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World Renewable Energy and Environment Conference WREEC2006, Sebha University Tripoli-Libya Energy Conservation Through Thermally Insulated Structures Ayoub Abu-Dayyeh* • *Engineer and Doctor of Philosophy • President of the society of Energy Conservation and Environmental sustainability P.O.Box: 830305 Amman 11183 Jordan • E-mail: [email protected] • Mobile no.: 00 962 79 5772533 • • 1 Abstract: The purpose of this paper is to explicate its title through investigating the different available thermal Insulating materials and the various techniques of application, as practiced in Jordan, in particular, and as practiced in many parts of the world in general, which will satisfy Jordanian standards in terms of heat transmittance and thermal comfort. A brief comparison with international standards will shed some light on the stringent measures enforced in the developed world and on our striving aspirations to keep pace. The paper consists of four main parts, pseudoally divided. The first part will deal with the mechanism of heat loss and heat gain in structures during summer and winter. It will also explain the Time-Lag phenomenon which is vital for providing thermal comfort inside the dwellings. The second part will evaluate the damages induced by the temperature gradients on the different elements of the structure, particularly next to exterior openings; The paper will also demonstrate the damages induced by water condensation and fungus growth on the internal surfaces of the structure and within its skeleton. A correlation between condensation and thermal insulation will be established. The third part of the paper will evaluate the different available thermal insulating materials and the application techniques which will satisfy the needs for thermal insulation and thermal comfort at the least cost possible. The criteria of an economical design shall be established. As a conclusion, the paper infers answers to the following different criteria discussed throughout the different parts of the paper. The main theme of questions can be summarized as follows: 1) How energy conservation is possible due to thermal insulation? 2) The feasibility of investing in thermal Insulation? 3) Is Thermal Comfort and a healthy atmosphere possible inside the dwellings during all seasons! What are the conditions necessary to sustain them? 4) What Environmental Impacts can exist due to thermally insulating buildings? 2 Introduction: The thermal properties of construction materials in buildings depend on the thermal conductivity (k-value) of building materials as well as on its thicknesses. The lower the K-value of a material is the better would be its resistance to heat movement in all three modes of heat transfer: conduction, convection and radiation. Density of the thermal material, its cell structure, the type of gas which is trapped within the cell structure and the durability of the material's matrix are all important factors in controlling its k-value. Table1 illustrates different thermal insulating materials of different densities with its equivalent k-value and its current prices in Jordan. It must be stressed here that choosing the thermal insulating material is not pricecontrolled only, but depends on many other factors as well, such as: Fire resistance of the thermal insulator, ability of material to work as a vapor barrier, moisture absorption and adsorption, thickness, health hazards in handing the material, irritation caused during handling, compressive strength, color, emissivity, effect of ultra violet light and transportation on the structure of the cells and so forth. Next illustration in figures 1 & 2 show the direction of heat flow through the exterior members of the structure, both in summer conditions and in winter. The figures also explicate the role of thermal insulation in resisting the heat flow and reducing the intensity of heat losses in any directions, illustrating the differences in heat resistance values when the direction of flow is opposite. 