Dehumidification And Humidifier Group; Dehumidification And Reheat - Carrier 48FP Controls Operation And Troubleshooting

Sequence of Operation — If the supply fan is off, all modes
are deactivated and the heating control valves are closed. For
IAQ Reheat to be active: IQMP > MDP and OAT < SASP.
When IAQ Reheat is active, control will issue 4 to 20 mA sig-
nal (at Channel 43) to hydronic heat control valve, to maintain
SAT control temp (IAQRR) at Supply Air sensor location.
Configuration — To configure, enable IAQ Mode (see IAQ
section for configuration) or enable OAC Mode (see OAC sec-
tion for configuration). Connect Hydronic Heat control valve
to channel 43.
Algorithms — When IAQ/OAC is active and OAT < SASP,
then IAQRR = SASP + (Space Temp Reset) – ECSO – 5.0. In
all other conditions, IAQRR = 0.
Table 31 — Indoor-Air Quality/
Outdoor-Air Control Reheat Definitions
ITEM
ECSO Economizer Set Point Offset
IAQ Indoor-Air Quality Function
IAQRR IAQ Reheat Reference Value
IQMP Final Minimum Damper Position
MDP Minimum Damper Position
OAC Outdoor-Air Control Function
OAT Outdoor-Air Temperature
SASP Supply-Air Set Point Temperature
Dehumidification and Humidifier Group —
group includes Dehumidification and Reheat, and Humidifier
Controls.
DEHUMIDIFICATION AND REHEAT — Dehumidifica-
tion will override comfort condition set points in order to deliv-
er cooler air to the space and satisfy a humidity set point at the
space or return air humidity sensor. Reheat will energize a gas
heating section concurrent with compressor operation should
the dehumidification operation result in cooling of the space
down to Occupied Heating set point. Reheat is not available on
units equipped with factory-installed electric heaters. Dehu-
midification and Reheat (High Humidity Override) is
Mode 41. The unit must be equipped with the control options
module (available as a factory-installed option or field-installed
accessory on size 034-074 units and is standard on 078-104
units). A humidity sensor (field-supplied and -installed) is also
required for operation. See Table 32.
Dehumidification — The Master Loop (ML) reads the Return
Air or Space Humidity sensor. When the relative humidity
(RH) value exceeds the High Humidity limit set point, the ML
will issue CCSR value at low limit (typically 40 F) to the CSL.
The CSL will initiate steps of cooling operation to maintain
supply air temperature leaving unit at CCSR value. Cooling
operation will continue until the RH value at sensor location
equals the HHL set point. The ML will return CCSR value to
maintain set point SAT. Stages of cooling capacity will be re-
duced until SAT rises back to the set point.
Reheat — For units with gas heat, when return air temperature
(VAV) or space temperature (CV) drops below the Occupied
Heating set point, the Master Loop issues a SHSR value to the
SHSL (while maintaining Dehumidification CCSR at CSL).
The SHSL initiates the staged heating cycle operation (operat-
ing simultaneously with Dehumidification/Cooling operation).
During reheat, HIR relay will be energized, forcing the room
terminals to minimum heating position. Reheat via staged heat-
ing continues until OHSP is satisfied. When satisfied, the ML
issues minimum value SHSR and the SHSL terminates heating
cycle. If the humidity level at sensor location continues to ex-
ceed the set point, Dehumidification/Cooling operation will
continue.
DEFINITION
This
For units with electric heaters, simultaneous operation of
cooling and electric heaters is never permitted on 50FP,JP,NP
units. If the unit control detects that a compressor stage is ac-
tive, then electric heater operation is blocked. When the last
compressor stage is turned off, then Occupied Heat mode will
be permitted. Heating will continue until either the OHSP is
satisfied or RH exceeds the HHL set point. If RH, again, ex-
ceeds the HHL set point, reheat will be terminated immediately
and Dehumidification will be re-initiated.
For units with hydronic heating coil, when return-air tem-
perature (VAV) or space temperature (CV) drops below the Oc-
cupied Heating set point, the Master Loop calculates a required
Leaving-Air Temperature value (HCSR) required to maintain
return air or space temperature at Occupied Set Point. The
Master Loop issues an HCSR to the HCSL (while maintaining
Dehumidification CCSR at CSL). The HCSL will modulate
heating coil control valve to maintain desired HCSR at the
Supply-Air Temperature sensor location. During Reheat, the
HIR relay will be energized, forcing room terminals to Mini-
mum Heating position. Reheat will be terminated when RAT
(CV) or SPT (CV) returns to Occupied Set Point.
Configuration — To configure for a humidity sensor, press
to enter into the Service function. Enter the pass-
word. Press to enter into the User Configuration sub-
function. Scroll down to HUSN. The current configuration will
be shown. The default is 0 (no sensor). The acceptable range of
values is 0 to 2, where 0 is no sensor, 1 is differential humidity
(2 sensors), and 2 is one return air or space sensor. Press
to enable the humidity sensors.
ENTER
To set the high humidity limit value, press
into the Service function. Enter the password. Press
to enter into the Cooling subfunction. Scroll down to HHL.
The current configuration will be shown. The default is 99%
(relative humidity). The acceptable range of values is 0 to
100%. To change the set point, press the new number (example
) and press
ENTER
NOTE: To permit Reheat on VAV unit, unit must be config-
ured for Occupied Heating. Simultaneous heating-cooling
operation is permitted only on units with gas heating section or
hydronic heating system.
Table 32 — Dehumidification and
Reheat Definitions
ITEM
CCSR Cooling Submaster Reference
CSL Cooling Submaster Loop
CV Constant Volume
HCSL Heating Coil Submaster Loop
HCSR Heating Coil Submaster Reference
HHL High Humidity Limit (Set Point)
HIR Heat Interlock Relay
HUSN Humidity Sensor(s) Option
ML Master Loop
OHSP Occupied Heating Set Point
RAT Return-Air Temperature
RH Relative Humidity
SAT Supply-Air Temperature
SHSL Staged Heating Submaster Loop
SHSR Staged Heating Submaster Reference
SPT Space Temperature
VAV Variable Air Volume
28
. See Table 33.
DEFINITION
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