Refrigeration Cycle Bypass Control for Stable Compressor Discharge
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Solution Overview
Problem
Conventional refrigeration cycle devices face inefficiencies and reduced heating capacity at low ambient temperatures due to the inability to control the refrigerant state in the bypass channel, leading to excessive superheating and poor operation of the compressor.
Innovation Solution
The refrigeration cycle device includes a control system that detects low refrigerant mass flow rates in the bypass channel, increasing pressure reduction at the main and bypass expansion sections to accelerate evaporation, ensuring the refrigerant changes to a liquid state and achieves saturation quickly, thereby preventing abnormal compressor discharge temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bypass expansion valve is opened during heating operation at extremely low ambient temperature, then refrigerant flow rate in bypass channel is increased, but refrigerant is heated to excessive degree by subcooling heat exchanger causing abnormal increase in compressor discharge temperature
Solution Approach 1:
The control unit continuously monitors the outlet temperature of the subcooling heat exchanger and adjusts the bypass expansion valve opening based on this feedback. When the outlet temperature exceeds a predetermined threshold, the control unit reduces the bypass expansion valve opening to prevent excessive heating of refrigerant, thereby controlling compressor discharge temperature while maintaining heating capacity.
Solution Approach 2:
The system dynamically changes the opening degree parameter of the bypass expansion valve based on operating conditions, particularly the outlet temperature of the subcooling heat exchanger. This parameter adjustment allows the system to optimize refrigerant flow and temperature control, preventing abnormal compressor discharge temperatures while maintaining effective heating operation.
2Temperature
If bypass expansion valve is closed to prevent excessive heating, then compressor discharge temperature is controlled, but bypass channel cannot be used resulting in poor efficiency and insufficient heating capacity
Solution Approach 1:
The bypass expansion valve opening is dynamically adjusted based on real-time temperature monitoring rather than being fixed closed or open. The control unit modifies the valve opening degree according to the outlet temperature of the subcooling heat exchanger, allowing the system to maintain both temperature control and heating capacity under varying operating conditions.
Solution Approach 2:
The system changes the operational parameter (valve opening degree) of the bypass expansion valve based on temperature feedback, enabling the bypass channel to remain functional while preventing excessive compressor discharge temperature. This dynamic parameter adjustment resolves the contradiction between temperature control and heating efficiency.
3Temperature
If conventional subcooling heat exchanger is used, then refrigerant subcooling is achieved, but refrigerant state at bypass channel outlet cannot be controlled to be wet state leading to excessive superheating
Solution Approach 1:
The control unit uses outlet temperature feedback from the subcooling heat exchanger to adjust the bypass expansion valve opening, enabling precise control of refrigerant state at the bypass channel outlet. This feedback mechanism ensures the refrigerant maintains appropriate subcooling while preventing excessive superheating, achieving both subcooling function and refrigerant state control.
Solution Approach 2:
The subcooling heat exchanger serves multiple functions: it provides refrigerant subcooling, controls refrigerant state at the bypass channel outlet, and prevents excessive superheating through integrated temperature monitoring and control. This multi-functionality resolves the contradiction between achieving subcooling and maintaining proper refrigerant state control.
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 enhances heating capacity and efficiency at low ambient temperatures by swiftly controlling the refrigeration cycle, maintaining a stable refrigerant state and preventing excessive discharge temperatures, thus improving operational reliability and energy efficiency.
Implementation Method 1
subcools mainstream refrigerant by exchanging heat between the mainstream refrigerant and bypass-flow refrigerant
Implementation Method 2
subcooling refrigerant flowing out of the radiator by causing expanded refrigerant to flow into the subcooling heat exchanger
Implementation Method 3
increasing amounts of pressure reduction at the main expansion section and the bypass expansion section
Implementation Method 4
evaporation of refrigerant at the evaporator on a low-pressure side is accelerated
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A refrigeration cycle device (1A) according to the present disclosure includes a first temperature sensor (61) for detecting a temperature of refrigerant at an outlet of a bypass channel, a first pressure sensor (51) for detecting a pressure of refrigerant to be sucked into a compressor (21), a second temperature sensor (62) for detecting a discharge temperature of the compressor, and a control device (4). The control device performs control of reducing openings of a main expansion valve (24) and a bypass expansion valve (31), when a degree of superheating of refrigerant at the outlet of the bypass channel (3) is great and a temperature increase value, within a predetermined period of time, of a temperature of refrigerant discharged from the compressor (21) becomes equal to or greater than a predetermined value. Accordingly, an abnormal increase in the discharge temperature at the start of flow of refrigerant through the bypass channel may be suppressed.