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Dehumidification
Dehumidification enable can be selected based on
any of the following sensor readings: outside air
temperature, indoor dew point, indoor relative humidity,
or outside dew point.
• Outside Temperature: Dehumidification is enabled
when the OA temperature is greater than the cold
coil setpoint plus an offset (10°F). Dehumidification
is disabled when the OA temperature falls below the
enable point by a hysteresis (2°F).
The following enable setpoints may be used
separately or in conjunction with one another. Each
has a setpoint to enable dehumidification and uses
a temperature or humidity hysteresis to disable
dehumidification.
Indoor Dew Point
-
Indoor RH
-
Outside Dew Point
-
A constant call for dehumidification must be
present for the duration of the enable delay for the
dehumidification mode to become enabled. The
call remains active until conditions are satisfied
and dehumidification mode has been active for the
minimum active time.
• Cooling Coil Setpoint: When an indoor humidity
sensor or temperature and humidity sensors (space
or return) are installed, the controller can adjust the
cold coil leaving air temperature setpoint between the
minimum (50°F) and maximum (55°F) setpoint. This
function can be enabled or disabled by selecting the
reset mode for the setpoint.
Reheat
While the unit is dehumidifying, the supply air
temperature is maintained by controlling the reheat
device to the supply air setpoint.
• Hot Gas Reheat (valve): The microprocessor
controller modulates to maintain setpoint.
• Reheat Plus: The microprocessor controller can
be configured to use the primary heat source as
secondary reheat.
Supply Fan VFD Sequence
The factory installed VFD is wired to the controller.
Supply fan speed needs to be set during test
and balance of the unit. If equipped with BMS
communications, the user can also directly command
the supply fan speed. The following sequences are
selectable for supply fan control. The fan speed is
constrained by its min and max speed setpoints.
• Constant Volume: Supply fan operates at a constant
speed based on a constant volume setpoint based on
occupancy.
Sequence of Operation
• 0-10 VDC: The supply fan is enabled by the unit
controller. An external field-supplied 0-10 VDC signal
is responsible for modulating the supply fan's speed.
• CO
Control: The supply fan modulates to maintain
2
CO
setpoint based on a sensor located in the space
2
or return duct. A CO
value is required for this sequence.
• Duct Static Pressure: The supply fan modulates to
maintain an adjustable duct static setpoint based on
a sensor located in the supply duct. A static pressure
sensor or BMS communicated value in required for
this sequence.
• Space Static Pressure: The supply fan modulates to
maintain a space static pressure setpoint based on a
sensor located in the space. A space static pressure
sensor or BMS communicated value in required for
this sequence.
• Single Zone VAV: The controller will control the
supply air temperature and supply fan speed in order
to maintain the space temperature.
- Heating Mode - The supply temperature
setpoint will be increased before increasing the
supply fan speed in order to maintain the space
temperature setpoint. If the calculated supply
temperature setpoint is greater than the current
space temperature, the supply fan speed will be
increased while the supply temperature setpoint is
increased.
- Cooling Mode - The supply temperature setpoint
will be decreased before increasing the supply fan
speed in order to maintain the space temperature
setpoint.
• Two Speed: The supply fan is enabled by the unit
controller. An external field-supplied digital contact is
responsible for enabling high speed operation. The
supply fan min (50%) and max (100%) speeds are
used for the low and high speed settings.
Exhaust Fan VFD Sequence
The factory installed VFD is wired to the controller.
Exhaust fan speed needs to be set during test
and balance of the unit. If equipped with BMS
communications, the user can also directly command
the exhaust fan speed. The following sequences are
selectable for exhaust fan control. The fan speed is
constrained by its min and max speed setpoints.
• Constant Volume: Exhaust fan operates at a
constant speed based on a constant volume setpoint
based on occupancy.
• 0-10 VDC by Others: The exhaust fan is enabled by
the unit controller. An external field-supplied 0-10
VDC signal is responsible for modulating the exhaust
fan's speed.
sensor or BMS communicated
2
Microprocessor Controller for DOAS
7
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