Greenheck Fan 90, HRE-20, 55 Sequence Of Operation, Basic Unit, Summer Operation, Winter Operation

SEQUENCE OF OPERATION

Basic Unit

The HRE units are pre-wired such that when a call for outside air is made (via field supplied 24 VAC control signal wired to unit control center), the supply fan, exhaust fan and energy wheel are energized and the motorized dampers open.. The HRE units can be supplied with or without heating and cooling coils.. For units with coils, controls can be supplied by Greenheck or by the controls contractor.. If supplied by the controls contractor, they would provide, mount, and wire any temperature controllers and temperature or relative humidity sensors required for the unit to discharge air at the desired conditions..

Summer Operation

A sensible wheel preconditions the outdoor air (temperature is decreased) by the transfer of energy from the cool exhaust air coming out of the indirect evaporative cooler..

Units supplied with a direct evaporative cooling coil can further cool the air coming off the wheel to levels near 55ºF..

Economizer Operation: See Economizer Application/Operation section

Winter Operation

Outdoor air is preconditioned (temperature is increased) by the transfer of energy from the warmer exhaust air via the sensible recovery wheel..

Units supplied with heating coils can further heat the air coming off the wheel to levels at or above room design..

Frost Control Operation: See Frost Control Application/Operation section

41