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Re-Circulating Control Options
The ratio of outdoor to indoor air in the discharge supply air can be adjusted through the MUA board
output. The board will output a
0-10V DC
signal to command the position of the damper. There are several
options for controlling the position of this damper. Use the HMI panel to change options:
Factory Settings > Unit Options > Outdoor Air Config> Outdoor Air Ctrl
Powered Exhaust
The powered exhaust fan is located by the intake damper assembly and is designed to prevent the
building from over pressurizing. When there is excessive static in the building’s return ductwork, the
powered exhaust fan will assist exhausting air directly outdoors to balance the building’s internal pressure.
The powered exhaust fan will actuate depending on the outdoor air configuration’s settings and supply fan
activation.
Outdoor Air Configuration
When Outdoor Air % or Schedule is selected, “Outdoor Air Deadband” will be active. This setting checks
the delta T between outdoor and return air. If the difference between these two temperatures is less than
or equal to the dead band setting (default setting is 5 degrees), the MUA board will not alter its output to
the damper assembly.
Off
- Outdoor air control from the control board will not output a signal. May be used when damper is
controlled by a photohelic gauge or a Building Management System (BMS).
Manual
- The fresh air dampers can be manually controlled from the HMI panel corresponding to a 0-10V
DC output signal from the control board. This output voltage signal can be manually adjusted. This will
allow the user to manually set the dampers to match the building ventilation requirements.
2 Position
- The fresh air dampers can be controlled by a two-position switch (a field-supplied switching
device) to select closed position or 100% open. The control board sends out a constant 10V DC signal to
the actuator. The field supplied switch will break or make the signal from the control board to the outdoor
air damper. When the switch is used to disconnect power (open the circuit), or if a power failure occurs, or
if the control board is shut-off, the return air damper will open by spring return. If using a two-position
switch, connect in series to the control board at connection A+ and D+.
Outdoor Air %
- The dampers can be controlled from the HMI to position the dampers from 0% to 100%
fresh air. The MUA board utilizes an internal algorithm to alter its 0-10V output to the damper assembly to
maintain an exact outdoor air percentage.
100% OA
- If this damper control is chosen, anytime the blower is running, the damper will be fully open.
The board logic will send 10 volts to open the damper. When there is no call for the blower, the board logic
will send 0 volts to close the damper.
Analog Control -
When this is set to ON, the damper will modulate linearly between the min and max OA
voltage for both occupied and unoccupied modes.
Pressure Control
- Damper position will modulate to maintain building pressure. Building pressure below
the set point will increase the amount of outdoor air supplied to increase pressure.
NOTE: When Scheduling is enabled, separate occupied and unoccupied set points will be available
for outdoor air control settings.
Programmable Thermostat
The programmable thermostat can be set off the discharge sensor set point. This allows the unit to
modulate for the programmed space set point. An example would be, if the discharge set point is set for
65°F, and the space calls for heat/cooling cycle, the unit will modulate to meet the discharge set point.
The thermostat can also work off blower mode. This setting will look at the intake air temperature. The unit
will modulate to avoid bringing in too hot or too cold of air into the space.
