Vapor compression system and method for controlling vapor compression system
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Solution Overview
Problem
Vapor compression systems with variable speed compressors face challenges in efficiently controlling refrigerant flow and superheat without relying on costly pressure sensors or additional temperature sensors, which can destabilize operations and increase costs.
Innovation Solution
A method that uses existing sensors for equipment protection and monitoring, leveraging the relationship between compressor speed, outdoor air temperature, and discharge temperature to control superheat, employing a mapping and feedback control loop to regulate refrigerant flow without additional sensors, and using a transition function to stabilize system operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure sensors and additional temperature sensors are used to directly measure superheat, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses existing sensors (compressor discharge temperature sensor and outdoor air temperature sensor) that are already installed for other purposes to estimate superheat, rather than adding dedicated superheat measurement sensors. The existing sensors serve dual purposes: their original functions plus superheat estimation, eliminating the need for additional hardware.
Solution Approach 2:
The system introduces an intermediary estimation approach using a mapping relationship between outdoor air temperature, compressor discharge temperature, and superheat. Instead of directly measuring superheat with dedicated sensors, the system uses the relationship between other measurable parameters (outdoor air temperature and discharge temperature) to infer superheat values through predefined mappings or lookup tables.
2Adaptability or versatility
If variable speed compressors and variable position valves are used, then adaptability is improved, but control stability deteriorates
Solution Approach 1:
The system implements a closed-loop feedback control mechanism where the estimated superheat values are continuously monitored and used to adjust the expansion valve position. The feedback controller compares the estimated superheat with target values and dynamically adjusts valve opening to maintain optimal refrigerant flow, stabilizing system operation despite variable compressor speeds.
Solution Approach 2:
The system dynamically adapts the mapping relationship between outdoor air temperature, discharge temperature, and superheat based on current operating conditions. As compressor speed and outdoor temperature vary, the system updates the estimation mapping to reflect current system state, allowing the control strategy to remain effective across varying operational conditions.
3Productivity
If refrigerant flow rate is increased, then cooling capacity is improved, but system efficiency deteriorates
Solution Approach 1:
The feedback controller continuously monitors estimated superheat and adjusts the expansion valve position to optimize refrigerant flow rate. By maintaining superheat within optimal ranges, the system ensures that the refrigerant completely evaporates in the evaporator without carrying liquid into the compressor, maximizing cooling capacity while minimizing energy waste from improper refrigerant management.
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 system efficiency and stability while minimizing component costs by controlling refrigerant flow and superheat using existing sensors, ensuring stable operation of vapor compression systems with variable speed compressors.
Implementation Method 1
a compressor having a speed for compressing and pumping refrigerant through the system
Implementation Method 2
Cooling an environment 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
Implementation Method 3
a condenser for releasing heat to an environment from the refrigerant
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A method controls a vapor compression system including a variable speed compressor. A desired discharge temperature of the compressor is determined using a mapping between values of the discharge temperature of the compressor and values of speed of the compressor and outdoor air temperature. A transition function for transitioning a current discharge temperature to the desired discharge temperature is determined, such that the transition function is continuous and a rate of change of the transition function is limited. Next, a valve of the vapor compression system is controlled such that the discharge temperature is transitioned to the desired discharge temperature based on the transition function.