Compressor Group Coordination for MT Suction Pressure Control
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Solution Overview
Problem
In compressor cascade systems, starting low temperature (LT) compressors can result in undesirable suction pressure levels for high temperature (MT) compressors, potentially violating operational limits and triggering alarms or malfunctions, while starting MT compressors may also lead to suboptimal suction pressures, necessitating coordinated control to ensure safe operation.
Innovation Solution
A method and control unit that coordinate the operation of LT and MT compressor groups by monitoring suction pressures within a neutral zone, allowing simultaneous startup within this zone, preventing startup if pressures are outside the safe range, and synchronizing refrigerant injection to maintain optimal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LT compressors are started to reject heat, then heat rejection capability is improved, but suction pressure in MT compressor circuit becomes too high causing operational limits to be violated
Solution Approach 1:
The control method checks the suction pressure in the MT compressor circuit before allowing LT compressors to start. If the pressure is within the neutral zone, LT compressors are permitted to start. This preliminary check prevents excessive pressure buildup in the MT circuit by ensuring LT compressors only operate when conditions are favorable.
Solution Approach 2:
The system continuously monitors suction pressure in the MT compressor circuit and uses this feedback to control LT compressor operation. When pressure rises above the neutral zone, LT compressors are stopped; when pressure returns to the neutral zone, LT compressors can restart. This feedback loop maintains pressure within safe operational limits.
2Object-affected harmful factors
If MT compressors are started to reduce suction pressure, then suction pressure control is improved, but heat rejection capability is reduced due to MT compressor operational limits
Solution Approach 1:
Before starting MT compressors, the system checks whether suction pressure is below the neutral zone and whether LT compressors are already running. MT compressors are only started when these conditions are met, ensuring they operate to reduce pressure rather than unnecessarily limiting heat rejection capability.
Solution Approach 2:
The system uses continuous pressure monitoring to trigger MT compressor operation only when suction pressure falls below the neutral zone. This feedback-based control ensures MT compressors activate only when needed for pressure management, minimizing their impact on heat rejection capability.
3Object-affected harmful factors
If coordinated control is implemented to maintain suction pressure within neutral zone, then operational safety is improved, but system complexity increases due to additional control logic
Solution Approach 1:
The control method divides the operational logic into distinct segments: one set of rules for LT compressor control (start when pressure is in neutral zone, stop when pressure rises) and another set for MT compressor control (start when pressure is below neutral zone and LT compressors are running, stop when pressure returns to neutral zone). This segmentation makes the complex control logic more manageable and implementable.
Data Source
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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.