14
Marvair Wall Mount Heat Pump I&O Manual
11/2021 New
Energy Management System (EMS)
Relay to control the heat pump. Available in 24, 120 or 240 VAC. Field or factory installed.
Electric Reheat for Dehumidification
Control provides simultaneous operation of compressor when in cooling mode and the electric elements
to provide dehumidification without over cooling the room. The electric element (kW) must be properly
sized for each model for proper operation. Factory installed. Available on all MAA units. Consult factory
for details.
Hot Gas Reheat (HGR)
Marvair
®
heat pumps equipped with the Hot Gas Reheat (HGR) allow the indoor humidity of the controlled
environment to be maintained at or below a certain humidity set point. These units do not have the ability
to add humidity to the classroom.
Dehumidification is achieved by operating mechanical cooling in conjunction with a hot gas reheat coil.
The coil is sized approximately to the sensible capacity of the total tonnage of the machine.
Speed Control for GreenWheel
®
ERV Exhaust Blower
For separate control of the exhaust blower. When used, the standard speed controller operates the intake
blower and the optional second controller the exhaust blower. Individual blower control allows positive
pressurization of the classroom. Can be factory or field installed.
1.8 Economizer Operation and Components
Damper Actuator
The damper actuator is a motor that modulates the position of the damper blade. It is controlled by the
enthalpy controller and powered by the 24 VAC control transformer. It is capable of driving a full 90
degrees within 90 seconds. The assembly has a spring return to close the damper during power outage.
Controls
The economizer is controlled by an enthalpy sensor or optional dry bulb sensor.
Economizer Changeover Control
The enthalpy sensor responds to the total heat content of the outdoor air to provide changeover to outside
air for free cooling. The change point is adjustable from 63°F @ 50% RH (full clockwise) to 73°F @
50% RH (full counterclockwise). Refer to Figure 3.
Once the enthalpy sensor has selected outside air, the mixed air sensor will limit the air temperature
delivered to the space by modulating the damper blade to "mix in" a quantity of inside air to provide a
constant 50° to 63°F. (Adjustable minimum potentiometer is optional.)
The sensor modulates the position of the outside air damper in response to input from the enthalpy and
mixed air sensors. The controller is designed to maintain the supply air temperature between 50
o
to 56
o
F
by mixing warm indoor air with cooler outdoor air.
On a call for cooling from the wall-mounted thermostat, if outdoor conditions are suitable, the sensor will
open the damper and admit outside air (i.e., economizer cooling). If the outdoor ambient is too hot or
humid, the sensor will place the actuator in the closed or minimum open position and activate mechanical
cooling. The compressor is locked out during the economizer cooling mode.
