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—37—
Hot Gas Reheat Mode
When the humidity levels in the space require humidity con-
trol, a hot gas solenoid valve (specific to hot gas reheat mode
only) will open to bypass a portion of hot gas refrigerant
around the condenser coil (see Fig. 43).
This hot gas will mix with liquid refrigerant leaving the con-
denser coil and flow to the subcooling/reheat dehumidification
coil. Now the conditioned air coming off the evaporator will be
cooled and dehumidified, but will be warmed to neutral conditions
(72 F to 75 F) by the subcooling/reheat dehumidification coil.
The net effect of the rooftop when in hot gas reheat mode is to
provide nearly all latent capacity removal from the space when
sensible loads diminish (when outdoor temperature conditions are
moderate). When in hot gas reheat mode, the unit will operate to
provide mostly latent capacity and extremely low sensible heat
ratio capability.
Similar to the subcooling mode of operation, hot gas reheat
mode operates only when the outside-air temperature is warmer
than 40 F. Below this temperature, a factory-installed outside air
temperature switch will lock out this mode of operation.
See Table 30 for the dehumidification system sequence of
operation.
Table 30 — Perfect Humidity Dehumidification System Sequence of Operation and
System Response — Single Compressor Unit
LEGEND
NOTE: On a thermostat call for W1, all cooling and dehumidification will
be off.
THERMOSTAT INPUT ECONOMIZER FUNCTION 581B UNIT OPERATION
H Y1 Y2 OAT. < Economizer Set Point Economizer Comp. 1 Subcooling Mode Hot Gas Reheat Mode
Off — — Normal Operation
On On On No Off On Yes No
On On Off No Off On Yes No
On On On Yes On On Yes No
On On Off Yes On On No Yes
On Off Off No Off On No Yes
OAT — Outdoor Air Temperature
Fig. 42 — Perfect Humidity Subcooling
Mode Operation
Fig. 43 — Perfect Humidity Hot Gas
Reheat Mode Operation
Fig. 41 — Perfect Humidity™ Normal
Design Cooling Operation