. Selkowitz, S., "Effective Daylighting in Buildings", Parts 1 and 2, Lighting Design and Application, February and March 1979 . These papers briefly summarize the technical aspects of maximizing the use of daylight in buildings. Lam, W., "Lighting for Architecture", Architectural Engineering/Environmental Control, R. Fisher (ed.), McGraw-Hill (1964) New York, pp. 118-164 . This article contains excellent design case studies and a theory of lighting design based on principles of human visual perception. I bI) Cii • • I I I UJ I Ie 78 • '" v'0 ;;:; ;J v v (j) :> U w "d 1:: ;:s ,5 '2 .,:>'" » ~I ~ <r: 'w I'0 (f) E I p:; I I I • •e I'" (f) '"u W v UJto: •... I I I I u /I I '" Q) 0: c..? '"if)8Q) <:0: •... 00. u Q) 0: ~ '"C co "0:co:r=:if)u;J.,3 ..c: Q) [fJ > ~ ~ 0: P U U ·2 '"·2 .:': p:; ·5 -0 .iJ3 [fJ b.O b.O b.O <>:: •... 8 B :>, [fJ if) Q) if) v~>-0 co •... Q 0: co ) b.O co co 0: Q) ~5;) Q) •... I • ••• Lam. W., Perception and Lighting as Formgivers for Architecture, McGrawHill (1977) New York. Lighting design based on a Gestalt theory of perception of environments. Case studies are presented from concept to details, with good photographs and graphics. Hopkinson, R., and Kay, ]., The Lighting of Buildings, Praeger (1969) New York. This book treats both daylighting and electric lighting in fairly nontechnical terms. First three chapters provide a good discussion of the principal issues of lighting design. Larson, L., Lighting and Its Design, Whitney Library of Design (1964) New York. Excellent treatment of concepts of lighting design. Includes photographs and case studies of architecturally important buildings. Phillips, D., Lighting in Architectural Design, McGraw-Hill (1964) New York. Basic book on lighting by European expert; includes some technical material on lighting calculations. Progressive Architecture, 54: 9, September 1973. Summary of architectural design issues surrounding lighting in buildings, types of light sources, street lighting and other topics. "Estimating Daylight in Buildings", Parts 1 and 2, Building Research Station Digest (Second Series), Her Majesty's Stationery Office (London) December 1963 and January 1964. A calculation method utilized by British engineers for overcast sky conditions is described; tables and nomograms are provided. Daylight protractors and a description of the method are available from Pendragon Books, Publishers and Distributors, 2595 E. Bayshore Rd. Palo Alto, CA. 79 l?(j) CiJ <:: rfJ CiJ <:: '2 •...(j) 00-,:: '0 (j) »EI [/) B CfJ u u '" [/) ~ ,:: '">E [/) u '" '" "'0 > OJ UJ > P-. ~ "a ,5 '";J 1:: Ii: B ';:J ;c bJ) (j) •... CfJ ..c: ::J <:: bJ) bJ) >"-< CiJ <:: (:Q (j) <>:: bJ) '" ~'u) '0 •... (j) (j) <:: •... SiJ I CfJ I • • • • 0• Pritchard, D., Lighting, Environmental Physics Series, Second Edition, Longman Publishing Co. (New York) 1978, Chapter 6: "Daylighting of Buildings" . Summary treatment of the British methods of daylighting design, including integration with electric lighting systems ("PSALI" systems). Evans, B., "The Use of Models for Evaluation of Daylighting Design Alternatives", in Window Design Resource Package, Unit 8, Design Methods: Physical Models, LBL (1980) Berkeley, CA 94720. Describes the techniques of building models for the study of qualitative and quantitative aspects of daylighting spaces. Includes description and manufacturers of various light measurement devices for use inside the models. Hopkinson, R., Architectural Physics-Lighting, Office (1963) London. Her