Specifications

25
RG SERIES ENGINEERING GUIDE
Hot Gas Reheat - Controls
The reheat option is available with the Aurora or FX10 control.
Three control schemes are available:
Room wall dehumidistat
An optional room wall dehumidistat that controls the reheat mode
thru a 24VAC ‘Hum’ input (On or Off). Setpoint and deadband is
determined by the dehumidistat.
Duct humidity sensor (FX10 only)
An optional duct humidity sensor is installed. The FX10 control
reads the humidity from the sensor and determines operation
mode. Setpoint and deadband are internally set by the FX10
control and are adjustable. Continuous blower operation is a
requirement for this mode to accurately measure relative humidity
during the off cycle.
Room wall humidity sensor (FX10 only)
An optional wall humidity sensor is installed. The FX10 control
reads the humidity from the sensor and determines operation
mode. Setpoint and deadband are internally set by the FX10
control and are adjustable. Continuous blower operation is NOT a
requirement for this mode.
The unit will cycle thru a ‘flush cycle’ to purge refrigerant and
oil from the idle heat exchanger once every 24 hours when in
cooling mode. The FX10 control will provide an option to set back
reheat to an adjustable unoccupied humidity set point during
unoccupied time periods. This option is factory set to “OFF”
so reheat will control to one set point at all times. If set back is
required during unoccupied times the option must be set to “ON”
in the field by the building automation system or a user interface.
The dehumidification set back will only work when using a duct
humidity sensor or room wall humidity sensor.
Mode of Operation
Please refer to the refrigeration circuit diagram (Hot Gas Reheat -
Refrigerant section) and the hot gas reheat wiring schematic
.
Heating Mode Operation
Upon a call for heating (Y), blower relay is energized immediately,
and the compressor contactor will be energized after a 90
second delay.
Cooling Mode Operation
Upon a call for cooling (Y, O), blower relay and reversing valve
coil are energized immediately, and the compressor contactor
is energized after a 90 second delay. If there is a call from the
de-humidistat or the internal control logic see the humidity sensor
has reached set point the blower cfm will be reduced by 15% to
increase the unit’s latent capacity.
Dehumidification Mode Operation
Upon a call for dehumidification, the blower relay and reversing
valve coil are energized immediately, and the compressor
contactor will energize after a 90 second delay. The reheat valve
coil will energize once the compressor has been operational for
30 seconds.
If a call for space heating is received during reheat operation the
compressor will shut down for 5 minutes and the unit will restart
in the heating mode. Once the requirement for space heating has
been satisfied the unit will shut down for 5 minutes and re-start in
reheat mode.
If a call for space cooling is received during reheat operation
the reheat valve coil will be disabled until the space cooling
requirements have been satisfied. Once the space cooling
requirements have been satisfied the reheat valve coil will be
energized with out shutting down the compressor.
Dehumidification Set Point
(used only with a humidity sensor)
The factory default set point for dehumidification is 52% this is field
adjustable from 30% to 60%. In addition there is a factory default
differential of 5% field adjustable from 5% to 15%. The control will
enable re-heat when the space humidity rises above the set point
plus the differential. Depending upon the environmental conditions
within the building and the operating parameters of the water
source heat pump, the unit may not be capable of maintaining the
lower control limit of 30% relative humidity over extended periods
of time.
Reheat operation during periods of un-occupancy
This unoccupied set point is useful to reduce energy use in
dehumidification. Many system designs greatly reduce or even
eliminate fresh air makeup during the unoccupied hours and
the need for reheat is lessened. The control logic contains an
unoccupied set point that can be used for the unoccupied mode
if desired. The factory default for the set point is 60% and is
adjustable from 30% to 60%. The unoccupied setback must be
enabled either through a building automation system or with a user
interface. Factory default for unoccupied setback is off.
Space Humidity High and Low Alarm Limit
(building automation system only)
The control has a high and low alarm limit that can be enumerated
over a building automation system. The factory default set point
for these alarm limits is 0% for the low alarm and 100% for the
high alarm limit. These limits can be adjusted though a building
automation system. Caution should be used in selecting these
limits so as not to cause nuisance alarms.