Heat Pump Bypass Valve Control for Compressor Liquid Injection
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Solution Overview
Problem
Conventional heat pump systems face challenges in maintaining compressor reliability and operating efficiency, particularly when the compression ratio is large, due to inadequate liquid injection flow rates and risks of liquid compression, especially with variable-capacity compressors.
Innovation Solution
A heat pump system with a variable-type bypass depressurization mechanism that controls liquid injection to match the compressor's operating capacity, setting an upper limit for the bypass depressurization mechanism based on the main depressurization mechanism's opening degree to prevent liquid compression and ensure reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solenoid on-off valve and capillary tube are used as the bypass depressurization mechanism, then the flow passage resistance is suitable for small operating capacity conditions, but the liquid injection flow rate becomes inadequate under large operating capacity conditions
Solution Approach 1:
The patent replaces the fixed flow resistance configuration (solenoid on-off valve and capillary tube) with a variable flow resistance mechanism (electromagnetic valve with adjustable opening degree). This allows the bypass depressurization mechanism to dynamically adjust its flow characteristics according to operating conditions, enabling adequate liquid injection flow rate under both small and large operating capacity conditions while maintaining compressor reliability.
2Reliability
If the liquid injection flow rate is increased to maintain compressor reliability under large compression ratios, then the risk of liquid compression increases, but if the flow rate is limited to prevent liquid compression, then the operating capability cannot be increased
Solution Approach 1:
The patent implements feedback control by monitoring the discharge temperature and using it to adjust the opening degree of the electromagnetic valve. The discharge temperature serves as an indicator of liquid injection adequacy and compressor health. By continuously adjusting the bypass depressurization mechanism based on discharge temperature feedback, the system maintains optimal liquid injection flow rate that prevents liquid compression while enabling full operating capability under large compression ratios.
Solution Approach 2:
The patent changes the flow rate parameter of the bypass depressurization mechanism dynamically based on operating conditions. By adjusting the opening degree of the electromagnetic valve, the system varies the liquid injection flow rate to match the compressor's operating capacity and compression ratio, thereby preventing liquid compression while maintaining desired operating capability across different load conditions.
3Productivity
If the bypass depressurization mechanism is controlled without considering the main depressurization mechanism's opening degree, then the liquid injection flow rate can be maximized, but the refrigerant circulation balance is disrupted
Solution Approach 1:
The patent uses the opening degree of the main depressurization mechanism as a feedback parameter to determine the upper limit opening degree of the bypass depressurization mechanism. This ensures that the bypass mechanism's operation is coordinated with the main mechanism, maintaining proper refrigerant circulation balance while still achieving adequate liquid injection flow rate when needed.
Solution Approach 2:
The patent dynamically adjusts the upper limit opening degree parameter of the bypass depressurization mechanism based on the opening degree parameter of the main depressurization mechanism. This parameter coordination ensures that the bypass mechanism operates within safe limits that maintain refrigerant circulation balance while enabling sufficient liquid injection under varying operating conditions.
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 configuration maintains compressor reliability and achieves desired operating capability even under high compression ratios by adjusting liquid injection flow rates and preventing liquid compression, enhancing controllability and efficiency.
Implementation Method 1
the bypass tube is provided with a depressurization mechanism (bypass depressurization mechanism) for depressurizing the refrigerant flowing through the bypass tube
Implementation Method 2
a variable-capacity compressor
Implementation Method 3
an indoor heat exchanger (radiator) for functioning as a refrigerant radiator during air-warming operation
Implementation Method 4
an outdoor heat exchanger (evaporator) for functioning as a refrigerant evaporator during air-warming operation
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The heat pump system (1) has a bypass circuit (30) for forming a connection to the intake side of a compressor (21) from the portion of a main refrigerant circuit (20) that extends from the outlet of a usage-side heat exchanger (41) to a heat-source-side expansion valve (28), the main refrigerant circuit (20) being formed by connecting a variable-capacity compressor (21), a usage-side heat exchanger (41), a variable-type heat-source-side expansion valve (28), and a heat-source-side heat exchanger (26). The bypass circuit (30) has a bypass tube (31), and a bypass expansion valve (32) for depressurizing the liquid refrigerant flowing through the bypass tube (31). The bypass expansion valve (32) is a variable-type bypass expansion valve. A controller (1a) performs liquid injection control for controlling the bypass expansion valve (32) so that the discharge temperature (Td) of the compressor (21) is equal to a target discharge temperature (Tds); and determines the upper limit opening degree (OPix) of the bypass expansion valve (32) in liquid injection control by a correlation value with respect to the opening degree (one) of the heat-source-side expansion valve (28).