Microchannel Heat Exchanger Defrosting via Warm Header Bypass
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Solution Overview
Problem
Microchannel heat exchangers in heat pumps face challenges during defrost cycles, as hot refrigerant gas struggles to effectively melt frost on all portions of the heat exchanger, leading to incomplete defrosting and increased energy consumption due to heat loss and extended defrost times.
Innovation Solution
A defrost valve system that directs hot refrigerant gas through a header of the heat exchanger without passing through cross tubes, combined with a reversed fan operation to counteract natural convection, ensuring efficient defrosting of all areas and reducing heat loss during the defrost cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hot refrigerant gas is delivered to the outdoor air heat exchanger through conventional pathways, then the heat exchanger is heated to melt frost, but the defrosting is incomplete and energy consumption increases due to heat loss
Solution Approach 1:
The patent segments the heat exchanger into multiple zones (headers and cross tubes) and delivers hot refrigerant gas to different segments simultaneously through separate pathways. This ensures complete coverage of all frost-affected areas, improving defrosting completeness while optimizing energy utilization by targeting specific zones rather than relying on conventional single-pathway heating that results in energy loss.
Solution Approach 2:
The patent introduces an intermediary component (the outdoor air fan) that is reversed during defrost mode to actively counteract natural convection. This intermediary mechanism prevents warm air from rising and escaping, thereby reducing heat loss and improving energy efficiency during the defrosting process while ensuring complete defrosting of the heat exchanger.
2Reliability
If hot refrigerant gas is delivered to the outdoor air heat exchanger, then frost melts on the heat exchanger, but defrost cycle duration increases leading to occupant discomfort
Solution Approach 1:
By segmenting the heat exchanger into multiple zones and delivering hot refrigerant gas to different segments simultaneously through separate pathways (headers and cross tubes), the patent achieves parallel heating of multiple areas. This significantly reduces the overall defrost cycle duration compared to sequential heating methods, while ensuring complete defrosting of all zones, thereby minimizing occupant discomfort.
Solution Approach 2:
The patent implements preliminary action by reversing the outdoor air fan before and during the defrost cycle to counteract natural convection. This preliminary measure prevents heat loss and ensures that the heat generated during defrosting remains concentrated on the heat exchanger, accelerating the defrosting process and reducing cycle duration without compromising completeness.
3Loss of energy
If natural convection occurs during defrost cycle, then warm air rises and heat is lost to the environment, but preventing this requires additional control mechanisms
Solution Approach 1:
The patent applies inversion by reversing the outdoor air fan's rotation direction during defrost mode. Instead of the fan operating in its normal direction that would promote natural convection and heat loss, it is inverted to blow air in the opposite direction, actively counteracting the natural convection current. This elegant inversion prevents heat loss without requiring complex additional control mechanisms, as it utilizes the existing fan's bidirectional 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 enables faster, more complete defrosting of microchannel heat exchangers, reducing energy consumption and occupant discomfort by minimizing heat loss and defrost cycle duration.
Implementation Method 1
hot refrigerant gas is delivered to a first connection point of a first heat exchanger and is passed through the first heat exchanger from the first connection point to a second connection point
Implementation Method 2
hot refrigerant gas is delivered to the outdoor air heat exchanger heating the heat exchanger and melting frost that has accumulated on the heat exchanger
Implementation Method 3
the fan that is used to blow air through the first heat exchanger is operated in a reversed direction during at least part of the defrost cycle to counteract natural convection through the first heat exchanger during the at least part of the defrost cycle
Data Source
AI summary
Heat pumps with improved defrost cycles and methods of defrosting heat exchangers, for example, having microchannel outdoor heat exchangers. A heat exchanger has three types of connection points that are used during a defrost cycle. Two connection points are used to deliver hot refrigerant gas to the heat exchanger and one connection point is where refrigerant exits the heat exchanger. Two of the connection points are at the same header and during at least part of the defrost cycle, at least part of the hot refrigerant gas is passed through that header without passing through any cross tubes of the heat exchanger. A defrost valve in a refrigerant conduit opens during the defrost cycle to deliver hot refrigerant gas to the connection point on the header. In a number of embodiments, the defrost valve is open only during a portion of the defrost cycle.