Majesty's Stationery Basic theory of light and lighting; primarily a technical text. Hopkinson, R., Petherbridge, Heinemann (1966) London. P., and Longmore, ]., Daylighting, The authoritative text on all aspects of daylighting, based on years of practice and research at the British Research Station. Turner, D., Windows and Environment, Pilkington Environmental Advisory Service, Architectural Press (1971) London. This publication contains a good qualitative treatment of daylighting, as well as technical methods for quantitative evaluation. Kaufmann, J. (ed), I.E.s. Lighting Handbook: The Standard Lighting Guide, Fifth Edition, Illuminating Engineering Society (1972) New York. This book is the authoritative handbook for lighting systems design. 80 <lJ (,) 01.::: en 01 1:: •...<lJ ~ 0'2 0 8 :>, UJ en .::: <lJ • 1J • • OJ ~ >E '"d >U ~ 01 ~ '2 is: ~U3 '5 :a b/) co <lJ •... .::: co en co ..c:: <lJ .::: ;::1 .::: :..::s b/) p.., .::: co <lJ i:Q .1:: b/) b/) u '0 .5 UJ UJ •... <lJ U co co > ~'0 '00 •~ •... <lJ .::: en • • • • Rubinstein, F., "Strategies and Techniques for Lighting Control of Buildings", in Window Design Resource Package, Unit 10, Design Methods: SupPlementary Electric Lighting, Lawrence Berkeley Laboratory (1980) Berkeley, CA 94720 . Resource material for automatic lighting control systems in response to available daylight. McGuinness, W., Stein, B., and Reynolds, ]., Mechanical and Electrical EquiPment for Buildings, Sixth Edition, ]. Wiley & Sons (1979) New York. This new edition of the standard reference of the field includes sections on solar heating and cooling. An excellent basic text on all aspects of heating, cooling and lighting systems. American Society of Heating, Refrigerating and Air Conditioning Engineers, ASHRAE Handbook and Product Directory, 1973 Systems, ASHRAE (1973) New York. Standard engineers' reference handbook on mechanical systems. Sumner, ]., An Introduction to Heat Pumps, Prism Press (1976) London. A short, non-technical book on heat pumps: how they work and how to use them. California Energy Commission, Solar for Your Present Home, CEC Publications Unit (1978) 1111 Howe Avenue, Sacramento, CA 95825. This text provides simplified long-hand calculations for heat loss and system sizing, shading, sun angles and economic analysis; includes materials to construct a solar site survey device. Los Alamos Scientific Laboratory, Solar Energy Group, Pacific Regional Solar Heating Handbook, U.S. Government Printing Office (1976) Washington, D.C. Discussion of effect of orientation, tilt, collector area and thermal storage capacity on active system performance. Graphs provided. Available through local U.S. Government bookstore. 81 0I: CiJ <!) S en CiJ<!) I: ... 1:: 2oS >. (fJ en P<!) • • Sheet Metal and Air-Conditioning Contractor's National Association, "Installation Standards for One- and Two-Family pwellings and Multifamily Housing, Including Solar, SMACNA (1977) Viena, Virginia 22180 . Simple method for sizing active solar systems. Duffie, ]., and Beckman, W., Solar Energy Thermal Processes, John Wiley & Sons, Inc. (1974) New York. Principal reference text on technical aspects of solar energy systems. 