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4 Energy Use in Building (建筑能耗) All buildings use energy for lighting, heating or cooling. This chapter explains the use of energy in buildings and includes the technical basis for defining thermal comfort. The mechanisms for the heat loss and gains relating to buildings are analysed and calculated so that you can understand the energy use of particular buildings. this chapter describes: 4.1 Energy use 4.2 Thermal comfort 热舒适 4.3 Heat losses 失热量 4.4 Heat gains 得热量 4.5 Heat balance 热平衡 4.6 Energy consumption 能耗 4.1 Energy use 4.1.1 Energy terms (1) A fuel is a substance that is a source of energy (2)fossil fuels 化石燃料 coal, crude oil and natural gas (3)non-renewable energy 不可再生能源 is from sources which can only use once fossil fuels (4)renewable energy 可再生能源 is from sources which are replenishable可补给的 wind power, wave power潮汐能 (5)primary energy 一次能源 is the total energy contained in natural reserves coal,oil,natural gas (6)transformation 能源的转化 Is an activity that converts primary energy into another form Fuels to electricity, crude oil to petroleum (7)secondary energy 二次能源 Is the energy contained in a fuel which results from a transformation process. Electricity, manufactured gas, surplus hot water (8)delivered energy 输出能源 Is energy content as it is received by the consumer. Pay for money (9)useful energy有用能 Is the energy required to perform a given task. 4.1.1 Energy units The scientific unit of energy is the joule. Megajoules 1MJ=106J Gigajoules 1GJ=109J Tonne of oil equivalent 吨石油当量 1 tonne of oil equivalent = 41.87gigajoules = 107kilocalcories = 11630 kWh = 396.8 therms 4.4.1 calorific values 热值 Calorific value is a measure of the primary heat energy content of a fuel expressed in terms of unit mass or volume. Some typical calorific values are quoted in table 4.1 Table 4.2 shows typical use of energy on the large scale of national usage. 4.2 Thermal comfort The thermal comfort of human beings governed by many physiological(生理学 的)mechanisms of the body ,Vary from person to person. The body constantly produces heat energy from the food energy it consumes. This heat needs to be dissipated (散失)at an appropriate rate to keep the body at constant temperature. The transfer of the heat from the body is mainly by the processes of convection, radiation and evaporation. Are you or your employees feeling uncomfortable with the temperature in the workplace? The term ‘thermal comfort’ describes a person’s state of mind in terms of whether they feel too hot or too cold. There’s more to it than just room temperature. 4.2.1 Factors affecting thermal comfort Personal variables Activity Clothing Age Sex Physical variables Air temperature Surface temperature Air movement humidity The Six Basic Factors 4.2.1 Activity The greater the activity of the body the more heat it gives off. The rate of heat emission depends upon the individual metabolic rate (代谢率)of a person and upon their surface area. The average rate of heat emission decreases with age. Table 3.1 lists typical heat output from an adult male for a number of different activities. The output from adult females is about 85% that of males. 4.2.2 Clothing Clothes act as a thermal insulator for the body and help to maintain the skin at a comfortable temperature. a scale of clothing(服装的数值体系) has been developed: the clo-value. 1clo=0.155m2K/W of insulation and values range form 0clo to 4clo. Table 3.2 shows the value of different types of clothing and indicates how the room temperature required for comfort varies with clothing. 4.2.3 Room temperature When sitting near the cold surface of a window, do you feel comfort? Why? Different types of temperatures are described below Inside air temperature tai 室内空气温度 Mean radiant temperature tr 平均辐射温度 Inside environmental temperature tei室内环境温度 Dry resultant temperature tres ????