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Optional Component Overview
Electric Heater
Factory installed electric heaters can be provided for
preheat frost control. An electric preheater warms the
outdoor air prior to the energy recovery wheel to prevent
frosting on the wheel. Electric heaters are available in
208, 230, or 460 VAC (refer to heater nameplate for
voltage).
Preheaters: Preheaters are standard as single-stage
on/off control. Preheaters are single point wired at the
factory. A thermodisc temperature sensor (with a 5°F
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 and the wheel
pressure drop sensor is triggered, the preheater will
turn on.
Access to the preheater control panel is through the
outdoor air filter door.
Economizer
The energy wheel operation can be altered to take
advantage of economizer operation (free cooling). Two
modes are available:
1. Stopping the wheel
2. Modulating the wheel
Stopping the wheel: A field-supplied call for cool (Y1)
is required. De-energizing the wheel is accomplished
one of three ways:
1. The outdoor air temperature is less than the
outdoor dry bulb set point (DRYBLB SET)
2. The outdoor air temperature is less than the return
air temperature
3. The outdoor air enthalpy is within the preset
enthalpy curve
Effectively, the two sensors create a deadband where
the energy recovery wheel will not operate and free
cooling from outside can be brought into the building
unconditioned.
Modulating the wheel (factory): A variable frequency
drive is fully programmed at the factory. A "call for
cool" must be field wired to the unit (terminals provided
in unit-refer to wiring diagram in unit control center)
to allow for initiation of economizer mode. The unit
recognizes economizer conditions based one of the
previously mention sensors and set points. The unit will
then modulate the wheel speed to maintain the mixed
air temperature set point (MAT SET).
Modulating the wheel (by others): A variable
frequency drive is fully programmed at the factory.
A field-supplied 0-10 VDC signal will be required for
operation of the energy wheel. The field will be required
to have full control of the energy wheel speed at all
times. If no 0-10 VDC signal is provided, the energy
wheel will run at the factory default of 3 Hz and no
energy transfer will be captured.
®
Exhaust Only Operation
This option allows for the exhaust fan to run
continuously while the supply fan is off.
Frost Control
Extremely cold outdoor air temperatures can cause
moisture condensation and frosting on the energy
recovery wheel. Frost control is an optional feature
that will prevent/control wheel frosting. Three options
are available:
1. Timed exhaust frost control
2. Electric preheat frost control
3. Modulating wheel frost control
All of these options are provided with a thermodisc
mounted in the outdoor air intake compartment and a
pressure sensor to monitor pressure drop across the
energy wheel.
An outdoor air temperature of below 5ºF and an
increase in pressure drop would indicate that frost is
occurring. Both the pressure sensor and the outdoor air
thermodisc must trigger in order to initiate frost control.
The two sensors together ensure that frost control is
only initiated during a real frost condition.
Timed exhaust frost control includes a timer in
addition to the thermodisc and wheel pressure sensor.
When timed exhaust frost control is initiated, the timer
will turn the supply blower off. Time exhaust using
default timer setting will shut down the supply fan for
5 minutes every 30 minutes to allow exhaust to defrost
energy wheel. Use the test procedure in the Optional
Start-Up Accessories section for troubleshooting.
Electric preheat frost control includes an electric
heater (at outdoor air intake) in addition to the
thermodisc and pressure sensor on wheel. When
electric preheat frost control is initiated, the electric
preheater will turn on and warm the air entering the
energy wheel to avoid frosting. Use the test procedure
in the Optional Start-Up Accessories section for
troubleshooting.
Modulating wheel frost control includes a variable
frequency drive (VFD) in addition to the thermodisc and
pressure sensor. When modulating wheel frost control
is initiated, the VFD will reduce the speed of the wheel.
Reducing the speed of the energy wheel reduces its
effectiveness, which keeps the exhaust air condition
from reaching saturation, thus, eliminating condensation
and frosting. If the outdoor air temperature is greater
than the frost threshold temperature OR the pressure
differential is less than the set point, the wheel will run
at full speed. If the outdoor air temperature is less than
5ºF AND the pressure differential is greater than the
set point, the wheel will run at reduced speed until the
pressure differential falls below the set point. The VFD
will be fully programmed at the factory.
Energy Recovery Ventilator
11
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