Microprocessor Controller for DOAS
6
®
Outdoor Air and Recirculated (Recirc) Air
Damper Control
If equipped with a modulating outdoor air and
recirculated air damper, the recirculated air damper will
operate inverse of the outdoor air damper. The outdoor
air damper will open to a Minimum Outdoor Air Position
(Min OA) when in occupied mode. If the controller
is configured to modulate the supply fan speed, the
minimum and maximum OA positions can be reset
based on supply fan speed. If equipped with BMS
communications, the user can also directly reset the
damper position up to the maximum OA position.
•
Optional Space CO
2
Sensor:
The controller will
proportionally modulate the OA/RA dampers based
upon a comparison of the CO
2
setpoint to the actual
CO
2
level reported from the sensor. As the CO
2
level
rises, the controller will proportionally modulate the
outdoor air damper open, between the minimum OA
damper position and maximum CO
2
position.
•
Optional Building Pressure:
The OA/RA dampers
will modulate based upon the signal from a building
static pressure sensor. The controller will modulate
the dampers, between the minimum and maximum
OA positions, based upon a comparison of the
building static pressure setpoint to the actual building
static pressure level reported from the sensor.
Energy Recovery Wheel Sequences
Economizer (optional):
If the unit is equipped with an
energy recovery wheel, the economizer will modulate/
stop the energy wheel to achieve 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.
•
Stop Wheel:
When economizer mode is enabled
and there is a signal for cooling, the wheel will stop
rotating to allow free cooling.
•
Modulate Wheel:
When economizer mode is
enabled and there is a signal for cooling, the
controller modulates wheel speed to maintain the
supply temperature setpoint.
•
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 (optional):
The microprocessor
controller will activate the frost control method when
the outdoor air temperature is less than the defrost
setpoint (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
outdoor air 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
minimum 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 minimum normal
operating cycle time (30 minutes).
Sequence of Operation
