PGC, Inc 500-1000 CFM Air Handler May 2006
Appendix A A-3
THEORY OF OPERATION
PGC’s method of control is the
same for both reach-in
chambers and conditioning
systems. The environment to be
conditioned is controlled at a
targeted dew point temperature,
and then reheated to the desired
air temperature. This
methodology follows a proven
technique that maintaining a
constant dew point and air
temperature will produce a very
constant relative humidity. The
desired air temperature and
relative humidity or water
temperature are set via the
SmartPad™. If equipped with
an optional recorder, it can be
wired to record the actual air
temperature and relative
humidity or water temperature.
The air is cooled by means of a
water spray which constantly
sprays water across the air
stream, saturating the air. A
submerged refrigeration
evaporator coil operates 1°C-
2ºC (1.8°F-3.6°F) below the
desired dew point and cools the
water that is sprayed across the
air stream. The air is then re-
heated before it is returned to
the test chamber.
NOTE
Dew point is the temperature at which the air can contain no more moisture and
some moisture begins to condense.
A portion of the air can be diverted around the water spray saturator by a bypass damper. If the
air does not pass through the water spray, it will not be cooled; if the air is not cooled, it will not
require as much (if any) air heat to be applied before it is returned to the test chamber. The
amount of air that passes through the saturator, or bypasses the saturator, is determined by the air
temperature control loop.
Mechanical
Sprayed Coil
Supply Air
Blower
Air Filter
Return Air
Dampers
Figure A-1 - Generic Conditioning Unit
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