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Marvair Wall Mount Heat Pump I&O Manual
06/2023 Rev.7
Ventilation Options
ASHRAE standard 62 requires 15 cfm of outside air per occupant of a classroom. To meet this requirement,
Marvair offers seven ventilation packages for every budget and requirement.
Configuration “C”: Up to 100% Modulating Economizer
The economizer reduces the cost of air conditioning by using outside air when acceptable to cool the
room (Free Cooling). The factory installed Marvair® economizer has integral pressure relief.
Control Board Logic:
Upon a “Call for Cooling”, the economizer control board calculates whether the
HVAC operates in economizer mode or mechanical cooling mode based on outdoor temperature (dry bulb)
or temperature/humidity (enthalpy). When outdoor conditions are favorable for economizer cooling, the
damper drives open and modulates to maintain a 55ºF mixed air temperature through the supply grille.
When outdoor conditions are not favorable for economizer cooling, the economizer damper remains
closed, and the HVAC unit will operate in mechanical cooling mode.
Features Designed for Telecommunication applications:
Hydrogen Fault Input:
When 24VAC is applied to the Emergency Ventilation (EV) input, the economizer
board forces the damper to open 100% for emergency ventilation. The compressor does not operate during
Hydrogen Fault/Emergency Ventilation.
Forced Mechanical Cooling:
When 24VAC is applied to the FC input of the economizer board, the
economizer damper is forced closed, and the HVAC will operate in mechanical cooling mode. This is
considered as economizer override in the event economizer cooling is not sufficient for the heat load.
Thermostat must provide the fan “G” signal to HVAC to activate the indoor blower.
Economizer Status:
The economizer board has contacts that when used with the Marvair CommStat 4
Telecom HVAC Controller, change state to provide feedback to the CommStat 4 to indicate when the
HVAC is in economizer mode verses mechanical cooling mode. This feedback allows the CommStat 4
to initiate the forced cooling feature to override economizer cooling and force mechanical cooling.
When used with minimum position potentiometer (optional), the Marvair® economizer can meet
requirements of ASHRAE Std. 62.
Configuration “D”: Two-Position Motorized Fresh Air Damper w/Pressure Relief Ventilation
Control Board Logic:
The 92589 control board allows the position of the “D” damper to be set for desired
outside air intake from fully closed to fully open. Setting 15 of the control board configuration menu
allows the user to set the position from 20 (2VDC / Closed) to 100 (10VDC 100% open). The damper
position can be adjusted in 1VDC increments to any position from closed to 100% open as required.
Operation:
Anytime the indoor blower operates, the damper drives open to the position selected in the
control board configuration menu setting 15. When the indoor blower stops operation the motorized
damper spring returns to the fully closed position.
Note:
This circuit does not interrupt the compressor or heater operation.
