Microprocessor Controller for DOAS
8
Sequence of Operation
Energy Wheel Control
Economizer:
If the unit is equipped with an energy
recovery wheel, the economizer will modulate/stop the
energy wheel to achieve free cooling.
•
Stop Wheel:
When economizer mode is enabled
and there is a call for cooling, the wheel will stop
rotating to allow free cooling. Jog wheel control is
available during stop wheel economizer operation.
This sequence allows the wheel to rotate for a short
period of time exposing a new section to the air
stream.
•
Modulate Wheel:
When economizer mode is
enabled and there is a call for cooling, the controller
modulates wheel speed to maintain the supply
temperature set point.
•
Energy Wheel Bypass Dampers, if equipped:
During normal operation, the dampers shall remain
closed to allow full operation of the energy wheel.
During economizer sequences, the dampers will be
open to bypass the energy wheel.
Frost Control (Polymer):
The microprocessor
controller will activate the frost control method when
the OA temperature is less than the defrost set point
(5°F) and the wheel pressure switch is closed due to
a high wheel pressure drop. Once the pressure drop
decreases below the pressure switch point or the OA
temperature increases, the unit will resume normal
operation.
•
Electric Preheater:
When frosting is occurring, the
preheater is energized to defrost the wheel.
•
Modulate Wheel:
When frosting is occurring, the
wheel slows to allow defrosting to occur.
•
Cycle Wheel:
When frosting is occurring, the
energy wheel is cycled off for a defrost cycle time
(5 minutes). After the defrost cycle time, the wheel
is re-energized to continue normal operation. The
controller will not allow another defrost cycle for a
min normal operating cycle time (30 minutes).
•
Timed Exhaust:
When frosting is occurring, the
supply fan is cycled off along with the tempering
for a defrost cycle time (5 minutes). The exhaust
fan will continue to run allowing the warm exhaust
air to defrost the wheel. After the defrost cycle
time, the supply fan and tempering are re-energized
to continue normal operation. The controller will
not allow another defrost cycle for a min normal
operating cycle time (30 minutes).
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 36°F (adj.), the wheel is modulated to
maintain a 36°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 set point, 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.).
•
Other Alarms:
Wheel Rotation, High Wheel Pressure,
High/Low Refrigerant Pressure.
•
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.
