Modern HVAC systems manage refrigerant flow across complex thermal circuits where pressure differentials, heat exchanger loads, and operating temperatures constantly shift. Field measurements show that inefficient flow control can reduce system efficiency by up to 30% and lead to compression ratio imbalances that stress mechanical components. These challenges become particularly acute in variable-load applications where rapid adjustments are needed to maintain optimal thermal transfer.

The fundamental challenge lies in precisely regulating refrigerant distribution while balancing system pressure, heat exchange efficiency, and compressor protection across varying operational demands.

This page brings together solutions from recent research—including dynamic expansion valve control strategies, dual-path flow configurations for enhanced temperature regulation, and integrated reservoir systems for adaptive refrigerant management. These and other approaches focus on maintaining optimal thermal transfer while protecting system components and maximizing energy efficiency across different operating conditions.

1. Control System for Heat Exchangers with Dynamic Compressor and Refrigerant Reserve Regulation Based on Temperature Differential

QINGDAO HAIER AIR-CONDITIONER CO LTD, 2025

Control method and device for heat exchanger systems that optimizes refrigerant flow through the system by dynamically regulating compressor operation and refrigerant reserve levels based on temperature differences. The method monitors temperature differences between indoor and outdoor environments and adjusts compressor operation frequency and refrigerant reserve levels accordingly. This enables optimal refrigerant flow when temperatures are within predetermined ranges, while preventing excessive refrigerant flow when temperatures are outside these ranges.

2. Flow Control Device for Dynamic Regulation of Primary Fluid Flow Rate Based on Secondary Fluid Temperature in HVAC Systems

BELIMO HOLDING AG, 2024

Operating an HVAC system with enhanced thermal management capabilities through a flow control device that dynamically regulates the primary fluid flow rate based on the secondary fluid temperature. The device monitors both primary and secondary fluid temperatures and adjusts the primary fluid flow rate to maintain optimal temperature differential between the primary and secondary fluid streams. This enables precise control over the thermal energy transfer process, ensuring reliable operation and energy efficiency while maintaining safe operating conditions.

3. Air Conditioner with Integrated Liquid Reservoir for Dynamic Refrigerant Management

QINGDAO HISENSE HITACHI AIR-CONDITION SYSTEM CO LTD, 2024

Air conditioner with a built-in liquid reservoir that enables dynamic refrigerant management through a single control system. The air conditioner includes an outdoor unit with a compressor, first and second heat exchangers, and a liquid reservoir connected to the refrigerant circuit. The liquid reservoir stores refrigerant during normal operation, while the compressor and heat exchangers operate as usual. When the air conditioner enters an operating mode, the liquid reservoir can be used to supplement the compressor's refrigerant supply, while the compressor's normal operation is maintained. This allows the air conditioner to operate with a variable refrigerant capacity, enabling precise control over the amount of refrigerant used during different operating conditions.

4. Air Conditioning System with Autonomous Valve-Controlled Refrigerant Circulation Adjustment and Liquid Storage Integration

QINGDAO HAIER INTELLIGENT TECHNOLOGY DEVELOPMENT CO LTD, 2024

Air conditioning system with autonomous refrigerant circulation adjustment to improve performance. The system has a liquid storage tank connected to the refrigerant piping between the outdoor heat exchanger and indoor heat exchangers. Valves control refrigerant exchange between the tank and system. The valve states are adjusted based on parameters like compressor and heat exchanger superheats to optimize refrigerant flow. This allows dynamic refrigerant circulation adjustment based on load to prevent over/under flow issues.

CN118408310A-patent-drawing

5. Method for Dynamic Refrigerant Branch Valve Control via Condensation Temperature Regulation

MIDEA GROUP CO LTD, 2024

A method for optimizing air conditioner operation through dynamic control of refrigerant branch valves. The method enables precise temperature control during heat transfer by dynamically regulating the refrigerant branch valves based on condensation temperature. This approach eliminates the need for standard refrigerant fill rates and allows continuous monitoring of the refrigerant system. The control method is implemented through a storage medium containing the control program, which can be executed by a processor to implement the dynamic valve control strategy.

CN117704580A-patent-drawing

6. Air Conditioner with Ambient Temperature and Operation Mode-Based Refrigerant Quantity Calculation

QINGDAO HISENSE HITACHI AIR CONDITIONING SYSTEM CO LTD, 2024

Air conditioner that determines refrigerant quantity based on ambient temperature and system operation mode. The system calculates the refrigerant amount difference between actual and optimal operating conditions, enabling precise refrigerant quantity determination regardless of system configuration. This approach eliminates the need for manual refrigerant charging and provides accurate refrigerant quantity monitoring across various operating modes.

