Supercritical Refrigeration Cycle Control Using Pseudo-Condensation Points
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Solution Overview
Problem
Conventional air-conditioning systems operating in a subcritical state lack a method to determine representative points for controlling the expansion device and compressor rotation speed effectively, especially when transitioning to a supercritical state, which affects heat exchange capacity and Coefficient of Performance (COP).
Innovation Solution
A refrigeration cycle apparatus with a refrigerant circuit connecting a compressor, a first heat exchanger, and an expansion device, where the opening degree of the expansion device is controlled based on a temperature difference between a predetermined enthalpy point and an outlet temperature sensor, and the compressor rotation speed is adjusted based on a second representative point under supercritical refrigerant pressure, ensuring optimal heat exchange and high COP.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a supercritical refrigeration cycle is used to achieve high heat exchange capacity, then the heat exchange capacity is improved, but the control complexity increases due to the lack of a defined condensing temperature
Solution Approach 1:
The patent changes the control parameter from condensing temperature (undefined in supercritical state) to pseudo-condensation temperature (defined by maximum specific heat at constant pressure). This parameter substitution enables effective control of the expansion device and compressor in supercritical refrigeration cycles, resolving the control complexity issue while maintaining high heat exchange capacity
Solution Approach 2:
The patent introduces the concept of pseudo-condensation temperature as an intermediary parameter that bridges the gap between traditional subcritical control methods and supercritical operation. This intermediary enables the use of conventional control strategies adapted to supercritical conditions, reducing control complexity
2Loss of energy
If the expansion device is controlled based on pseudo-condensation temperature to maintain high COP, then the energy efficiency is improved, but the device complexity increases due to additional temperature measurement requirements
Solution Approach 1:
The patent replaces complex multi-point temperature measurement systems with a simplified approach using outlet temperature sensor data combined with pseudo-condensation temperature calculations. This substitution maintains energy efficiency while reducing measurement system complexity
Solution Approach 2:
The system uses readily available outlet temperature sensor data to calculate pseudo-condensation temperature, eliminating the need for additional dedicated measurement devices. The existing sensors serve multiple functions, reducing overall device complexity
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 approach maintains required heat exchange capacity while achieving high COP and energy savings by effectively controlling the expansion device and compressor speed in a supercritical refrigeration cycle.
Implementation Method 1
the refrigerant removing heat from the air and is heated with the air that has been heated by the refrigerant transferring its heat
Implementation Method 2
the other one of the first heat exchanger and the second heat exchanger is operated as a evaporator by making the refrigerant in a low-pressure two-phase state flow therethrough
Implementation Method 3
the refrigeration cycle is carried out in a supercritical state in which the refrigerant pressure in a gas cooler on the high-pressure side exceeds its critical pressure
Data Source
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AI summary
To provide a refrigeration cycle apparatus capable of achieving energy saving. In the invention, control of the expansion device 16 is carried out based on the temperature difference between the refrigerant temperature of the first representative point that becomes a predetermined enthalpy under the refrigerant pressure of the gas cooler and the detection temperature of the outlet temperature sensor, and control of the rotation speed of the compressor 10 and/or the rotation speed of the heat medium sending device is/are carried out based on the second representative point that is, under the refrigerant pressure of the gas cooler, a temperature different from the first representative point.