29
Occupied Setpoint (Setpoints
RH.SP) during the occupied
period and Space RH Unoccupied Setpoint (Set-
points
RH.UN) during unoccupied periods. If the Space
Humidity Sensor (SP.RH) value is above the Space RH Set-
point (RH.SP), then dehumidification is needed. If the
Space Humidity Sensor (SP.RH) value is below the Space
RH Setpoint (RH.SP) minus the Space RH Deadband (Set-
points
RH.DB), then dehumidification is no longer need-
ed. If the unit is configured for space sensor control (Con-
figuration
UNIT
U.CTL = 3), then the setpoint Reheat
Heat SP Deadband (Setpoints
RH.HB) applies. This con-
figuration sets the offset above the heating set point at
which a unit in Reheat2 mode will turn off. This is a protec-
tion against over cooling the space and causing a heat de-
mand.
NOTE: When there is a dehumidification demand, the economizer
damper position is limited to its minimum damper position (Oper-
ating Mode
ECON
EC.MP).
REHEAT MODES
Dehumidification (reheat) is a cooling mode function. Refer to
Cooling Operation for cooling mode control. With Humidi-MiZer
units there are three additional HVAC Mode (HVAC) expanded
texts available for the user: Reheat1, Reheat2, and Reheat1/Re-
heat2. Selection of the reheat mode for each refrigerant circuit is
determined by the dehumidification demand and the cooling de-
mand. Table 10 shows the corresponding circuit mode and output
status for the different demand combinations. Units with multiple
circuits can operate with a combination of Reheat1 and Reheat2
circuits, as determined by the amount of space cooling demand.
See Appendix B for complete tables of unit operation response to
thermostat and humidity inputs.
NOTE: Compressor staging control for Humidi-MiZer units re-
quires that circuit A always operates when circuit B is on. This ap-
plies to normal operation, service test, and for control alarm re-
sponses. This operation difference is required due to the fact that
the Motormaster outdoor fan control senses circuit A only.
Operation of the revised refrigerant circuit for each mode is de-
scribed below.
NOTE: x = refrigerant circuit A or B
Normal Cooling
For 48/50HC04-12 units, refrigerant flows from the outdoor con-
denser through the normally open Cooling Liquid Valve (CLV.x)
to the expansion device. Reheat Liquid Valve (RLV.x) and Reheat
Discharge Valve (RDV.x) are closed. (See Fig. 9.) For 48/
50HC14-28 units, refrigerant flows from the outdoor condenser
through the de-energized 3-way Liquid Diverter Valve (LDV.x) to
the expansion device. Reheat Discharge Valve (RDV.x) is closed.
(See Fig. 10.)
Reheat 1 (Subcooling Mode)
This mode increases latent cooling and decreases sensible cooling
compared to normal cooling.
For 48/50HC04-12 units, refrigerant flows from the outdoor con-
denser, through the normally open Reheat Liquid Valve (RLV.x),
and through the reheat condenser coil to the expansion device.
Cooling Liquid Valve (CLV.x) and Reheat Discharge Valve
(RDV.x) are closed. (See Fig. 11.)
For 48/50HC14-28 units, refrigerant flows from the outdoor con-
denser, through the energized 3-way Liquid Diverter Valve
(LDV.x), and through the reheat condenser coil to the expansion
device. Reheat Discharge Valve (RDV.x) is closed. (See Fig. 12.)
Reheat 2 (Hot Gas ReheatMode)
This mode provides maximum latent cooling with little to no sen-
sible capacity. This mode can operate to provide dehumidification
when there is no cooling demand. Similar to Reheat 1 mode, re-
frigerant flows from the outdoor condenser, through the normally
open Reheat Liquid Valve (RLV1.x), or through the energized 3-
way Liquid Diverter Valve (LDV.x), and through the reheat con-
denser coil to the expansion device. Reheat Discharge Valve
(RDV.x) is open which provides some compressor discharge gas
to the reheat condenser to further increase the reheat of the evapo-
rator air stream (See Fig. 13 or 14 based on unit and size).
Table 10 — Control Modes with Humidi-MiZer System
Output and Valve States versus Circuit Mode .x = Circuit A or B identifier
DEMAND AND MODE OUTPUTS 48/50HC 04-12 VALVES 48/50HC 14-28 VALVES
Space
Humidity
Circuit
Cooling
Demand
Circuit
Mode
Circuit
Compressor
(CMP.x)
Cooling-
Reheat
Control
(CRC)*
Reheat2
Valve
(RH3.x)
CLV.x Valve
2-way
RLV.x Valve
2-way
RDV.x
Valve 2-way
RLV.x Valve
3-way
RDV.x
Valve 2-way
— — No power Off Off Off Off (open) Off (open) Off (closed) Off Off (closed)
Low No Off Off Off Off Off (open) On (closed) Off (closed) Off Off (closed)
Low Yes Cool On Off Off Off (open) On (closed) Off (closed) Off Off (closed)
High Yes Reheat1 On On Off On (closed) Off (open) Off (closed) On Off (closed)
High No Reheat2 On On On On (closed) Off (open) On (open) On On (open)
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