Ejector Refrigeration Control for Receiver Pressure Balance
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Solution Overview
Problem
Vapour compression systems face challenges in efficiently controlling pressure within the receiver to balance compressor work and system efficiency across a wide range of ambient temperatures, especially when using transcritical refrigerants like CO2, as high pressure in the receiver can decrease system efficiency and increase compressor work.
Innovation Solution
A method that involves detecting the pressure of refrigerant leaving the evaporator and the state of the compressor unit to selectively connect the evaporator's outlet to either the ejector's secondary inlet or the compressor unit, adjusting the pressure inside the receiver by operating the compressor unit to maintain optimal refrigerant flow and pressure thresholds, thereby optimizing the mass flow of refrigerant to the ejector and reducing compressor work.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the pressure inside the receiver is increased to reduce compressor work, then the work required by the compressor is reduced, but the system efficiency decreases and the pressure inside the heat rejecting heat exchanger increases
Solution Approach 1:
The system dynamically adjusts the receiver pressure setpoint based on ambient temperature conditions. The controller modifies the target pressure level to optimize the balance between compressor work and system efficiency for each operating condition, rather than maintaining a fixed high pressure.
Solution Approach 2:
The invention changes the pressure parameter inside the receiver according to ambient temperature. By adjusting the pressure setpoint as a variable parameter rather than a constant, the system adapts to different operating conditions to maintain optimal efficiency while managing compressor work requirements.
2Use of energy by moving object
If more refrigerant is supplied from the evaporator outlet to the ejector secondary inlet to increase pressure and reduce compressor work, then the pressure of refrigerant supplied to compressors increases, but the pressure of refrigerant leaving the evaporator may decrease below acceptable levels
Solution Approach 1:
The system uses feedback control by continuously monitoring the evaporator outlet pressure and adjusting the receiver pressure setpoint accordingly. When evaporator outlet pressure approaches acceptable minimum levels, the controller responds by adjusting the receiver pressure to maintain proper balance in the refrigerant circulation.
Solution Approach 2:
The receiver pressure acts as an intermediary parameter that mediates between the evaporator outlet pressure and the compressor inlet pressure. By controlling the receiver pressure setpoint, the system indirectly regulates the pressure distribution throughout the system to prevent evaporator outlet pressure from dropping below acceptable levels while still optimizing compressor work.
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 allows for efficient control of refrigerant flow, maintaining acceptable pressure levels and reducing compressor work, thereby enhancing the overall efficiency of the vapour compression system across varying ambient temperatures.
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 a vapor compression system (1) is disclosed, the vapor compression system (1) comprising an ejector (5). The method comprises controlling a compressor unit (2) in order to adjust a pressure inside a receiver (6), on the basis of a detected pressure of refrigerant leaving an evaporator (8). The portion of refrigerant leaving the evaporator (8) which is supplied to a secondary inlet (15) of the ejector is maximized and the portion of refrigerant supplied directly to the compressor unit (2) is minimized, while ensuring that the pressure of refrigerant leaving the evaporator (8) does not decrease below an acceptable level.