THIẾT kế THÔNG GIÓ NHÀ vệ SINH

Design a ventilation system for the toilets in an Auditoria as shown in the accompanying
drawings.
The Male Toilet and Female Toilet should each have separate extract ventilation systems to
avoid ‘cross-talk’ and spread of smoke within the ductwork system.
The mechanical ventilation rate from Table 3.1 CIBSE Guide B2 (2001) is at least 3 air
changes per hour.
For the purposes of this exercise use a value of 8 AC/h.


MALE TOILET
4.5 x 3.0 x 2.7 m = 36.45 m3

The volume of the Male Toilet is:
The ventilation rate in m3/h is:
Ventilation Rate (m3/h)

=

Room volume (m3) x air change rate (ac/h)

Ventilation Rate (m3/h )
=
36.45 m3
x
3
=
291.6 m /h.
Divide by 3600
The ventilation rate is

8 AC/h

= 0.081 m3/s.

A simple method of duct sizing would be:
Duct area = volume flow rate / air velocity.
An appropriate maximum air velocity for a toilet is 4 m/s.
(See Ventilation - Ventilation Design section)
Therefore duct area

=

0.081 / 4 =

If a square duct is used then the duct size is:
= 0.142 m x 0.142 m

0.02025 m2.
( 0.02025 )0.5

The nearest standard size is 0.150 m x 0.150 m
or, 150mm x 150mm.
The drawing below shows the ductwork layout for the Toilets.

The flexible ductwork may be sized using the same technique as above.


Volume flow rate through each flexible

=

0.081 m3/s / 2

=

0.041 m3/s.

A simple method of duct sizing would be: Duct area = volume flow rate / air velocity.
An appropriate air velocity for a flexible in this situation is 4 m/s
Therefore duct area
=
0.041 / 4 =
0.01025 m2.
Cross sectional area
=
p . d2 / 4
d
=
( 4 . CSA / p )0.5
0.5
Therefore flexible diameter
=
( 4 x 0.01025 / p )
=
0.114
m
=
114 mm diameter.
The nearest standard size of PVC flexible is 125mm.
The flexible size should be smaller than the duct to which it is attached to enable a boot or
branch to be spot welded into position, as shown below.

The Female Toilet may be sized using the same method but since the physical dimensions
are so close to the Male Toilet then the same duct sizes can be used, this also standardizes
the complete ventilation system so that the two fans are also identical.
Fans
To choose suitable fans for this example the duct pressure drop and fittings pressure drop
would be calculated.
If the total pressure drop is assumed to be 200 Pa and the flow rate is 0.081 m3/s (81 litres/s)
then a suitable catalogue can be used to pick the fan.
See . Go to Other Fans section.
A tube fan or boxed fan can be used for this project.