Compressor Coordination for Cascade Cooling Suction Pressure Control
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Solution Overview
Problem
In compressor cascade systems, starting the low temperature (LT) compressors can result in undesirable suction pressure for the high temperature (MT) compressors, potentially leading to faulty operation or alarms, and there is a need to synchronize refrigerant injection to ensure proper heat rejection.
Innovation Solution
A method and control unit that coordinate the operation of LT and MT compressor groups by investigating the status of MT compressors, establishing and maintaining suction pressure within a neutral zone, and synchronizing the start and stop of compressors to prevent pressure deviations, ensuring safe operation and efficient heat exchange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LT compressors are started to reject heat, then the heat rejection function is improved, but the suction pressure of the MT compressors becomes too high causing faulty operation or alarms
Solution Approach 1:
The control system checks the suction pressure in the MT compressor circuit before allowing the LT compressors to start. If the pressure is already too high, the LT compressors are prevented from starting. This preliminary check prevents the harmful effect of excessive suction pressure on MT compressors while still allowing heat rejection when conditions are appropriate.
Solution Approach 2:
The system continuously monitors the suction pressure in the MT compressor circuit and uses this feedback to control the starting of LT compressors. The control unit receives pressure signals and adjusts compressor operation accordingly, creating a closed-loop control system that prevents undesirable pressure conditions while maintaining heat rejection capability.
2Productivity
If the MT compressors are started to operate, then the cooling capacity is improved, but the suction pressure in the MT compressor circuit becomes too low causing faulty operation or alarms
Solution Approach 1:
The control system checks the suction pressure in the MT compressor circuit before allowing the MT compressors to start. If the pressure is already too low, the MT compressors are prevented from starting. This preliminary check prevents the harmful effect of excessive low suction pressure on MT compressors while still allowing cooling operation when conditions are appropriate.
Solution Approach 2:
The system continuously monitors the suction pressure in the MT compressor circuit and uses this feedback to control the starting of MT compressors. The control unit receives pressure signals and adjusts compressor operation accordingly, creating a closed-loop control system that prevents undesirable pressure conditions while maintaining cooling capacity.
3Ease of operation
If the LT compressors are allowed to start without coordination, then the operational independence is improved, but the system reliability deteriorates due to pressure violations
Solution Approach 1:
The control systems of the LT and MT compressor groups are merged into a coordinated control arrangement. The control unit of the LT compressor group can request permission to start from the MT compressor group's control unit, and vice versa. This merging ensures that both compressor groups operate independently in function but are coordinated in control, preventing pressure violations while maintaining operational flexibility.
Data Source
AI summary
A method for coordinating operation between at least two groups of compressors in a cooling circuit is disclosed. A first group of compressors forms part of a low temperature (LT) part of the cooling circuit and a second group of compressors forms part of a high temperature (MT) part of the cooling circuit. Each of the compressor groups comprises one or more compressors, and each of the compressor groups comprises a controller, the controllers being capable of exchanging signals. In the case that the LT compressor group needs one or more of the LT compressors to start operation, it is investigated whether or not one or more of the MT compressors is/are operating. If this is the case, one or more of the LT compressors is/are allowed to start operation. If it is not the case, the suction pressure in the MT part of the cooling circuit is established, e.g. measured, and compared to a lower and an upper limit of a neutral pressure zone, said neutral pressure zone lying within an operating pressure zone of the MT part of the cooling circuit. Finally, the MT compressors and the LT compressors are operated based on the comparing step. The cooling system may be a cascade system or a booster system.