12
Energy Recovery Ventilator
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.
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
2
Sensor
This accessory is often used in Demand Control
Ventilation (VDC) 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.
Rotation Sensor
The rotation sensor monitors energy wheel rotation. If
the wheel should stop rotating, the sensor will close a
set of contacts in the unit control center. Field-wiring
of a light (or other alarm) between terminals R and
12 in the unit control center will notify maintenance
personnel when a failure has occurred.
Dirty Filter Sensor
Dirty filter sensors monitor pressure drop across the
outdoor air filters, exhaust air filters, or both. If the
pressure drop across the filters exceeds the set point,
the sensor will close a set of contacts in the unit
control center. Field-wiring of a light (or other alarm)
to these contacts will notify maintenance personnel
when filters need to be replaced. The switch has not
been set at the factory due to external system losses
that will affect the switch. This switch will need minor
field adjustments after the unit has been installed
with all ductwork complete. The dirty filter switch is
mounted in the exhaust inlet compartment next to the
unit control center or in unit control center.
Service Outlet
120 VAC GFCI service outlet ships loose for field
installation. Requires separate power source so
power is available when unit main disconnect is
turned off for servicing.