7. Refrigerant Circulation Device with Dual-Path Flow Configuration for Pre-Cooling and Condenser Temperature Regulation

GREE ELECTRIC APPLIANCES INC OF ZHUHAI, 2024

A refrigerant circulation device, air conditioner, and control method that enables precise temperature control through a novel refrigerant path configuration. The device employs a switching component that divides the refrigerant flow into two paths: one for the evaporator and another for the condenser. This path configuration allows the refrigerant to be pre-cooled before entering the condenser, while also enabling the condenser to operate at lower temperatures. The device achieves temperature control through the precise control of refrigerant flow between the evaporator and condenser, enabling dynamic temperature adjustments while maintaining optimal system performance.

CN117515935A-patent-drawing

8. Heat Pump Air Conditioner with Valve Plate Mechanism for Adaptive Refrigerant Path Regulation

GREE ELECTRIC APPLIANCES INC ZHUHAI, 2024

Heat pump air conditioner with adaptive refrigerant management through a novel valve plate mechanism. The valve plate enables controlled opening and closing of a conductive hole in the cylinder, allowing precise regulation of the refrigerant path during both heating and cooling cycles. This valve plate system enables the heat pump to optimize refrigerant usage and maintain system pressure during heating, while also storing excess refrigerant during cooling to prevent pressure surges.

9. HVAC Flow Control System with 3-Way Valve and Integrated Flow Sensor

BELIMO HOLDING AG, 2023

Flow control system for HVAC systems that enables precise control of fluid flow between two circuits through a single valve. The system employs a 3-way valve with a 2-way return port, a flow sensor, and a controller. The valve switches between circuit connections based on circuit selection, while the flow sensor measures flow through the valve's output port. The controller controls the valve position based on setpoint values, flow rate, and temperature differential. The system achieves precise flow control by maintaining the valve position when flow is below maximum limits, and dynamically adjusting position when flow exceeds maximum limits.

EP4198673A1-patent-drawing

10. Control Method and Device for Air Conditioners with Dynamic Expansion Valve Adjustment for Refrigerant Flow Distribution

HAIER SMART HOME CO LTD, 2023

Control method and device for air conditioners that improves refrigerant distribution and heat transfer efficiency through a novel expansion valve strategy. The method involves dynamically adjusting the expansion valve opening to optimize refrigerant flow distribution between evaporator branches. By increasing the expansion valve opening when the branch temperature difference between inlet and outlet exceeds a predetermined threshold, the method enhances the evaporator's heat transfer capacity while preventing excessive refrigerant flow into the shunt. This approach ensures more uniform refrigerant distribution between evaporator branches and maintains optimal subcooling conditions in the condenser.

CN116241961A-patent-drawing

11. HVAC System Control Method with Mode-Based Adaptive and Balanced Temperature Regulation

TRANE INTERNATIONAL INC, 2023

A method for controlling heating and cooling in HVAC systems to achieve both targeted cooling and heating temperatures. The method involves selecting an operating mode based on cooling and heating demands, and then operating the system in that mode. The modes include adaptive cooling, adaptive heating, and balanced cooling/heating. The adaptive modes unload the compressor when the temperature exceeds a threshold. The balanced modes control the flow of fluids to meet target temperatures.

12. Air Conditioner Refrigeration System with Branch Control Valve for Uniform Temperature Plate Integration

QINGDAO HAIER INTELLIGENT TECHNOLOGY DEVELOPMENT CO LTD, 2023

A control method and air conditioner for an air conditioner refrigeration system that improves heat dissipation efficiency of the electric control board while maintaining temperature regulation performance. The method enables controlled heat dissipation of the electric control board through a novel branch control valve configuration that directs refrigerant flow through a uniform temperature plate on the high-temperature board area. This configuration enables precise temperature regulation while maintaining system efficiency, particularly in high-temperature operation conditions.

13. Air Conditioner with Compact Internal Heat Exchanger and Flow Rate Adjusting Device in Refrigerant Circuit

MITSUBISHI ELECTRIC CORP, 2023

Air conditioner that can achieve further performance improvement of a refrigeration cycle using an internal heat exchanger while keeping the size of the internal heat exchanger small. The air conditioner includes a refrigerant circuit, an internal heat exchanger, an external heat exchanger, and a flow rate adjusting device.

