A method for controlling suction pressure of a vapour compression system
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Solution Overview
Problem
In vapour compression systems with ejectors, there is a challenge in controlling the compressor unit to maintain appropriate suction pressure, especially when transitioning between 'summer mode' and 'winter mode', which can lead to excessive pressure levels in the refrigerant path.
Innovation Solution
A method that involves measuring pressures at the evaporator and compressor unit, comparing them to reference values, and controlling the compressor unit based on the pressure error values to ensure appropriate operation and prevent excessive pressure levels, using a non-return valve and bypass valve to manage refrigerant flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressor unit is controlled based on evaporator outlet pressure to ensure appropriate evaporator performance, then the evaporator operates efficiently, but excessive pressure levels may occur in the refrigerant path between the receiver and compressor unit
Solution Approach 1:
The control system continuously monitors both evaporator outlet pressure and suction line pressure, using feedback from both sensors to dynamically adjust compressor operation. This dual-pressure feedback mechanism allows the system to maintain evaporator performance while preventing excessive pressure buildup in the suction line by comparing actual pressures against reference values and adjusting compressor capacity accordingly.
Solution Approach 2:
The system dynamically switches between different control modes based on operating conditions. When the non-return valve is closed or suction line pressure approaches reference levels, the system transitions from evaporator-pressure-based control to suction-line-pressure-based control. This dynamic adaptation allows optimal evaporator performance under normal conditions while preventing pressure excursions during transitions between summer and winter modes.
2Adaptability or versatility
If a non-return valve is used to automatically switch between summer mode and winter mode, then the system adapts to ambient temperature changes, but the pressure in the refrigerant path between receiver and compressor unit may reach unacceptable levels
Solution Approach 1:
The control system uses feedback from suction line pressure sensors to detect when pressure is approaching unacceptable levels during mode transitions. When suction line pressure nears reference values, the system receives feedback to adjust compressor operation or delay mode switching, preventing pressure buildup while maintaining the ability to switch between summer and winter modes as ambient temperatures change.
Solution Approach 2:
The system takes preliminary action by monitoring suction line pressure before excessive pressure levels are reached. When pressure approaches reference thresholds during non-return valve operation, the control system proactively adjusts compressor capacity or modifies refrigerant flow distribution to prevent pressure from reaching harmful levels, rather than reacting after pressure becomes excessive.
3Use of energy by moving object
If all refrigerant from the evaporator is supplied to the secondary inlet of the ejector during summer mode, then power consumption is reduced, but the system cannot adapt when ambient temperature drops to winter conditions
Solution Approach 1:
The system dynamically adjusts refrigerant distribution between the ejector and compressor based on ambient temperature and operating conditions. During summer mode, maximum refrigerant flow is directed to the ejector for energy-efficient operation. During winter mode or transition periods, the system dynamically redirects refrigerant flow to the compressor inlet, allowing adaptation to changing temperature regimes while maintaining optimal performance for each operating condition.
Solution Approach 2:
The control system enables the refrigerant distribution system to serve multiple functions: during summer conditions, the ejector provides energy-efficient refrigerant compression; during winter conditions, the compressor provides reliable refrigerant circulation. The system universally handles both operating modes through a single integrated control mechanism that monitors ambient temperature and automatically adjusts refrigerant flow paths to optimize performance for the current season.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method ensures efficient operation of the evaporator while preventing excessive pressure levels in the refrigerant path, maintaining optimal performance and safety during changes in ambient temperature.
Implementation Method 1
An ejector is a type of pump which uses the Venturi effect to increase the pressure energy of fluid at a secondary inlet (or suction inlet) of the ejector by means of a motive fluid supplied to a primary inlet (or motive inlet) of the ejector.
Data Source
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AI summary
A method for controlling a vapour compression system (1) is disclosed. The vapour compression system (1) comprises an ejector (4), and has a non-return valve (11) arranged in the refrigerant path between an outlet (12) of an evaporator (7) and an inlet (10) of a compressor unit (2), in such a manner that a refrigerant flow from the outlet (12) of the evaporator (7) towards the inlet (10) of the compressor unit (2) is allowed, while a fluid flow from the inlet (10) of the compressor unit (2) towards the outlet (12) of the evaporator (7) is prevented. A pressure, P0, of refrigerant leaving the evaporator (7) is measured and a value being representative for a pressure, Psuc, of refrigerant entering the compressor unit (2) is obtained. The pressures, P0 and Psuc, are compared to respective reference pressure values, P0,ref and Psuc,ref. In the case that ε0>εsuc, where ε0=P0-P0,ref and εsuc=Psuc-Psuc,ref, the compressor unit (2) is controlled based on P0, and in the case that εsuc>ε0, the compressor unit (2) is controlled based on Psuc.