Greenheck Fan HEAT RECOVERY UNIT WITH EVAPORATIVE COOLING HRE-20 - Manual (Page 41)

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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 .
Basic Unit
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
Summer 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
Winter Operation
SEQUENCE OF OPERATION