Refrigerant Bypass Control for Stable Simultaneous Cooling and Heating
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Solution Overview
Problem
Air-conditioning systems face challenges in maintaining efficient simultaneous cooling and heating operations, particularly in reducing the heat exchanger conductance (AK value) to prevent on/off switching and ensure comfort and energy-saving performance, especially when the compressor operates at low capacity or in low outdoor temperatures.
Innovation Solution
The air-conditioning apparatus includes a compressor, a heat source unit-side heat exchanger, a four-way valve, and a relay unit connected by pipes to form a refrigerant circuit, with a controller regulating the flow rate and bypassing refrigerant to manage the heat exchange capacity based on temperature and operation capacity ratios, ensuring stable simultaneous cooling and heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the AK value of the heat exchanger is reduced to improve heat recovery performance, then the heat exchange capacity is improved, but the low-pressure side pressure decreases causing evaporating temperature to drop below 0°C
Solution Approach 1:
The heat exchanger is divided into multiple segments (first heat exchanger segment and second heat exchanger segment) with different AK values. The first segment has a smaller AK value optimized for heat recovery, while the second segment has a larger AK value to maintain sufficient heat exchange capacity and prevent evaporating temperature from dropping below 0°C.
Solution Approach 2:
Different portions of the heat exchanger are assigned different thermal conductance characteristics. The first segment is designed with lower AK value for efficient heat recovery when cooling load equals heating load, while the second segment maintains higher AK value to ensure minimum heat exchange capacity and stabilize low-pressure side pressure.
2Temperature
If the flow rate of air through the outdoor fan is increased to maintain compressor cooling, then the compressor temperature is controlled, but the AK value cannot be reduced sufficiently
Solution Approach 1:
The heat exchanger is segmented into first and second segments with different AK values. This allows the overall AK value to be reduced for improved heat recovery performance while the second segment maintains sufficient heat exchange capacity to work effectively with the outdoor fan's air flow rate for compressor cooling.
Solution Approach 2:
The thermal conductance parameters (AK values) of different heat exchanger segments are optimized to different values. The first segment has lower AK for heat recovery efficiency, while the second segment has higher AK to maintain compatibility with compressor cooling requirements under various outdoor fan operating conditions.
3Reliability
If the flow velocity of water is increased to prevent pitting corrosion, then the heat exchanger durability is improved, but the AK value cannot be reduced to the desired value
Solution Approach 1:
The water heat exchanger is divided into first and second segments with different AK values. The first segment has lower AK value for optimized heat recovery performance, while the second segment has higher AK value that can work effectively with increased water flow velocity to prevent pitting corrosion while maintaining overall heat exchange capacity.
Solution Approach 2:
Different segments of the water heat exchanger are assigned different thermal conductance characteristics. The first segment is optimized for heat recovery with lower AK value, while the second segment maintains higher AK value to accommodate higher water flow velocities needed for corrosion prevention.
4Use of energy by moving object
If the heat exchanger is divided into segments to reduce heat transfer area, then the AK value is reduced, but the device complexity increases
Solution Approach 1:
The heat exchanger is divided into first and second segments with different AK values. The first segment has smaller heat transfer area and lower AK for heat recovery optimization, while the second segment has larger heat transfer area and higher AK to maintain sufficient heat exchange capacity, achieving the desired AK value through functional segmentation.
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 prevents on/off switching of indoor units, maintains heating capacity, and enhances energy-saving performance by controlling the refrigerant flow and heat exchange, ensuring comfort and efficiency in both cooling and heating operations.
Implementation Method 1
a compressor (101) compressing and discharging the refrigerant
Implementation Method 2
a heat source unit-side heat exchanger (103) exchanging heat between the refrigerant and water
Implementation Method 3
a four-way valve (102) switching between refrigerant passages
Implementation Method 4
a plurality of use-side heat exchangers (105) exchanging heat between the refrigerant and air to be conditioned
Implementation Method 5
a plurality of indoor expansion devices reducing the pressure of the refrigerant
Data Source
AI summary
An air-conditioning apparatus includes an outdoor unit, indoor units, and a relay unit, and forms a refrigerant circuit. The air-conditioning apparatus further includes a fourth flow control device that regulates the flow rate of refrigerant flowing into the heat source unit-side heat exchanger, a switching valve that regulates the flow rate of the refrigerant passing through a bypass pipe, and a control unit that controls the first heat-source-unit flow control device and the switching valve based on a pressure on a refrigerant inlet side of the heat source unit-side heat exchanger, an inlet temperature and an outlet temperature of a medium passing through the heat source unit-side heat exchanger, and the ratio of a cooling operation capacity to a heating operation capacity of the use-side heat exchangers.