温度 Room centre comfort temperature tc房间中心舒适温度 (1)Inside air temperature tai 室内空气温度 The inside air temperature is the average temperature of the bulk air inside a room . It is usually measured by an ordinary dry bulb thermometer which is suspended in the centre of the space and shielded from radiation. (2)Mean radiant temperature tr 平均辐射温度 The mean radiant temperature is the average effect of radiation from surrounding surfaces. A1t1 A 2 t 2 ..... tr A1 A 2 ..... The mean radiant temperature should be kept near the air temperature but not more than 3 ℃ below it, otherwise conditions are sensed as “stuffy” (3)Inside environmental temperature tei 室内环境温度 Inside environmental temperature Is a combination of air temperature and radiant temperature. The exact value depends upon convection and radiation effects. For average conditions it can be derived from the following formula t ei 2 / 3t r 1 / 3t ai Environmental temperature is recommended for the calculation of heat loss and energy requirements (4)Dry resultant temperature tres 室内综合温度 Is a combination of air temperature, radiant temperature and air movement. When the air movement is low it can be derived form the following formula t res 1 / 2t r 1 / 2t ai (5)Room centre comfort temperature tc 房间中心舒适温度 Is a measure of temperature which gives an acceptable agreement with thermal comfort. When air movement is low, the dry resultant temperature at the centre of a room is commonly-used comfort temperature The globe thermometer黑球温度计 is a regular thermometer fixed inside a blackened globe of specified diameter This globe temperature can be used to calculate other temperatures and when air movement is small it approximates to the comfort temperature. 球体, 地球仪, 地球, 世界 4.2.4 Air movement 空气流速 The movement of air in a room helps to increase heat lost from the body by convection Can cause the sensation of draughts Air movement above 0.1m/s in speed require higher air temperature to give the same degree of comfort Measure air movement A hot-wire anemometer and a Kata thermometer 热线流速计 卡塔温度计(冷却温度表) May be used to measure air movement. Both devices make use of the cooling effect of moving air upon a thermometer. 4.2.5 Humidity 湿度 Humidity is caused by moisture in the air Relative humidity within the range of 40-70% is required for comfortable conditions 1 High humidities and high temperatures → feel oppressive (难以忍受的) → natural cooling by perspiration(排汗)is decreased 2 High humidity and low temperature → cause the air to feel chilly 3 Low humidity → dryness of throats and skin Static electricity 4.2.6 Ventilation 通风 Ventilation Is necessary to provide oxygen and to remove contaminated (受污染的)air Ventilation Has a great effect on the heat loss from buildings and condensation in buildings A number of statutory regulations(法定规章)specify minimum rates of air supply in occupied spaces. Table 3.4 gives some typical fresh air-supply rates Statutory 法令的, 法定的 Statutory regulations 法定规章 4.2 Thermal comfort 4.2.1 4.2 .2 4.2. 3 activity Factors affecting thermal comfort clothing room temperatures Inside air temperature tai 室内空气温度 Mean radiant temperature tr 平均辐射温度 Inside environmental temperature tei室内环境温度 Dry resultant temperature tres 室内综合温度 Room centre comfort temperature tc房间中心舒适温度 4.2.4 air temperature 4.2.5 humidity 4.2.6 ventilation Factors affecting thermal comfort 4.3 Heat losses 失热量 4.3.1 Factors affecting heat loss Figure 3.1 Heat losses from a building Some important factors are listed below Insulation of building Area of the external shell 建】房屋的框架 Temperature difference Air change rate 换气率 Exposure to climate Efficiency of services Use of building 4.3.2 Calculation of heat loss 失热量计算 Fabric heat loss 结构失热量 Fabric heat loss from a building is caused by the transmission of heat through the materials of walls, roofs and floors. Assuming steady state conditions, the heat loss for each element can be calculated by the following formula. Pf UAt Ventilation loss 通风失热量 Ventilation heat loss from a building is caused by the loss of warm air and its replacement by air that is colder and has to be heated. C V NVt PV 3600 External temperature 室外温度 When designing heating system of buildings it is necessary to assume a temperature for the outside environment temperature In winter: = outside air temperature for design purpose For heat transfer calculation in summer it is necessary to take account of solar radiation as well as air temperature. In summer: = sol-air temperature teo sol-air temperature(室外空气综合温度) is an environmental temperature for the outside air which include the effect of solar radiation 1。