How do big shopping complexes, offices and commercial
buildings cool their indoor space?
For big buildings, we need big cooling capacities. Central
air-conditioning systems using chillers are used. Chilled
water is the most convenient way to collect the heat from
the indoor spaces. We just need pipes. Miles and miles of
them.
Chilled water from the chillers is about 44 degree Fahrenheit
(about 7 deg C). In order for the room heat to be transfered
to the water efficiently, the air in the room is circulated
through tubes containing flowing chilled water.
That is the main function of the air handling unit in a
central air-conditioning chilled water system.
Another function of an air handling unit is to clean the air.
It does this by filtration.
A most basic air handling unit, or AHU, contains a fan, a
cooling coil, and an air filter enclosed in a box-like
structure.
Normally, air contains moisture. When air is passed through
the cooling coils, water usually condenses out at the surfaces
of the coils. Collection pans are installed below the cooling
coils to collect any condensed water. This water is removed
through drain pipes.
The whole box-like enclosure is heat insulated to prevent
condensation at their surfaces. Many enclosures are sound
insulated and are installed on vibration damping pads. Many
others have damper vanes for controlling the air flow.
The most common AHU's have their fans and motors enclosed
inside the box. Other specialized AHU's have motors outside
the box. There are some with steam coils too.
They can be made in numerous configurations too. Tall, short,
wide, long, supply up, supply to side, and so on....
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