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Optional Component Overview
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 mentioned 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 Components for troubleshooting.
Electric preheat frost control includes an electric
heater (at outdoor air intake), a thermodisc (5°F set
point) and pressure sensor on the energy 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. Preheaters are standard
as single-stage on/off control and single point wired at
the factory. Electric preheaters are available in 208, 230,
or 460 VAC (refer to nameplate for voltage). Access to
the preheater control panel is through the outdoor air
filter door.
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.
Variable Frequency Drives (VFD)
VFDs are used to control the speed of the fan as either
multi-speed or modulating control. Multi-speed VFDs
reference a contact which can be made by a switch or
a sensor with a satisfied set point. Modulating control
references a 2-10 VDC signal to the VFD which will vary
the fan speed from a minimum 50% to full 100% rpm.
An optional CO 2 sensor is available to provide both a
set point contact or a modulating 2-10 VDC signal.
CO
Sensor
2
This accessory is often used in Demand Control
Ventilation (DCV) applications. The factory provided
sensors can either be set to reference a set point for
multi-speed operation, or output a 2-10 VDC signal to
modulate the fan speed. These can either be shipped
loose to mount in the ductwork, or can be factory
mounted in the return air intake. Follow instructions
supplied with sensor for installation and wiring details.
Energy Recovery Ventilator
15
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