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• Cooling — For all cooling control types: A High Cool
HVAC mode will be requested internally to the control to
maintain diagnostics, although the end user will see a
Dehumidification mode at the display. In addition, for
multi-stage cooling units the cooling control point will
be set to Configuration
reset is applied).
• Reheat When Cooling Demand is Present — For reheat
control during dehumidification: If reheat follows an
offset subtracted from return-air temperature (Configu-
ration
DEHU
D.SEL = 2), then no heating will be
initiated and the alarm relay will be energized. If
Configuration
DEHU
tion
HEAT
HT.CF = staged gas or hot water valve,
then the selected heating control type will operate in the
low heat/modulating mode.
• The heating control point will be whatever the actual
cooling setpoint would have been (without any supply air
reset applied).
• Reheat During Vent Mode — If configured (Configura-
tion
DEHU
D.V.CF = 0), the heating control point
will be equal to RAT – D.V.RA. If configured (Configu-
ration
DEHU
D.V.CF=1), the heating control point
will be equal to the D.V.HT setpoint.
Ending Dehumidification and Reheat Control — When ei-
ther the humidity sensor fall 5% below the setpoint (Configu-
ration
DEHU
D.RH.S) or the discrete input reads
"LOW", the Dehumidification mode will end.
Humidi-MiZer
®
Adaptive
Units with the factory-equipped Humidi-MiZer
System —
option are capable of providing multiple modes of improved
dehumidification 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, utiliz-
ing a common subcooling/reheat dehumidification coil located
downstream of the standard evaporator coil. This allows the
rooftop unit to operate in both a Dehumidification (Subcool-
ing) mode and a hot gas Reheat Mode for maximum system
flexibility. The Humidi-MiZer package is factory installed and
will operate whenever there is a dehumidification requirement
present. The Humidi-MiZer system is initiated based on input
from a factory installed return air humidity 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 required), or third-party
controller. Dehumidification and reheat control are allowed
during Cooling and Vent modes in the occupied period.
SETTING UP THE SYSTEM — Settings for Humidi-MiZ-
er system can be found at the local display at Configura-
tion
DEHU. See Table 70.
OPERATION
Mode Qualifications — An HVAC: Off, Vent or Cool mode
must be in effect to launch a Humidi-MiZer mode.
Sensor Failure — If an associated sensor responsible for con-
trolling Humidi-MiZer system fails, dehumidification will not
be attempted (SPRH, RARH).
Initiating a Humidi-MiZer Reheat or Dehumidification
Mode — To call out a Reheat mode in the "Vent" or the "Off"
HVAC mode, or to call out a Dehumidification mode in a
"Cool" 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 falls 5% below the setpoint
(Configuration
DEHU
D.RH.S) or the discrete input reads
"LOW," the Humidi-MiZer mode will end.
DEHU
D.C.SP (no SASP
D.SEL = 1 and Configura-
Dehumidification
Relevant Outputs — The Humidi-MiZer 3-way valve (reheat
valve) commanded output can be found in Outputs
COOL
RHV.
The Humidi-MiZer Condenser Modulating Valve (Con-
denser EXV) position output can be found in Outputs
COOL
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
COOL
B.EXV. The bypass position will be provided as per-
cent open.
HUMIDI-MIZER MODES
Dehumidification Mode (Subcooling) — This mode will be
engaged to satisfy part-load type conditions when there is a
space call for cooling and dehumidification. Although the tem-
perature 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 humidity (RH). Desired SHR for equip-
ment in this scenario is typically from 0.4 to 0.7. The Humidi-
MiZer unit will initiate Dehumidification mode when the space
temperature and humidity are both above the temperature and
humidity setpoints, and attempt to meet both setpoint require-
ments.
Once the humidity requirement is met, the unit can continue
to operate in normal cooling mode to meet any remaining sen-
sible 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.
Reheat Mode — 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 sit-
uation requires the equipment to operate at a low SHR of 0.0 to
0.2. With no cooling requirement and a call for dehumidifica-
tion, the A Series Humidi-MiZer adaptive dehumidification
system will cycle 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 con-
trols allow the discharge air to be reheated to either the return
air temperature minus 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 set-
point, without a demand for cooling.
System Control — The essential difference between the De-
humidification mode and the Reheat mode is in the supply air
setpoint. In Dehumidification mode, the supply air setpoint is
the temperature required to provide cooling to the space. This
temperature is whatever the cooling control point would have
been in a normal cooling mode. In Reheat mode, the supply air
setpoint will be either an offset subtracted from return air tem-
perature (D.V.RA) or the Vent Reheat Setpoint (D.V.HT). Both
values are configurable. For both Dehumidification mode and
Reheat mode, the unit compressor staging will decrease the
evaporator discharge temperature to the Dehumidify Cool Set-
point (D.C.SP COOL) in order to meet the latent load and re-
heat the air to the required cooling or reheat setpoint. There is a
thermistor array called Temperatures_AIR.T_CCT connected
to the RCB. This thermistor array serves as the evaporator dis-
charge temperature (EDT). See Fig. 17.
The A Series Humidi-MiZer
modulation valves that provide accurate control of the leaving
air temperature as the evaporator discharge temperature is de-
creased to meet the latent load. As the refrigerant leaves the
compressor, the modulating valves vary the amount of refriger-
ant that enters and/or bypasses the condenser coil. As the by-
passed and hot refrigerant liquid, gas or two-phase mixture
passes through the Humidi-MiZer coil, it is exposed to the cold
supply airflow coming from the evaporator coil. The refriger-
ant is subcooled in this coil to a temperature approaching the
71
®
system uses refrigerant flow
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