Direction: An office has an area of 60 sq.m with floor height of 3 m and occupancy of 5 persons. The external wall area is 40 sq.m which includes 4 sq.m of double glazed windows. The thermal trans-mittance rate (U) of external wall is 0.35 and window is 2.00. External and internal design temperatures are 34°C and 22°C respectively.
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The heat gain through the external walls and windows (in watts) will be______
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- 247.2 watts
- 248 watts
- 249 watts
- 250 watts
Correct Option: A
To calculate the amount of heat transfer, Φ = A × U × (T1 – T2)
Where Φ is the heat transfer in watts, U is the thermal transmittance, T1 is the temperature on one side of the structure, T2 is the temperature on the other side of the structure and A is the area in square metres.
Φ = 36 × 0.35 × (34 – 22) + 4 × 2.0 × (34 – 22)
= 151.2 + 96 = 247.2 watts
