Dehumidification And Reheat - Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting

OPERATION
For operation, PID control will be utilized. The process will
run at the rate defined by the Configuration  HUMD 
H.PID  HM.TM. The first part of humidity control tests the
humidity control configuration and will turn on corresponding
configurations to read space or return air relative humidity. If
the supply fan has been ON for 30 seconds and the space is oc-
cupied, then the humidification is started.
Actuator Control
Control is performed with a generic PID loop where:
Error = HM.SP – humidity sensor value (SP.RH or RA.RH,
depending on configuration).
The PID terms are calculated as follows:
P = K * HM.P * error
I = K * HM.I * error + "I" last time through
D = K * HM.D * (error – error last time through)
Where K = HM.TM/60 to normalize the effect of changing the
run time rate
Relay Output Control
If the humidity sensor reading is greater than the humidity set
point then the humidity relay (Outputs  GEN.O  HUM.R) is
closed. The relay will open when the humidity is 2% less than
the humidity set point.
CONFIGURING THE HUMIDIFIER ACTUATOR
Every actuator used in the N Series control system has its own
unique serial number. The rooftop control uses this serial num-
ber to communicate with the actuator. The actuator serial num-
ber is located on a 2-part sticker affixed to the side of the actu-
ator housing. Remove one of the actuator's serial number la-
bels and paste it onto the actuator serial number records label
located inside the left-hand access panel at the unit's control
panel. Four individual numbers make up this serial number.
Program the serial number of the actuator in its Humidifier Ac-
tuator Configurations group, ACT.C (SN.1, SN.2, SN.3, SN.4).
NOTE: The serial numbers for all actuators can be found inside
the control doors of the unit as well as on the actuator itself. If
an actuator is replaced in the field, it is a good idea to remove
the additional peel-off serial number sticker on the actuator and
cover up the old one inside the control doors.
Control Angle Alarm (Configuration  HUMD  ACTC 
C.A.LM)
The humidifier actuator learns what its end stops are through a
calibration at the factory. Field-installed actuators may be cali-
brated in the Service Test mode. When an actuator learns its
end stops through calibration, it determines its control angle.
The actuator will resolve this control angle and express its op-
eration in a percent (%) of this learned range.
If the humidifier actuator has not learned a sufficient control
angle during calibration, the actuator will be unable to control
humidity. For this reason, the humidifier actuator has a config-
urable control angle alarm low limit (C.A.LM). If the control
angle learned through calibration is less than C.A.LM, an alert
will occur and the actuator will not function.
NOTE: This configuration does not typically need adjustment.
It is configurable for the small number of jobs, which may re-
quire a custom solution or workaround.

Dehumidification and Reheat

The Dehumidification function will override comfort condition
set points based on dry bulb temperature and deliver cooler air
to the space in order to satisfy a humidity set point at the space
or return air humidity sensor. The Reheat function will ener-
gize a suitable heating system concurrent with dehumidifica-
tion sequence should the dehumidification operation result in
excessive cooling of the space condition.
The dehumidification sequence requires the installation of a
space or return air humidity sensor or a discrete switch input. A
CEM (option or accessory) is required to accommodate an RH
(relative humidity) sensor connection.
Reheat is possible using a hot gas reheat coil (special order,
factory-installed Humidi-MiZer).
Supplemental Reheat is possible with Staged/Modulating gas
heat and hydronic heat if Humidi-MiZer is unable to provide
sufficient heat.
Dehumidification and reheat control are allowed during Cool-
ing and Vent modes in the occupied period.
On constant volume units using thermostat inputs (C.TYP = 3),
the discrete switch input must be used as the dehumidification
control input. The commercial Thermidistat™ device is the
recommended accessory device.
For an occupied unit with thermostat inputs (C.TYP =3), a de-
humidification demand can push the HVAC MODE from OFF
to VENT and later VENTING DEHUM mode.
SETTING UP THE SYSTEM
The settings for dehumidification can be found at the local dis-
play at Configuration  DEHU.
Dehumidification Configuration (D.SEL)
The dehumidification configuration can be set for the follow-
ing settings:
• D.SEL = 0 — No dehumidification and reheat.
• D.SEL = 1 — The control will perform both dehumidifica-
tion and reheat with modulating valve (hydronic). The valid
Heat source for this option is Hydronic Heat (HT.CF = 4).
• D.SEL = 2 — The control will perform dehumidification
and reheat with staged gas only. The valid heat source for
this option is Staged Gas Heat or Modulating Gas Heat
(HT.CF = 3).
• D.SEL = 3 — The control will perform both dehumidifica-
tion and reheat with third party heat via an alarm relay. In
the case of D.SEL=3, during dehumidification, the alarm
relay will close to convey the need for reheat. A typical ap-
plication might be to energize a 3-way valve to perform
hot gas reheat. The valid Heat sources for this option are
HT.CF = 0, 1, 2 and 5.
• D.SEL = 4 — The control will use the Humidi-MiZer
adaptive dehumidification system.
• D.SEL = 5 — The control will perform both dehumidifica-
tion and reheat with third party heat reclaim via the heat
reclaim output. The heat reclaim output (H.SEL) must be
configured before D.SEL.
Dehumidification Sensor (D.SEN)
The sensor can be configured for the following settings:
• D.SEN = 1 — Initiated by return air relative humidity sensor.
• D.SEN = 2 — Initiated by space relative humidity sensor.
• D.SEN = 3 — Initiated by discrete input.
Economizer Disable in Dehum Mode (D.EC.D)
This configuration determines economizer operation during
Dehumidification mode.
• D.EC.D = YES — Economizer disabled during dehumidi-
fication (default).
• D.EC.D = NO — Economizer not disabled during dehu-
midification.
Vent Reheat Set Point Select (D.V.CF)
This configuration determines how the vent reheat set point is
selected.
• D.V.CF = 0 — Reheat follows an offset subtracted from
return air temperature (D.V.RA).
89
®