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the percentage of total reheat capacity adjustment that will be
made per degree Fahrenheit of supply air temperature error.
OPERATION
Mode Qualifications
An HVAC: Off, Vent, Cool, or Heat mode must be in effect to
launch a Humidi-MiZer mode.
Sensor Failure
If an associated sensor responsible for controlling Humidi-MiZer
fails, dehumidification will not be attempted (SPRH, RARH).
Initiating a Humidi-MiZer Reheat (Venting Dehumidifica-
tion or Heating Dehumidification) or Dehumidification
(Cooling Dehumidification) Mode
To call out a Reheat (Venting Dehumidification) mode in the
"Vent" or the "Off" HVAC mode, Heating Dehumidification in
the "Heat" HVAC mode, or Dehumidification (Cooling Dehumid-
ification) 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 set point
(Configuration
DEHU
D.RH.S) or the discrete input reads
"LOW", the Humidi-MiZer mode will end.
Relevant Outputs
The Humidi-MiZer 3-way valve (reheat valve) commanded out-
put 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) po-
sition output can be found in Outputs
pass position will be provided as percent open.
HUMIDI-MIZER MODES
Cooling Dehumidification Mode
This mode will be engaged to satisfy part load type conditions
when there is a space call for cooling and dehumidification. Al-
though the temperature may have dropped and decreased the
sensible load in the space, 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
equipment in this scenario is typically from 0.4 to 0.7. The Hu-
midi-MiZer unit will initiate Dehumidification mode when the
space temperature and humidity are both above the temperature
and humidity set points, and attempt to meet both set point re-
quirements. Once the humidity requirement is met, the unit can
continue to operate in normal cooling mode to meet any remain-
ing sensible capacity load. Alternatively, if the sensible load is
met and humidity levels remain high, the unit can switch to
Venting Dehum mode to provide neutral, dehumidified air.
Venting Dehumidification Mode
This mode is used when dehumidification is required without a
need for cooling, such as when outside air is 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 P Series Humidi-MiZer adap-
tive 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 set point. The P Series Humid-MiZer system
COOL
RHV.
COOL
COOL
B.EXV. The by-
controls allow for the discharge air to be reheated to either the re-
turn-air temperature minus a configurable offset or to a configu-
rable Reheat set point (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.
Heating Dehumidification Mode
This mode is used when dehumidification is required and heating
is required, such as when the outside air is at a low temperature but
high humidity exists. The system operates the same as in the Vent-
ing Dehumidification mode but the discharge air is reheated to the
SASP HEAT set point. Note that the Humidi-MiZer system is
only intended to supply neutral temperature air and has minimal
heating capacity. It will only be able to reheat to a heating set point
at moderate outside air temperatures and/or low airflows. If dehu-
midification and reheat to a heating temperature is truly required, a
staged, modulating gas, hydronic, or third-party heat unit should
be used.
System Control
The essential difference between the Cooling Dehumidification,
Venting Dehumidification, and Heating Dehumidification modes
is in the supply air set point. See Table 74. In Cooling Dehumidifi-
cation mode, the supply air set point 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 Venting Dehumidification mode, the supply air set point will be
either an offset subtracted from return air temperature (D.V.RA) or
the Vent Reheat Set Point (D.V.HT). Both values are configurable.
In Heating Dehumidification mode, the supply air set point is
whatever the heating control point would have been in a normal
heating mode. For all modes, the unit compressor staging will de-
crease the evaporator discharge temperature to the Dehumidify
Cool Set Point (D.C.SP COOL) in order to meet the latent load
and reheat the air to the required cooling or reheat set point. There
is a thermistor array called Temperatures
nected to the RCB. This thermistor array serves as the evaporator
discharge temperature (EDT). See Fig. 14.
The P-Series Humid-MiZer
lation valves that provide accurate control of the leaving air tem-
perature as the evaporator discharge temperature is decreased to
meet the latent load. As the refrigerant leaves the compressor, the
modulating valves vary the amount of refrigerant that enters and
bypasses the condenser coil. As the bypassed and hot refrigerant
liquid, gas or two-phase mixture passes through the Humidi-MiZ-
er coil, it is exposed to the cold supply airflow coming from the
evaporator coil. The refrigerant is subcooled in this coil to a tem-
perature approaching the evaporator leaving air temperature. The
liquid refrigerant then enters a thermostatic expansion valve
(TXV) where the refrigerant pressure is decreased. The refrigerant
enters the TXV and evaporator coil at a temperature lower than in
standard cooling operation. This lower temperature increases the
latent capacity of the evaporator. The refrigerant passes through
the evaporator and is turned into a superheated vapor. The air
passing over the evaporator coil will become colder than during
normal operation. However, as this same air passes over the
Humidi-MiZer reheat coil, it will be warmed to meet the supply
air set point temperature requirement. See Fig. 15.
The Humidi-MiZer circuit has no digital scroll nor minimum load
valve. Dehumidification is an air change requiring process. As
such the evaporator load needs to be adequate to keep the TXV
open with most or all of the Humidi-MiZer circuit active. This al-
lows for stable operation of the Humidi-MiZer circuit and intro-
duces adequate air changes of dry air for dehumidification. VAV
systems cannot typically operate at cooling minimums and ade-
quately dehumidify.
95
AIR.T
CCT con-
system uses refrigerant flow modu-
®
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