Heat Pump Defrost Control to Limit Compressor Liquid Backflow
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Solution Overview
Problem
Existing air-conditioning systems face challenges in accurately detecting and preventing liquid backflow during defrosting operations, particularly in low-pressure shell compressors, which can lead to reduced compressor reliability due to viscosity changes in refrigerant oil.
Innovation Solution
An air-conditioning apparatus with a controller that adjusts the compressor operation frequency to a lower setting during the transition from heating to defrosting, and further adjusts based on the degree of superheat of the refrigerant oil, to minimize liquid backflow and maintain compressor reliability without increasing system cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bypass circuit with heater and capillary tube is provided to reduce liquid backflow, then liquid backflow is reduced, but device complexity and cost increase
Solution Approach 1:
The invention extracts and eliminates the need for complex additional components (bypass circuit, heater, capillary tube) by using the existing compressor capacity control mechanism. The compressor's capacity is modulated through frequency adjustment alone, removing the need for separate liquid backflow prevention hardware while achieving the same protective effect.
Solution Approach 2:
The compressor's frequency control mechanism, originally designed for capacity regulation, is made to serve a dual function: both capacity control and liquid backflow prevention. By adjusting the operation frequency during defrosting operations, the same control system prevents liquid backflow without requiring dedicated components, thus achieving multi-functionality.
2Reliability
If operation frequency of compressor is increased in stages during defrosting operation, then liquid backflow is reduced, but device complexity increases due to bypass circuit requirement
Solution Approach 1:
The invention removes the bypass circuit requirement entirely by achieving liquid backflow prevention through frequency modulation of the existing compressor. The capacity control mechanism alone suffices to prevent liquid backflow when properly timed and adjusted, eliminating the need for extraction of additional protective components.
Solution Approach 2:
The invention changes the operational parameters of the compressor (operation frequency) to achieve liquid backflow prevention. By adjusting the frequency from 20 Hz to 40 Hz during defrosting operations, the system modifies the compressor's characteristics to prevent liquid backflow without structural modifications or additional components.
3Reliability
If compressor operation frequency is reduced during transition to defrosting, then liquid backflow is minimized, but defrosting efficiency may be affected
Solution Approach 1:
The invention performs preliminary action by reducing the compressor operation frequency before liquid backflow can occur during the transition to defrosting operation. This preventive frequency reduction is timed to occur at the moment of operation switching, preventing the harmful effect before it manifests while maintaining overall defrosting effectiveness through subsequent normal operation.
Solution Approach 2:
The invention applies periodic modulation of the compressor operation frequency during defrosting cycles. The frequency is temporarily reduced at the critical transition moment, then restored to normal levels during the defrosting operation itself, creating a periodic pattern that prevents liquid backflow while maintaining defrosting efficiency.
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 approach effectively reduces the viscosity impact of liquid backflow on the compressor, ensuring reliability and efficient defrosting performance while avoiding costly modifications to the system.
Implementation Method 1
a compressor which compresses refrigerant into high-temperature high-pressure gas
Implementation Method 2
a four-way valve which switches the flow of refrigerant
Implementation Method 3
an indoor-side heat exchanger, an expansion valve functioning as a decompressing unit and an outdoor-side heat exchanger
Implementation Method 4
The low-pressure gas passes through the four-way valve and is sucked into the compressor
Implementation Method 5
The condensed liquid is adiabatically expanded at the expansion valve to change into low-pressure refrigerant
Implementation Method 6
after flowing out of the compressor, high-temperature, high-pressure gas passes through the bypass pipe passage, enters the outdoor-side heat exchanger, and melts the frost adhering to the surface of the outdoor-side heat exchanger
Implementation Method 7
melts the frost adhering to the surface of the outdoor-side heat exchanger
Implementation Method 8
liquid refrigerant condensed in the outdoor-side heat exchanger during the defrosting
Implementation Method 9
a large amount of refrigerant is dissolved in refrigerating machine oil for lubrication of the inside of the compressor. As a result, the viscosity of the refrigerating machine oil is reduced
Data Source
AI summary
An air-conditioning apparatus includes: a refrigerant circuit in which a compressor, a four-way valve, a heat source-side heat exchanger, an expansion valve and a load-side heat exchanger are connected; and a controller which controls a refrigeration cycle in which refrigerant is circulated in the refrigerant circuit, to switch a flow passage for the refrigerant in accordance with which of a cooling operation, a heating operation and a defrosting operation is performed. The controller includes: a refrigeration-cycle control unit which controls the four-way valve to switch the flow passage of the refrigerant when the operation to be performed is switched from the heating operation to the defrosting operation; and a compressor control unit which sets an operation frequency of the compressor at a value lower than an operation frequency which is applied during the heating operation, when the operation is switched from the heating operation to the defrosting operation.