82 • 'S I: en > ~ "0 ..c: b/) (fJ > ~ b/) I: p., ;J CiJ b/) 'S U u ~ 1: :j:Q p:; .S 'S '0 ...3 ;a (;s fJ 0,5 <!) <!) OJ OJ ::> <!) "'u...'0I:U OJ <!) OJ OJ OJ b/) I: '00 ~~ <!) en Index Absorption refrigeration, 66 Active solar heating systems flat-plate collector, 62 focusing collector, 62 heat storage, 62-63 solar warm water system, 63 solar warm air system, 63 performance characteristics, 63-64 domestic hot water, 63-64 solar-assisted heat pump, 61, 64 Air-cooled luminaries, 72 Attached greenhouse (see Sunspace) Ballasts, dimming, 56 Bibliography, 73 Brightness, 51-55 Btu,3 Building envelope configuration, 32-34 orientation, 32-34 materials, 34 openings, 34 component assemblies, 35-38 Chilled water storage, 65 Chiller, 65, 70 Circulation loop heat recovery coil, 71 Clerestories, 52, 55, 56 Coefficient of performance, 64-65 Cogeneration, 66 Comfort, 1-2 Compressor, 61-62, 65-66 Concentrated mass systems, 39, 40 Condenser, 61-62, 65-66 Conduction, definition, 14 Convection, definition, 14 Cooling systems COP, 64-65 mechanical refrigeration, 61, 65 evaporative cooler, 64-65 compressor, 61-62, 65-66 condenser, 61-62, 65-66 evaporator, 61-62, 65-66 cooling tower, 65, 67-68 chiller, 65, 70 night ventilation, 70 load management, 65, 70 chillled water storage, 65 absorption refrigeration, 66 Cooling tower, 65, 67-68 Core zone, 32 Courtyards and atriums, 53 Dayligting general concepts, 51 providing adequate illumination, 51 sky illumination, 51-53 surround illumination, 51, 53-54 sky brightness distribution, 52 daylight aperture, 52 overcast sky, 52 clear sky, 52 glare control, 4, 54-56 dimmable control systems, 56, 58 source brightness, 53 distributions in spaces, 54 models, 54, 58 effect on heat gain, 33 Dimmable control systems, 56 Direct systems-heating definition, 39 effect of thermal mass, 40 surface area of mass, 40 amount of required mass, 40 location of thermal mass, 40-41 effect of carpets and walls, 40 orientation of glazing, 40 visual comfort issues, 40, 55 Disability glare, 55 Distributed mass sytsems, 39, 40 Dual-duct system, 67-68 Earth-sink systems, 50 Economizer cycle, 69 Efficacy of light sources, 6, 72 Electric heating systems electric resistance heating, 61 heat pump, 61, 64, 65 Energy definition, 2 equivalences, 4 transfer mechanisms, 6 process energy, 32 balance, 19, 36 Envelope-dominated design, 32 Evaporation, 20 Evaporative cooler, 64-65 Evaporator, 61-62, 65-66 Footcandle, 3 .' Gas-fired heating systems characteristics, 60 warm air systems, 60 convective systems, 60 radiant systems, 60 Glare, 4, 54-56 Glare control, 4, 54-56 Glass properties of, 10-14, 17, 19 greenhouse effect, 10-12 reflective, 12, 19 heat-absorbing, 12, 19 shading coefficient, 12-13 energy balances, 19 solar gain and daylighting, 19 Heat general, 2 units, 3 transfer mechanisms, 8-20 Heat pipe, 71 Heat pump description, 61 solar-assisted heat pump, 61, 64 comparison to mechanical refrigeration, 61, 65 Heat recovery subsystems thermal wheel, 70 circulation-loop heat recovery coil, 71 runaround cycle, 71 heat pipe, 71 Heat sinks, 49-50 Heating systems gas-fired systems, 60 electric resistance systems, 61 active solar systems, 61 heat pump, 61-64, 65 83 Heat-of-light cooling load, 72 Horsepower, 4 Hydronic systems, 59 HVAC systems simultaneous heating and cooling, 67 reheat system, 67 dual-duct system, 67-68 multizone system, 67-68 variable-air-volume (VAV) systems, 69 economizer cycle, 69 Indirect systems-heating definition, 42 thermal wall, 42-44 roof pond, 44-46 Infiltration, 18 Internal load, 32 Isolated systems-heating definition, 47 sunspace, 47 attached greenhouse, 47 Kilojoule, 3 Landform and topography, 24 Light general, 3 units, 3 efficacy of source, 6, 72 Light shelf, 56 Lighting systems (see also Daylighting) task lighting, 71 system