Typical Phase Monitor

Optional Economizer

The energy 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

•Turn both temperature and override thermostats down as low as they go. The wheel should be rotating.

•Turn the temperature sensor up as high as it goes, and keep the override sensor as low as it will go. The wheel should stop rotating.

•Turn both sensors as high as they will go. The wheel should start rotating.

•Set the temperature sensor at desired point 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

•Turn unit power off. 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.

•Turn unit power off. Reconnect

620 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

Enthalpy

energize and rotate.

Controller

 

If the steps above provide the results described, the enthalpy economizer is working properly.

•Turn unit power off. Reconnect C7400 solid state enthalpy sensor to terminal So.

20Model ERCH-HP Energy Recovery Unit

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. 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 (TOA ) is the outdoor air temperature set point, (TRA ) is the return air temperature set point, and (TSA ) is the supply air discharge thermostat set point.

TAO > TRA

Wheel runs at full speed.

(maximum energy recovery)

 

 

 

TAO < TRA

Wheel is stopped.

and

(no energy recovery)

TAO > TSA

 

TAO < TRA

Wheel will modulate to maintain

and

discharge temperature.

TAO < TSA

 

Phase Monitor

The unit control circuitry includes a phase monitor that constantly checks for phase

reversal, loss of phase or a power brownout. It requires

24 VAC to operate and when it detects a fault, it cuts off the 24 VAC that goes to the low voltage terminal strip, thereby shutting off all motors.

Variable Frequency Drive (VFD)

If a VFD was provided and installed at the factory, it has been preset to control the speed of the blower motor for optimum performance. The motor speed needs to be verified during test and balance of the unit.

Typical Variable Frequency Drive (VFD)

Refer to unit-specific documentation.

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Greenheck Fan 473501 manual Optional Economizer, Phase Monitor, Variable Frequency Drive VFD
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473501 specifications

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