8
Marvair Classic AVPA/HVPA/HVPSA Heat Pump I&O Manual
11/2017 Rev. 7
How It Works
During the summer, cool dry air from the classroom is exhausted through the GreenWheel
®
ERV to the
outside. As the air passes through the rotating wheel, the desiccant becomes cooler and drier. Simultaneously,
hot humid air is being pulled across the rotating wheel. The cool, dry desiccant absorbs moisture and
heat from the incoming air. The cooler, drier air is mixed with the return air from the classroom and
distributed throughout the room.
In the winter, warm moist air is exhausted through the GreenWheel
®
ERV to the outside. As the air passes
through the rotating wheel, the desiccant becomes warmer and absorbs moisture. Simultaneously, cold
dry air is being pulled across the rotating wheel. The cold, dry air absorbs heat and moisture from the
desiccant. The warmed air is mixed with the return air from the classroom and distributed throughout
the room.
Quality Components
The GreenWheel
®
module consists of a desiccant wheel, two blowers and the drive motor and belt. The
two blowers simultaneously pull fresh air from outside and exhaust air from the classroom through the
rotating wheel. Two variable speed blowers ensure that up to 450 CFM of outside air can be brought into
the room and the indoor air is properly exhausted. Variable speed blowers permit that the desired quantity
of outside air is delivered into the room. Optional independent exhaust air blower control allows positive
pressurization of the classroom, i.e., more outside air can be introduced through the GreenWheel
®
ERV
than is exhausted.
GreenCube
®
ERV (Ventilation Option “Q”)
The GreenCube ERV is an enthalpy plate heat exchanger that transfers both sensible and latent energies
between outgoing and incoming air streams in a cross flow arrangement. Except for two air movers, it has
no moving parts. The media is impregnated with a RC134 polymeric desiccant that exchanges water by
direct vapor transfer using molecular transport without the need of condensation. The GreenCube
®
ERV
will operate at temperatures as low as 10°F without a defrost mechanism. In addition, the desiccant is a
bactericide. Two MERV 6 type filters are used on both sides of the enthalpy core. The fresh air and exhaust
motors have independent speed controllers to permit each of the motors to be regulated independently.
The GreenCube
®
ERV is available in heat pumps with nominal cooling capacities of 24,000 through
60,000 BTUH. See the Marvair Classic product data sheet for cabinet dimensions..
Hot Gas Reheat (HGR) Dehumidification Mode (Special Option “G”)
When the HGR is in the dehumidification mode, the hot gas reheat (HGR) coil is energized. The cooled,
dehumidified air exits the evaporator coil and is blown through the HGR coil. This coil is sized to the
sensible capacity of the unit. The heat in the HGR coil is transferred to the air stream. The use of the HGR
coil allows the indoor humidity of the classroom to be maintained at or below a certain set humidity set
point without over cooling the classroom. These units can not add humidity to the classroom.
The operation of the HGR coil is controlled by a humidity controller. If the humidity rises above the set
point on the controller and the temperature in the classroom is satisfied, both mechanical cooling and
the HGR coil operate to temper the air and lower the humidity. If the temperature in the classroom rises
above or falls below the set point of thermostat and the unit is operating in the dehumidification mode,
the need for cooling or heating will override the call for dehumidification and the HGR coil is disengaged
until the thermostat is satisfied. This assures the classroom temperature is maintained as first priority
and humidity control is second.
The humidity controller or BAS control is required for proper operation of the HGR coil.
