Viii-Hot Gas Re-Heat - Lennox LGM Series Manual

VIII-FACTORY-INSTALLED Hot Gas Re-Heat
General
Hot gas reheat units provide a dehumidifying mode of op-
eration. 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 32 for 156 and 180 re-
heat refrigerant routing, figure 33 for 156 and 180 normal
cooling refrigerant routing, figure 34 for 210, 240, and 300
reheat refrigerant routing and figure 35 for 210, 240, and
300 normal cooling refrigerant routing.
L14 and L30 Reheat Coil Solenoid Valves
When Unit Controller (P298-5 or J299-8) indicates room
conditions require dehumidification, reheat valves L14
and L30 are energized (Unit Controller J394-1 or J394-3)
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 mobile service app 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 in-
door relative humidity falls 3% (57% default) or the digital
output de-energizes. The reheat deadband can be adjust-
ed at Settings - Control menu.
A91 Humidity Sensor
Relative humidity should correspond to the sensor (A91)
output voltage listed in table 22. 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.
Relative Humidity (%RH + 3%)
20
30
40
50
60
70
80
90
Check-Out
Test hot gas reheat operation using the following proce-
dure.
1 - Make sure reheat is wired as shown in wiring
section.
2 - Make sure unit is in local thermostat mode.
3 - Use mobile service app (the QR is located in the
control area) menu path to select:
SERVICE > TEST > DEHUMIDIFIER
The blower, compressor 1 and compressor 2 (reheat)
should be operating. Reheat mode will appear on the mo-
bile service app display.
4 - Deselect:
SERVICE > TEST > DEHUMIDIFIER
Compressor 1 and 2 (reheat) should de-energize, blower
should still be energized.
Default Reheat Operation
Reheat will operate as shown in table 23 once this condi-
tion is met:
1 - 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 Control-
ler manual.
Additional Cooling Stages
Units are shipped from the factory to provide two stages
of cooling. 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 44
TABLE 22
Sensor Output (VDC)
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00