Mixing Box Controls
The mixing box (shown at right) includes outdoor air and return air low leakage control dampers in a face and bypass configuration. Either two inch pleated or aluminum mesh filters are available within the mixing box section. Double wall construction is optional.
A mixing box control option must be specified for every
Mixing Box Controls with Economizer Cooling
The economizer controls package enables free cooling using outdoor air. All EC options include a modulating actuator for controlling outdoor and return air dampers, and a minimum outdoor air positioner. During a call for heating the economizer is locked out and the outdoor air damper holds at the minimum position.
EC1: Outdoor Temperature Reference
The economizer controller positions the mixing box dampers to achieve 55° F mixed temperature when the thermostat calls for cooling AND the outdoor air temperature is below the economizer
setpoint. If outdoor air temperature is
between 55° F and the economizer setpoint, the dampers will modulate to the 100% outdoor air position. Above the setpoint, the outdoor air damper is held at the minimum position. The setpoint is field adjustable and the outdoor air sensor
is factory mounted.
EC2: Outdoor Enthalpy Reference
Same as EC1, except economizer setpoint is based on outdoor air enthalpy.
EC3: Airstream Temperature Reference
The economizer controller compares the temperatures of the outdoor air and return air when the thermostat calls for cooling. The mixing box dampers are then
positioned to maximize the airflow of the cooler airstream. When outdoor air temperature is sufficiently cool, the mixing
box dampers will modulate to provide 55° F mixed air. The outdoor air sensor is factory mounted. The return air sensors are field installed.
EC4: Airstream Enthalpy Reference
Same as EC3, except airstream enthalpy values are compared.
Mixing Box Controls (no economizer)
In addition to the EC options described above, Greenheck offers four MB mixing box control options for applications where a factory provided economizer package is not desired.
MB1: Minimum Outdoor Air Positioner
The MB1 option includes a modulating actuator and potentiometer that control the outdoor air and return air damper positions. When the unit is energized, the dampers will travel to the position corresponding to the potentiometer
setting, providing the desired amount of outdoor air. When the unit is powered off, the outdoor air damper closes to prevent backdrafting. To adjust the damper settings, simply dial the potentiometer (shown above) to desired operating position of the outdoor air damper.
MB2: 2-10 Volt External Signal
The MB2 option includes a modulating actuator that is controlled by an external
4
automation system that will control the mixing box dampers.
MB3: 4-20 mA External Signal
The MB3 option includes a modulating actuator that is controlled by an external
MB4: Manual Quadrant
The MB4 option consists of a manual quadrant that enables the outdoor air and return air dampers to be secured into a single position. The primary
function is to introduce the specified minimum outdoor air volume during operation. Dampers remain in the same position when the unit is powered off.
