Bypass Expansion Valve Control for Low-Temperature Hydronic Heating
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Solution Overview
Problem
Conventional refrigeration cycle apparatuses face inefficiency and insufficient heating ability at low outside air temperatures due to the bypass expansion valve controlling temperature differences, leading to an overheated refrigerant state and abnormal compressor discharge temperature rises.
Innovation Solution
A refrigeration cycle apparatus with a bypass passage and control device that adjusts the bypass expansion valve to maintain the refrigerant outlet at saturation temperature, increasing compressor rotations in stages to prevent overheating and enhance heating efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the bypass expansion valve is opened to increase refrigerant flow through the bypass passage, then the heating ability is improved, but the refrigerant becomes extremely heated and the compressor discharge temperature abnormally rises
Solution Approach 1:
The control device increases the number of rotations of the compressor in stages after the compressor is actuated, before fully opening the bypass expansion valve. This preliminary action prepares the system by gradually building compression capacity, preventing the refrigerant from becoming excessively heated when the bypass passage is activated, thus avoiding abnormal compressor discharge temperature rises while still achieving sufficient heating ability.
Solution Approach 2:
The system dynamically adjusts both the compressor rotation speed and the bypass expansion valve opening degree in a coordinated manner. The control device monitors the operating conditions and modifies the refrigerant flow through the bypass passage and compressor speed in real-time, ensuring that the refrigerant state remains within safe temperature ranges while maximizing heating performance under varying load conditions.
2Ease of operation
If the bypass expansion valve is controlled to maintain temperature difference, then the system operates simply, but the refrigerant state cannot be brought into a moist state and efficiency is poor at low temperatures
Solution Approach 1:
The control device uses feedback from temperature sensors to detect the refrigerant state and adjusts the bypass expansion valve opening degree and compressor rotation speed accordingly. By monitoring the refrigerant temperature and pressure, the system dynamically optimizes the bypass flow to achieve the desired moist refrigerant state, significantly improving heating efficiency at low temperatures while maintaining automated control that simplifies operation.
3Power
If the compressor rotations are increased to improve heating output, then the heating ability is enhanced, but the refrigerant overheating worsens and discharge temperature rises abnormally
Solution Approach 1:
The control device increases the number of rotations of the compressor in stages after actuation, gradually building compression capacity before fully activating the bypass passage. This staged approach prevents sudden refrigerant overheating that would occur if high compressor speed and full bypass flow were activated simultaneously, allowing the system to achieve high heating output while maintaining safe refrigerant temperatures.
Solution Approach 2:
The system changes multiple operating parameters simultaneously and coordinately - compressor rotation speed, bypass expansion valve opening degree, and refrigerant flow distribution - to achieve the desired heating output. By adjusting these parameters in a coordinated manner rather than independently, the system maintains optimal refrigerant temperature and prevents abnormal discharge temperature rises while delivering enhanced heating capability.
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 ensures efficient operation and sufficient heating ability even at low temperatures by controlling the refrigerant state and reducing compressor discharge temperature, thereby improving overall efficiency and reliability.
Implementation Method 1
a supercooling heat exchanger which heat-exchanges between a mainstream refrigerant and a bypassing refrigerant, thereby supercooling the mainstream refrigerant
Implementation Method 2
thereby supercooling the mainstream refrigerant
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A refrigeration cycle apparatus of the present invention includes a first temperature sensor (61), a pressure sensor (51), a second temperature sensor (62), and a control device (4). The control device (4) controls operation of a bypass expansion valve (31) such that a temperature at an outlet of the bypass passage (3) becomes equal to a saturation temperature in a section until a number of rotation of the compressor (21) reaches a predetermined compressor target number of rotations after the compressor (21) is actuated. When the temperature at the outlet of the bypass passage (3) reaches the saturation temperature, the control device (4) increases the number of rotation of the compressor (21) to a number of rotations of a next stage, and the control device (4) controls the refrigeration cycle into an appropriate refrigeration cycle state.