Reverse defrost system and methods
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Solution Overview
Problem
Reverse cycle defrost refrigeration systems face limitations such as low defrost capacity in low ambient temperatures, high defrost capacity leading to thermal shock and steaming in high ambient temperatures, and potential compressor flooding due to lack of a receiver or extensive piping, especially with flow reversal.
Innovation Solution
A method and system that includes a four-way reversing valve and a bi-flow capable receiver with a baffle plate, along with a controller that selects defrost mode procedures based on ambient conditions, adjusts system components, and employs warm liquid injection and defrost evaporation control to manage pressure and temperature differentials, preventing thermal shock and flooding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If reverse cycle defrost is used in low ambient temperature conditions, then defrosting can be achieved, but defrost capacity is too low resulting in prolonged or incomplete defrost
Solution Approach 1:
The system performs a pump-down operation before defrost to accumulate refrigerant liquid in the receiver, ensuring sufficient refrigerant availability for effective defrosting in low ambient temperature conditions
Solution Approach 2:
The controller adjusts operating parameters based on ambient temperature conditions, selecting different defrost mode procedures to optimize defrost capacity across varying temperature ranges
2Productivity
If reverse cycle defrost is used in high ambient temperature conditions, then defrosting can be achieved, but defrost capacity is too high causing thermal shock and steaming
Solution Approach 1:
The controller selects from multiple predetermined defrost mode procedures based on ambient temperature, adjusting system parameters to reduce defrost capacity in high ambient conditions and prevent thermal shock and steaming
Solution Approach 2:
The system provides controlled defrost capacity by partially opening the expansion valve and regulating refrigerant flow to match the actual defrosting need, avoiding excessive heat input that causes steaming
3Productivity
If flow reversal is implemented for defrost, then indoor coil can be defrosted, but compressor flooding occurs
Solution Approach 1:
The system performs pump-down before defrost to remove refrigerant from the indoor coil and accumulate it in the receiver, preventing compressor flooding during flow reversal
Solution Approach 2:
The receiver extracts and stores refrigerant liquid before defrost operation, separating it from the indoor coil to prevent flooding the compressor during reverse cycle defrost
4Reliability
If receiver is added to prevent flooding, then compressor protection is improved, but device complexity increases
Solution Approach 1:
The receiver serves multiple functions: storing refrigerant during normal operation, accumulating refrigerant before defrost to prevent flooding, and facilitating pump-down operation, thereby protecting the compressor without requiring additional dedicated 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
The solution effectively manages defrost capacity, prevents thermal shock and steaming, and reduces the risk of compressor flooding, ensuring efficient and reliable defrosting across varying ambient conditions.
Implementation Method 1
The receiver includes a baffle plate that defines a first direction of flow from a first opening at a first end of the receiver to a second opening at a second end of the receiver
Implementation Method 2
the refrigerant is circulatable in a first direction to transfer heat out of air in a controlled space when the system is operating in a refrigeration mode, and in which the refrigerant is circulatable in a second direction at least partially opposite to the first direction when the system is operating in a defrost mode
Implementation Method 3
a compressor input port through which a refrigerant is flowable toward a compressor of the refrigeration system and a compressor output port through which the refrigerant exiting the compressor is flowable
Implementation Method 4
an expansion valve downstream from the receiver when the refrigerant is flowing in the second direction
Implementation Method 5
an outdoor coil downstream from the expansion valve when the refrigerant is flowing in the second direction
Implementation Method 6
an indoor coil upstream from the reversing valve when the refrigerant is flowing in the first direction
Data Source
AI summary
A method of defrosting an indoor coil in a refrigeration system in which, with a controller of the refrigeration system, a selected one of a number of predetermined defrost mode procedures is selected. Each predetermined defrost mode procedure is associated with a predetermined range of values of one or more predetermined parameters. Each predetermined defrost mode procedure includes adjustment of one or more components of the refrigeration system upon commencement of the defrost mode for optimum operation of the refrigeration system in the defrost mode, when the predetermined parameter is within the predetermined range of values upon commencement of operation in the defrost mode. With the controller, the component of the refrigeration system is adjusted in accordance with the selected one of the predetermined defrost mode procedures.