Greenheck DGX Installation, Operation And Maintenance Manual page 29

Operation - Recirculating / VAV Units
The self adjusting burner by-pass damper is a device used in variable volume and recirculation units. Its function
is to maintain proper combustion by providing a constant airflow over the burner when outside air volumes are
changed. It is located underneath the burner as shown in figure #58.
Burner
By-Pass
Damper
Figure 58. Burner By-Pass Damper
Manual Quadrant Damper Control
A manual quadrant damper in the return airflow controls the amount of recirculated air. This damper can be
adjusted by hand and locked in position for either 100% outside air or maximum recirculation air.
2-Position Damper Control
A 2-position spring return actuator is used to control the return air amounts. The damper moves from open to
closed. If power is cut to the unit, the damper will fail close. The volume of recirculation air is set in the factory
by baffles in the return air opening. These baffles should not be removed or adjusted in the field.
Potentiometer Control
A modulating spring return actuator is used to control the return air amounts. The damper moves from fully open
to fully closed. The amount of return air is determined by the position of a remote potentiometer.
Building Pressure Control
A modulating spring return actuator is used to control the return air amounts according to input from a pressure
sensing device. The recirculation damper moves from fully open to fully closed.
Variable Volume Operation (Optional)
2-Speed Control
A 2-speed motor is used to control air volumes. The motor can be switched to low or high speed from a remote
control panel. One-half or one-third reduction motors are used.
Potentiometer Control
A variable frequency drive is controlled by input from a remote speed selector (potentiometer). This unit allows
easy manual adjustment of make-up air volumes.
Building Pressure Control
A variable frequency drive is controlled according to input from a pressure sensing device.
Variable Frequency Drives
For maintenance issues associated with the variable frequency drives, please consult the drive's manual
supplied with the unit. The drives are programmed in the factory and should not need any adjustment during
installation and start-up. For kitchen applications, the drive is located in the kitchen, not in the unit.
Burner By-Pass Damper
80/20 Operation (Optional)
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WARNING!
The burner by-pass damper is set-up at the
factory. The weights and springs should not be
adjusted in the field. The damper may not fully
close during minimum outside air mode.