Parallel Compressor Oil Return Piping with Bypass for Inverter Restart
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Solution Overview
Problem
In large-scale air-conditioning systems with multiple compressors, the pressure difference between the discharge and suction sides of compressors can lead to excessive load on the motor when the inverter compressor is restarted, potentially causing starting failures due to unequal pressures in the oil return piping system.
Innovation Solution
The refrigeration apparatus includes oil separators in the discharge pipes of each compressor, with oil return piping featuring a pressure reducing means and a solenoid valve that forms a bypass circuit to equalize the discharge and suction sides, allowing for reliable restart of the first compressor after operation stoppage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oil return piping with pressure reducing means is provided to return refrigerator oil between compressors, then proper refrigerator oil amount is maintained in compressors, but excessive load is applied to the motor when the inverter compressor is restarted due to large pressure difference between discharge and suction sides
Solution Approach 1:
The solenoid valve is activated before compressor restart to equalize pressures through the bypass circuit, preparing the system in advance to prevent excessive load during motor startup. This preliminary pressure equalization action resolves the contradiction by ensuring restart capability while maintaining proper oil levels through the pressure reducing means during normal operation.
Solution Approach 2:
The bypass circuit with solenoid valve acts as an intermediary mechanism that temporarily bypasses the pressure reducing means during restart. This mediator allows pressure equalization without going through the capillary tube, preventing motor overload while the oil return system maintains proper oil levels during steady-state operation.
2Reliability
If a capillary tube is used as pressure reducing means in oil return piping, then refrigerator oil is returned between compressors, but unequal pressure is created between discharge and suction sides when compressor is stopped
Solution Approach 1:
The oil return system is segmented into two parallel paths: one through the pressure reducing means (capillary tube) for normal oil return, and another through the bypass circuit with solenoid valve for pressure equalization during shutdown. This segmentation allows the pressure reducing means to maintain oil levels while the bypass path prevents excessive pressure differences.
Solution Approach 2:
The system changes the flow path parameter dynamically by switching the solenoid valve state. During normal operation, refrigerant flows through the capillary tube to maintain oil levels. During shutdown, the solenoid valve opens to change the flow path, allowing pressure equalization and preventing harmful pressure differences.
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 ensures the first compressor can be restarted reliably by equalizing the pressures, preventing motor overload and ensuring proper lubrication, thus enhancing the system's operational stability and reliability.
Implementation Method 1
first oil return piping (114) having a pressure reducing means
Implementation Method 2
a solenoid valve that selectively forms a bypass circuit with respect to the pressure reducing means is connected in parallel with the pressure reducing means of the first oil return piping
Data Source
Figure 1~2
AI summary
In a refrigeration apparatus having a plurality of compressors, which are connected in parallel and are operated, in an outdoor unit, a compressor (inverter compressor) is started surely after the stoppage of operation. In the refrigeration apparatus in which the outdoor unit 100 includes two compressors of a first compressor 110 and a second compressor 120, which are connected in parallel with each other; an oil separator 111, 121 is provided on the discharge side of each of the compressors; a first oil separator 111 on the first compressor side is connected to a suction pipe 164 of the second compressor via first oil return piping 114 including a pressure reducing means 115, and a second oil separator 121 on the second compressor side is connected to a suction pipe 163 of the first compressor via second oil return piping 124 including a pressure reducing means 125; and the first compressor is an inverter compressor, and the second compressor is a constant-speed compressor, a solenoid valve 116 is connected in parallel with the pressure reducing means 115 of the first oil return piping 114, and before the restart of the first compressor (inverter compressor) 110, the solenoid valve 116 is turned on to cause the discharge side and the suction side to be approximately equalized.