A method and controller for controlling a vapour-compression system with thermodynamic constraints satisfaction
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Solution Overview
Problem
The non-linear behavior of vapor-compression systems, particularly associated with compressors and valves, poses a challenge for effective control, despite the development of advanced control methods.
Innovation Solution
A method of controlling a vapor-compression system by determining a cooling demand, setting preliminary and final thermofluidic property objective values, and adjusting the compressor and expansion device operations based on these values to achieve targeted properties of the working fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If advanced control methods are used to regulate the vapor-compression system, then the control precision is improved, but the system complexity increases due to non-linear behavior of compressors and valves
Solution Approach 1:
The patent transforms the control problem from directly managing complex non-linear component behaviors to controlling thermodynamic state parameters (temperature, pressure, enthalpy) at key locations. By monitoring and controlling these state parameters instead of directly controlling compressor speed or valve positions, the system achieves precise control while avoiding the complexity of modeling and controlling non-linear component characteristics.
Solution Approach 2:
The patent introduces thermodynamic state parameters as intermediary variables between the control inputs and the desired cooling output. Instead of directly controlling the non-linear relationship between compressor/valve and cooling demand, the system uses thermodynamic states (temperature, pressure, enthalpy) as mediators that linearize the control problem and simplify the control strategy.
2Productivity
If the cooling demand is precisely met by adjusting compressor and expansion device operations, then the cooling effectiveness is improved, but the energy consumption increases due to frequent adjustments
Solution Approach 1:
The patent uses thermodynamic state monitoring to predict cooling demands before they fully manifest. By continuously monitoring temperature, pressure, and enthalpy at key locations, the control system can anticipate required adjustments to compressor and expansion device operations, allowing smoother transitions and reducing the frequency of aggressive adjustments that consume excess energy.
Solution Approach 2:
The patent implements a feedback control system that continuously monitors thermodynamic states and adjusts compressor/expansion device operations accordingly. This closed-loop feedback ensures cooling effectiveness while optimizing energy consumption by making adjustments only when and where thermodynamic deviations occur, rather than continuous or frequent adjustments.
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 enables precise control of the vapor-compression system, addressing the non-linear behavior challenges and improving the system's efficiency and effectiveness in meeting cooling demands.
Implementation Method 1
an evaporator configured to facilitate heat transfer from a thermal source into the working fluid
Implementation Method 2
vapour-compression system for circulating a working fluid
Data Source
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AI summary
The present disclosure relates to a method of controlling a vapour-compression system 400, 400', 400" for circulating a working fluid. The vapour-compression system 400, 400', 400" comprises a compressor 402, an expansion device 406 and an evaporator 408A, 408B configured to facilitate heat transfer from a thermal source 407A, 407B into the working fluid. The method comprises: determining or receiving 310 a cooling demand, the cooling demand being associated with a demand to cool the thermal source 407A, 407B; determining 350 a preliminary thermofluidic property objective value based on the cooling demand; determining 200 a final thermofluidic property objective value based on the preliminary thermofluidic property objective value and one or more thermofluidic property objective value thresholds, wherein the final thermofluidic property objective value relates to a target thermofluidic property of the working fluid at a control location within the vapour-compression system; and controlling 800, 900 at least one of the compressor 402 and the expansion device 406 based on the final thermofluidic property objective value.