Outdoor Unit Refrigerant Bypass Layout for Liquid Pipe Pressure Relief
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Solution Overview
Problem
In refrigeration apparatuses, when the operation of a load device is stopped, leading to blocked refrigerant circulation, the pressure in the liquid pipe of the outdoor unit can exceed the design pressure, particularly when using refrigerants like CO2 in a supercritical state, posing a risk of pipe failure.
Innovation Solution
The outdoor unit incorporates a third expansion valve and receiver on the injection flow path, along with an on-off valve on a third flow path, to manage pressure by branching refrigerant flow and using a receiver to store refrigerant, ensuring subcooling and reducing pipe pressure through controlled decompression and flow rate adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If refrigerant circulation is blocked on the load device side during pump down operation, then the refrigeration system can stop operation, but the pressure in the liquid pipe exceeds the design pressure
Solution Approach 1:
A third flow path is introduced as an intermediary channel connecting the liquid pipe to the receiver. This mediator flow path allows pressure relief from the liquid pipe to the receiver, preventing excessive pressure buildup while maintaining system reliability during pump down operations
Solution Approach 2:
The on-off valve is pre-positioned on the third flow path to enable rapid pressure relief when needed. The receiver is pre-configured to receive and store high-pressure refrigerant, creating a preliminary pressure management system that activates automatically during pump down operations to prevent design pressure exceedance
2Productivity
If CO2 refrigerant in supercritical state is used to achieve high efficiency refrigeration, then cooling performance is improved, but discharge pressure becomes excessively high causing pipe pressure to exceed design pressure
Solution Approach 1:
The refrigeration system is segmented into distinct pressure zones: the high-pressure supercritical CO2 circulation loop for efficient heat exchange, and a separate pressure management pathway (third flow path with on-off valve) that segments the liquid pipe pressure from the evaporator pressure, allowing independent pressure control
Solution Approach 2:
The receiver acts as an intermediary pressure buffer between the high-pressure supercritical CO2 discharge and the lower-pressure liquid pipe. The third flow path with on-off valve provides a mediator mechanism to transfer excess pressure to the receiver, maintaining discharge pressure for efficiency while protecting the liquid pipe from excessive pressure
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 configuration effectively prevents pressure from exceeding design limits during sudden increases, such as during pump-down operations, thereby preventing potential leaks and allowing the use of standard design pressure components, even with supercritical refrigerants like CO2.
Implementation Method 1
a third expansion device disposed on the second flow path
Implementation Method 2
a receiver disposed on the second flow path in order from a branch point where the second flow path is branched from the first flow path
Implementation Method 3
an on-off valve disposed on the third flow path
Implementation Method 4
a compressor, a condenser, and a second expansion device disposed on the first flow path
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
An outdoor unit (2) includes a first flow path (F1), a second flow path (F2), a third flow path (F3), and an on-off valve (78). The first flow path (F1), which is a flow path from a refrigerant inlet port (PI2) to a refrigerant outlet port (PO2), is configured to form, together with a load device (3), a circulation flow path through which refrigerant circulates. A compressor (10), a condenser (20), and a second expansion device (40) are disposed on the first flow path (F1). A second flow path (F2) is configured to branch from the first flow path (F1), and to return, to the compressor (10), the refrigerant that has passed through the condenser (20). A third expansion device (71) and a receiver (73) are disposed on the second flow path (F2) in order from a branch point where the second flow path (F2) is branched from the first flow path (F1). A third flow path (F3) is configured to connect a portion of the first flow path (F1) between the second expansion device (40) and the refrigerant outlet port (PO2), to a refrigerant inlet of the receiver (73). The on-off valve (78) is disposed on the third flow path (F3).