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Frost Control (Aluminum): The microprocessor controller
will activate the frost control based on the following
methods.
• Electric Preheater: When the outdoor air temperature
is less than 10°F (adj.), the preheater is energized to
defrost the wheel.
• Modulate Wheel: When the exhaust air temperature is
less than 25°F (adj.), the wheel is modulated to maintain
a 25°F exhaust air temperature.
Enthalpic Core Control
Economizer: If the unit is equipped with an energy
recovery enthalpy core heat exchanger, the economizer
will modulate the bypass damper open to achieve free
cooling.
• Modulate Damper: When economizer mode is enabled
and there is a call for cooling, the controller modulates
the core bypass damper open to maintain the supply
temperature setpoint.
Frost Control (Enthalpic Core): The microprocessor
controller will activate the frost control based on the
following methods.
• Electric Preheater: When the outdoor air temperature
is less than 10°F (adj.), the preheater is energized to
defrost the wheel.
• Modulate Bypass Damper: When the exhaust air
temperature is less than 30°F (adj.), the bypass
damper is modulated to maintain a 30°F exhaust air
temperature.
Alarms
The microprocessor controller monitors alarms and will
alarm on the following conditions:
• Dirty Filter Alarm: If the outside air or return air filter
differential pressure rises above the differential pressure
switch setpoint, the microprocessor controller will
activate an alarm.
• Supply and Exhaust Air Proving Alarm:
Microprocessor controller monitors fan proving on each
blower and displays an alarm in case of blower failure.
• Sensor Alarm: Microprocessor controller will send
an alarm if a failed sensor is detected (temperature,
pressure, relative humidity).
• Supply Air Low Limit: If the supply air temperature
drops below the supply air low limit (35°F), the controller
disables the unit and activate the alarm output after a
preset time delay (300 sec.).
• Condensate Overflow: Microprocessor controller
monitors the float switch installed in the drain pan
and will disable the unit and activate an alarm on high
condensate.
• Other Alarms: Wheel Rotation, High Wheel Pressure,
High Refrigerant Pressure.
Sequence of Operation
Microprocessor Controller for DOAS
9
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