Issue:
Hot Start - Hot Operation
Resolution:
If the compressors on a chiller are started when both the evaporator and condenser are hot, the potential exists to trip the high pressure cutout and/or overload the compressors, resulting in a nuisance lockout. In addition, when the evaporator is hot and the condenser is cool, the unit may trip the low pressure cutout.
To avoid these problems, the UCM has two modes of operation which provide for control of these conditions, Hot StartUp and Hot Operation. Both modes are based on the Leaving Solution Temperature (LST) exceeding a user selectable Hot Start Load Limit Setpoint (HSLLS):
- Hot StartUp - After the unit transitions from Loop Stabilization to Process Cooling or Comfort Cooling, until the end of the Hot Startup Time Interval, the unit will go into Hot Startup Mode whenever the LST exceeds the HSLLS. Once in Hot Startup mode, the unit shall inhibit the second compressor on each refrigeration circuit, and will continue to operate in this manner until the LST falls below the HSLLS by 5 degrees or more. Hot Startup mode is canceled and normal compressor operation is allowed after the LST falls 5 degrees or more below the HSLLS.
After the Hot Startup Time Interval has expired, the unit will respond according to the Hot Operation mode described below. If in Hot Startup mode when the Hot Startup Time Interval is reached, the unit will immediately transition to the Hot Operation mode and respond according to the selected Hot Operation Response Option.
- Hot Operation - The unit goes into the Hot Operation mode whenever the unit is running in Process Cooling or Comfort Cooling Mode, the Hot Startup Time Interval has expired, and the LST exceeds the HSLLS. The Hot Operation mode is determined by the selected Hot Operation Response option as described below:
- Hot Operation Response Option 1: Do not limit capacity. Set Informational Diagnostic until the LST falls 5 degrees or more below the HSLLS.
- Hot Operation Response Option 2: Limit unit to 50% capacity, one compressor on each circuit. Set Auto Reset Diagnostic until the LST falls 5 degrees or more below the HSLLS.
- Hot Operation Response Option 3: Shutdown and lockout compressors. Log Manual Reset Diagnostic.
NOTE: Hot StartUp/Hot Operation is not active during Ice Building modes.
Notes:
Changes:
Other Question/Problem/Cause Statements:
- Hot Start - Hot Operation
Facts:
- Intellipak Air-Cooled Chiller 20-60
Original HUB Document: DOC-77071
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.