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31NetworkAIR FM DX 60 Hz Operation, Maintenance, and Troubleshooting
Control the Environment
The System controls the room environment by engaging one of four modes: Cool, Dehumidify, Reheat,
or Humidify. These modes may work differently depending on the options and equipment installed in the
Modules.
Note: The environmental controls are set when your System is installed. Making changes to
the settings described in this section after the System has been commissioned may result in
improper operation.
How the modes work
DX Cool. Cool mode output is determined by the difference between the setpoint and the average return
air temperature of each of the Modules in the System (if more than one Module is present). The
deadband is used to engage the compressors incrementally with increasing demand. Each compressor in
the System is assigned an equal division of the deadband. As the average return temperature rises above
the setpoint, a compressor is engaged. If the average return temperature reaches the setpoint plus the
entire deadband, all of the compressors will be engaged. As the temperature drops through each
increment of the deadband a compressor will be disengaged. When the temperature drops below the
setpoint the remaining compressor will disengage.
See “Deadbands” on page 34 for instructions on setting the DX cool deadband.
Fluid Coil Cool. When the cool mode uses a MultiCool or Economizer coil, the output is determined
by the difference between the setpoint and the average return air temperature of each of the Modules in
the System (if more than one Module is present). The Proportional plus Integral plus Derivative (PID)
control loop calculates the output as demand increases and opens the valve controlling the flow of
coolant into the coil. As the average return temperature increases, the output will increase until it reaches
100 percent of capacity. For Modules with an Economizer coil, one stage (compressor) of DX cooling
can be engaged per Module to help meet the demand. The rule for engaging the compressor is the same
as for DX cool.
See “PID controls” on page 38 for a description of the PID controls and see “How to tune the
PIDs” on page 38 for instructions on tuning the fluid coil PID loop.
Reheat (Electric SCR). The silicon controlled rectifier (SCR) electric reheat function is controlled by
the reheat PID controller. When the return temperature of the Module drops below the reheat setpoint,
the reheat output will increase as the return temperature drops until output reaches 100%.
See “PID controls” on page 38 for a description of the PID controls and see “How to tune the
PIDs” on page 38 for instructions on tuning the reheat PID loop.