14. HVAC System with Modulating Valve for Dynamic Refrigerant Distribution to Dual Heat Exchangers

JOHNSON CONTROLS TECH CO, 2022

HVAC system that enables precise temperature and humidity control through dynamic refrigerant flow management. The system employs a modulating valve that directs refrigerant to two distinct heat exchangers: a condenser coil and a reheat coil. The valve's control circuit monitors air flow conditions and dynamically apportions refrigerant between these heat exchangers based on the air flow's operating parameters. This enables precise temperature and humidity management of the supply air flow, allowing for more accurate space conditioning compared to traditional vapor compression systems.

US2022397296A1-patent-drawing

15. Air Conditioner with Compact Internal Heat Exchanger and Flow Rate Adjustment Mechanism

MITSUBISHI ELECTRIC CORP, 2022

An air conditioner with a compact internal heat exchanger that enhances refrigeration performance through optimized heat transfer. The system employs a novel heat exchanger design where the heat transfer medium is maintained between the refrigerant circuits. A flow rate adjustment device controls the heat medium flow rate to the heat exchanger, while a temperature sensor monitors the heat medium temperature. This enables precise control of heat transfer while maintaining the compact size of the internal heat exchanger.

WO2022230034A1-patent-drawing

16. Two-Pipe Heat Recovery System with Dynamic Refrigerant Flow Direction Control Using Solenoid Valves

ZHUHAI GREE ENERGY SAVING AND ENVIRONMENTAL PROTECTION REFRIGERATION TECHNOLOGY RESEARCH CENTER CO LTD, 2022

A two-pipe heat recovery multi-line system that enables dynamic control of refrigerant flow direction based on cooling and heating demand. The system integrates an outdoor unit refrigeration system, a mode converter, and multiple indoor units, with a flow control device that determines operating mode based on demand analysis. The device controls the flow direction of refrigerant through strategically positioned solenoid valves, enabling automatic mode switching between cooling and heating modes. This enables enhanced user experience by automatically adapting operating modes to changing demand conditions.

17. Three-Tube Heat Recovery Multi-Split Air Conditioning System with Adaptive Evaporator Temperature Control and Intermediate Pressure Regulation

GD MIDEA HEATING & VENTILATING EQUIPMENT CO LTD, 2021

A three-tube heat recovery multi-split air conditioning system that dynamically adjusts cooling indoor unit evaporator temperature in response to ambient conditions. The system integrates a low temperature cooling and anti-freezing module with a refrigerant distribution device, featuring a heat exchange assembly with four-way valves. When the indoor unit's evaporator temperature falls below a predetermined threshold, the system automatically adjusts the evaporator temperature by generating intermediate pressure between the low temperature cooling module and the low-pressure air tube. This adaptive control ensures optimal evaporator temperature matching to ambient conditions while preventing freezing.

18. Control Method for Multi-Line System with Dynamic Throttle Adjustment Based on Heat Transfer Metrics

Midea Group Co., Ltd., GD MIDEA HEATING AND VENTILATING EQUIPMENT CO LTD, MIDEA GROUP CO LTD, 2021

Control method for a multi-line system that optimizes refrigerant flow through an air treatment device by dynamically adjusting the throttle element's opening based on the device's actual heat transfer requirements. The method measures the device's superheat or subcooling levels in both cooling and heating modes, and uses this information to control the throttle element's opening. This enables precise control of refrigerant flow rates while maintaining optimal heat transfer performance.

CN111486579B-patent-drawing

19. Method for Controlling Refrigerant Distribution to Regulate Indoor Unit Evaporator Temperature

广东美的暖通设备有限公司, MIDEA GROUP CO LTD, Midea Group Co., Ltd., 2021

Air conditioner control method that prevents indoor unit freezing during low-temperature operation. The method maintains the indoor unit evaporator temperature at a predetermined value while controlling the refrigerant distribution device's valve opening. When the system enters low-temperature mode, the evaporator temperature is set based on the indoor unit evaporator temperature and the distribution device's outlet temperature. The control method ensures the refrigerant distribution device maintains a safe operating temperature, preventing the indoor unit from freezing during low-temperature operation.

CN111473500B-patent-drawing

20. Air Conditioner with Parallel Piping and Separate Return Paths for Controlled Refrigerant Flow Management

MITSUBISHI ELECTRIC CORP, 2021

Air conditioner with optimized refrigerant circulation and heat transfer by introducing a novel piping configuration. The system employs a parallel piping arrangement between the heat source and utilization units, with separate return paths that enable controlled refrigerant flow management. This configuration enables the system to dynamically regulate refrigerant flow between the heat source and utilization units, allowing efficient heat transfer and improved system performance across both heating and cooling modes.

