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Accessories
Economizer Control (Free Cooling)
Take advantage of cool outdoor air to handle space loads. A call for cool air is sent to the unit’s control center
which triggers one of a few different options to bring in fresh cool air:
Energy Wheel On/Off
The wheel cycles off when it’s in the free cooling range (temperature or enthalpy), and
cycles on when outdoor air is too warm or too cold. This option is recommended when the
air is being supplied to an air handling unit or duct heater, and not directly to the space.
Energy Wheel Modulation
The wheel speed modulates to maintain a 55°F discharge temperature. Above 55°F,
the wheel is off up to a high-limit temperature setting (typically 70°F). This option is
recommended when the air is supplied directly to the space from the ERV or when more
precise temperature control is needed.
Frost Protection
Cold climates, in combination with higher indoor humidity levels, may cause frost to form on the energy wheel
during normal operation. To protect against frost, we measure the outdoor temperature and the energy wheel
pressure drop. When it’s cold enough and the wheel pressure is increasing, the wheel is frosting. Only then will
the frost methods described below engage. See the “Frost Control Strategy Recommendations” chart on this
page for which of the three Greenheck frost methods we recommend for your building.
Timed Exhaust Frost Control
The supply blower cycles on and off based on a
factory provided timer. With the supply blower
off, the warm exhaust air melts the frost. Once the
wheel pressure decreases, the supply blower turns
backon.
Modulating Wheel Frost Control
A factory installed variable frequency drive (VFD)
slows the wheel down making it less effective.
In other words, the slow rotating wheel spends
enough time in the warm exhaust airstream to melt
the frost. Once the wheel pressure decreases,
it returns to full speed. Both blowers operate
continuously during this frost mode. Modulating
wheel frost control is available on all sizes except
the ERV-251.
Preheat Frost Control
An electric preheater is built into the ERV outdoor air intake. When frost occurs, the heater engages, and
increases the outdoor air temperature above the frost threshold to melt the wheel. Once the pressure
decreases, the heater shuts off.
Frost Control Strategy Recommendations
Winter Outside Air
Design
Winter Indoor Air
Design
Recommended
Frost Control
Strategy
≥ 10°F (-12.2°C) ≤ 50% RH None
≥ -5°F (-20.6°C) <
10°F (-12.2°C)
≤ 35% RH Timed Exhaust
≥ 10°F (-12.2°C) ≤ 50% RH
Electric Preheat
≥ -5°F (-20.6°C) <
10°F (-12.2°C)
≤ 35% RH
≥ -5°F (-20.6°C) Any RH
The map at left indicates the frost control
options, if any, that are appropriate based
on climactic conditions during typical
16hour per day operation.
Preheat Frost Control Recommended*
Timed Exhaust Frost Control Recommended*
No Frost Control Needed
*Modulating Wheel Frost Control can also be used in these areas.