3 Concrete Stone Cladding Vertical CrossSection Through exterior walls In out Thermal Insulation plastering In out Section b Section a Heat Flow Direction in Summer Figure 1 4 Vertical CrossSection Through exterior walls Thermal Insulation out In out In Heat Flow Direction in Winter Figure 2 5 الجمعية العلمية الملكية- من دليل مواد العزل الحراري:Table (1) Material Density K valve W/m2.k Cost US $/ m3 2005 (Author Judgment) Aluminum 2800 200 Cast Iron 7000 40 Concrete 2300 1.75 Lime Stone 2200 1.53 Normal Glass 2500 1.05 Concrete Hollow Blocks 1200 0.77 Plastering 1570 0.53 Polystyrene (expanded) 15 0.040 90 Glass Wool 64 0.038 150 Polystyrene (expanded) 20 0.036 100 Polystyrene (extruded) 28-35 0.035 125 Rock Wool 50-100 0.035 90 Polystyrene (expanded) 25 0.034 110 Polyurethane (on site) 30 0.026 300 6 Design: The choice of type, thickness and density of the thermal insulating • material is controlled by the designer's needs and by the criteria of design. The Jordanian thermal insulation code published in 2002, specifies a minimum of thermal transmittance value (U -value) of 1.8 W /m2.k for exterior walls (Including exterior openings) and a value of 1 W/m2.k for roofs exposed to the exterior atmosphere. A traditional wall in Jordan is made out of an over whole thickness of 30 cm consisting primarily of plain concrete and stone cladding (3-5 cm thick) with cement-sand plastering from the inside, almost 2 cm thick. We shall name this traditional wall: Wall 1. • Recently, the construction industry has been using a similar sort of • construction by introducing hollow blocks made of concrete, 10 cm thick, 40 cm in length and 20 cm in height. They are used as a replacement to formwork from the inside, keeping the total thickness of the wall in the range of 30 cm. The section consists of an extra 2 cm of cement-sand plastering from the inside as. So, here we have assembled our second traditional wall which we will name: Wall 2. These two types may be called traditional walls in modern and contemporary • Jordanian building industry of middle class upwards dwellings. Neither wall satisfies the Jordanian code for thermal insulation as we shall see in the coming detailed calculations. 7 • Definitions of symbols: • K (Thermal Conductivity); R (Thermal Resistance) = d / k ; U (Thermal Transmittance); e ( Emissivity ) ; d ( Thickness ) • • • • • • • • • • • • • U – value calculations: U = 1 ÷ R ; R = d ( Thickness ) ÷ K ( Thermal Conductivity ) Ri = 0.13 ; Ro = 0.04m2.k/W For Wall 1 U1 = 1 ÷ (Ri + Ro + (0.05 ÷ 1.53) + (0.25 ÷ 1.72) + (0.02 ÷ 0.53) = 1 ÷ 0.383 = 2.6 W/m2.k For Wall 2 U2 = 1 ÷ (Ri + Ro + (0.05 ÷ 1.53) + (0.15 ÷ 1.75) + (0.10 ÷ 0.77) + (0.02 ÷ 0.53) = 1 ÷ 0.46 = 2.19 W/m2.k For Wall 3 U3 = 1 ÷ (Ri + Ro + (0.05 ÷ 1.53) + (0.15 ÷ 1.75) + (0.03 ÷ 0.035) + (0.10 ÷ 0.77) +(0.02 ÷ 0.53) • = 1 ÷ 1.32 • = 0.76 W/m2.k 8 • Energy Saving: If we add exterior opening effects on the over whole U-value of the walls (Doors and Windows), which we assume they constitute 20 % of the total exterior peripheral area, we can then calculate the saving attained in energy and fuel consumption due to thermally insulating the exterior walls only. The calculations follow: • Assume that the average U-Value for exterior openings U-value (Windows & Doors) = 4 W/m2.k • The average U-value becomes:• 0.76 × 0.8 + 4 (0.2) • = 1. 4 < 1.8 • • This is okay for the existing Jordanian thermal Insulation code, but we are striving to reduce this value by 50% which will still be dramatically higher than the values recommended by many European standards. • The average U-value for the traditional wall: • 2.6 x 0.8 + 4 x 0.2 • = 2.88 W/m2.k • Percentage saving = 2.88-1.4/2.88 = 51.3% 9 • • • • • • • • • • • • • • Fuel Saving: Assuming that the air exchange stays the same before and after applying the new insulated section, and also assuming that the flat is loosing heat from four directions only. Where the roof is occupied by neighbors and heated. The area of the flat is 15 × 10 =150m2. Where U1 & U3 represent Walls 1 & 3 Q saved = (U1-U3) x A x T (Ti-To) Where U1=2.88, U3 = 0.76, A= 125m2, T = 20 K (Average temperature change) The flat in question has a wall surface area of 125 m2. Q = (2.88 – 1.4) × (125 m2) (20) = 3700W = 3.7 Kj/second = 3.7x3600 Kj/ hour One liter of diesel = 7000 K.calory = 7000x4.2 Kj ( 1calory=4.2 joules) Saving in diesel/hour = 3.7x3600/7000x4.2 = 0.45 lt./ hour If we Assume that Amman needs 1300 Heating Hour Day and 700 cooling hour day, then the total consumption is: 0.45x2000 = 900 lt. yearly This means nearly 200 US$ Saving on fuel only by thermally insulating walls only, if we add reduction in maintenance and spare parts and increasing the time life of the electromechanical system, this number is easily doubled. Therefore saving is up to 400$ yearly. Remember that if improvement on the thermal properties of the roof is also administered, the savings are far greater. 