Building Services Engineering 5th Edition Handbook

Ventilation and air conditioning 137
Quantity of fresh air entering the ductwork is:
Q f = 8 × 110
10 3 m 3 /s
= 0.88 m 3 /s
Quantity of recirculated air is:
Q f = Q − Q r
= 3.63 − 0.88 m 3 /s
= 2.75 m 3 /s
Exhaust air quantity is:
Q ex = Q e − Q r
= 3.27 − 2.75 m 3 /s
= 0.52 m 3 /s
EXAMPLE 5.3
There are 35 people in a gymnasium, each producing CO 2 at a rate of 10 × 10 −6 m 3 /s. If the
maximum CO 2 level is not to exceed 0.4%, find the air supply rate necessary. The outdoor
air CO 2 concentration is 0.03%. Explain what this means to the ventilation designer.
P
Q = m 3 /s
C r − C s
35 × 10 × 10−6
=
(0.4 − 0.03) × 10 −2 m3 /s
= 0.095 m 3 /s
This is a very small air flow of outdoor air through a gymnasium where strenuous activity by
35 athletic people is to take place. The outdoor air of 95 l/s may be able to be provided by natural
ventilation through controlled low- and high-level vents to the outside. Additional recirculated
air flow to control the air temperature with heating or cooling systems is provided if the climate
required mechanical air treatment.
Removal of heat gains
Ventilation air is used to remove excess heat gains from buildings. Two types of heat gain are
involved: sensible and latent.
Sensible heat gains result from solar radiation, conduction from outside to inside during hot
weather, warm ventilation air, lighting, electrical machinery and equipment, people and industrial
processes. Such heat gains affect the temperature of the air and the building construction.