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SGH/SCH036, 060, 120, 240
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 valve, L14 (and L30 on 240 units), routes 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 35 through 37 for reheat refrigerant routing.
L14/L30 Reheat Coil Solenoid Valve
When Unit Controller input (Unit Controller J298-5 or
J299-8) indicates room conditions require
dehumidification, L14/L30 reheat valve is 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.
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 (120 & 240 Units)
Relative humidity should correspond to the sensor (A91)
output voltage listed in table 28. 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.
TABLE 28
Relative Humidity (%RH + 3%)
Sensor Output (VDC)
20
2.00
30
3.00
40
4.00
50
5.00
60
6.00
70
7.00
80
8.00
90
9.00
REHEAT MODE REFRIGERANT ROUTING 036/060
FIGURE 35
COMPRESSOR
EXPANSION
VALVES
REHEAT
VALVE
CHECK
VALVE
REFRIGERANT
CIRCUIT 1
EVAPORATOR
OUTDOOR
COIL
AIR
CONDENSER
COIL
