Internal Heat Exchanger Layout for Heat Pump Refrigerant Distribution
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Solution Overview
Problem
Conventional heat pump systems face inefficiencies in cooling and heating operations due to uneven refrigerant distribution and increased superheat, leading to decreased performance, especially in cooling modes and when operating in humid conditions, where frost formation can further reduce heating performance.
Innovation Solution
Incorporating an internal heat exchanger that switches between cooling and heating pathways, allowing the refrigerant to flow through high-pressure and low-pressure passages, which helps in maintaining a low vapor quality, thereby improving refrigerant distribution and reducing pressure loss across the outdoor unit, enhancing both cooling and heating efficiencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an accumulator is provided upstream of the compressor with a return hole for lubricant, then lubricant can be returned, but superheat of the refrigerant cannot decrease before entering the compressor, resulting in small enthalpy difference in the evaporator and decreased cycle efficiency
Solution Approach 1:
A subcooler is introduced as an intermediary component between the condenser and the evaporator. The subcooler serves as a mediator that further cools the refrigerant after condensation, enabling the refrigerant to enter the evaporator at a lower temperature. This resolves the contradiction by providing both lubricant return capability and sufficient superheat reduction to maintain high cycle efficiency.
2Power
If two-phase refrigerant is distributed to multiple tubes of the outdoor unit in heating operation, then heat exchange capacity increases, but uniform distribution is difficult, causing liquid refrigerant concentration in some tubes and reduced effective area of the outdoor unit
Solution Approach 1:
The refrigerant state parameters (temperature, pressure, vapor quality) are optimized before entering the outdoor unit. By controlling the refrigerant to be in a specific two-phase state with controlled vapor quality, the system achieves both high heating capacity and uniform distribution across multiple tubes, resolving the contradiction between power and distribution stability.
3Power
If the outdoor unit functions as an evaporator in heating operation during winter, then heating can be provided, but in humid conditions frost forms on the surface, decreasing heating performance
Solution Approach 1:
The system converts the harmful effect of low temperature (which causes frost) into a beneficial feature by using the outdoor unit as an evaporator to absorb heat from the ambient air. The controlled refrigerant parameters and subcooling mechanism prevent frost formation while maintaining the heat absorption function, thus converting the potential harm into benefit.
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
The internal heat exchanger system improves refrigerant distribution and reduces pressure loss, leading to enhanced cooling and heating performance, and prevents frost formation by maintaining low vapor quality, thus increasing the overall efficiency of the heat pump system.
Implementation Method 1
an internal heat exchanger that includes a high-pressure passage through which a high-pressure refrigerant flows, and a low-pressure passage through which a low-pressure refrigerant flows, the internal heat exchanger exchanging heat between the refrigerant flowing through the high-pressure passage and the refrigerant flowing through the low-pressure passage
Implementation Method 2
an accumulator that separates the refrigerant into a gas refrigerant and a liquid refrigerant
Implementation Method 3
the outdoor unit functions as an evaporator... the refrigerant flowing through the outdoor unit absorbs heat from the air and is evaporated
Implementation Method 4
the outdoor unit functions as a condenser in a cooling operation
Data Source
AI summary
A heat pump system includes a compressor that compresses and discharges a refrigerant, a decompressor that decompresses the refrigerant, an outdoor unit that exchanges heat between the refrigerant and an outside air, an evaporator that evaporates the refrigerant, a condenser that condenses the refrigerant, an internal heat exchanger, an accumulator that separates the refrigerant into a gas refrigerant and a liquid refrigerant, and a flow pathway changing portion. The internal heat exchanger includes a high-pressure passage through which a high-pressure refrigerant flows, and a low-pressure passage through which a low-pressure refrigerant flows, the internal heat exchanger exchanging heat between the refrigerant flowing through the high-pressure passage and the refrigerant flowing through the low-pressure passage. The flow pathway changing portion that switches between a cooling pathway and a heating pathway. According to this heat pump system, a cooling capacity and a heating capacity can be improved.