Refrigerant control method
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Solution Overview
Problem
Conventional refrigeration systems with flash tanks and shell-side evaporators face challenges in controlling refrigerant levels and flow, particularly when using tube-side condensers and shell-side evaporators that do not superheat refrigerant, leading to unstable operation, high costs, and unsuitability for certain evaporator types.
Innovation Solution
A control methodology using a tube-side condenser and shell-side evaporator with a flash tank, where condenser outflow subcooling regulates inflow to the flash tank, and an orifice controls outflow from the flash tank, with multi-parameter control including compressor capacity, to maintain stable operation and optimize chiller performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional superheating-based control is used in flash tanks, then refrigerant level control is achieved, but it is incompatible with shell-side evaporators that do not superheat refrigerant
Solution Approach 1:
The patent changes the control parameter from superheating (temperature-based) to subcooling (temperature difference-based). By measuring the subcooling of condenser outflow rather than the superheating of evaporator outflow, the system becomes compatible with shell-side evaporators that do not produce superheated refrigerant, while maintaining reliable control of refrigerant levels in the flash tank
Solution Approach 2:
The patent implements a feedback control system where condenser outflow subcooling is continuously measured and used to regulate the feed valve. The control system adjusts the refrigerant flow to the flash tank based on the measured subcooling, creating a closed-loop control that maintains stable operation regardless of evaporator type
2Measurement precision
If complex multi-parameter control is implemented, then control precision is improved, but system complexity increases
Solution Approach 1:
The patent uses compressor capacity as a feedforward control parameter, anticipating changes in refrigerant demand before they affect flash tank levels. By pre-adjusting the feed valve based on compressor capacity changes, the system achieves better control precision without requiring complex real-time adjustments
Solution Approach 2:
The control system combines feedback from condenser outflow subcooling measurements with feedforward from compressor capacity signals. This dual-parameter approach improves control precision by accounting for both actual system state and anticipated changes, while keeping the control logic manageable through structured parameter integration
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 reduces system costs, improves reliability, and enhances chiller efficiency and capacity by using subcooling and compressor speed feedback for precise control, making it suitable for various evaporator types and reducing refrigerant charge.
Implementation Method 1
condensing, by a condenser, refrigerant vapour into a condensate
Implementation Method 2
receiving, by a flash tank, the condensate from the condenser and at least partially vaporizing the condensate into condensate vapour
Implementation Method 3
receiving, by an evaporator, a mixture of liquid condensate and condensate vapour from the flash tank and vaporizing the condensate into the refrigerant vapour
Implementation Method 4
receiving, by a compressor, the refrigerant vapour from the evaporator and compressing the refrigerant vapour for return to the condenser
Data Source
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AI summary
A refrigeration system is provided, such as for use with chillers. The system uses a tube-side condenser (24), such as a microchannel condenser, along with a shell-side evaporator (32) such as a falling film evaporator. A flash tank economizer (26) is disposed between the condenser and the evaporator, and an inlet valve (28) to the flash tank is controlled based upon subcooling of condensate from the condenser. The vapor exiting the flash tank may be fed via an economizer line to a system compressor. Liquid phase refrigerant combined with some gas phase refrigerant exits the flash tank and is directed through an orifice (30) before entering the evaporator.