Perfect Humidity Adaptive Dehumidifica; Tion System; Perfect Humidity Modes; Perfect Humidity System Components - Bryant Preferred Series Service And Maintenance Instructions

SEAT
5/8" HEX
0.47
PERFECT HUMIDITY ADAPTIVE DEHUMIDIFI-
CATION SYSTEM
Units with the factory-equipped Perfect Humidity option are capa-
ble of providing multiple modes of improved dehumidification as
a variation of the normal cooling cycle. The design of the Perfect
Humidity system allows for two humidity control modes of opera-
tion of the rooftop unit, utilizing a common subcooling/reheat de-
humidification coil located downstream of the standard evaporator
coil. This allows the rooftop unit to operate in both a dehumidifi-
cation (Subcooling) mode and a hot gas Reheat Mode for maxi-
mum system flexibility. The Perfect Humidity package is factory-
installed and will operate whenever there is a dehumidification re-
quirement present.
The Perfect Humidity system is initiated based on an input from a
discrete input from a mechanical space or return air humidistat.

Perfect Humidity Modes

DEHUMIDIFICATION MODE (SUBCOOLING)
This mode will be engaged to satisfy part-load type conditions
when there is a space call for cooling and dehumidification. Al-
though the temperature could have dropped, decreasing levels of
the sensible load in the space, the outdoor and/or space humidity
levels can be higher. A typical scenario could be when the outside
air is 85°F (29°C) with 70% to 80% relative humidity (RH). De-
sired sensible heat ratio (SHR) for equipment in this scenario is
typically from 0.4 to 0.7. The Perfect Humidity unit will initiate
Dehumidification mode when the space temperature and humidity
are both above the temperature and humidity setpoints and will at-
tempt to meet both setpoint requirements.
Once the humidity requirement is met, the unit can continue to op-
erate in normal cooling mode to meet any remaining sensible ca-
pacity load. Alternatively, if the sensible load is met and humidity
levels remain high the unit can switch to Hot Gas Reheat mode to
provide neutral, dehumidified air.
1. CoreMax is a registered trademark of Fastest, Inc.
1/2-20 UNF RH
0.596
30°
WASHER
This surface provides a metal to metal seal when
torqued into the seat. Appropriate handling is
required to not scratch or dent the surface.
Fig. 13 — CoreMax
CORE
(Part No. EC39EZ067)
1/2" HEX
O-RING
Access Port Assembly
1
REHEAT MODE
This mode is used when dehumidification is required without a
need for cooling, such as when the outside air is at a neutral tem-
perature, but high humidity exists. This situation requires the
equipment to operate at a low SHR of 0.0 to 0.2. With no cooling
requirement calling for dehumidification, the Perfect Humidity
adaptive dehumidification system will turn on both compressors
and open the two hot gas bypass valves allowing refrigerant flow
to the Perfect Humidity coil to reheat the unit's supply air to a neu-
tral temperature.
As the hot bypassed refrigerant liquid (gas or two-phase mixture)
passes through the Perfect Humidity coil, it is exposed to the to the
cold supply airflow coming from the evaporator coil. The refriger-
ant is subcooled in this coil to a temperature approaching the evap-
orator leaving air temperature. The liquid refrigerant then enters a
Thermostatic Expansion Valve (TXV) decreasing the air pressure.
The refrigerant enters the TXV and evaporator coil at a tempera-
ture lower than the temperature in the standard cooling operation.
This lower temperature increases the latent capacity of the evapo-
rator. The refrigerant passes through the evaporator turning it into
a superheated vapor. The air passing over the evaporator coil be-
comes colder than it would during normal operation. As this same
air passes over the Perfect Humidity Reheat Coil, it will be
warmed to the neutral supply air temperature.

Perfect Humidity System Components

The Perfect Humidity uses the standard unit compressor(s), evap-
orator coil and Round Tube-Plate Fin (RTPF) condenser coil. Ad-
ditional refrigeration system hardware includes a subcooler/reheat
coil and solenoid valves. On 581J models, the evaporator coil in-
cludes a TXV as a standard feature. Units with Perfect Humidity
FIOP also include a factory-installed head pressure control system
(Motormaster I) to provide proper liquid pressure during reheat
modes. Unique controls include a Reheat Relay Board (RHB),
evaporator coil freezestat, secondary low pressure switch and a
low outdoor temperature lockout switch (LTLO). Units with two
refrigeration circuits include a solenoid valve, TXV, freezestat and
low pressure switch for each circuit. See Fig. 14.
10
45°
DEPRESSOR PER AHRI 720
+.01/-.035
FROM FACE OF BODY
7/16-20 UNF RH