Refrigeration cycle device and method for controlling same
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Solution Overview
Problem
The use of zeotropic refrigerants in refrigeration systems leads to a decrease in evaporator inlet temperature due to temperature glide, resulting in frost formation during heating operations, and existing solutions involving additional expansion valves and evaporator division increase manufacturing costs.
Innovation Solution
A refrigeration cycle device with a refrigerant circuit that includes multi-stage compressors and an intermediate pressure injection system, controlled by a controller to adjust compressor rotation speeds and refrigerant flow, thereby maintaining evaporator inlet temperature without additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a zeotropic refrigerant is used to supplement pressure, then the refrigerant pressure is improved, but the evaporator inlet temperature decreases due to temperature glide
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the opening degree of the expansion valve based on detected evaporator inlet temperature. When the temperature drops below a predetermined threshold, the controller increases the expansion valve opening to reduce refrigerant flow resistance, thereby raising the evaporator inlet temperature while maintaining the pressure benefits of the zeotropic refrigerant mixture.
2Temperature
If a second expansion valve is added to suppress temperature glide effects, then the evaporator inlet temperature is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies universality by making the existing expansion valve perform multiple functions: it serves as the primary refrigerant flow control device during normal operation and automatically adjusts to compensate for temperature glide effects when the evaporator inlet temperature drops. This eliminates the need for a separate second expansion valve while maintaining temperature control functionality.
Solution Approach 2:
The system applies self-service through automatic control where the controller continuously monitors the evaporator inlet temperature and autonomously adjusts the expansion valve opening degree without manual intervention. The system self-regulates to maintain optimal temperature conditions, eliminating the need for additional manual control mechanisms or complex mechanical assemblies.
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
The solution effectively suppresses frost formation on the evaporator while maintaining refrigeration performance and reducing costs by utilizing existing refrigerant circuit components, without the need for additional expansion valves or evaporator division.
Implementation Method 1
when a zeotropic refrigerant is used, the temperature of the refrigerant changes during a condensation process and an evaporation process. This change in the refrigerant temperature is called a temperature glide.
Implementation Method 2
an evaporation process when a single-component refrigerant is used is represented by the dashed line
Implementation Method 3
when a single-component refrigerant is used, the temperature of the refrigerant remains constant during a condensation process and an evaporation process
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
Regarding a refrigerant circuit using a zeotropic refrigerant, a refrigeration cycle device that can suppress a decrease in an inlet temperature of an evaporator due to a temperature glide while keeping costs down, and a method for controlling this refrigeration cycle device are provided. A refrigeration cycle device (1) includes a refrigerant circuit (10) through which a zeotropic refrigerant flows, and a controller (20) that controls elements composing the refrigerant circuit (10). The refrigerant circuit (10) has: a low-stage compressor (11) and a high-stage compressor (12) that are connected in series and compress the refrigerant; a first heat exchanger (13) and a second heat exchanger (14); a first depressurization part (15); and an intermediate pressure injection part (30) that supplies the high-stage compressor (12) with the refrigerant at an intermediate pressure that is reduced with respect to a pressure of the refrigerant having undergone a condensation process. The controller (20) controls rotation speeds of the low-stage compressor (11) and the high-stage compressor (12) based on an index indicating an evaporator inlet temperature or when a predetermined mode for mitigating a decrease in the evaporator inlet temperature is set.