10 • It must be noted here that air gaps do not have the ability to resist heat more than 0.18 W /m. k, no matter how thick the gap is (provided the gap is bounded by traditional construction materials, such as concrete). Actually the wider the gap is the worse would be its resistance to heat transfer as convection currents become more effective in wasting energy in winter (see figure 3 for details). • If we calculate U3, for wall 3 once again using an air gap 2cm wide, then the U-value becomes as follows: • U3 = 1 ÷ (Ri + Ro + (0.05 ÷ 1.53) + (0.15 ÷ 1.75) + (0.03 ÷ 0.035) + (0.10 ÷ 0.77)+ 0.18 ( see figure 3, the value 0.18 is illustrated by arrows) + (0.02/0.53) • U3 = 1/1.46 • = 0.67 W/m2.k • It is clear now that not much change has been achieved through adding the effect of the air gap, that is from 0.76 to 0.67W/m2.k. Whatever width the air gap is, no more resistance to heat flow is attained. Actually the opposite happens as the wider the gap becomes the lesser the resistance to heat flow the air gap sustains. 11 7 0.6 R- value Air gap trapped between two layers of Aluminum foil 0.4 Air gap trapped between two layers of construction material (Concrete and Blocks) 0.2 0 0 R-value = 0.18 2 4 6 8 Thickness of Air Gap Figure 3 12 • One way the resistance of air gaps can be improved is by introducing a reflective surface on at least one surface inside the cavity. This is illustrated in more details in Figure 4. • In that case, R is increased from 0.22 (for roofs) to a value reaching up to 1.00. This happens in summer where the heat flow is from the upward direction towards downwards. This improvement in thermal resistance is due to a trapped air cavity up to 60 mm in width. This value is achieved by using a single aluminum foil as a reflective membrane, provided that it is exposed to the air gap in order to function effectively in reflecting heat by radiation. • This characteristic can also be achieved by introducing reflective surfaces inside the cavity. The more polished the surface is the better, the lower emissivity value means the lesser heat is emitted from its surfaces. • Where as in winter, while heat is moving from inside the dwelling to the outside cooler temperature due to the high temperature and high pressure, in most cases. The R value for a cavity is increased from 0.15 to 0.30 only, regardless of the thickness of the cavity (see figure 4) 13 BS 6993:PART1-1989 Thermal resistance -R-value (m 2. K / W) 1.2 Heat Flow Direction in Summer Aluminum Foil Cavity 1 Heat Flow Direction in Winter 0.8 Cavity with with one one Cavity aluminum surface surface aluminum 0.6 Cavity uncoated 0.4 0.2 0 0 10 20 30 40 Cavity thickness (mm) Figure 4 50 60 14 • • • • Time lag and thermal comfort phenomena: we saw in figures 1 &2 the heat flow direction, now we see in figure 5 how the heat wave enters through the exterior wall in summer and how it is reduced according to the type of construction, building materials used and the thicknesses applied. The lesser the decrement factor is the lesser the variations in temperatures would be on the inside surfaces between night and day. The smaller the decrement factor the more comfortable living inside the house will be. See figure 5 a for details about thermal comfort and its relationship with the ambient internal temperature and the average temperature of the internal surfaces. It must be noted that a difference of more than 3ْ c between the Mean Radiant Temperature of the surface of the wall or roof and the temperature of the ambient air inside the house will make a human being uncomfortable. Other factors get into the formula as well, such as the relative humidity, clothing, wind speed and human nature. These differences will be illustrated further in Iso-thermal analysis of Walls 1 & 3. It must be noted that the internal ambient temperature inside the house is recommended to be 20 degrees in winter, for energy saving and thermal comfort purposes, meanwhile, in summer, it is allowed to keep rising up to 26degrees and the atmosphere will still be comfortable. The other problem that might arise from bigger differences between the ambient temperature and the mean radiant temperature of the surface of walls and roofs is water vapor condensation in winter, invoking the growth of Fungus and creating an unhealthy atmosphere inside the house. 