Greenheck PVe (472846) - Manual (Page 12)

12 Model PVe Heat Recovery Unit
Optional Component Overview
Economizer
Under certain conditions, the most efficient use of
the unit includes bypassing the incoming outdoor air
around the plate heat exchanger. When cooling air is
being called for and the outdoor air temperature is
below a pre-set point, the unit will switch to economizer
mode. Integral face and bypass dampers will cycle into
a bypass condition, allowing incoming cool air to flow
past the cube, rather than flow through it. Economizer
mode is strictly temperature initiated and dependent
on the temperature sensor with override located in the
control center.
Frost Control
Cold climates, in combination with higher indoor
humidity levels, may cause frost to form on the plate
heat exchanger. To protect against the formation of
frost, a temperature sensor is installed to measure the
temperature of the air leaving the plates in the exhaust
airstream. There are two different methods of frost
control that may optionally be used. These options are
installed, wired and pre-set at the factory. To identify
specific components, see the included unit-specific
schematic wiring diagram.
1. Timed exhaust frost control
The supply blower cycles on and off based on a
factory provided and installed timer. The timer is
located on the right hand side (low voltage side) of
the control module.
2. Plate heat exchanger bypass – open/closed
When the exhaust air leaving the exchanger (cube)
drops below the adjustable set-point, both the
face and bypass dampers will allow air to bypass
the cube. This allows warm exhaust air to melt any
frost on the cube. Once the exhaust air temperature
rises above the set-point, the unit returns to normal
operation.
Timed exhaust frost control includes a timer in
addition to the thermostat and pressure sensor. The
timer is located on the right hand side of the control
module (low voltage side). When timed exhaust frost
control is initiated, the timer will turn the supply blower
on and off to allow the warm exhaust air to defrost the
cube. Default factory settings are 5 minutes off and 30
minutes on.
Plate (cube) bypass. The plate bypass frost control
function is essentially the same as economizer mode
except that it is initiated by temperature sensors for the
purpose of frost removal or prevention.
Variable Frequency Drives (VFD)
Variable frequency drives 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 (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.
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.
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.