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112
tioning. The basic pieces of equipment are the filters, preheat coils,
humidifiers, dehumidifiers, reheat coils, additional cooling coils, fans
and controls. The control of air purity can be achieved in various de-
grees. As a minimum control some sort of filtering must be done near
the entrance of the air-conditioning system. Possibly the most effi-
cient filtering device is the electrostatic precipitator.
In order to establish the size and operational requirements of an
air-conditioning system, the maximum probable heating and co-
demands have to be calculated. The maximum probable heating de-
mand is usually for winter air conditioning and it involves heating
and humidifying. The maximum probable cooling demand is gener-
ally for summer applications and requires cooling and dehumidifying.
The inside design conditions depend entirely upon the purpose for
which air conditioning is used. Certain industrial process requirements
and human comfort are the two major factors to be considered. With
ever increasing tendencies to use air-conditioning a building engineer
must have sound knowledge of the subject.
As far as ventilation is concerned the modern theory to this ef-
fect can be summed up in the statement that for places of general as-
sembly the purpose of ventilation is to carry away excess heat and
odours and that normally 10 cu. ft per minute of outside air per person
is sufficient to accomplish this objective
. In buildings such as homes,
the leakage of air through cracks in doors and windows is usually suf-
ficient to meet this requirement. Although ventilation was formerly
concerned with the supply of fresh air to and the removal of hot and
contaminated air from the space it gradually came to be associated with
cleaning of air.
Industrial buildings often present special problems
in ventilation.
There are certain industrial processes that are accompanied by the production of
air-born dust, fumes, toxic vapours and gases which are hazardous to the health
of workers. Three types of ventilation are in use so that to control dangerous
gases and dusts: exhaust systems
, dilution systems and combinations of both.
The contaminated air is exhausted at high velocity from hoods which have suf-
ficient entrance velocity to pick up the contaminants
.
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