Greenheck Fan APEX-200 Installation, Economizer Application/Operation, Modulating the Wheel

Installation

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 or 2) Modulating the wheel.

De-energizing the wheel is accomplished with a signal from a Temperature or Enthalpy sensor mounted in the supply air inlet compartment (see FIGURE 15). This Primary sensor will de-energize the energy wheel when the outdoor air temperature (factory default is 65°F) or enthalpy (factory default is the ‘D’ setting) is below the field adjustable set point. An Override temperature sensor is also furnished in the supply air inlet compartment to deactivate economizer mode (see FIGURE 15). The Override (with field adjustable set point) is set at some temperature lower than the Primary sensor (factory default is 50°F). 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 (terminals referenced below are in the unit control center — see FIGURE 7, Item #7) 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

FIGURE 15

Enthalpy Sensor (Primary Sensor)

Timed Exhaust

should start rotating.

Override

Frost Control

•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 65°F and 50°F, respectively).	Probes

Enthalpy sensor with Override

•A factory-installed 620 ohm resistor is connected across terminals SR and +. The Override sensor should be turned down below current temperature in unit. Turn the unit on; LED on the sensor should be off. Confirm continuity across terminals 1 and 2 and no continuity across terminals 2 and 3.

•Disconnect the 620 ohm resistor from terminals SR and +. LED should turn on. Confirm continuity across terminals 2 and 3 and no continuity across terminals 1 and 2.

•Turn Override sensor above current temperature in unit. Confirm continuity across terminals 3 and 6. Set the Override sensor to the desired point for economizer operation to end (factory default is 50°F).

•Reconnect the factory-installed jumper.

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:

TOA > TRA	:	Wheel runs at full speed (maximum energy recovery)
TOA < TRA and TOA > TSA	:	Wheel is stopped (no energy recovery)
TOA < TRA and TOA < TSA	:	Wheel will modulate to maintain discharge temperature

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 (nominal 60°F – not adjustable).

11®