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8
ELECTRIC HEATER APPLICATION/OPERATION
Factory installed electric heaters can be provided for preheat and/or post-heat (see FIGURE 11). 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 outdoor air 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 4-stage, step control. Post-heaters are not single point wired
(see ELECTRICAL CONNECTIONS, page 5). The functionality of a 4-stage heater is the same
as the 2-stage preheater above, except it has an additional two stages of heat control.
Post-heaters supplied with Greenheck temperature control package are 3-stage with binary
control that provides 7 steps of heating. For example, a 35 kW heater with three stages will be
composed of 5, 10, and 20 kW stages. The stages essentially ‘mix and match’ to provide heat
output from 5 kW to 35 kW, in 5 kW increments.
FIGURE 11
Electric Post-Heater
The post-heater is not single
point wired to the ERH control
center (requires separate
power). The post-heater and the
ERH each have their own
disconnect located in the UNIT
control center.
If required, access to the post-
heater control panel is through
the exhaust filter door.
Electric Preheater
The preheater is single point wired to the ERH control
center (does not require separate power). Access to the
preheater control panel is through the supply filter door.