Method for controlling ejector capacity in a vapour compression system
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Solution Overview
Problem
Vapour compression systems face challenges in efficiently managing ejector capacity and distributing it among different types of ejectors to optimize energy efficiency and handle liquid refrigerant flow effectively, as existing systems lack a method to dynamically adjust ejector capacity based on varying operating conditions.
Innovation Solution
A method that involves obtaining a parameter value representing the flow rate of liquid refrigerant from the evaporator to the return pipe and adjusting the ejector capacity accordingly, including shifting capacity between low-pressure and high-pressure ejectors, by manipulating valves to control the primary and secondary flows, ensuring optimal energy efficiency and efficient removal of liquid refrigerant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a liquid ejector (low pressure ejector) is used, then the pressure difference between primary inlet and outlet is small, but the pressure lift capability is high; however, energy efficiency is reduced compared to gas ejectors
Solution Approach 1:
The system dynamically switches between liquid ejectors and gas ejectors based on real-time operating conditions. The control unit monitors system state and activates the appropriate ejector type, making the ejector configuration adaptive rather than static, thereby optimizing energy efficiency across varying operational scenarios.
Solution Approach 2:
The invention changes the operational parameters by switching between different ejector types (liquid vs. gas) depending on the pressure difference conditions. When pressure difference is small, liquid ejectors are used; when pressure difference is large, gas ejectors are used, optimizing performance across different parameter ranges.
2Use of energy by moving object
If a gas ejector (high pressure ejector) is used, then energy efficiency is high, but the pressure difference requirement is large; however, pressure lift capability is reduced compared to liquid ejectors
Solution Approach 1:
The system dynamically selects between gas ejectors and liquid ejectors based on the required pressure difference. The control unit adjusts the ejector configuration in real-time, switching to gas ejectors when high pressure difference is available and needing efficient energy use, and to liquid ejectors when pressure difference is limited.
Solution Approach 2:
The invention adapts to different pressure difference parameters by switching ejector types. When the system operates with large pressure differences, gas ejectors are activated for optimal energy efficiency. When pressure difference is constrained, liquid ejectors provide adequate performance without excessive energy consumption.
3Device complexity
If ejector capacity is fixed, then system structure is simple, but the system cannot adapt to varying operating conditions and liquid refrigerant flow rates
Solution Approach 1:
The ejector system is segmented into multiple independent ejectors (liquid ejectors and gas ejectors) that can be independently controlled. This segmentation allows the system to activate only the necessary ejector capacity based on current operating conditions, providing adaptability while maintaining relatively simple individual component structures.
Solution Approach 2:
The system achieves multi-functionality by incorporating both liquid ejectors and gas ejectors that can handle different operating conditions. The control unit selectively activates appropriate ejectors based on refrigerant flow rate and pressure conditions, making the system universally applicable across varying operational scenarios without requiring complex variable-geometry components.
4Device complexity
If liquid refrigerant is not removed from the return pipe, then the system is simple, but liquid refrigerant reaches the compressor unit causing damage
Solution Approach 1:
The ejector system serves dual functions: it maintains the refrigeration cycle while simultaneously removing liquid refrigerant from the return pipe. The secondary inlet of the ejectors is connected to the return pipe, allowing the ejectors to automatically suction liquid refrigerant away from the compressor inlet, providing self-protection without additional dedicated components.
Solution Approach 2:
The ejectors are designed with multi-functionality, serving both the primary refrigeration purpose and the secondary function of liquid refrigerant removal. By connecting the secondary inlet to the return pipe, the same ejector mechanism that boosts refrigerant pressure also protects the compressor from liquid ingestion, eliminating the need for separate protection devices.
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 method ensures that the vapour compression system operates with the most energy-efficient ejector type, effectively handling liquid refrigerant flow by dynamically adjusting ejector capacity based on real-time conditions, thereby enhancing overall system performance and preventing liquid refrigerant from reaching the compressor.
Implementation Method 1
An ejector is a type of pump which uses the Venturi effect to increase the pressure energy of fluid at a suction inlet (or secondary inlet) of the ejector by means of a motive fluid supplied to a motive inlet (or primary inlet) of the ejector.
Data Source
AI summary
A method for controlling ejector capacity in a vapour compression system (1) is disclosed. A parameter value being representative for a flow rate of liquid refrigerant from the evaporator(s) (8, 10) and into a return pipe (12, 13) is obtained, and the capacity of the ejector(s) (6) is adjusted based on the obtained parameter value. Ejector capacity may be shifted between low pressure ejectors (liquid ejectors) (6a, 6b, 6c, 6d) and high pressure ejectors (gas ejectors) (6e, 6f).