Building Services Engineering 5th Edition Handbook

136 Ventilation and air conditioning
If the duct side is l m, then A = l 2 m 2 . Therefore:
l = √ A m
= √ 0.106 m
= 0.325 m
EXAMPLE 5.2
A lecture theatre has dimensions 25 m × 22 m × 6 m high and has 100 occupants; 8 l/s of
fresh air and 25 l/s of recirculated air are supplied to the theatre for each person. A singleduct
ventilation system is used. If 10% of the supply volume leaks out of the theatre,
calculate the room air change rate and the air volume flow rate in each duct.
supply air quantity = (8 + 25) l s × 1m3
Hence,
Now,
Q = 0.033 × 110 m 3 /s
= 3.63 m 3 /s
Q = NV
3600
and hence,
= 0.033 m 3 /s
N = 3600 Q
V
3600 × 3.63
= air changes/h
25 × 22 × 6
= 3.96 air changes/h
Leakage from the theatre is:
Q 1 = 10% × Q
= 0.1 × 3.63 m 3 /s
= 0.36 m 3 /s
10 3 l
Quantity of air extracted from the theatre is:
Q e = 3.63 − 0.36 m 3 /s
= 3.27 m 3 /s