A method for controlling a vapour compression system at low superheat
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Solution Overview
Problem
Existing methods for controlling vapour compression systems, such as refrigeration and air conditioning systems, struggle to maintain a superheat value of refrigerant leaving the evaporator that is both energy efficient and safe, as low superheat values can lead to unstable control and potential liquid refrigerant reaching the compressor.
Innovation Solution
A method that calculates a reference superheat value by adding a variance quantity to a minimum acceptable superheat value, ensuring the superheat remains above a critically low value even in unstable operating conditions, thereby preventing liquid refrigerant from reaching the compressor while maintaining energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the superheat value is reduced to enhance energy efficiency, then the energy efficiency is improved, but the control stability deteriorates and liquid refrigerant may reach the compressor
Solution Approach 1:
The patent applies dynamics by making the superheat setpoint adjustable and adaptive rather than fixed. The system dynamically adjusts the superheat setpoint based on operating conditions (such as load, temperature, pressure), allowing it to operate at lower superheat values when conditions permit, thereby improving energy efficiency while maintaining reliability through real-time adaptation to changing system states
Solution Approach 2:
The patent changes the parameter of superheat setpoint from a fixed value to a variable parameter that can be adjusted based on system conditions. By modifying this key parameter dynamically, the system achieves lower average superheat values for improved energy efficiency while preventing liquid refrigerant damage through adaptive control that responds to actual operating conditions
2Loss of energy
If the superheat value is reduced to improve energy efficiency, then the energy efficiency is improved, but the risk of liquid refrigerant reaching the compressor increases
Solution Approach 1:
The patent implements feedback control by continuously monitoring system parameters (temperature, pressure, superheat) and using this information to adjust the expansion device and maintain appropriate superheat levels. This feedback mechanism ensures that even when operating at lower superheat values for energy efficiency, the system automatically responds to conditions that might indicate approaching liquid refrigerant, thereby preventing compressor damage
Solution Approach 2:
The system dynamically adjusts the superheat setpoint based on real-time operating conditions, allowing lower superheat values when safe and automatically increasing them when risk of liquid refrigerant is detected. This dynamic adjustment resolves the contradiction by making the superheat level adaptive rather than static, improving energy efficiency while maintaining compressor protection
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 allows the vapour compression system to operate at lower superheat values than previous methods, enhancing energy efficiency while ensuring safe operation by maintaining a stable superheat value above the minimum acceptable level.
Implementation Method 1
The refrigerant leaving the heat rejecting heat exchanger is supplied to the expansion device, where it undergoes expansion before being supplied to the evaporator
Implementation Method 2
When passing through the evaporator, the liquid part of the refrigerant is at least partly evaporated, while heat exchange takes place with the ambient or a secondary fluid flow across the evaporator, in such a manner that heat is absorbed by the refrigerant
Implementation Method 3
In the heat rejecting heat exchanger, heat exchange takes place between the refrigerant and the ambient or a secondary fluid flow across the heat rejecting heat exchanger, in such a manner that heat is rejected from the refrigerant
Implementation Method 4
Refrigerant flowing in the refrigerant path is compressed by the compressors of the compressor unit before being supplied to the heat rejecting heat exchanger
Data Source
AI summary
A method for controlling a vapour compression system (1) includes a compressor unit (2), a heat rejecting heat exchanger (3), an expansion device (4) and an evaporator (5) arranged in a refrigerant path. A superheat value of refrigerant leaving the evaporator (5) is derived, and a quantity being representative for a variance of the derived superheat value is calculated. A reference superheat value is calculated, based on the calculated quantity and on a minimum acceptable superheat value, by adding the calculated quantity to the minimum acceptable superheat value. The expansion device (4) is operated in accordance with the calculated reference superheat value, and in order to obtain a superheat of refrigerant leaving the evaporator (5) which is equal to the reference superheat value.