Humidi-Mizer Adaptive Dehumidification System - Carrier WeatherMaker 48A2020 Controls, Start-Up, Operation, Service And Troubleshooting Instructions

Humidi-MiZer Adaptive Dehumidification System

Units with the factory-equipped Humidi-MiZer
pable of providing multiple modes of improved dehumidifica-
tion as a variation of the normal cooling cycle. The design of the
Humidi-MiZer system allows for two humidity control modes of
operation of the rooftop unit, utilizing a common subcooling/re-
heat dehumidification coil located downstream of the standard
evaporator coil. This allows the rooftop unit to operate in both a
Dehumidification (Subcooling) mode and a hot gas Reheat
Mode for maximum system flexibility. The Humidi-MiZer pack-
age is factory installed and will operate whenever there is a de-
humidification requirement present. The Humidi-MiZer system
is initiated based on input from a factory installed return air hu-
midity sensor to the large rooftop unit controller. Additionally,
the unit controller may receive an input from a space humidity
sensor, a discrete input from a mechanical humidistat (CEM re-
quired), or third-party controller. Dehumidification and reheat
control are allowed during Cooling, Vent, and Heating modes in
the occupied period. In Heating mode, Humidi-MiZer will at-
tempt to reach the higher heating control point, but if it cannot
satisfy heating demand at full capacity, then Staged Gas supple-
mental heating will activate, if installed.
SETTING UP THE SYSTEM
Settings for Humidi-MiZer system can be found at the local

display at Configuration
OPERATION
Mode Qualifications
An HVAC: Off, Vent or Cool mode must be in effect to launch
a Humidi-MiZer mode. If Staged Gas Heat is available for sup-
plemental reheat, then an HVAC Heat mode may also allow
Humidi-MiZer to activate. When Humidi-MiZer reaches full
capacity, if heating demand persists, then Supplemental Staged
Gas heat will activate.
Sensor Failure
If an associated sensor responsible for controlling Humidi-
MiZer system fails, dehumidification will not be attempted
(RARH).
Initiating a Humidi-MiZer Reheat or Dehumidification Mode
To call out a Dehumidification mode in any HVAC mode, one
of the following must be true:
• The space is occupied and the humidity is greater than the
relative humidity trip point (D.RH.S).
• The space is occupied and the discrete humidity input is
closed.
Ending a Humidi-MiZer Reheat or Dehumidification Mode
When either the humidity sensor reading falls below the set-
 
point (Configuration DEHU
saved in the Relative Humidity Dead Band (Configuration->
DEHU->DH.DB, default 5%, range 1 to 30%), or the discrete
input reads "LOW," the Humidi-MiZer mode will end.
Relevant Outputs
The Humidi-MiZer 3-way valve (reheat valve) commanded
output can be found in Outputs
The Humidi-MiZer Condenser Modulating Valve (Condenser
EXV) position output can be found in Outputs
C.EXV. The condenser position will be provided as percent open.
The Humidi-MiZer Bypass Modulating Valve (Bypass EXV)
position output can be found in Outputs
The bypass position will be provided as percent open.
HUMIDI-MIZER MODES
Dehumidification Mode (Cooling Dehum mode 23)
Three modes exist: Cooling Dehum, Venting Dehum, and
Heating Dehum. Cooling Dehum was previously subcooling.
option are ca-
®
DEHU. See Table 69.
 
D.RH.S) by an amount
 
COOL RHV.
 
COOL
 
COOL B.EXV.
The Humidi-MiZer coil will reheat to the current normal cool-
ing control point if it is greater than the dehumidification cool
control point. Venting Dehum is the second reheat mode based
on control type temperature demand.
The Dehumidification mode will be engaged to satisfy part-
load type conditions when there is a space call for cooling and
dehumidification. Although the temperature may have dropped
and decreased the sensible load in the space, the outdoor and/or
space humidity levels may have risen. A typical scenario might
be when the outside air is 85°F and 70 to 80% relative humidi-
ty (RH). Desired SHR for equipment in this scenario is typical-
ly from 0.4 to 0.7. The Humidi-MiZer unit will initiate Dehu-
midification mode when the space temperature and humidity
are both above the temperature and humidity setpoints, and at-
tempt to meet both setpoint requirements.
Once the humidity requirement is met, the unit can continue to
operate in normal cooling mode to meet any remaining sensi-
ble capacity load. Alternatively, if the sensible load is met and
humidity levels remain high the unit can switch to Hot Gas Re-
heat mode to provide neutral, dehumidified air.
Venting Dehum mode (24)
This mode is used when dehumidification is required without a
need for cooling, such as when the outside air is at a neutral
temperature but high humidity exists. This situation requires
the equipment to operate at a low SHR of 0.0 to 0.2. With no
cooling requirement and a call for dehumidification, the A Se-
ries Humidi-MiZer adaptive dehumidification system will cy-
cle on enough compressors to meet the latent load requirement,
while simultaneously adjusting refrigerant flow to the Humidi-
MiZer coil to reheat the air to the desired neutral air setpoint.
The A Series Humidi-MiZer system controls allow the dis-
charge air to be reheated to either the return air temperature mi-
nus a configurable offset or to a configurable Reheat setpoint
(default 70°F). The hot gas reheat mode will be initiated when
only the humidity is above the humidity setpoint, without a de-
mand for cooling.
Heating Dehum mode (25)
If heating demand occurs along with Dehumidification de-
mand, then the Heating Control setpoint HEATCPNT will be
set to 85°F. If the unit is equipped with Staged Gas heat and
Humidi-MiZer reaches full capacity while heating and dehum
demand persists, then supplemental staged gas heat will add to
the heat created by Humidi-MiZer, in order to meet the higher
heating control point.
System Control
The essential difference between the three Dehumidification
modes is in the supply air setpoint. In Cooling Dehumidification
mode, the supply air setpoint is the temperature required to pro-
vide cooling to the space. This temperature is whatever the cool-
ing control point would have been in a normal cooling mode. In
Venting Dehum mode, the supply air setpoint will be either an off-
set subtracted from return air temperature (D.V.RA) or the Vent
Reheat Setpoint (D.V.HT). Both values are configurable. For
Heating dehum the equipment setpoint for reheat will become the
Heating control point or go to full heat based on the demand seen
for the control type. For all three Dehumidification modes, the unit
compressor staging will decrease the evaporator discharge tem-
perature to the Dehumidify Cool Setpoint (D.C.SP COOL) in or-
 
der to meet the latent load and reheat the air to the required cooling
or reheat setpoint. There is a thermistor array called Tempera-
tures_AIR.T_CCT connected to the RCB. This thermistor array
serves as the evaporator discharge temperature (EDT). See
Fig. 17. In Heating Dehum the Humidi-MiZer setpoint will be-
come the Heating control setpoint in order to maximize heat from
the reheat coil.
The A Series Humidi-MiZer
lation valves that provide accurate control of the leaving air tem-
perature as the evaporator discharge temperature is decreased to
75
® system uses refrigerant flow modu-