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.
NetworkAIR FM DX 60 Hz Operation, Maintenance, and Troubleshooting | 31 |
