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.
