Hot Gas Reheat Start-Up And Operation; Reheat Setpoint; Humidity Sensor; Default Reheat Operation - Lennox LGH180H Installation Instructions Manual

Hot Gas Reheat Start-Up And Operation

General
Hot gas reheat units provide a dehumidifying mode of
operation. These units contain a reheat coil adjacent to
and downstream of the evaporator coil. Reheat coil
solenoid valves, L14 and L30, route hot discharge gas
from the compressor to the reheat coil. Return air pulled
across the evaporator coil is cooled and dehumidified;
the reheat coil adds heat to supply air.
See figure 29 for 156, 180H and 210 reheat refrigerant
routing, figure 30 for 156, 180H and 210 normal cooling
refrigerant routing, figure 31 for 240H and 300S reheat
refrigerant routing and figure 32 for 240H and 300S
normal cooling refrigerant routing.
L14 and L30 Reheat Coil Solenoid Valves
When Unit Controller (P298-5 or J299-8) indicates room
conditions require dehumidification, L14 and L30 reheat
valves are energized (Unit Controller P269-3 or P269-4)
and refrigerant is routed to the reheat coil.

Reheat Setpoint

Reheat is factory-set to energize when indoor relative
humidity rises above 60% (default). The reheat setpoint
can be adjusted by changing Unit Controller Settings -
Control menu. A setting of 100% will operate reheat from
an energy management system digital output. The reheat
setpoint can also be adjusted using an optional Network
Control Panel (NCP).
Reheat will terminate when the indoor relative humidity
falls 3% (57% default) or the digital output de-energizes.
The reheat deadband can be adjusted at Settings -
Control menu.
A91 Humidity Sensor
Relative humidity should correspond to the sensor (A91)
output voltage listed in table 25. For example: if indoor air
relative humidity is 80% + 3%, the humidity sensor output
should read 8.00VDC.
Check the sensor output annually for accuracy. Keep the
air intake openings on the sensor clean and free of
obstructions and debris.
Check-Out
Test hot gas reheat operation using the following
procedure.
1- Make sure reheat is wired as shown in wiring section.
2- Make sure unit is in local thermostat mode.
3- Select Unit Controller Service - Test.
LGH/LCH156, 180, 210, 240, 300S
Relative Humidity (%RH + 3%)
20
30
40
50
60
70
80
90
The blower, compressor 1 and compressor 2 (reheat)
should be operating. L14 and L30 LED's on the Unit
Controller should also be ON, indicating the reheat valves
are energized. Reheat mode will appear on the Unit
Controller display.
4- Deselect Unit Controller Service - Test.
Compressor 1 and 2 (reheat) should de-energize, L14
and L30 LED's should go OFF, blower should still be
energized.

Default Reheat Operation

Reheat will operate as shown in table 26 once three
conditions are met:
1- Blower must be operating.
2- System must be in occupied mode.
3- System must NOT be operating in heating mode.
IMPORTANT - Free cooling does not operate during
reheat.
For other reheat control options, refer to the Unit
Controller manual.
Additional Cooling Stages
Units are shipped from the factory to provide two stages of
cooling.
Three stages of cooling is available in zone sensor mode.
Three stages of cooling is also available by installing a
transfer relay and a three-stage thermostat. Refer to the Main
Control Operation section in the Unit Controller manual when
using the transfer relay.
Four stages of cooling is available in zone sensor mode on
units with four compressors (240, 300S).
Compressors are not de-energized when unit operation
changes from cooling to reheat or from reheat to cooling.
Instead, L14 and L30 reheat valves are energized
(reheat) or de-energized (cooling).
NOTE - Another thermostat staging option is available
which allows both compressors to be energized during
free cooling. See Unit Controller manual for details.
Page 48
TABLE 25
Sensor Output (VDC)
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00