Heat Pump Passive Defrost Using Refrigerant Bypass Flow
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Solution Overview
Problem
Conventional heat pump systems face efficiency losses due to frost formation on outdoor heat exchanger coils, which requires energy-intensive reverse-cycle defrosting, leading to heat loss and discomfort during defrost operations.
Innovation Solution
A passive defrost method is implemented, where the compressor is disabled, and a low-resistance bypass path allows refrigerant to flow from the condensing coil to the evaporating coil, utilizing residual heat to melt frost without additional energy expenditure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reverse-cycle defrost is used to remove frost from outdoor HX coils, then frost is effectively removed, but heat is lost to the outdoor ambient and energy efficiency is reduced
Solution Approach 1:
The patent converts the harmful cold temperature of the evaporating coil (which causes frost formation) into a beneficial heat source for defrosting. By reversing the refrigerant flow direction and allowing refrigerant to flow from the condensing coil to the evaporating coil, the system uses the temperature differential to melt frost on the evaporating coil without losing heat to the outdoor ambient.
Solution Approach 2:
The patent inverts the conventional defrost approach by reversing the refrigerant flow direction. Instead of using the condensing coil to heat the evaporating coil through the compressor (conventional reverse-cycle), the system allows refrigerant to flow directly from the condensing coil to the evaporating coil through a bypass valve, effectively swapping the traditional heating and cooling roles during defrost operation.
2Reliability
If reverse-cycle defrost is used to defrost outdoor HX coils, then frost is removed, but supplemental heat is consumed to temper indoor air adding to energy penalty
Solution Approach 1:
The system performs self-service defrosting by using its own refrigerant and temperature differential to melt frost on the evaporating coil. The condensing coil provides the heat necessary for defrosting without requiring external supplemental heating, making the defrost process self-sufficient and energy-efficient.
3Loss of energy
If compressor is disabled during passive defrost, then refrigerant can flow from condensing to evaporating coil, but system cannot perform normal heating function
Solution Approach 1:
The system implements periodic defrost cycles where the compressor is temporarily disabled to allow refrigerant flow reversal for defrosting, then resumes normal heating operation. The controller manages these periodic transitions between defrost mode and heating mode, ensuring that defrosting occurs at appropriate intervals without continuously impacting heating productivity.
4Loss of energy
If low-resistance bypass path is provided between condensing and evaporating HX coils, then refrigerant flows efficiently during passive defrost, but system complexity increases
Solution Approach 1:
The bypass valve serves multiple functions: it enables the low-resistance refrigerant flow path during passive defrost mode, and can be integrated with the existing four-way valve to manage refrigerant direction. This multi-functional approach allows the system to achieve efficient defrosting without adding significant complexity, as the bypass mechanism leverages existing system components.
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 enhances the overall efficiency of the heat pump system, reduces energy consumption, and provides greater comfort by eliminating the need for supplemental heating during defrosting, while maintaining system performance.
Implementation Method 1
The bypass path allows the refrigerant to flow from the condensing HX coil to the evaporating HX coil while the compressor is disabled
Implementation Method 2
utilizing residual heat to melt frost without additional energy expenditure
Implementation Method 3
The compressor is configured to compress the refrigerant, thereby causing the refrigerant to have a greater pressure in the condensing HX coil than in the evaporating HX coil
Implementation Method 4
causing a pressure differential between the refrigerant in a condensing HX coil and in an evaporating HX coil
Data Source
AI summary
A heat pump system includes a controller and a closed system that includes a condensing heat exchanger coil, an evaporating heat exchanger coil, a refrigerant and a compressor. The compressor is configured to compress the refrigerant, thereby causing the refrigerant to have a greater pressure in the condensing heat exchanger coil than in the evaporating heat exchanger coil. The controller is configured to perform a passive defrost of the evaporating heat exchanger coil. The passive defrost includes disabling the compressor and providing a bypass path between the condensing and evaporating heat exchanger coils that bypasses the compressor. The bypass path allows the refrigerant to flow from the condensing heat exchanger coil to the evaporating heat exchanger coil while the compressor is disabled.