Oil return control method of multifunctional multi-split system with two four-way valves
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Solution Overview
Problem
Multi-split air conditioner systems face challenges in oil return control, particularly when switching from heating or refrigeration modes to oil return mode, leading to risks of water freezing, compressor burnout due to oil accumulation, and inefficient energy recovery.
Innovation Solution
The method employs two four-way valves and electronic expansion valves to adjust operational modes, ensuring oil return while preventing freezing and maintaining system reliability by adjusting fan states and valve openings based on previous operation modes, allowing for efficient energy recovery and oil recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydraulic modules are converted into water refrigeration state for oil return, then refrigerant can flow back to compressor, but water temperature becomes very low causing risk of water freezing and bursting pipeline
Solution Approach 1:
The system performs preliminary heating of water in hydraulic modules before converting to water refrigeration mode. The control unit detects the operation mode and prevents water temperature from dropping below a preset threshold, thereby eliminating the harmful effect of water freezing while still enabling oil return through the hydraulic modules.
Solution Approach 2:
The control unit acts as an intermediary that monitors water temperature and operation mode, preventing the conversion to water refrigeration mode when temperature is too low. This intermediary control mechanism resolves the contradiction by blocking the harmful action (conversion to water refrigeration) while allowing the beneficial action (oil return) under safe conditions.
2Reliability
If hydraulic modules are converted into water refrigeration state for oil return, then refrigerant flow is enabled, but hot water temperature is reduced causing user complaints
Solution Approach 1:
The system performs preliminary heating to maintain water temperature above a preset threshold before enabling oil return mode. This preliminary temperature maintenance ensures that even when refrigerant flows through the hydraulic modules, the water temperature remains sufficient for user needs, thus resolving the contradiction between oil return effectiveness and temperature maintenance.
3Use of energy by moving object
If hydraulic modules are kept in off state for energy saving, then energy consumption is reduced, but refrigerant in high-pressure gas pipe cannot flow causing oil accumulation and compressor burnout
Solution Approach 1:
The system implements periodic oil return operations where the hydraulic modules are temporarily activated to enable refrigerant flow and oil return to the compressor. After the oil return is complete, the modules return to off state for energy saving. This periodic activation resolves the contradiction by balancing energy consumption with periodic reliability maintenance.
Solution Approach 2:
The system discards the energy-saving off state temporarily to recover oil from the high-pressure gas pipe and return it to the compressor. This temporary activation allows the system to recover the harmful oil accumulation, then returns to the energy-saving state, thus resolving the contradiction between energy saving and compressor protection.
4Reliability
If all indoor units are converted to refrigeration state for oil return, then oil return is enabled, but system functionality is reduced and energy efficiency decreases
Solution Approach 1:
The system enables oil return locally through hydraulic modules rather than requiring all indoor units to convert to refrigeration state. This localized approach allows specific modules to perform oil return function while other modules maintain their original heating or refrigeration functions, thus resolving the contradiction between oil return capability and system versatility.
Solution Approach 2:
The hydraulic modules are designed to perform multiple functions: water heating, water refrigeration, and oil return. By utilizing the multi-functionality of these modules, the system can perform oil return without requiring all indoor units to change mode, thus maintaining system versatility while enabling oil return 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 solution ensures effective oil return, prevents pipeline freezing, and enhances system reliability by optimizing energy consumption and functionality across various operating conditions.
Implementation Method 1
the refrigerant in the system pipeline can flow back to the compressor with the flow of the refrigerant
Implementation Method 2
the water temperature in the hydraulic modules will be very low, and the risk of water freezing and bursting the pipeline
Implementation Method 3
opening degrees of the first electronic expansion valves of the indoor heat exchangers and the first electronic expansion valves of the hydraulic heat exchangers
Implementation Method 4
an output end of the compressor is respectively connected to a first port (port D) of the first four-way valve
Data Source
Figure 1~2
AI summary
Herein disclosed is an oil return control method of a multi-functional multi-split system with two four-way valves. The multi-functional multi-split system includes an outdoor unit, at least one set of hydraulic modules and at least one set of indoor modules. When the multi-split system is switched from a normal operation mode to an oil return mode, a first four-way valve and a second four-way valve are powered down, and operation modes of each set of indoor modules and each set of hydraulic modules, the on/off state of fans of an indoor heat exchanger and a hydraulic heat exchanger, opening degrees of a first electronic expansion valve of the indoor heat exchanger and a first electronic expansion valve of the hydraulic heat exchanger, and the on/off state of a first electromagnetic valve and a second electromagnetic valve are correspondingly adjusted based on the previous operation modes of each set of indoor modules and each set of hydraulic modules.