A new business centre to be located in Edinburgh is being designed with a basement that has a 200-mm-thick wall. Average inner and outer basement wall temperatures are Ti = 25°C and To = 10°C, respectively.
The architect can specify the wall material to be either aerated concrete block with thermal conductivity of 0.15 W/m.K, or stone mix concrete block with thermal conductivity of 1.4 W/m.K. To reduce the conduction heat flux through the stone mix wall to a level equivalent to that of the aerated concrete wall, what thickness of extruded polystyrene sheet must be applied onto the inner surface of the stone mix concrete wall?
The dimensions of the basement are 20 m × 30 m X 2 m, and the expected energy rental usage rate is £15/m2/ month (for the aerated concrete block). What is the yearly cost, in lost energy rental income, if the stone mix concrete wall without the polystyrene insulation is used? Take the thermal conductivity of the polystyrene to be 0.03 W/m.K.
The architect can specify the wall material to be either aerated concrete block with thermal conductivity of 0.15 W/m.K, or stone mix concrete block with thermal conductivity of 1.4 W/m.K. To reduce the conduction heat flux through the stone mix wall to a level equivalent to that of the aerated concrete wall, what thickness of extruded polystyrene sheet must be applied onto the inner surface of the stone mix concrete wall?
The dimensions of the basement are 20 m × 30 m X 2 m, and the expected energy rental usage rate is £15/m2/ month (for the aerated concrete block). What is the yearly cost, in lost energy rental income, if the stone mix concrete wall without the polystyrene insulation is used? Take the thermal conductivity of the polystyrene to be 0.03 W/m.K.
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A guideline number for the thermal resistance to heat flow through the wall is (thickness / conductivity)
For aerated concrete this gives Ra = 0.2 / 0.15 =1⅓ which is (m².K)/W
For stone mix = Rm = 0.2 / 1.4 = 0.143
1. To get the stone mix to the same value as the aerated we need to increase its resistance by
1⅓ - 0.143 = 1.19
If the thickness of expanded polystyrene needed to do this = T then T/0.03 = 1.19
Hence T = 1.19 ͯ 0.03 = 0.0357 m = 3.6 cm. or 1.4 inches
2. Heat flow difference through walls = 15 ͯ [80+1200] ͯ [1/(0.143) - 1/(1.333)] = 18.8 kW
We multiply this by 365 ͯ 24 to arrive at 164000 kW.h per year.
i don't know what "energy rental usage rate" means but you do need to multiply the above 82000 by a cost per kW.h (cost of a unit of electricity for example if it's electric heating) to get the total cost. It'll probably land at around 16000 pounds.
Note : This calculation does not consider heat loss through floor and ceiling.
For aerated concrete this gives Ra = 0.2 / 0.15 =1⅓ which is (m².K)/W
For stone mix = Rm = 0.2 / 1.4 = 0.143
1. To get the stone mix to the same value as the aerated we need to increase its resistance by
1⅓ - 0.143 = 1.19
If the thickness of expanded polystyrene needed to do this = T then T/0.03 = 1.19
Hence T = 1.19 ͯ 0.03 = 0.0357 m = 3.6 cm. or 1.4 inches
2. Heat flow difference through walls = 15 ͯ [80+1200] ͯ [1/(0.143) - 1/(1.333)] = 18.8 kW
We multiply this by 365 ͯ 24 to arrive at 164000 kW.h per year.
i don't know what "energy rental usage rate" means but you do need to multiply the above 82000 by a cost per kW.h (cost of a unit of electricity for example if it's electric heating) to get the total cost. It'll probably land at around 16000 pounds.
Note : This calculation does not consider heat loss through floor and ceiling.
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Thanks but you were a bit fast. I wanted to correct the number 82000 in the second last paragraph - it should of course read 164000.
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