design, 71 luminaire design, 72 efficient sources, 72 air-cooled luminaires, 72 water-cooled luminaries, 72 heat-of-light cooling load, 72 specular reflectors, 72 Load management, 4, 65, 70 Lumen, 3 Lumen-to-watt ratio, 6 Lux, 3 Mass (see Thermal Mass) Materials properties (see Properties of Materials) Mechanical energy systems, 59 Mechanical refrigeration cycle, 61, 65 Multizone system, 67-68 Natural ventilation, 26-27, 32-35 Night ventilation of building mass, 49, 70 Nocturnal radiation cooling, 10 Olgyay method, 36 Overall heat transfer coefficient, 17 Passive systems-cooling definition, 49 84 heat sinks, 49 direct systems, 49 indirect systems, 49 isolated systems, 49 roof ponds, 20, 44-46, 49 earth-sink system, 50 Passive systems-heating definition, 38 in larger buildings, 38 general concepts, 39 direct systems, 39-42 concentrated mass systems, 39 distributed mass systems, 39, 40 indirect systems, 39, 42-44 thermal wall system, 39, 42-44 roof pond system, 39, 44-46 isolated system, 39, 47-49 sunspace, 39, 47-49 attached greenhouse, 39 Passive systems-lighting (see Daylighting) Perimeter zone, 32 Power demand definition, 4 load management, 4, 65, 70 equivalences, 4 conversion efficiency, 5 Process energy, 32 Properties of building materials absorptance, 8-9 conductance, 17 emittance, 9 reflectance, 8 transmittance, 8 thermal mass, 20-22 Radiant heat, 6 Reflectance, 8 Resistance (see Thermal Resistance) Reheat system, 67 Roof ponds description of system, 44 architectural issues,· 46 evaporation to improve cooling performance, 20, 46 multi-story applications, 46 heating performance enhancement, 46 diurnal temperature swings, 45 sizing, 45 planning felxibility, 46 Runaround cycle, 71 Shading mask, 38 Site issues, 24-30 Sky brightness distribution, 52 Sky illumination, 51-53 Solar access general, 28-29 subdivision example, 29 solar envelope, 29 Solar control, 35-37, 55 Solar energy wavelength spectrum, 6 greenhouse effect, 11-12 Solar energy systems (see Active solar or Passive Systems-Heating) Solar interference boundaries, 29 Sun movement general descriptions site planning techniques, 28-29 Sunshade devices, 35-37, 55 Sunspace characterization, 39 variations in design, 47 design issues, 48 use for food production, 49 Surround illumination, 51, 53-54 Task lighting, 71 Temperature, 2 Thermal bridges, 17 Thermal mass (see also Passive Systems-Heating and Passive Systems-Cooling) definition, 20 indirect coupling to solar inputs, 20 direct coupling to solar inputs, 20 performance characteristics, 20-22 role in passive heating and cooling, 20-21 combined with insulation, 22 combined with night ventilation, 49,70· Thermal radiation materials properties related to, 8-12 difference from solar spectrum, 9 suppression of, 9-10 nocturnal radiation cooling, 10 Thermal resistance definition, 14 table of representative values, 15 of air spaces, 16 of air films, 16 Thermal wall system description, 42-43 effect of water versus masonry, 43 effect of insulation, 43 architectural issues, 43-44 sizing, 44 Thermal wheel, 70 Total energy system, 66 Transmittance, 8 Underground building-insulation detail, 35 U-value, 17 Variable-air-volume (VAV) system, 69 Vegetation, 25 Ventilation natural, 26-27, 33 fresh-air requirements, 69 economizer cycle, 69 night ventilation, 49, 70 Visual comfort, 3 Warm air heating systems, 59-64 Warm water heating systems, 59-64 Water-cooled luminaires, 72 Watt, 4 Wind, 25-27 Wind barrier design, 26 82231- 306 250J - OSP 85