15 External surface Internal surface Maximum temperature Reached during the day Maximum surface temperature Minimum surface temperature Minimum temperature Reached during the night Structural member Time Lag 24 Hours Figure 5 Decrement Factor 16 Average Temperature of Ambient Air 35 30 Very Hot Zone 20 Comfort Zone 10 Very Cold Zone 0 55 10 10 15 15 20 20 25 25 Average surface temperature of internal walls Figure 5 a 17 Table 2 Averages of weight of water vapor produced by a family in Jordan consisting of an average of 5 persons 1 Breathing and Sweating 4 – 7 kg 2 Using petrol based fuel in heaters of no exhausts 10 – 15 Kg 3 Cooking 2 – 6 kg 4 Bathing (Twice weekly) 1 – 3 kg 5 Washing activities 1 – 2 kg 6 Laundry 2 – 4 kg 7 Drying clothes 4 – 8 kg 8 Washing and drying dishes 0.5 – 1 kg 9 Other activities, plants, .. etc 0.5 – 1 kg Total 25 – 47kg 18 • In table 2, it is shown that a typical family in Jordan produces nearly 25-47 kg of water daily, this exists as water vapor inside the dwelling. By looking at any psychometric chart available, it can be seen that water vapor will be condensating on the internal surfaces of walls in winter, nearly all the time, particularly on traditional wall types Wall 1 & Wall 2 . This will happen at about 60 % relative humidity. Although the ambient air temperature is 20 degrees, but the exterior wall's surface temperature from the inside will be around 13 degrees as seen in figure 6b, 6d and 7b, exactly at the corners where two walls meet. This value of relative humidity ( 60%) is easily reached daily in winter with a family of an average of 5-6 persons, which is very common and considered as an average in Jordan. On the other hand, a wall type Wall 3, will be subjected to water vapor condensation at corners only if the relative humidity reaches 90 %, which is a value rarely approached in dwellings in Jordan due to natural air exchanges. Note that the temperature of the surface of the meeting walls does not go below 18.2 degrees ( see figure 8b and 8d). • Condensation due to the lack of thermal Insulation in buildings does not only trigger the growth and multiplication of Fungus, but causes surface cracks due to the continuous shrinkage and drying of the surface on which condensation takes place and due to the thermal movement induced by the temperature gradient. • Different modes of cracks also appear in areas where a temperature gradient sharply persists. In plates 1 & 2, the temperature gradient due to placing the window far on the outside or far on the inside will definitely encourage cracks in that area. Cracks follow the area where the temperature gradient exists. These cracks can also be seen in plate 3. 19 Plate 1 Outside 0k Window Frame Area of a Sharp Temperature Gradient Plate 1 Winter Condition Inside 20 k 20 Plate 2 outside Area of extremely sharp temperature gradient T e Plate 2 m p e r a t u r e 21 Plate 3 Cracks elongated on the interface of two areas of different temperature gradient similar to the damage seen In the cases displayed in plates 1 & 2 Cold Joint Temperature Gradient Cracks 22 • Cold Joints: Heat is lost in winter as the ambient outside temperature decreases to 0ْ c or less. We need to keep the ambient temperature inside the house near 20ْ c in order to allow the residents in the dwellings to feel comfortable. This requires a thermal design capable of maintaining the mean radiant temperature of the inside surface at around 17ْ c in winter. That is to reduce the fluctuations to a maximum of 3 degrees. • Notice in figure 6 that wall 3, even at 18.2 degrees at corners (see Figure 8b & 8d) where exterior walls meet, falls in the comfortable region. While wall 1 and wall 2 being at a surface temperature of 13 degrees fall in the uncomfortable region (The very cold zone). • Now, the heat lost from inside to outside cold air is moderate in thermally insulated areas, whereas in areas were the surface temperature is quite low, it means there is a greater loss of energy. This usually happens at corners and at places we call them cold-joints. One cold joint area we have seen earlier at the sides of a window where some sections of the cavity had no insulation due to bad workmanship. A problem which most under developed countries in general suffer from. In the following slides some examples of cold23 Joints are demonstrated: picture 1-1. 