CO2 Cascade Refrigeration Pressure Control for Peak Cooling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional refrigeration devices using carbon dioxide as a refrigerant face challenges in controlling the high pressure side pressure of the low stage side refrigerant circuit, leading to suboptimal cooling capability and efficiency, especially during high outdoor temperatures, due to the dependence on throttling degree of the expansion valve and lack of precise pressure control.
Innovation Solution
Incorporation of a pressure adjusting expansion valve controlled by a controller that sets an optimum high pressure side pressure target based on outdoor air temperature, along with the use of cascade heat exchangers and an accumulator to prevent liquid backflow and ensure sufficient refrigerant charge, allowing for precise subcooling and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the high pressure side pressure of the low stage side refrigerant circuit is increased to improve cooling capability and efficiency, then the refrigerating capability and COP improve, but the pressure control becomes difficult due to dependence on expansion valve throttling degree
Solution Approach 1:
The patent introduces a pressure adjusting expansion valve that actively controls the high pressure side pressure by adjusting the throttling degree parameter. The valve changes its opening position based on detected pressure values to maintain optimal pressure (e.g., 10.5 MPa at 38°C outdoor temperature), resolving the contradiction between achieving high pressure for better cooling and maintaining controllable pressure levels.
Solution Approach 2:
The patent implements a feedback control system where a pressure detector continuously monitors the high pressure side pressure and feeds this information to a controller. The controller adjusts the pressure adjusting expansion valve based on the pressure feedback, creating a closed-loop control system that maintains optimal pressure despite varying operating conditions, thus solving the pressure control difficulty.
2Loss of energy
If the high pressure side pressure is increased to maximize cooling efficiency, then the specific enthalpy difference increases and COP improves, but abnormal pressure rises may occur especially during high outdoor temperatures
Solution Approach 1:
The patent introduces an accumulator on the suction side of the low stage side compressor to prevent liquid backflow beforehand. Additionally, the pressure adjusting expansion valve proactively controls pressure to stay below abnormal thresholds even during high outdoor temperatures, cushioning against potential pressure instability before it occurs.
Solution Approach 2:
The pressure detector and controller work together to provide continuous feedback control, monitoring the high pressure side pressure and adjusting the expansion valve to prevent abnormal pressure rises. This feedback mechanism ensures pressure stability and reliability by correcting deviations from the optimal pressure range in real-time.
3Productivity
If a pressure adjusting expansion valve is introduced to control high pressure side pressure, then precise pressure control and improved cooling capability are achieved, but the device complexity increases
Solution Approach 1:
The pressure adjusting expansion valve serves multiple functions: it acts as both a refrigerant flow control valve and a pressure regulation device. By integrating pressure control functionality into the expansion valve, the patent avoids adding separate pressure control components, thus minimizing the increase in device complexity while achieving precise pressure control.
Solution Approach 2:
The system uses the existing refrigerant flow path and the expansion valve's inherent ability to regulate flow, combining it with pressure feedback control. The pressure adjusting expansion valve self-regulates the refrigerant flow based on pressure conditions, utilizing the system's own components and operating principles to achieve pressure control without requiring entirely new mechanisms.
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 solution enables the refrigeration device to achieve improved cooling capability and efficiency by maintaining the high pressure side pressure at an optimum value, preventing abnormal pressure rises, and ensuring efficient compressor operation, even during peak summer temperatures.
Implementation Method 1
a cascade heat exchanger to evaporate a refrigerant of the high stage side refrigerant circuit, thereby cooling a high pressure side refrigerant of the low stage side refrigerant circuit
Implementation Method 2
there is disposed a pressure adjusting expansion valve to adjust a high pressure side pressure of the low stage side refrigerant circuit
Implementation Method 3
an accumulator to prevent liquid backflow
Data Source
AI summary
There is disclosed a refrigeration device in which a cooling capability and efficiency can be improved by controlling a high pressure side pressure of a low stage side refrigerant circuit into an optimum value. A refrigeration device 1 includes a high stage side refrigerant circuit 4, first and second low stage side refrigerant circuits 6A and 6B, and cascade heat exchangers 43A and 43B to evaporate a refrigerant of the high stage side refrigerant circuit 4, thereby cooling high pressure side refrigerants of the low stage side refrigerant circuits 6A and 6B, and carbon dioxide is charged as the refrigerant in each of the refrigerant circuits 4, 6A and 6B, and in the device, there are disposed pressure adjusting expansion valves 31 to adjust high pressure side pressures of the low stage side refrigerant circuits 6A and 6B.