Expansion Valve Control Using Discharge Temperature Variation Ratio
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Solution Overview
Problem
Conventional refrigeration cycle apparatuses face challenges in accurately controlling the expansion valve due to temperature sensor errors, leading to degraded coefficient of performance (COP) and capacity, especially in low-load operations and when refrigerant flow is insufficient.
Innovation Solution
A refrigeration cycle apparatus with a controller that computes the variation in discharge temperature resulting from changes in the expansion valve's opening degree, determining the optimal opening degree to improve COP and capacity by correlating the ratio of temperature variation to opening degree variation, regardless of temperature sensor errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the expansion valve is controlled based on comparison between discharge temperature and upper temperature limit, then the discharge temperature can be kept within limit, but the control accuracy is degraded due to temperature sensor errors
Solution Approach 1:
The patent implements feedback control by continuously monitoring discharge temperature and adjusting the expansion valve opening degree based on the detected temperature. The controller computes the variation amount of discharge temperature and uses this feedback to determine the appropriate opening degree, ensuring reliable temperature control despite sensor errors.
Solution Approach 2:
The patent changes the control parameter from absolute temperature value to temperature variation amount. By controlling based on the variation amount of discharge temperature rather than the absolute temperature value, the system becomes insensitive to sensor accuracy errors while maintaining effective temperature control.
2Measurement precision
If the expansion valve opening degree is adjusted to compensate for temperature sensor errors, then measurement accuracy improves, but the system complexity increases
Solution Approach 1:
The patent simplifies the control system by changing the control parameter to temperature variation amount, which eliminates the need for complex error compensation mechanisms. The controller only needs to calculate the difference between current and reference temperature values, significantly reducing system complexity while maintaining measurement precision.
3Measurement precision
If the expansion valve is controlled using subcooling degree detection, then control accuracy improves under normal conditions, but the system fails in low-load operations with insufficient refrigerant
Solution Approach 1:
The patent changes the control parameter from subcooling degree to discharge temperature variation amount. This parameter change enables the system to adapt to various operating conditions including low-load operations and insufficient refrigerant conditions, as discharge temperature can be detected and controlled in all these scenarios.
Solution Approach 2:
The patent creates a universal control method that functions across all operating conditions. By using discharge temperature variation as the control basis, the system achieves multi-functionality, working effectively whether the refrigerant is subcooled or not, and adapting to different load conditions and pipe lengths.
Data Source
AI summary
A refrigeration cycle apparatus includes a discharge temperature sensor that detects a discharge temperature of refrigerant discharged from a compressor, and a controller that controls the opening degree of an expansion valve. The controller computes an amount of variation of the discharge temperature resulting from varying the opening degree of the expansion valve, computes a ratio of the amount of variation of the discharge temperature to an amount of variation of the opening degree of the expansion valve, and determines the opening degree to be set to the expansion valve on the basis of the opening degree of the expansion valve that causes a change of the ratio.