Encyclopedia of Environmental Science and Engineering, Volume I and II

522 INDUSTRIAL HYGIENE ENGINEERING

2) Ducts can be damaged allowing leakage or

restriction,

3) Fan blades can be deposited with dirt,

4) Fan blades can be corroded or worn away,

5) Fan motors can be seized or corroded due to being

in an uncongenital airstream,

6) Dampers can be corroded, seized or deposited

with dirt,

7) Filters or air cleaners can be blocked or missing,

8) Weather protection devices may be corroded or

damaged.

Faulty Procedures Ventilation systems are often left

to the shop floor operators to control either by an on/off

switch or by opening and closing dampers when required.

There is a danger that the system is not turned on because

of unpopularity or that the opening and shutting of damp-

ers unbalances the system particularly if all dampers are left

fully open. Arguments can occur on the shop floor because

of unpopularity often as a result of faulty design and sys-

tems are left switched off. No ventilation system should be

controlled thus but it should be interlocked electrically with

the process so that it is running when the process is. Multi-

branch systems must be either inherently balanced or have

their controlling dampers locked in position.

Air Conditioning

Air conditioning plant is normally designed to take air at

outside conditions which varies in temperature and moisture

content from the very cold and dry in the depth of winter to

warm and moist in the height of summer. The plant either

heats and humidifies or cools and dehumidifies the air to

supply it to the spaces to be ventilated at such a temperature

and moisture content to deal with the heat gains and losses

and the moisture gains and losses in that space.

Room heat gains and losses vary in intensity with time

over the day and year due to variations in the use of the space

such as changes in occupancy and/or the use of machinery,

plant and equipment, external influences such as movement

of the sun and variations in outside air temperature.

Room moisture gains occur due to occupancy and the

evaporation of water from plant and equipment in use.

Moisture losses are rare but do occur in certain textile and

paper manufacturing plants.

If several rooms have similar patterns of heat and mois-

ture gains and losses, they can be grouped together into a

zone which can have the same supply of air, conditioned by

common controls and plant.

Because the supplied air is the vehicle for heating and

cooling, larger volume flows are normally required just

for providing fresh air, therefore, for reasons of economy,

FIGURE 8 Chart for estimating energy requirements for heating.

1

2

3

4

10 20 25

10

20

30

40

50

60

–20 –10 0

Air temperature °C

Power required kW Ventilation pressure loss kPa

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