Greenheck Fan HEAT RECOVERY UNIT WITH EVAPORATIVE COOLING HRE-20 - Manual (Page 17)

17
Electric Heater Application/Operation
Factory installed electric heaters can be provided for preheat and/or post-heat . An electric preheater warms
the outdoor air prior to the energy recovery wheel to prevent frosting on the wheel . An electric post-heater
warms the air leaving the energy recovery wheel to a user specified discharge temperature . Electric heaters are
available in 208, 230, or 460 Vac (refer to heater nameplate for voltage) .
Preheaters: Preheaters are standard as 2-stage, step control . Step control heaters are designed with
multiple stages made up of equal increments of heating capability . For example, a 10 kW
heater with two stages will be composed of two 5-kW stages . Preheaters are single point
wired at the factory . A temperature sensor (with field adjustable set point) is mounted in the
outdoor airstream after the preheater to turn the preheater on . See Frost Control Application
/Operation for typical set points . If the temperature falls below the set point, the first stage of
the preheater will turn on . If the first stage does not satisfy the set point, the second stage will
also turn on .
Post-heaters: Post-heaters are standard as SCR control . Post-heaters are not single point wired (see
Electrical Connections) . A temperature sensor (with field adjustable set point) is mounted in
the outdoor airstream after the post-heater to turn the post-heater on . A SCR heater provides
an infinitely modulating control of the heat to provide an accurate discharge temperature . A
call for heat is required .
Electric Post-Heater
Post-Heater Control Panel
The post-heater is not single point
wired to the HRE control center .
Separate power must be supplied
to the post-heater disconnect
(located in unit control center) .
Access to the post-heater control
panel is through the exhaust filter
door . The indirect evaporative
cooling media must be removed
from the unit along with the exhaust
filters to access .
Electric Preheater
The preheater is single
point wired to the HRE
control center . Access to the
preheater control panel is
through the supply filter door .
OPTIONAL ACCESSORIES