Operation Of Dx Cooling - Data Aire dap4 User Manual

Operation of DX Cooling

The following types of safeties are used to protect the compressors.
Pressure Safeties:
For safety reasons, the High / Low pressure alarm functions are not performed by
the dap4 controller. The compressor is shut down externally and the dap4 will
indicate and log the alarm.
General Safeties:
All compressors will be shut down under the following conditions: Freeze Alarm,
Floor Water Alarm (if set to turn off compressors), Condensation Alarm, Water
Flow Alarm (if set to turn off compressors), BMS Cooling Inhibit command, Air
Flow Alarm, Low Discharge Temp Alarm (if set to turn off compressors), EVD Off-
line Alarm, EVD memory fault.
Circuit Specific Safeties:
The compressors of the circuit will be shut down under the following conditions:
Repetitive High Pressure Alarms or an Out of Envelope Alarm (types of alarm that
must be reset on alarm screen), Low Evap Temp Alarm, High Evap Temp Alarm,
Suction Line Temp Sensor Failure, Suction Line Pressure Sensor Failure, Hot Gas
Temp Alarm, High Superheat Alarm, Low Superheat Alarm, EVD valve motor
alarm.
Timing Safeties:
The next compressor will not stage on until the "Delay Btw Stages" time cycle is
completed. Once a compressor is turned off (for any reason) it must complete a 5-
minute Minimum Off Time cycle before it can be run again (This time delay is
increased by 1 minute following a compressor short-cycle alarm). When the
variable compressor is started, it must complete a "Minimum Run Time" cycle
before it can turn off.
Variable Speed Compressor Envelope Safeties:
The variable compressor must operate within an area called an "envelope". Once
the compressor is started, it must be inside the envelope before the Start-up delay
time (0-99s with default of 60s) expires. An Out of Envelope alarm will occur if the
compressor runs outside of the envelope for more than the Run Outside Delay
time setting (0-99 seconds with default setting of 1s). This alarm will lock out the
compressor requiring a manual reset. If the compressor starts running near the
perimeter of the envelope (referred to as zones 2-5), corrective logic will force the
speed of the compressor higher or lower. If after 30 seconds of corrective action
the compressor did not move back into the normal zone, an Out of Envelope alarm
will occur.
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