Reznor SHH (Indoor PreevA) Unit Installation Manual - Manual (Page 56)

Form I-PDH/SDH/PEH/SHH/PXH, Page 56
Cooling Stages
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20%
40%
60%
80%
100%
0 1 2 3 4 5 6 7 8 9 10
WCSP into the Cooling proportional band, CPB. The cooling stages are based on C1,
C2 and C3 value.
Example: If the working cooling setpoint (WCSP) is 72°F, stage 1 cooling turns on
when space temp (discharge air temp) increases to 73°F (10% of the 10°F CPB).
Stage 2 turns on when space temp increases to 76°F (40% of the 10°F CPB).
Stage 3 turns on when the space temperature increases to 81°F (90% of the 10°F
CPB).
As the space temperature moves back towards WCSP, stage 3 turns off at 40% call for
cooling, stage 2 turns off at 10% call for cooling, and stage 1 turns off at 5% cooling
call. There is a non-adjustable minimum 240 second interstage time delay. In addi-
tion, cooling ambient temperature lockout values prevent individual stages from being
enabled until the outside air temperature is above oC, oC2, and oC3 values.
Compressor inter-stage delay time and compressor minimum on time are controlled by
the nciClgStgTime which is defaulted at 240 seconds. This means that if stage 1 has
just begun, stage 2 cannot start for 240 seconds. Once stage 1 has begun, it must run
for 240 seconds before it will be turned off.
8.3 Digital Controls for Heating/Cooling, Makeup Air and Dehumidification (cont’d)
8.0 Controls and Operation (cont’d)
8.3.1 Optional Digital
Heating/Cooling/
Makeup Air Controls,
Options DG1, DG2,
DG5, DG6 - PDH and
SDH; PXH (cont’d)
will modulate to 100% full fire for 180 seconds to ensure proper
burner ignition. With modulating control (Option DG2 or DG6),
the gas valve will then modulate to a position, linearly with the
proportional band, “HPB”. For staged control (Option DG1 or
DG5), the unit will switch to low fire when the heating output
required from the proportional band is less than the SSO (5%
default) for 30 seconds. The unit switches back to high fire if the
gas signal calls for 90% capacity or “SHH” value. Heating will
completely turn off when the space or discharge air temperature
is above HSP + deadband “HDB.”
Example: Heating will enable when
Temperature < WHSP – HSP – HDB < 72°F – 5°F –
0°F < 67°F
So, when the space temperature drops below 67°F, the sig- 0%
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40%
60%
80%
100%
-5 -4 -3 -2 -1 0 1 2 3 4 5
Heating Output
67°F 68°F 69°F 70°F 71°F 72°F 73°F 74°F 75°F 76°F 77°F
Temperature Difference From
Setpoint and Heating Output
nal to the gas valve is 100% and the burner ignites. After the 180 seconds, if the temperature is 72°F, the signal to
the gas valve will be 50%.
Heating is disabled when the ambient temperature is above the lockout value “oH” (default 62°F).
Cooling Operation
The unit will initiate cooling if the temperature sensed at the space sensor (discharge air sensor) climbs above the