围护结构外表面的热平衡图 太阳辐射 大气 长波 辐射 长波辐射换热量 对流换热量 太阳 直射 辐射 太空 散射 辐射 环境长波辐射 2。建筑物外表面单位面积上 得到的热量: q out (t air 地面 长波 地面反射 辐射 t w ) aI Q辐射 lw Qlw aI out (t air ) t w out (t z t w ) out out 对 流 换 热 壁体得 q out (t air t w ) aI Qlw 大气 长波 辐射 Qlw aI out (t air ) t w out (t z t w ) out out 式中 q 太阳 直射 辐射 太空 散射 辐射 环境长波辐射 对 流 换 热 壁体得热 地面 长波 地面反射 —建筑物外表面单位面积上得到的热量,W/m2 辐射 辐射 out—围护结构外表面的对流换热系数,W/ m2℃ t air —室外空气温度,℃ t w —围护结构外表面温度,℃ a —围护结构外表面对太阳辐射的吸收率 I —太阳辐射照度,W/ m2 Qlw —围护结构外表面与环境表面的长波辐射换热量,W/ m2 Worked example 4.1 A window measuring 2 m by 1.25 m has an average Uvalue, including the frame, of 6.2 W/m2K. Calculate the rate of fabric heat loss through this window when the inside comfort temperature is 20℃ and the out side air temperature is 4 ℃. know U= 6.2 W/m2K A=2X1.25=2.5m2⊿t=20-4=16 ℃ using Pf UAt 6.2 2.5 16 248 So fabric loss=248W Worked example 4.2 A simple building is 4 m long by 3 m wide by 2.5 m high. In the walls there are two windows, each 1 m by 0.6 m, and there is one large door 1.75 m by o.8 m. The construction has the following U-values in W/m2K: windows 5.6, door 2.0, roof 3.0, floor 1.5. The inside environmental or comfort temperature is maintained at 18 ℃while the outside air temperature is 6 ℃. The volumetric specific heat capacity of the air is taken to be 1300J/m3 ℃. There are 1.5 air change per hour. Calculate the total rate of heat loss for the building under the above conditions. Step1: sketch the building with its dimensions, as in figure 3.2. calculate the areas and the temperature difference. Step 2: tabulate the information and calculate the rate of fabric heat losses using Pf UAt Step3: calculate the ventilation heat loss. CV= 1300J/m3 ℃, N=1.5/h V=4X3X2.5=30m3, ⊿t=18-6=12 ℃ using P C V NVt V 3600 1300 1.5 30 12 195 3600 So rate of ventilation heat loss = 195W Step4: total rate of heat loss = fabric heat loss + ventilation heat loss= 1734.24+195=1929.24W 4.3.3 Non-steady condition 非稳定条件 For situations where the steady state assumption is invalid, it is necessary to consider the effects of Cyclic (daily) variations in the outside temperature, Variations in solar radiation and Changes in the internal heat input Thermal admittance(蓄热系数)or Y-value is a property of an element (构件)or a room which controls fluctuations(波动) in the inside temperature. Unit : W/m2K Thermal transmittance 传热系数 Heavyweight structures have smaller temperature swings(温度波动 ) than lightweight structures. Figure 3.3 thermal response damping阻尼, 减幅, 衰减 Figure 4.3 Thermal response McMullan For very thin units, such as glass, the admittance becomes the same as the U-value. 传热系数和蓄热系数是相反的概念。传热系数表示热传 导的能力,蓄热系数表示储存热量的能力。 4.3 Heat loss 4.3.1 factors affecting heat loss Insulation of building Area of the external shell 建】房屋的框架 Temperature difference Air change rate 换气率 Exposure to climate Efficiency of services Use of building 4.3.2 calculation of heat loss This is about what we we Fabric heat loss did last lesson. Do you P UAt f Ventilation loss C V NVt PV 3600 remember? Now I want some one to summary in Chinese. 4.3.3 Non-steady condition 非稳定条件 Thermal admittance(蓄热系数)or Y-value 4.4 Heat gains Figure 4.4 Typical heat gains in a building McMullan typical heat gains in a building 1)Solar heat gains from the sun 2)Casual heat gains from occupants and equipment in the building 1)Solar heat gains from the sun Depends on many factors Table 4.9 seasonal solar gain through windows Sun controls to Prevent excessive heat gain and glare(眩光) caused by direct sunshine. External controls (外遮阳) Internal controls (内遮阳) Special glasses (特殊玻璃) 公共建筑可调节的金属材质遮阳装置 External controls External controls 2)Casual heat gains from occupants and equipment in the building Heat from people Heat from