Greenheck Microprocessor Controller (475595 IOM) TAP v2.10 April 2014 (RVE, ERCH-01, ERT-01) - Manual (Page 5)

Exhaust Fan VFD Sequence
If the factory has installed a VFD and wired it to the
controller, it is intended to operate at a constant speed
during operation. This 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.
• Optional Building Static Pressure Sensor: The
controller will modulate the exhaust fan based upon
a comparison of the building static pressure set point
to the actual building static pressure level reported
from the sensor.
• Optional Supply Fan Tracking: The controller will
proportionally modulate the exhaust fan based upon
the supply fan speed.
• Optional Outdoor Air Damper Tracking: The
controller will proportionally modulate the exhaust fan
based upon the outdoor air damper position.
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 Room CO2 Sensor: The controller will
proportionally modulate the OA/RA dampers based
upon a comparison of the CO2 set point to the actual
CO2 level reported from the sensor. As the CO2 level
rises, the controller will proportionally modulate the
outdoor air damper open, between the minimum and
maximum OA 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 set point 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.
• 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 set point.
• Energy Wheel Bypass Dampers (optional): 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 set
point (5°F) and the wheel pressure switch is closed, due
to a high wheel pressure drop. Once either 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
(2 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 (5 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).
Alarms
The microprocessor controller includes a digital output
for remote indication of an alarm condition. Possible
alarms include:
• 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 proving switch 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
microprocessor controller will de-energize the unit
and activate the alarm output after a preset time
delay (300s).
• Other Alarms: Wheel Rotation, High Wheel
Pressure, High/Low Refrigerant Pressure.
5 DDC Controller for Tempered Air Products
®