Installation, Operation and Maintenance Manual
Marvel Mini
26
Subject to change without notice.
120.9-IM (1218)
Modulating Hot Gas Bypass by Supply
Temperature (option)
Modulating Hot Gas Bypass for Supply Air Temperature
control is an option used to control the Supply Air
Temperature as close to the Supply Air Temperature set
point as possible This option requires a factory provided
Supply Air Temperature Sensor and a factory provided
Modulating Hot Gas Bypass Valve The Cooling Demand
will increase or decrease based on the Discharge Air
Temperature Set Point and Discharge Air Temperature
Band Set Point The compressors are then staged up/down
based on Cooling and Compressor Demands As the Supply
Air Temperature falls below the Supply Air Temperature Set
Point, the controller will modulate the hot gas bypass valve
open to regulate the amount of hot gas to the evaporator
coil in order to maintain the supply air temperature as close
to the supply air temperature set point as possible
If the Supply Air Temperature starts to increase, less hot
gas will be required to maintain the Supply Air Temperature
At that point, the controller will modulate the hot gas valve
closed as much as required to maintain the supply air
temperature as close to the supply air temperature set
point as possible Likewise if the load in the space starts to
decrease, the supply air temperature may start to decrease
At that point, the modulating hot gas valve will be modulated
open again to maintain the supply air temperature at or as
close to the supply air temperature set point as possible
Dehumidification Mode (option)
If the Room/Return Air Humidity is above the Room/Return
Humidity Set point plus ½ the Room/Return Air Humidity
Band Set point, the dehumidification demand will be 100%.
The Demand for Dehumidification is placed into the Cooling
Demand in order to stage the compressors ON/OFF based
on each Compressor’s Start and Hysteresis Set points
Dehumidification plus Reheat Mode (option)
If the Room/Return Air Humidity is above the Room/
Return Humidity set point plus ½ the band set point,
the dehumidification demand will be 100% and the
compressor(s) will energize for dehumidification.
If the Room/Return Air Temperature falls below the Room/
Return Air Temperature Set Point minus ½ the band set point
during dehumidification, the heating demand will become
100% The compressor(s) will continue operating and
reheat will stage on/off or modulate to satisfy the optional
reheat function The reheat type could be Hot Gas Reheat,
Electric Reheat, or a Hot Water or Steam Coil
Humidification (option)
Each system with the Humidification option will have a
Modulating Humidifier controlled through the controller
via Modbus Communications. Humidification is based on
the Humidification Demand. The Humidification Demand
is based on Room/Return Air Humidity, Room/Return Air
Humidity Set Point, and Room/Return Air Humidity Band
Set point. The Humidification Demand shall be 100% when
the Room/Return Air Humidity is equal to or greater than
the Room/Return Humidity Set point plus ½ of the Room/
Return Air Humidity Band Set Point
Dedicated Outdoor Air System Control
(option)
For the Dedicated Outdoor Air System Control to control the
system correctly, the unit must be purchased as a DOAS
system This means the unit is designed with the coils and
refrigeration system as well as a cabinet structure designed
to handle 100% Outdoor Air Even though the control
software has the ability to operate the unit as a Dedicated
Outdoor Air System if the unit is not designed for this, it
will most likely not dehumidify and reheat to condition the
outdoor air properly
In order to understand the system’s dehumidification mode,
it is important to understand there are several factors
involved in the dehumidification process.
Dehumidification is based on the following set point values:
(a) Outdoor Dry Bulb Temperature
(b) Outdoor Wet Bulb Temperature
(c) Supply Air Dew Point Temperature
(d) Supply or Space Air Dry Bulb Temperature
Dehumidification mode is based on seasonal outdoor
air, dry bulb temperature and wet bulb temperature
averages The average seasonal temperatures vary
significantly throughout different geographic regions. Since
dehumidification is based upon these temperatures, it will
be important for United CoolAir to know the location where
the unit will be installed because each controller is set up
with the Outdoor Air Dry Bulb and Wet Bulb, Temperature
Set Points for the particular region of installation
Though these set points are preset, they are not fixed set
points as they may be readjusted by service technicians
under the technician’s menu It is important to understand
that changes to these set points may affect the performance
of the system so minor adjustments at a time are strongly
recommended These set points are located under a
