Reznor RXH (Outdoor PreevA) Unit Installation Manual - Manual (Page 55)

Form I-RDH/REH/RHH/RXH (12-14), P/N 215210 R14, Page 55
(high fire). The analog output 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 “SSH” 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 signal
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%.
0%
20%
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
Heating is disabled when the ambient temperature is above the lockout value “oH”
(default 62°F).
Cooling Stages
0%
20%
40%
60%
80%
100%
0 1 2 3 4 5 6 7 8 9 10
Cooling Operation - The unit will initiate cooling if the
temperature sensed at the space sensor (discharge air sensor)
climbs above the WCSP into the Cooling proportional band, CPB.
The cooling stages are based on C1, C2, and C3 values.
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 addition, 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.
8.3.2 Optional Digital
Heating/Cooling/
Dehumidification
(Reheat) Controls,
Options D12B, D12C,
D12D, D12E, D12G
- applies to RDH,
REH, RHH, or RXH
[required with all
dehumidification units,
Option AU7]
These digital control options are for neutral air control and can have an optional space
reset control. These are the only control options that apply to RDH, REH, RHH, and
RXH units with dehumidification (Option AU7L or AU7R).
The programmable controller (
FIGURE 49) used with these options has a built-in time
clock card for energy savings and better management of the specific application. If
equipped with the optional serial communication card, the controller is compatible with
either the LON or N2open BAS protocol.
If your unit was ordered with either Option D12B, D12C, D12D, D12E, or D12G, refer to
Form CP-PREEVA-D12 B/C/D/E/F/G in the Literature Bag, for more detailed informa-
tion on these four digital control systems.
The microprocessor unit (Model FX06,
FIGURE 49) in control Options D12B, D12C,
D12D, D12E, and D12G is custom programmed for the Reznor ® PREEVA ® models.
Control features include:
• Custom 3-step control sequence of cooling and dehumidification
(reheat) control
• Modulation or 2-stage gas heat control
• SCR control or two stage electric heat
• Fully integrated outdoor ambient lockouts based
on outdoor dry bulb/dewpoint or enthalpy