2399 A concrete wall in a cold storage room measures 3.2 m high and 4.7 m wide. The inside wall is to be covered by a layer of wood in order to reduce the rate of heat flow through the wall. The cold room is to be maintained at 2°C and the outside is 16°C. The thermal resistance of concrete is 0.26 m2-°C/W. Part Description Answer Save Status A. Determine the required thermal resistance of the wood (units of m2-°C/W) so that the heat flow through the wall is 476 Watt.

Wood Resistance = 0.18 m².°C/W

Explanation:

The formula for heat flow in terms of thermal resistance is:

Q/A = ΔT/R

R = AΔT/Q

where,

R = Total Resistance = Resistance of Concrete + Resistance of wood = Resistance of wood + 0.26 m².°C/W

A = Surface Area of Wall = 3.2 m x 4.7 m = 15.04 m²

ΔT = Difference in temperature = 16°C - 2°C = 14°C

Q = Heat Flow = 476 Watt

Therefore,

0.26 m².°C/W + Wood Resistance = (15.04 m²)(14°C)/(476 W)

Wood Resistance = 0.44 m².°C/W - 0.26 m².°C/W

Wood Resistance = 0.18 m².°C/W

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