CN113439188A-patent-drawing

21. Refrigerant Heat Dissipation Device with Temperature-Dependent Valve Control and Real-Time Monitoring

MIDEA GROUP CO LTD, 美的集团股份有限公司, 广东美的暖通设备有限公司, 2021

A refrigerant heat dissipation device for air conditioning systems that enables precise control of heat dissipation through temperature-dependent valve opening. The device features a refrigerant heat exchanger arranged to dissipate heat to components, with control valves strategically positioned to manage refrigerant flow. The system monitors real-time temperature conditions in both the heat exchanger and components, automatically adjusting valve opening degrees based on temperature thresholds. This enables optimized heat dissipation while maintaining component safety and system performance.

22. Control Method for Multi-Line Refrigeration Systems with Dynamic Refrigerant Flow Adjustment Based on Ambient Temperature Differences

MIDEA GROUP CO LTD, Guangdong Midea HVAC Equipment Co., Ltd., Midea Group Co., Ltd., 2019

A control method for multi-line refrigeration systems that dynamically adjusts refrigerant flow based on ambient temperature differences between indoor and outdoor units. The method monitors temperature deviations between indoor and outdoor units, then automatically adjusts the flow through each unit's flow regulator based on the temperature differences. This ensures optimal refrigerant distribution across the system, even when the indoor unit's set temperature differs significantly from the outdoor temperature.

23. VRF Air Conditioning System with Integrated Dual Control Architecture for Temperature and Humidity Management

MIDEA GROUP CO LTD, GD MIDEA HEATING & VENTILATING EQUIPMENT CO LTD, 2018

VRF air conditioning system with dual control over temperature and humidity that enables rapid defrosting without compromising normal operation. The system employs a unique control architecture where each indoor unit's control valves, solenoids, and heat exchanger are integrated into the system's control architecture. When the system is operating in heating mode, the control system automatically switches between heating and dehumidification modes based on temperature and humidity conditions. During defrosting, the system automatically transitions to condenser mode for the dehumidified indoor unit while maintaining normal operation for the other units. This dual-control approach enables rapid defrosting while maintaining system efficiency and comfort.

US10101054B2-patent-drawing

24. Air Conditioner with Dynamic Refrigerant Flow Regulation and Pressure Adjustment Mechanism

SAMSUNG ELECTRONICS CO LTD, 2017

Air conditioner that optimizes refrigerant flow during system operation by dynamically regulating refrigerant storage and circuit pressure. The system monitors refrigerant state transitions between supercooled and liquid phases, and adjusts circuit pressure and refrigerant flow accordingly. This enables precise control of refrigerant quantity during switching operations, ensuring optimal system performance and minimizing pressure losses.

US2017276413A1-patent-drawing

25. Air-Conditioning System with Relay-Controlled Dynamic Refrigerant Flow for Simultaneous Multi-Unit Heating and Cooling

MITSUBISHI ELECTRIC CORP, 2017

Air-conditioning system with simultaneous cooling and heating capabilities through a novel control strategy. The system employs a relay device that dynamically switches between cooling and heating operations among multiple indoor units. Each unit is equipped with a heat exchanger that exchanges heat with the refrigerant, while the relay device controls the flow of refrigerant through the heat exchanger based on the total cooling and heating capacities of all units. This allows the system to maintain continuous operation while dynamically adjusting the refrigerant flow rate based on the heat load. The relay device enables efficient operation of multiple heat exchangers simultaneously, enabling higher overall capacity compared to traditional sequential operation.

US2017097177A1-patent-drawing

26. Air-Conditioning Apparatus with Dynamic Flow Switching System for Uniform Refrigerant Distribution in Heat Exchangers

MITSUBISHI ELECTRIC CORP, 2016

Air-conditioning apparatus that optimizes energy efficiency through controlled flow rate management in heat exchangers. The apparatus features a unique flow switching system where each heat exchanger's flow rate is dynamically adjusted based on resistance in the piping network. This approach ensures equal refrigerant flow rates across all heat exchangers regardless of their specific resistance characteristics, thereby eliminating pressure losses typically associated with unequal flow rates. The system enables precise control of heat exchanger performance during cooling or heating modes, enabling energy savings through optimized refrigerant flow distribution.

