Ejector Vapour Compression System Pressure Control for Mode Switching
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Solution Overview
Problem
Vapour compression systems with ejectors face challenges in maintaining appropriate pressure levels when switching between 'summer mode' and 'winter mode' due to the risk of excessive pressure in the refrigerant path, especially when using non-return valves.
Innovation Solution
A method for controlling the compressor unit by measuring and comparing pressures at the evaporator and compressor inlet, using reference values to determine whether to control based on the evaporator pressure (P0) or compressor inlet pressure (Psuc), ensuring appropriate evaporator performance while preventing excessive pressure levels in the refrigerant path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the vapour compression system uses a non-return valve to automatically switch between summer mode and winter mode, then the system can adapt to temperature changes, but there is a risk that excessive pressure may occur in the refrigerant path between the receiver and compressor unit
Solution Approach 1:
The control method continuously monitors pressure P0 at the evaporator outlet and pressure Psuc at the compressor inlet, comparing these values to reference pressures P0,ref and Psuc,ref. Based on the comparison results, the system dynamically adjusts compressor control strategy to prevent excessive pressure buildup in the refrigerant path while maintaining automatic mode switching capability
Solution Approach 2:
The system changes control parameters based on operating conditions by comparing pressure deviations (ε0 = P0 - P0,ref and εsuc = Psuc - Psuc,ref). When ε0 > εsuc, the system controls based on P0; when εsuc > ε0, it controls based on Psuc. This parameter switching allows the system to adapt to different temperature regimes while preventing harmful pressure excursions
2Productivity
If the compressor unit is controlled based on evaporator outlet pressure P0 to ensure appropriate evaporator performance, then the evaporator operates efficiently, but the pressure in the refrigerant path between the receiver and compressor unit may reach unacceptable levels
Solution Approach 1:
The control method dynamically switches between controlling based on P0 and controlling based on Psuc by comparing the pressure deviations ε0 and εsuc. This parameter change allows the system to maintain evaporator performance when P0 control is appropriate, while switching to Psuc control when pressure in the refrigerant path approaches harmful levels
Solution Approach 2:
The system uses feedback from both pressure sensors (P0 at evaporator outlet and Psuc at compressor inlet) to continuously monitor system state. The control strategy is adjusted based on real-time pressure comparisons, ensuring evaporator performance is maintained while preventing excessive pressure buildup in the refrigerant path
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 vapour compression system by maintaining appropriate pressure levels, preventing excessive pressure in the refrigerant path and ensuring optimal performance of the evaporator and compressor unit, even during temperature changes.
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
AI summary
A method for controlling a vapour compression system (1) is disclosed. The vapour compression system (1) includes 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.