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Why is my ACRP excessively cycling?

Issue:
Why is my ACRP excessively cycling?
 
Product line:
ACRD50x, ACRp10x
 
Environment:
Data Center Cooling
 
Cause:
 
Resolution:
Most refrigeration and air conditioning compressors would prefer to run continuously, rather than cycle excessively. Obviously, somewhere in-between these two extremes would be ideal. In general, refrigeration systems cycle at a higher rate than the typical air conditioning system, due to their basic design, loading, and controls. However, excessive compressor cycling can be a concern for both types of systems.

Too many compressor starts can cause the compressor oil to leave the machine, as on start up the crankcase pressure drops, which causes refrigerant in the oil to “fl ash” which causes the oil to foam and be lifted  through the compressor and pumped out with the discharge gas. Unless the system continues to operate for 5 -10 minutes oil will be left in the system. When short cycling continues, the oil left in the machine can become critical. 

The InRow RP works to prevent this by giving an "Excessive Compressor Cycling" alarm.  If the compressor cycles 12 times within an hour it will go into an excessive compressor cycling alarm that has to be cleared manually.  The ACRP DX needs to be given a constant heat load of at 12kW or more. If there is empty rack space without blanking panels, the cold air flowing to the hot aisle will reduce the heat load that the RP is given. With the supply air and cool setpoints both at 68F, you will likely see very high fan speeds. In the Inrow configuration, the supply air setpoint controls the temperature of the air the unit supplies to the cold aisle with compressor control. The cool setpoint controls the fan speed based on the maximum rack inlet temperature. The higher the rack inlet temperature is, the higher the fan speed will be (relative to the cool setpoint). These 2 setpoints should typically be 3-7F apart. In low load situations, the optimal setpoints often differ based on the specific room configuration.
  1. Setting the cool setpoint between 72-74F and monitoring the unit performance, adjusting the cool and supply air setpoints as needed.
  2. Enable the heat assist function. This will enable the unit to use the heater to help prevent excessive cycling (this can be enabled under "configure unit" on the front display or from the web interface under the unit tab, then the configuration section).
  3. Installing blanking panels will definitely help prevent cycling of cool/warm air
Making these changing will help assist in the matter, but if the load is still too small then you may still have cycling issues.  Regardless of whether or not it goes into the alarm, if you notice a large amount of cycling it is not good for the compressor life.
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