Data Aire dap4 User Manual page 86

Variable + Fixed Speed Compressors – Controlling Discharge Air Temp.
The variable compressor (C1) turns on when the discharge air temperature rises
above the Setpoint + Deadband. As temperature continues to rise, the variable
compressor will run faster. Once it is running at 95% of maximum speed for the
"C2 On Delay" setting, the fixed speed compressor is allowed to run.
The Fixed speed compressor (C2) turns on when the discharge air temperature
rises above the Setpoint + Deadband + The Stage-to-Stage setting.
The Fixed speed compressor (C2) turns off when the discharge air temperature
drops below the Setpoint minus the Stage-to-Stage setting for the duration of the
C2 Off Delay time setting.
The variable speed compressor (C1) turns off when the discharge air temperature
drops below the Setpoint minus The C1 Offset setting (default of 1.0°F).
Modulation of the variable compressor to control the discharge air temperature will
be by a proportional + Integral + derivative (PID) algorithm. The tuning parameters
for this algorithm are in the Factory Setting menu.
Note if the Energy Saver mode is running (Wtr Vlv configured as Engy Svg Cool or
Aux Chill Wtr in factory menu). The variable compressor turns on when the
discharge air temperature rises above the Setpoint + Deadband + Stage To Stage
setting. It turns off when the discharge air temperature drops to the Setpoint.
Note: The variable compressor (C1) will always be the lead compressor as the
compressor rotation feature is disabled. However, C2 can be forced to run in the
event that it has not been used for the period of the "Exercise Time". This feature
can be enabled on the Fixed Compressor screen in the factory menu.
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