Cascade Refrigeration Startup Control for Low-Side Pressure Stability
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Solution Overview
Problem
The cascade refrigeration cycle apparatus experiences an excessive rise in high-pressure-side pressure in the low-temperature-side refrigeration circuit when both high-temperature-side and low-temperature-side compressors are started at the same operating frequency, leading to premature shutdown due to insufficient heat radiation from the low-temperature-side refrigerant in the cascade heat exchanger.
Innovation Solution
Incorporating an inverter and control section to set a higher operating frequency for the high-temperature-side compressor compared to the low-temperature-side compressor at the start of the refrigeration cycle, ensuring increased mass flow of the high-temperature-side refrigerant and preventing excessive pressure rise in the low-temperature-side circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If both high-temperature-side and low-temperature-side compressors are started at the same operating frequency, then the refrigeration cycle can start operation quickly, but the high-pressure-side pressure in the low-temperature-side refrigeration circuit rises excessively causing premature shutdown
Solution Approach 1:
The control section initiates the high-temperature-side compressor at a higher operating frequency before the low-temperature-side compressor to pre-cool the cascade heat exchanger and establish proper refrigerant flow conditions. This preliminary action prevents excessive pressure rise when the low-temperature-side compressor starts, ensuring reliable operation without premature shutdown.
2Reliability
If the high-temperature-side compressor operates at a higher frequency than the low-temperature-side compressor during startup, then the cascade heat exchanger can effectively radiate heat from the low-temperature-side refrigerant, but the control complexity increases due to differential frequency management
Solution Approach 1:
The control section monitors the operating frequencies of both compressors and dynamically adjusts them to maintain the required frequency difference during startup. This feedback mechanism ensures that the high-temperature-side compressor operates at a higher frequency than the low-temperature-side compressor, enabling effective heat radiation from the cascade heat exchanger while automatically managing the differential frequency control.
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 stabilizes the refrigeration cycle operation by maintaining a balanced pressure and preventing premature shutdown, allowing for efficient heat exchange and operation of the cascade refrigeration cycle apparatus.
Implementation Method 1
a cascade heat exchanger which allow heat to be exchanged between a refrigerant circulating through the high-temperature-side refrigeration circuit and a refrigerant circulating through the low-temperature-side refrigeration circuit
Data Source
AI summary
According to one embodiment, a cascade refrigeration cycle apparatus according to the present embodiment includes a high-temperature-side and a low-temperature-side refrigeration circuits, an inverter and a control section. The high-temperature-side refrigeration circuit includes a first compressor and a cascade heat exchanger. The low-temperature-side refrigeration circuit includes a second compressor and the cascade heat exchanger. The inverter connected to at least one of the compressors. The control section controls the inverter so that a set operating frequency for the first compressor is higher than a set operating frequency for the second compressor when an operation of the apparatus is started.