A method for controlling a supply of refrigerant to an evaporator in contingency mode
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Solution Overview
Problem
Existing vapor compression systems, such as refrigeration and air conditioning systems, face inefficiencies and safety risks when temperature sensors used for controlling refrigerant supply become unavailable or unreliable, leading to suboptimal operation and inability to adapt to changes in refrigeration load.
Innovation Solution
A method for controlling refrigerant supply to an evaporator in a vapor compression system that calculates a reference temperature based on previous measurements when a malfunctioning sensor is detected, allowing the system to maintain efficient operation and adjust to changes in refrigeration load by controlling the expansion valve's opening degree based on the calculated reference temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the opening degree of the expansion valve is reduced to a fixed percentage of the average opening degree during contingency mode, then liquid refrigerant is prevented from passing through the evaporator, but the system cannot adapt to changes in refrigeration load and operates inefficiently
Solution Approach 1:
The patent implements feedback control by continuously monitoring the temperature of refrigerant leaving the evaporator and using this information to dynamically adjust the expansion valve opening degree. The control method calculates a reference temperature based on previously obtained temperature values and compares it with the actual measured temperature to determine the appropriate valve opening, enabling the system to adapt to changing refrigeration loads while maintaining safety margins that prevent liquid refrigerant from passing through the evaporator.
2Reliability
If the opening degree of the expansion valve is maintained at a reduced fixed opening degree during contingency mode, then the system can continue operation without the unavailable sensor, but it is not possible to take changes in refrigeration load into account
Solution Approach 1:
The system performs self-service by using the temperature of refrigerant leaving the evaporator as a proxy indicator for refrigeration load changes. Instead of relying on the unavailable sensor, the control method derives load information from the refrigerant temperature measurements that are still available, allowing the system to automatically adjust its operation to match actual cooling demands while continuing to function safely without the malfunctioning sensor.
Data Source
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AI summary
A method for controlling a supply of refrigerant to an evaporator (2) of a vapour compression system (1), such as a refrigeration system, an air condition system or a heat pump. During normal operation, the opening degree of the expansion valve (3) is controlled on the basis of an air temperature, Tair, of air flowing across the evaporator (2) and/or on the basis of superheat of refrigerant leaving the evaporator (2). In the case that at least one sensor (5, 6, 23, 24) used for obtaining Tair or the superheat is malfunctioning, operation of the vapour compression system (1) is switched to a contingency mode. A reference temperature, Tout, ref, is calculated, based on previously obtained values of a temperature, Tout, of refrigerant leaving the evaporator (2), during a predefined previous time interval, and subsequently the opening degree of the expansion valve (3) is controlled on the basis of the obtained temperature, Tout, and in order to reach the calculated reference temperature, Tout, ref, of the refrigerant leaving the evaporator (2). Efficient operation of the vapour compression system (1) is obtained, allowing changes in refrigeration load to be taken into account.