Installation, Operation and Maintenance Manual
Marvel Plus
13
Subject to change without notice.
120.5-IM (1018)
Set Points (continued)
These are the set points for changeover between Cooling
and Heating Modes (when unit is used for heating in
applications without perimeter heat)�
Setpoint
is the setting the return air control will maintain�
Band
is the setting used to adjust the on/off points�
In applications without perimeter heating/VAV terminal box
heaters, the Return Air Temperature Set Point and Band are
used for changeover between Cooling and Heating modes
of operation�
Cooling Mode
The Return Air Temperature must be above the Return Air
Temperature Set Point plus the Band Set Point for Cooling
Mode to become active� Cooling Mode shall then remain
active until the Return Air Temperature falls below the
Re-turn Air Temperature Set Point� Compressors and/or
Economizer shall then be controlled by the cooling demand
which is determined by the Supply Temperature Cooling
Mode Set Points� The amount of compressors on or off is
determined by the cooling demand�
Heating Mode
Likewise, when the Return Air Temperature falls below the
Return Air Temperature Set Point minus the Band Set Point,
Heating Mode will become active� Once Heating Mode is
activated, heating mode shall remain active until the Return
Air Temperature rises above the Return Air Temperature Set
Point� The amount of heating stages or modulated heating
is then determined by the heating demand� Heating demand
is determined by the Supply Temperature Heating Mode Set
Point and Band�
Return Air
Humidity
Setpoint >
050.0°F
Band >
05.0°F
Return Air Humidity is used to set the control points for
optional dehumidification and humidification functions.
Setpoint
is the setting for the humidity control to try to
maintain�
Band
is the setting used to adjust the on/off points of the
dehumidification mode or humidification mode.
If the system has humidification, the humidifier is energized
when the Return Air Humidity falls below the Return Air
Humidity Set Point minus ½ the band set point�
If the system has dehumidification, the compressors are
energized when the Return Air Humidity rises above the
Return Air Humidity Set Point plus ½ the band set point�
Supply Temperature
Cooling Mode
Setpoint >
055.0°F
Band >
40.0°F
Heating Mode
Setpoint >
090.0°F
Band >
20.0°F
If the system is being used as a cooling/heating unit
(applications with perimeter/VAV box heaters), the Supply
Temperature screen is used to select the Supply Air
Temperature set points for both Cooling and Heating Modes
of operation� The Cooling Mode set point and Band are used
to determine the cooling demand� Cooling Demand will be
100% when the supply sir temperature equals the Cooling
Mode set point plus ½ of the Band setting� Example: Cooling
Mode set point is 55�0
°
F and the Band is 40�0
°
F� When the
Supply Air Temperature is equal to or greater than 75�0
°
F,
the Cooling Demand is 100%�
The Heating Mode set point and Band are used to determine
the Heating Demand� Heating Demand will be 100% when
the supply air temperature equals the Heating Mode Set
Point minus ½ of the Band setting�
Example:
Heating Mode Set Point is 90.0
°
F and the Band
is 20.0
°
F. When the supply air temperature is equal to or
less than 80.0
°
F, the Heating Demand is 100%.
