Bryant 551C - Manual (Page 50)

50
The liquid enters the evaporator coil at a temperature lower than
in standard cooling operation. This lower temperature increases
the latent capacity of the rooftop unit. The refrigerant passes
through the evaporator and is turned into a vapor. The air passing
over the evaporator coil will become colder than during normal
operation. However, as this same air passes over the subcooling
coil, it will be slightly warmed, partially reheating the air.
Subcooling mode operates only when the outside air
temperature is warmer than 40_F. A factory-installed temperature
switch located in the condenser section will lock out subcooling
mode when the outside temperature is cooler than 40_F.
The scroll compressors are equipped with crankcase heaters to
provide protection for the compressors due to the additional
refrigerant charge required by the subcooling/reheat coil.
When in subcooling mode, there is a slight decrease in system
total gross capacity (5% less), a lower gross sensible capacity
(20% less), and a greatly increased latent capacity (up to 40%
more).
C06135
Fig. 42 --- Perfect Humidityt Normal
Design Cooling Operation
C06136
Fig. 43 --- Perfect Humidity Subcooling
Mode Operation
C06137
Fig. 44 --- Perfect Humidity Hot Gas
Reheat Mode Operation
Hot Gas Reheat Mode
When the humidity levels in the space require humidity control, 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. 44.)
This hot gas will mix with liquid refrigerant leaving the
condenser 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 lockout this mode of operation.
See Table 34 for the Perfect Humidity adaptive dehumidification
system sequence of operation.
SERVICE
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could cause personal
injury or death.
When sevicing unit, shut off all electrical power to unit
and install lockout tag.
! WARNING
Step 1 —Cleaning
Inspect unit interior at the beginning of heating and cooling
season and as operating conditions require.
Evaporator Coil
1. Turn unit power off, tag disconnect. Remove evaporator
coil access panel.
2. If economizer or two-position damper is installed, remove
economizer by disconnecting Molex plug and
removing mounting screws.
3. Slide filters out of unit.
551B
,C