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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. Two options are
available:
1. Timed exhaust frost control
2. 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 5°F 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 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
5°F 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 setpoint. 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
setpoint contact or a modulating 2-10 VDC signal.
CO
Sensor
2
This accessory is often used in Demand Control
Ventilation (VDC) applications. The factory-provided
sensors can either be set to reference a setpoint 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-
12
Model APEX Energy Recovery Ventilator
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.
Microprocessor Controller
The controller is specifically designed and programmed
to optimize the performance of the unit with
supplemental heating and cooling. This option ensures
that the outdoor air is conditioned to the desired
discharge conditions. The controller and accompanying
sensors are factory-mounted, wired and programmed.
Default settings are pre-programmed, but are easily
field-adjustable.
The controller can be
interfaced with a Building
Management System
through LonWorks
®
,
BACnet
®
, or ModBus.
Please refer to the Microprocessor Controller for Energy
Recovery Installation, Operation and Maintenance
manual for detailed information.
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.
Vapor Tight Lights
Vapor tight lights provide light to each of the
compartments in the energy recovery unit. The lights
are wired to a junction box mounted on the outside of
the unit. The switch to turn the lights on is located in
the unit control center. The switch requires a separate
power source to allow for power to the lights when the
unit main disconnect is off for servicing.
®
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