Cool and Economical with Lightweight Concrete
By: Ir. Elisa Haryonugroho1
Convenience inside a house/building is very important. Convenience enables occupants to do their activities well and more productively. Determining factors of convenience are temperature, humidity, air circulation. Convenience can be attained by at least 2 things: good architectural planning and choosing the right materials. Convenience issue becomes crucial when the outer wall is facing westward. For several cases, air conditioning can be achieved by controlling passive air, for example by making window openings. However, for buildings in urban areas, it’s often difficult to do this. One of the obstacles is the polluted air and a dense surrounding.
Other possible solution to address air conditioning problem is using lightweight concrete wall. To see how much efficiency we can benefit from using lightweight concrete wall, below is an explanation of electricity cost saving if we use active air conditioning.
For a comparative illustration, we are going to use a room of 3m x 4m with 3m height to the ceiling. The first room use lightweight concrete roof plate and lightweight concrete block walls (Autoclaved Aerated Concrete) with PM-200 plaster/render (Picture 1). The second room of the same size uses conventional concrete plate and terracotta brick wall with cemment-sand palster. The calculation will measure the heat that passes through the wall material and roof plate, where the heat energy from the outside will be reduced by the material. This makes the room inside to become cooler (Picture 2). This reduction of heat depends on the material’s capacity to resist heat. The process is similar to that of electricity energy, that will decrease after passing a lamp or other electrical equipments (Picture 3).
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Lightweight concrete walls
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Terracotta brick walls |
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LIGHTWEIGHT CONCRETE’s density (ρ) = 575 kg/m3 |
Terracotta Brick’s Density (ρ) = 1.500 kg/m3 |
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The higher its ‘Thermal Resistance’, the better its heat insulation capacity.
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LIGHTWEIGHT CONCRETE
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Terracotta Brick
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| R of inner render = d/λ R of inner render = 0,01/0,35=0,0286 R of outer render = 0,01/0,35=0,0286 Total R = 0,79+0,0286+0,0286 = 0,847 |
R of plaster = d/λ R of inner plaster = 0,025/1,4=0,018 R of outer plaster = 0,025/1,4=0,018 Total R = 0,18+0,018+0,018 = 0,216 |
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Inner air layer Thermal Resistance (Rsi) dan outer air layer Thermal Resistance (Rse)
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The lower the air film’s ‘thermal transmittance’ on the surface of walls, the better its heat insulation capacity. |
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| Thermal transmittance (U)= 1/(Rsi+R+Rse) U beton ringan = 1/(0,13+0,847+0,04) = 0,983 |
Thermal transmittance (U)= 1/(Rsi+R+Rse) U of lightweight concrete = 1/(0,13+0,847+0,04) = 0,983 |
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The lower its ‘thermal transmittance’, the better its capcaity of heat insulation
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| LIGHTWEIGHT CONCRETE Roof Panel | Concrete Plate |
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LIGHTWEIGHT CONCRETE Roof Panel
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Concrete Plate
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| R screed PM-600 = d/λ R = 0,02/0,35 = 0,057 |
R plester = d/λ R = 0,02/1,4 = 0,014 |
| R of LIGHTWEIGHT CONCRETE Panel = d/λ R = 0,125/0,8 = 0,69 Total R = 0,057+0,69 = 0,747 |
R of concrete plate = d/λ R = 0,125/2,1 = 0,06 Total R = 0,014+0,06 = 0,074 |
| Thermal transmittance (U)= 1/(Rsi+R+Rse) U of lightweight concrete panel = 1/(0,13+0,747+ |
Thermal transmittance (U)= 1/(Rsi+R+Rse) U of concrete roof = 1/(0,13+0,074+0,08) = 3,52 |
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Energy Passing Through the LIGHTWEIGHT CONCRETE Wall and LIGHTWEIGHT CONCRETE Floor Panel |
Energy Passing through the Terracotta Brick Wall and Concrete Floor (Q) |
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Wall size (A of wall) = 39,3 m2 |
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| Q of lightweight concrete = U x A x at x T Q of lightweight concrete = 0,983×39,3×5x10 = 1.931 Q of lightweight concrete = 1,9 kWh |
Q of terracotta brick = U x A x at x T Q of terracotta brick = 2.59×39,3×5x10 = 5.089,35 Q of terracotta brick = 5,1 kWh |
| Q of lightweight concrete panel = U x A x at x T Q of lightweight concrete panel = 1,04×12x15×10 = 1,04×12x15×10 = 1.872 Wh Q of lightweight concrete panel = 1,87 kWh |
Q of terracotta brick = U x A x at x T Q of concrete roof = 3,52 x12×15x10 = 6.336 Wh Q of concrete roof = 6,3 kWh |
| Total Q = 1,9 + 1,87 = 3,77 kWh Usage in 30 days Q = 3,77 kWh x 30 = 113 kWh |
Total Q = 5,1 + 6,3 = 11,4 kWh Usage in 30 days Q = 11,4 kWh x 30 = 342 kWh |
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Using the assumption of household usage with the category R-1 2200 VA |
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| Block I 0 –20 kWh = 390,- x 20 = 7.800,- Block II 21-60 kWh = 445,- x 60 = 26.700,- Block III 61 kWh ≤ = 495,- x 33 = 16.335,- Total cost for 1 month = Rp 50.835,- |
Block I 0 –20 kWh = 390,- x 20 = 7.800,- Block II 21-60 kWh = 445,- x 60 = 26.700,- Block III 61 kWh ≤ = 495,- x 262 = 129.690,- Total cost for 1 month = Rp 164.190,- |
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Cost saving attained by using LIGHTWEIGHT CONCRETE material = Rp 164.190,– Rp 50.835,- = Rp 113.335,- |
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By using LIGHTWEIGHT CONCRETE material, a room of 3m x 4m can save electricty cost up to Rp 113.335,- per month. That’s worth saving, isn’t it?
1The writer is an architect, member of IAI and HDII