24 See picture 1-2 25 Picture 1 - 3 26 Figure 6 o 16.5 C o 33 C o o o 15 16 o 13 14 o 33 C o 32 o 31. C o 33.5 C o 20 C Wall 1 (Vertical section-Winter) 6(a) o 50 C inside o o 32 o 20 C o 31. C out side o 16.5 C 16 o o 0 C o 15 o 14 o o 0 C o 26 C inside 16.5 C Wall 1 - plan- Winter 6(b) Wall 1 - plan - Summer 6(c) 27 Figure 6d 28 Figure 7 o 17.2 o o 0 C o 20 C out side Wall 2 (Vertical cross-section) 7(a) o o 17.2 C 17 o 17.2 C 16 o 14.5 C o o 32 17.2 C o 20 C o 50 C inside Wall 2 - plan , Winter 7(b) 32.5 C o 16 o 32. C o 15 o 15 o o 0 C 33.5 o 26 C inside Wall 2 - plan , Summer 7(c) 29 Figure 8 Wall 3 (Vertical cross-section) 8(a) o 19.2 C o 20 C 19.2 Co o 0 C o 20 C 19 Co o 18.2 C o 50 C 27.2 Co 19.2 oC 19 Co o 0 C 27.2o o 28.2 C o Ambient temp. = 26 C Wall 3 - plan , Winter 8(b) Wall 3 - plan , Summer 8(c) 30 Iso-thermal Lines No 18 19.2K Figure 8 d 18.2K 31 Economical Design • When choosing foam concrete for thermal insulating walls and roofs, we have to choose the most suitable density in order to satisfy the criteria required: strength, cost, durability, thickness and the K-value. We need a minimum of 600 kg/m3 density for strength to allow the concrete to withstand walking loads and mechanical impacts. • Choosing a higher density concrete will give a lower K-value and then a thicker mass is required. For an economical design, thickness, density and price must be balanced (see figure 12 ). • The same argument applies for perlite concrete as using perlite is an advantage in sloped roofs compared to foam concrete which cannot withstand steep slopes. (see figure 10). • When using other thermal insulating materials such as polystyrene, rock wool.. etc.. (see figure11 ). There comes a stage when increasing the density will not affect the K-value much, thus to have an economical thermal design the most efficient density must be chosen. Note that for expanded polystyrene and rock wool, as shown in figure 11, the K-value hardly increases when the density is above 25 kg/m3, so it is a waste of money to apply high density thermal material of this sort. 32 0.25 K-value 0.20 0.15 0.10 0.05 0.00 1000 800 600 400 200 Density of Perlite Concrete Kg/m3 Figure 10 33 0.06 0.05 Rock Wool K- value (W/m. C ) o 0.04 Expanded Polystyrene 0.03 Figure 11 Polyurethane 0.02 0.01 0 10 20 30 40 50 60 70 80 90 100 Density of Thermal Insulating Materials Kg/m3 34 0.25 o THERMAL CONDUCTITY (W/ C) 0.20 Figure 12 0.15 0.10 0.05 0.00 1000 800 600 400 200 Density of Light Perlite Concrete ( Kg/m3) 35 • Conclusion: To be efficient designers, we must choose the best price-efficient product most suitable for our method of construction and our budget. For low cost housing we must be knowledgeable too of an important fact that the cost of thermal insulating a structure is not a costly procedure at all. It is actually a profitable procedure to the investor; as from the very beginning, that is as early as the design stage, the following reductions in cost occur during construction due to thermally insulating the structure. The reason is manifested in the dramatic reduction in the initial cost of installing mechanical works, central heating and air conditioning systems. In Jordan, we have proved that using, only, a wall 3 solution at an extra cost of 1000 US $ per 150 m2 flat is immediately refunded from the reduction in boiler capacity, quantity of radiators, diameter of pipes and capacity of pumps. • The profitable investment in thermal insulation persists and multiplies by time ever since the moment of occupying the building, as less fuel and electricity is spent on heating and cooling, and very little maintenance thereafter is needed. We have also proved in this paper that a saving of 400 $ per flat per year is achieved, only via heat losses through walls. This means that even if we did not consider the initial profit, the pay back period will be two and a half years, if fuel prices stay the same. • A more comfortable environment is also prevailing inside the house, whence thermal insulation is used. Less cracks on the internal surfaces, and less thermal movement within the insulated zone. No water condensation is actually possible and no fungus growth. And above all less fumes are emitted to the atmosphere. That means less pollution for the environment. • ----------------------- The End----------------------------- 36