Reheat Modes - Carrier 48HC 04-28 Controls, Start-Up, Operation And Troubleshooting

Occupied Setpoint (Setpoints
period and Space RH

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
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.
Output and Valve States versus Circuit Mode .x = Circuit A or B identifier
DEMAND AND MODE
Circuit
Space Circuit
Cooling
Humidity
Demand
— — No power
Low No
Low Yes
High Yes Reheat1
High No Reheat2

RH.SP) during the occupied
Unoccupied Setpoint

RH.HB) applies. This con-
Table 10 — Control Modes with Humidi-MiZer System
OUTPUTS
Cooling-
Circuit
Reheat
Compressor
Mode Control
(CMP.x)
(CRC)*
Off Off
Off Off Off
Cool On Off
On On
On On
Operation of the revised refrigerant circuit for each mode is de-
(Set- 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).
48/50HC 04-12 VALVES
Reheat2
CLV.x Valve RLV.x Valve
Valve
2-way
(RH3.x)
Off Off (open)
Off Off (open) On (closed) Off (closed)
Off Off (open) On (closed) Off (closed)
Off On (closed)
On On (closed)
29
48/50HC 14-28 VALVES
RDV.x RLV.x Valve
2-way Valve 2-way 3-way
Off (open) Off (closed) Off
Off
Off
Off (open) Off (closed) On
Off (open) On (open) On
RDV.x
Valve 2-way
Off (closed)
Off (closed)
Off (closed)
Off (closed)
On (open)