Cascade Refrigerating System Startup Sequence for Stable Pressure Rise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The cascade refrigerating system experiences inefficiencies and a decline in space heating capacity due to unstable refrigerating cycles and low pressure in the high temperature side, leading to a poor rate of rise and increased losses during startup.
Innovation Solution
The system starts the low temperature side compressor first, followed by the high temperature side compressor, ensuring the cascade heat exchanger temperature is raised before initiating the high temperature side compressor, thereby stabilizing the cycles and maintaining high pressure in the high temperature side refrigerating cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the high temperature side compressor is started first at system startup, then the high temperature side refrigerating cycle can begin operation immediately, but the low pressure in the high temperature side may fall too low and the rate of rise deteriorates
Solution Approach 1:
The low temperature side compressor is started in advance before the high temperature side compressor. This preliminary action raises the pressure in the high temperature side refrigerating cycle before the high temperature side compressor operates, preventing excessive pressure drop and improving the rate of rise during system startup.
2Productivity
If the high temperature side compressor is started first, then the startup sequence is simple, but space heating capacity falls due to cycle deterioration
Solution Approach 1:
The low temperature side compressor is operated preliminarily to establish stable pressure conditions in the high temperature side cycle before the high temperature side compressor starts. This sequence prevents deterioration of the refrigerating cycle and maintains space heating capacity, while the control device manages the two-stage startup process.
3Reliability
If the low temperature side compressor is started first, then the pressure in the high temperature side is maintained, but the startup sequence becomes more complex
Solution Approach 1:
The control device monitors the operating states of both compressors and the refrigerating cycle parameters, automatically managing the startup sequence. When the low temperature side compressor starts first, the control device detects the pressure rise and subsequently activates the high temperature side compressor, maintaining pressure stability while automating the complex sequence 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 approach ensures stable cyclic operation with an improved rate of rise and prevents a fall in space heating capacity by managing the startup sequence of compressors and maintaining optimal pressure in the high temperature side refrigerating cycle.
Implementation Method 1
a cascade heat exchanger, which thermally connects a low temperature side refrigerating cycle and a high temperature side refrigerating cycle
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A cascade refrigerating system includes a low temperature side refrigerating cycle (1) in which a low temperature side compressor (2), a cascade heat exchanger (21), a low temperature side expansion valve (3) and a low temperature side heat exchanger (4) are connected by low temperature side refrigerant piping and a high temperature side refrigerating cycle (10) in which a high temperature side compressor (11), a heat exchanger (20) for exchanging heat between high temperature side refrigerant and refrigerated medium (30), a high temperature side expansion valve (12) and the cascade heat exchanger (21) are connected by high temperature side refrigerant piping, the two cycles being thermally connected via the cascade heat exchanger (21), and the low temperature side compressor (2) is started when the cascade refrigerating system is to be started, and subsequently the high temperature side compressor (11) is started. This enables a fall in space heating capacity due to deterioration in the rate of rise to be restrained by suppressing losses at the time of rise of the refrigerating cycle in the cascade refrigerating system.