System and method for controlling vapor compression systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Vapor compression systems with variable speed compressors face challenges in efficiently controlling refrigerant flow and superheat temperature, often requiring costly and unreliable pressure sensors, which increases system costs and can destabilize operations.
Innovation Solution
A method that determines the correct refrigerant flow for the evaporator using only existing temperature sensors, mapping compressor discharge temperature and speed with outdoor air temperature, and employing a transition function to smoothly adjust valve positions, thereby controlling superheat without additional sensors and maintaining system stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure sensors are used to directly measure refrigerant superheat, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses an intermediary approach by measuring compressor discharge temperature instead of directly measuring refrigerant superheat at the evaporator. The discharge temperature serves as a proxy indicator that correlates with superheat conditions, allowing indirect measurement without requiring pressure sensors or multiple temperature sensors at the evaporator location. This intermediary measurement method resolves the contradiction by achieving sufficient measurement precision through a simpler, less invasive sensing approach.
Solution Approach 2:
The patent replaces the mechanical/physical sensing system (pressure sensors and multiple temperature sensors) with a computational approach. By using a model-based estimation algorithm that processes readily available data (compressor discharge temperature, evaporator inlet temperature, refrigerant properties), the system substitutes complex physical measurement infrastructure with software-based superheat calculation, thereby reducing device complexity while maintaining measurement precision.
2Adaptability or versatility
If variable speed compressors and variable position valves are introduced, then adaptability is improved, but control complexity increases
Solution Approach 1:
The patent implements a feedback control mechanism where the estimated superheat value is continuously monitored and used to adjust the expansion valve position. The control algorithm compares the estimated superheat against a target value and dynamically modulates the valve opening to maintain optimal refrigerant flow. This feedback loop enables the variable speed compressor and variable position valve to work together harmoniously, improving adaptability while managing control complexity through a straightforward closed-loop control strategy.
Solution Approach 2:
The control system performs self-adjustment by automatically modulating the expansion valve based on real-time superheat estimation without requiring manual intervention or complex external control systems. The algorithm autonomously balances the variable compressor speed and variable valve position to maintain optimal refrigerant circulation, allowing the system to serve itself and adapt to changing conditions while keeping the control architecture relatively simple.
3Productivity
If refrigerant flow rate is increased, then cooling capacity is improved, but system reliability deteriorates due to liquid ingestion risk
Solution Approach 1:
The patent employs feedback control where the estimated superheat at the evaporator outlet is continuously used to adjust the expansion valve position. When superheat drops (indicating risk of liquid refrigerant reaching the compressor), the system automatically reduces refrigerant flow by closing the valve slightly, thereby preventing liquid ingestion while maximizing cooling capacity under normal conditions. This real-time feedback mechanism dynamically balances productivity and reliability.
Solution Approach 2:
The system takes preliminary protective action by monitoring superheat trends and adjusting the expansion valve before liquid refrigerant can reach the compressor. The control algorithm anticipates potential liquid ingestion conditions by detecting declining superheat values and proactively reduces refrigerant flow to prevent the harmful event, rather than waiting for actual liquid ingestion to occur. This preliminary anti-action protects compressor reliability while maintaining high cooling capacity.
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 optimizes the efficiency and cost of vapor compression systems by stabilizing operations and reducing sensor requirements, ensuring efficient refrigerant control and preventing compressor damage, while maintaining system stability and efficiency.
Implementation Method 1
Cooling an environment (for example, a room in a house or a display case for food in a grocery store) is achieved by the evaporation of a refrigerant. The cooling includes evaporation process whereby a substance is converted from a liquid to a vapor. This process occurs as heat is absorbed by the refrigerant, thereby removing the heat from the space to be cooled.
Implementation Method 2
a variable speed compressor for compressing and heating refrigerant and for pumping the refrigerant through the system
Implementation Method 3
a condenser for releasing heat from the refrigerant to an environment
Data Source
AI summary
A method controls discharge temperature of a compressor of a vapor compression system. Using a mapping among discharge temperature, speed of the compressor, and outdoor air temperature, the method determines a desired discharge temperature for a new value of the speed of the compressor. The compressor is abruptly controlled to change the current speed of the compressor to the new value. A valve of the vapor compression system is smoothly controlled, such that the discharge temperature is transitioned to the desired discharge temperature according to a function of time representing a low pass filter with a time constant proportional to the thermal time constant of the compressor.