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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If 20 lit/sec/person of air is extracted from the office, the ventilation rate in terms of air changes/ hour is_____
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- 2.0
- 3.0
- 2.5
- 4.0
Correct Option: A
The fresh air supply to a room can be calculated as, q = n V
Where, q = fresh air supply (ft 3 /h, m3 /h)
n = air change rate (h–1)
V = volume of room (ft³, m³)
Ventilation rate in terms of N number of air changes per hour and the room volume is given by the formula:
V = N × room volume/ 3600 (3600 is the number of seconds in an hour)
Here, V = total number of people × ventilation rate in m³/sec/person.
20 × 5 × 0.001 = N × 60 × (3/3600) N = 2.0