lighting Heat from cooking and water heating Heat from machinery, refrigerators , electrical appliances Table 4.11 domestic seasonal heat gains Now I want you to turn to page 81 Now we will go on 4.5 Heat balance The thermal comfort of humans requires that the inside temperature of a building is kept constant at a specified level, and the storage of goods also needs constant temperatures. In order to maintain constant temperature the building will generally require heating or cooling, and both of these process involve the consumption of energy. Calculation of energy E Pt Heat balance Fabric Heat Losses ventilation + + Heat Losses solar casual = Heat + Heat gains gains Energy for + heating or cooling This is a general expression of balance which is true for summer and winter conditions. Seasonal energy requirements 季节性能耗 The energy requirement of a building at any particular time depends on the state of the heat losses and the heat gains at the same time. These factors vary but it is useful to consider the total effect over a standard heating season. It is important to note that the calculation of seasonal heat losses and gains assumes average temperature conditions and can not be used to predict the size of the heating or cooling plant required; such a prediction needs consideration of the coldest and hottest days. Seasonal heat calculations are valid for calculating total energy consumption and can be used to predict the quantity of fuel required in a season and how much it will cost. Worked example 4.3 Over a heating season of 33 weeks the average rate of heat loss from a certain semi-detached house(半独立 式住宅) is 2500W for the fabric loss and 1300W for the ventilation loss. The windows have areas: 6m2 south-facing, 5m2 east-facing, 6m2 north-facing. The house is occupied by three people and cooking is by gas. Use the values for seasonal heat gains given in table 3.7 and 3.9 and calculate : (a) The seasonal heat losses (b) The seasonal heat gains; and (c) The seasonal heat requirements. (a) total rate of heat loss= fabric loss+ ventilation loss = 2500W+1300W=3800W heat energy lost= rate of heat loss × time taken =3800W × (33×7 ×24 ×60 ×60)s = 75.842GJ(giga joules)千兆焦 so seasonal heat loss = 75.842GJ =75842MJ(mega joules) 兆焦 (b) Heat gains solar window gain ( table 3.7) south (680MJ/m2×6) 4080 east (410MJ/m2×5) 2050 north (250MJ/m2×6) 1500 casual gains ( table 3.9) body heat ( 1000MJ×3) 3000 cooking (gas) 6500 water heating 2000 electrical 3000 total 22130MJ So seasonal heat gain=22130MJ (c) Seasonal heat requirement = heat loss- heat gain =75842-22130 =53712MJ(mega joules兆焦) =53.712GJ(giga joules千兆焦) Efficiency 效率 The heat energy required for buildings is commonly obtained from fuels such as coal, gas and oil, even if the energy delivered in the form of electricity. Each type of fuel must be converted to heat in an appropriate piece of equipment The amount of heat finally obtained depends upon the original heat content of the fuel and the efficiency of the system in converting and distributing (分配)this heat. Efficiency 效率 Efficiency is a measure of the effectiveness of a system which converts energy from one form to another efficiency % useful energy 100 delivered energy Domestic heating efficiency →table 4.12 Delivered energy(供给能量) Useful energy (有用能) Worked example 4.4 The seasonal heat requirement of a house is 54GJ, which is to be supplied by a heating system with an overall house efficiency of 67%. The solid fuel used has a calorific value of 31MJ/kg. calculate the mass of fuel required for one heating season. Efficiency = 67/100, output= 54MJ, input energy=? Using efficiency % useful energy 100 delivered energy 67 54 100 input energy Input energy = 80597MJ Mass of fuel needed= energy required 80597MJ calorific value 2600kg 31MJ/kg 4.6 Energy regulations 能源规范 Why do we need energy regulations? Can help to minimise energy use in buildings Regulation about thermal insulation control heat loss from buildings Minimise the heat load for heating in winter Minmise the cold load for air