Himidi−Mizerr Dehumidification System - Carrier 50TC*17 Series Service And Maintenance Instructions

HIMIDI−MIZERR ADAPTIVE
DEHUMIDIFICATION SYSTEM
Units with the factory−equipped Humidi−MiZerR option
are capable of providing multiple modes of improved
dehumidification as a variation of the normal cooling
cycle. See Fig 16. The design of the Humidi−MiZerR
system allows for two humidity control modes of
operation of the rooftop unit, utilizing a common
subcooling/reheat dehumidification
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.
package is factory−installed and will operate whenever
there is a dehumidification requirement present.
The Humidi−MiZerR system is initiated based on an
input from a discrete input from a mechanical space or
return air humidistat.
Humidi−MiZerR Modes
Normal Cooling for Units A17 − A30
During the Normal Cooling mode, the liquid refrigerant
flows from the outdoor condenser through the normally
open (NO) Cooling System Valve (CSV) to the expansion
device. Both the Reheat1 (RH1.x) and Reheat2 (RH2)
valves are closed during the normal cooling mode.
During the Normal Cooling mode, the refrigerant flows
from the outdoor compressor through the condenser coil.
The Reheat2 (RH2.x) is closed, preventing the refrigerant
from bypassing the condenser coil. The refrigerant then
flows through the open Reheat2 (RH1.x) 3−way valve to
the TXV Metering Device, bypassing the Humidi−
MiZerR coil, and finally passing through the evaporator
coil before returning to the outdoor compressor. See Fig
16.
Reheat1 (Subcooling Mode) for Units A17 − A30
Th Reheat1 or Subcooling mode will be engaged to
satisfy part−load−type conditions when there is a space
call for cooling and dehumidification. Although the
temperature could have dropped and decreased the
sensible load in the space, the outdoor and/or space
humidity levels could have risen. A typical scenario could
be when the outside air is 85_F (29_C) with 70% to 80%
relative humidity (RH). Desired Sensible Heat Ratio
(SHR) for equipment in this scenario is typically from 0.4
to 0.7. The Humidi−MiZerR unit will initiate the
Dehumidification mode when both the space temperature
and humidity are above the temperature and humidity
setpoints while attempting 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 sensible capacity load. Alternatively, if the
sensible load is met and humidity levels remain high the
unit can switch to Hot Gas Reheat mode or Reheat2 mode
to provide neutral, dehumidified air.
coil located
The Humidi−MiZerR
During the Reheat1 or Subcooling mode, the liquid
refrigerant flows from the outdoor compressor through the
condenser coil to the Reheat1 (RH1.x) 3−way valve and
on to the Humid−MizerR coil. The Reheat2 (RH2.x)
valve is closed. The liquid refrigerant then passes through
the Humid−MizerR coil and then a metering device or
Thermostatic Expansion Valve (TXV). From the TXV, the
liquid refrigerant passes through the evaporator coil and
back to the outdoor comprssor. See Fig 17.
Reheat2 (Hot Gas Reheat Mode) for A17 − A30
This Reheat2 or Hot Gas Reheat mode is used when dehu-
midification 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 equip-
ment to operate at a low SHR of 0.0 to 0.2. With no cool-
ing requirement calling for dehumidification, the Humidi−
MiZerR adaptive dehumidification system will energize
both compressors, opening the two hot gas bypass valves,
allowing refrigerant flow to the Humidi−MiZerR coil to
reheat the unit's supply air to a neutral temperature.
The hot bypassed refrigerant liquid (gas or two−phase
mixture) exits the outdoor compressor and passes through
the open Reheat1 (RH1.x) at the same time it passes
through the condenser coil to the open Reheat2 (Rh2.x) to
the Humidi−MiZerR coil. After the refrigerant passes
through the Humidi−MiZerR coil, it enters a TXV
metering device, decreasing the air pressure, and on to the
evaporator coil. The refrigerant is subcooled in this coil to
a temperature approaching the evaporator leaving air
temperature. The liquid refrigerant then returns to the
outdoor compressor. See Fig. 18.
The refrigerant enters the TXV and evaporator coil at a
temperature lower than the temperature in the standard
cooling operation. This lower temperature increases the
latent capacity of the evaporator. The refrigerant passes
through the evaporator turning it into a superheated vapor.
The air passing over the evaporator coil becomes colder
than it would during normal operation. As this same air
passes over the Humidi−MiZerR Reheat Coil, it will be
warmed to the neutral supply air temperature.
Humidi−MiZerR System Components
The Humidi−MiZerR System uses the standard unit
compressor(s), evaporator coil and Round Tube−Plate Fin
(RTPF) condenser coil. Additional refrigeration system
hardware includes a subcooler/reheat coil and control
solenoid valves. On some models, the evaporator coil
includes a TXV as a standard feature. Units with
Humidi−MiZerR FIOP also include a factory−installed
head pressure control system (Motormaster I) to provide
proper liquid pressure during reheat modes. Unique
system controls include a reheat relay mode, and
evaporator coil freezestat, and secondary low pressure
switch.
Operating Sequences
The Humidi−−MiZerR system provides three sub−modes
of operation: Normal Cooling, Reheat1 and Reheat2.
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