Variable Refrigerant Chiller Control for Surge-Free Part Load
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Solution Overview
Problem
Conventional refrigeration systems are inefficient due to fixed refrigerant levels, leading to suboptimal performance under varying load conditions and a risk of surge, which can cause compressor damage.
Innovation Solution
A refrigeration system with an additional refrigerant vessel connected to the condenser and evaporator, allowing for variable refrigerant levels to be adjusted dynamically through controlled valves, enabling efficient operation and preventing surge by modifying heat transfer characteristics and refrigerant levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed amount of refrigerant is used in conventional chiller systems, then the system is optimized for one operating condition, but the system efficiency deteriorates under varying load conditions and over time due to fouling
Solution Approach 1:
The patent applies the dynamics principle by making the refrigerant amount variable rather than fixed. An additional refrigerant vessel is introduced that can dynamically adjust the refrigerant charge in the evaporator based on load conditions. The system transitions from a static refrigerant charge to a dynamic one, allowing the chiller to adapt its refrigerant level to match varying cooling demands and maintain optimal efficiency across different operating conditions.
Solution Approach 2:
The patent implements parameter changes by varying the refrigerant charge level as a controllable parameter. By changing the amount of refrigerant in the evaporator through the additional vessel, the system can optimize heat transfer characteristics and compressor operation for different load conditions. This parameter adjustment enables the chiller to maintain peak efficiency whether operating at full load, part load, or recovering from fouling conditions.
2Productivity
If refrigerant level is increased to improve heat transfer, then chiller efficiency improves, but surge risk increases during low load conditions
Solution Approach 1:
The system uses parameter changes by dynamically adjusting the refrigerant charge level based on load conditions. During high load conditions, higher refrigerant levels are maintained to maximize heat transfer and chiller efficiency. During low load conditions, the additional refrigerant vessel reduces the refrigerant charge to prevent surge. This dynamic parameter adjustment allows the system to optimize efficiency when needed while preventing harmful surge conditions.
Solution Approach 2:
The patent implements feedback control by monitoring compressor operation and load conditions, then adjusting the refrigerant level accordingly. The system detects when surge conditions are developing (through pressure differential monitoring or operational parameters) and responds by reducing refrigerant charge. This closed-loop feedback ensures the refrigerant level is continuously optimized to maintain efficiency while preventing surge, creating a self-regulating system that adapts to changing conditions.
3Adaptability or versatility
If multiple chiller geometrical variations are designed to handle different load conditions, then adaptability improves, but device complexity increases
Solution Approach 1:
The patent applies universality by making a single chiller configuration capable of handling multiple load conditions through variable refrigerant charging. Instead of requiring different geometrical designs for different loads, the universal chiller design uses the additional refrigerant vessel to adapt its performance characteristics. This single system performs the function of multiple specialized systems would otherwise be needed, reducing complexity while maintaining full adaptability across the operating range.
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 solution enhances chiller efficiency, reduces the need for multiple chiller geometrical variations, and provides significant annualized energy efficiency improvements by optimizing refrigerant use across different load conditions, thereby preventing surge and maintaining efficient operation.
Implementation Method 1
the evaporator effects a transfer of thermal energy between the refrigerant of the system and another liquid to be cooled
Implementation Method 2
a control loop utilizing the expansion (throttling) valve to control the height of the liquid level in the condenser vessel
Implementation Method 3
the vapor is compressed, to begin another refrigerant cycle
Data Source
AI summary
A refrigeration system includes a compressor, a condenser, an expansion device, an evaporator, and an additional refrigerant vessel connected in a closed refrigerant loop. The additional refrigerant vessel is connected to the condenser at the high pressure side by a first valve and to the evaporator at a low pressure side by a second valve. A controller controls operation of the first valve and the second valve. Only one of the first valve and the second valve may be open at the same time. Refrigerant from the additional refrigerant vessel may be added to the closed refrigerant loop when the controller receives a low refrigerant level indication of in the evaporator. Refrigerant may also be removed from the closed refrigerant loop when the controller receives a high refrigerant level indication in the evaporator.