conditioning in summer there are many regulations 4.6.1 Building regulations 建筑规范 Encourage or enforce energy efficiency in buildings How to realize energy efficiency in buildings by regulations? The regulations achieve this aim by controlling the following (1) Heat loss by transmission through the fabric (2) Heat loss by air leakage around openings and through the fabric (3) Control system for space heating and hot water (4) Heat loss from vessels and pipes used for water (5) Heat loss from hot water pipes and hot air ducts used for space heating (6) energy-efficient lighting sources and switching for the lighting Also should consider: Other essential performances such as structural stability, resistance to rain penetration and overheating The need for design details that are practical and within the capabilities of the construction workforce Building services that are easy for occupiers to manage successfully Regulations which are not too complex to interpret and enforce 4.6.2 Energy rating, SAP 用能评级 The overall energy efficiency of a dwelling , such as a house, can be given an Energy Rating by using a Standard Assessment Procedure (SAP) An SAP Energy Rating of a dwelling is found by using a standard method method to calculate the annual energy cost for space heating and water heating in the building SAP Energy Ratings are expressed on a scale of 0 to 100, The higher the SAP number the better the performance 4.6.3 Carbon Index,CI 碳指数 The Carbon Index (CI) is an energy rating based on the overall carbon dioxide emission figure for a building Carbon Index energy ratings are calculated using the information for a SAP rating and expressed on a scale of 0 to 10, The higher the CI the better the performance. 4.6.4 Insulation of the building fabric 围护结构保温 (1)Elemental method 构件法 Matching of standard U-values for individual construction elements Table 4.13 Elemental U-values for fabric insulation (2)Target U-value method 目标U值法 Compare the average U-value of the whole exposed fabric with a specified target U-value This method offers greater design flexibility than elemental method They are subject to poorest acceptable Uvalues that are specified for each element Also subject to limitations on thermal bridging and air infiltration. (3)Carbon index method 碳指标法 This method also offers design flexibility. Buildings with higher carbon index values will satisfy regulations They are subject to poorest acceptable Uvalues that are specified for each element Also subject to limitations on thermal bridging and air infiltration. (4)Commercial buildings 商业建筑 For buildings other than dwellings the design, construction and operation, needs to demonstrate that the building and its services are energy efficient. They are subject to poorest acceptable Uvalues that are specified for each element Also subject to limitations on areas of openings. 4.6.5 Other measurements for energy conservation 其他节能措施 Controlling the insulation of the building fabric Thermal bridging around openings Infiltration Space heating control Hot water controls and insulation of storage lighting Translate into Chinese metabolic rate Stack effect Non-renewable energy Renewable energy Primary energy Secondary energy Calorific values Dry resultant temperature sol-air temperature Air change rate Thermal admittance 1 SAP Energy Ratings are expressed on a scale of ( ) A 0 to 1.0 B 0 to 10 C 0 to 100 D 0 to 100% 2 Carbon Index energy ratings are calculated using the information for a SAP rating and expressed on a scale of ( ) A 0 to 1.0 B 0 to 10 C 0 to 100 D 0 to 100% 3( ) may contribute to energy efficiency A Controlling the insulation of the building fabric B avoid Thermal bridging around openings C mimise Infiltration D Space heating control E Hot water controls and insulation of storage F energy-efficient lighting source and control 4 Casual heat gains in a building include ( A heat from people B heat from lighting C heat from sun D heat from cooking and water heating E heat from machinery, refrigerators F heat from electrical appliances )