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Model ERV Energy Recovery Unit
Economizer Application/Operation
The energy recovery wheel operation can be altered
to take advantage of economizer operation (free
cooling). Two modes are available:
1. De-energizing the wheel
2. Modulating the wheel
A field supplied call for cool (Y1) is required.
De-energizing the wheel is accomplished with a signal
from a Temperature or Enthalpy sensor mounted
in the air intake compartment. This primary sensor
will de-energize the energy wheel when the outdoor
air temperature (factory default is 65ºF) or enthalpy
(factory default is the ‘D’ setting) is below the field
adjustable set point. An Override temperature
sensor is also furnished in the outdoor air intake
compartment to deactivate economizer mode. The
Override (with field adjustable set point) is set at
some temperature lower than the primary sensor
(factory default is 50ºF). Effectively, the two sensors
create a deadband where the energy recovery wheel
will not operate and free cooling from outside can be
brought into the building unconditioned.
Testing
Temperature Sensor with Override
• TurnbothTemperatureand
Override thermostats down as
low as they go. The wheel should
be rotating.
• TurntheTemperaturesensor
up as high as it goes, and keep
the Override sensor as low as it
will go. The wheel should stop
rotating.
• Turnbothsensorsashighastheywillgo.The
wheel should start rotating.
• SettheTemperaturesensoratdesiredpoint
for economizer operation to begin. Set the
Override sensor at desired point for economizer
operation to end (factory default is 65ºF and 50ºF,
respectively).
Enthalpy Sensor with Override
• Turnunitpoweroff.Disconnect
C7400 Solid State Enthalpy Sensor
from terminal So on the enthalpy
controller. Also, disconnect the
620 ohm resistor from
terminal Sr on the
enthalpy controller.
Turn unit power on. The
LED on the enthalpy
controller should light and the energy
recovery wheel should not rotate.
•Turnunitpoweroff.Reconnect620
ohm resistor to terminal Sr on the
enthalpy controller. Turn unit power
on. The LED on the enthalpy controller
should not light and the energy recovery wheel
should energize and rotate.
If these steps provide the results described, the
enthalpy economizer is working properly.
• Turnunitpoweroff.ReconnectC7400SolidState
Enthalpy Sensor to terminal So.
Modulating the Wheel
In applications in which an internal heat gain is
present in the space, the rotational speed of the
energy wheel may be modulated (via variable
frequency drive) to avoid overheating the space
during the winter. The speed of the energy wheel
will be controlled in response to the discharge
temperature set point.
Sequence of Operation: The variable frequency
drive is fully programmed at the factory (refer to VFD
section for more information). A “call for cool” must
be field wired to the unit (terminals provided in unit -
refer to wiring diagram in unit control center) to allow
for initiation of economizer mode. When the space
calls for cooling, factory supplied controls will drive
the following wheel operations:
Where (T
OA
) is the outdoor air temperature set point,
(T
RA
) is the return air temperature set point, and (T
SA
)
is the supply air discharge thermostat set point.
Temperature
Sensor with
Override
Enthalpy
Sensor with
Override
T
AO
> T
RA
Wheel runs at full speed.
(maximum energy recovery)
T
AO
< T
RA
and
T
AO
> T
SA
Wheel is stopped.
(no energy recovery)
T
AO
< T
RA
and
T
AO
< T
SA
Wheel will modulate to maintain
discharge temperature.
Enthalpy
Controller