Refrigeration cycle system
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Solution Overview
Problem
Existing refrigeration apparatuses using carbon dioxide in the secondary-side refrigerant circuit face challenges with transient increases in refrigerant discharge pressure, which can lead to excessive pressure on the discharge side of the compressor.
Innovation Solution
A refrigeration cycle system that includes a first cycle with a carbon dioxide refrigerant and a second cycle with a different heat medium, utilizing a cascade heat exchanger and a control unit to manage the start-up of the compressor and the state of an on-off valve to prevent excessive pressure increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the first compressor is started before heat medium flow is established in the cascade heat exchanger, then the refrigeration cycle can start operating, but the refrigerant discharge pressure excessively increases
Solution Approach 1:
The control unit establishes heat medium flow through the cascade heat exchanger before starting the first compressor. This preliminary action ensures the heat exchanger is ready to immediately absorb refrigerant heat, preventing excessive discharge pressure when the compressor starts.
Solution Approach 2:
The control unit monitors the operation state of the second compressor and uses this feedback to determine the appropriate timing for starting the first compressor and closing the on-off valve, ensuring coordinated operation between the two cycles.
2Ease of operation
If the on-off valve remains open during first compressor operation, then refrigerant can bypass, but the heat medium flow path becomes blocked
Solution Approach 1:
The on-off valve is closed immediately when the first compressor starts, preventing refrigerant from entering the bypass flow path. This preliminary action blocks the bypass before it can interfere with heat medium flow, while still allowing refrigerant to flow through the normal path via the three-way valve.
Solution Approach 2:
The three-way valve acts as an intermediary device that directs refrigerant flow away from the bypass path when the on-off valve is closed, ensuring refrigerant flows through the cascade heat exchanger and first heat exchanger without blocking heat medium flow in the bypass.
3Reliability
If the on-off valve closes immediately when first compressor starts, then refrigerant is directed through heat exchangers, but pressure buildup may occur
Solution Approach 1:
The three-way valve serves as an intermediary that provides an alternative flow path for refrigerant through the first heat exchanger when the bypass is closed. This ensures continuous refrigerant circulation while maintaining proper pressure levels by distributing flow through multiple heat exchangers.
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 system effectively suppresses the increase in refrigerant pressure on the discharge side of the compressor, ensuring stable operation and preventing excessive pressure buildup.
Implementation Method 1
a cascade heat exchanger, which connects the first cycle and the second cycle
Data Source
Figure 1
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AI summary
To suppress an increase in pressure of a refrigerant on a discharge side of a compressor in a secondary-side refrigerant circuit. A refrigeration cycle system (1) includes a primary-side refrigerant circuit (5a) and a secondary-side refrigerant circuit (10). The secondary-side refrigerant circuit (10) includes a secondary-side compressor (21), a cascade heat exchanger (35), a secondary-side expansion valve (36), and a utilization-side heat exchanger (52a-c), which are connected to each other, and a carbon dioxide refrigerant circulates through the secondary-side refrigerant circuit. The secondary-side refrigerant circuit (10) includes a third heat source pipe (25) connecting the secondary-side compressor (21) to the cascade heat exchanger (35), a fourth heat source pipe (26) connecting the cascade heat exchanger (35) to the secondary-side expansion valve (36), a suction flow path (23), and a bypass flow path (47) connecting at least one of the third heat source pipe (25) and the fourth heat source pipe (26) to the suction flow path (23). The primary-side refrigerant circuit (5a) includes the cascade heat exchanger (35), and a heat medium different from the carbon dioxide refrigerant circulates through the primary-side refrigerant circuit. In the case of using the cascade heat exchanger (35) as a radiator of the secondary-side refrigerant circuit (10) and a heat sink of the primary-side refrigerant circuit (5a), the control unit (80) starts the secondary-side compressor (21) of the secondary-side refrigerant circuit (10) after a flow of the heat medium generates in the cascade heat exchanger (35) in the primary-side refrigerant circuit (5a).