27. Air Conditioning System with Relay Valve for Dynamic Mode Switching and Temperature-Based Flow Control

MITSUBISHI ELECTRIC CORP, 2016

Air conditioning system that enables simultaneous operation of multiple air conditioning units while maintaining optimal performance. The system employs a relay valve that dynamically switches between air conditioning and heating modes for each unit, allowing them to operate together in a coordinated manner. The relay valve is controlled by a temperature-based flow control system that regulates the refrigerant flow between the air conditioning and heating units. This enables the system to maintain optimal operating conditions for both heating and cooling while minimizing energy consumption.

28. Air-Conditioning Apparatus with Single Flow Control Valve for Multi-Unit Refrigerant Distribution

MORIMOTO OSAMU, 2015

Air-conditioning apparatus that enables precise control of refrigerant flow to multiple indoor units through a single flow control device. The apparatus features a single flow control valve that can be opened or closed to control the refrigerant path for each indoor unit, allowing for real-time flow management and precise pressure control. This enables optimized startup times and reduced noise levels compared to traditional multi-valve systems.

29. Air-Conditioning System with Dynamic Heat Exchanger Switching and Refrigerant Flow Rate Control

MITSUBISHI ELECTRIC CORP, 2015

Air-conditioning system that enables simultaneous cooling and heating operation by dynamically switching between heat exchangers. The system employs a relay unit that controls the flow rate of refrigerant between the heat source and cooling/heating units. A temperature sensor monitors the temperature difference between the heat source and cooling/heating units, while a flow rate controller adjusts the refrigerant flow rate to maintain optimal temperature conditions. The system ensures continuous operation during both cooling and heating phases by automatically switching between heat exchangers based on temperature conditions.

EP2905552A1-patent-drawing

30. Refrigerant Circuit with Channel Change Valve System for Multi-Unit Air Conditioning Operation

MITSUBISHI ELECTRIC CORP, 2015

Air conditioning device that enables simultaneous operation of multiple air conditioning units while maintaining optimal indoor air quality and energy efficiency. The device employs a novel refrigerant circuit configuration that enables controlled operation of multiple air conditioning units through a single refrigerant circuit. The circuit features a unique channel change valve system that allows the device to selectively bypass or modify the refrigerant flow between the heat exchangers, enabling simultaneous operation of multiple units while maintaining optimal operating conditions.

31. Refrigerant Flow Control Device with Bypass Pipe and Throttling Devices for Heat Exchanger

MITSUBISHI ELECTRIC CORP, 三菱电机株式会社, 2015

A device for optimizing air conditioning system performance by dynamically controlling the refrigerant flow through a heat exchanger. The device features a refrigerant circulation loop with a bypass pipe that connects the heat exchanger to the refrigerant circulation loop. The bypass pipe has multiple throttling devices that control the refrigerant flow through the heat exchanger. This configuration enables precise control over the refrigerant flow rate, allowing the system to maintain optimal operating conditions while minimizing energy consumption. The device incorporates a thermal medium flow control system that uses a combination of valves and flow rate control devices to manage the refrigerant flow through the heat exchanger. This enables reliable operation of the system even when the refrigerant flow rate is reduced.

32. Air Conditioning System with Dual-Function Heat Recovery and Variable Flow Control

GREE ELECTRIC APPLIANCES INC OF ZHUHAI, 珠海格力电器股份有限公司, 2015

Air conditioning system with integrated heat recovery that optimizes both cooling and heating performance. The system employs a dual-function heat recovery system where the compressor's exhaust gas is cooled and then re-heated before entering the condenser. The system includes a heat recovery heat exchanger and a heat recovery pipeline assembly that connects to the compressor discharge. A flow control unit regulates the heat recovery pipeline's output flow, enabling precise control of both cooling and heating performance. This integrated approach enables optimal heat recovery while maintaining stable system operation.

33. Air-Conditioning Apparatus with Multi-Unit Heat Exchanger Subcooling Regulation via Flow Rate Control

DAIKIN IND LTD, 2015

Air-conditioning apparatus with improved subcooling control for refrigerant charging. The apparatus has multiple heat source units with adjustable subcooling degrees for each unit's heat exchanger. The subcooling adjustment mechanisms are controlled by flow rate regulators, ensuring uniform subcooling across all units. This approach prevents refrigerant drift by maintaining consistent subcooling conditions throughout the system. The system also employs flow rate regulators to maintain equal flow rates across all units, preventing uneven refrigerant distribution. The controller monitors subcooling and flow rates to maintain optimal conditions, ensuring precise refrigerant charging.

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