Receiver Pressure Control in Vapour Compression at Low Ambient
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Solution Overview
Problem
Vapour compression systems face inefficiencies at low ambient temperatures due to high pressure inside the receiver, which reduces the available gaseous refrigerant and increases energy consumption, making it challenging to maintain compressor operation and energy efficiency.
Innovation Solution
A method that involves calculating and adjusting a minimum setpoint value for the pressure inside the receiver based on the opening degree of expansion devices, ensuring the pressure remains at or above a calculated level to optimize energy efficiency and maintain sufficient gaseous refrigerant for compressor operation, even at low ambient temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the pressure inside the receiver is kept high, then the work required by compressors to compress gaseous refrigerant is reduced, but the amount of available gaseous refrigerant decreases and more liquid refrigerant is present
Solution Approach 1:
The invention applies dynamics by making the receiver pressure setpoint variable rather than fixed. The control method dynamically adjusts the minimum receiver pressure setpoint based on ambient temperature conditions, allowing the system to optimize between compressor work and gaseous refrigerant availability according to operating conditions. This resolves the contradiction by enabling the pressure to be high when needed for compressor efficiency and low when gaseous refrigerant availability is critical.
Solution Approach 2:
The invention changes the parameter of receiver pressure setpoint from a constant value to a variable value that depends on ambient temperature. By modifying this key parameter based on operating conditions, the system can resolve the trade-off between compressor work requirements and gaseous refrigerant availability, allowing optimal performance across different temperature ranges.
2Loss of energy
If the pressure inside the heat rejecting heat exchanger is kept low at low ambient temperatures, then the efficiency of the vapour compression system is improved, but the pressure inside the receiver increases reducing gaseous refrigerant availability
Solution Approach 1:
The control method dynamically adjusts the receiver pressure setpoint based on ambient temperature to resolve the conflict between system efficiency and gaseous refrigerant availability. At low ambient temperatures, the method allows lower heat rejecting heat exchanger pressure for efficiency while compensating by adjusting receiver pressure management to maintain sufficient gaseous refrigerant levels.
3Use of energy by stationary object
If a fixed high pressure setpoint is maintained in the receiver, then compressor work is minimized, but the system cannot adapt to low ambient temperature conditions where lower pressure is more efficient
Solution Approach 1:
The invention transforms the fixed pressure setpoint into a dynamic, adaptive parameter that responds to ambient temperature conditions. This allows the system to minimize compressor work when high pressure is beneficial while adapting to use lower pressure conditions when they improve overall system efficiency at low ambient temperatures, thereby resolving the contradiction between energy minimization and environmental adaptability.
Solution Approach 2:
The invention changes the receiver pressure setpoint parameter from fixed to variable, allowing it to adapt to different ambient temperature conditions. This parameter change enables the system to optimize compressor work at various operating conditions rather than being constrained by a fixed high pressure setting.
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 allows for energy-efficient operation of vapour compression systems at lower ambient temperatures by ensuring sufficient gaseous refrigerant is available, reducing energy consumption and maintaining compressor functionality.
Implementation Method 1
the pressure of the refrigerant is thereby reduced. Furthermore, the refrigerant leaving the high pressure valve or the ejector will normally be in the form of a mixture of liquid and gaseous refrigerant, due to the expansion taking place
Implementation Method 2
In the receiver, liquid refrigerant is separated from gaseous refrigerant
Implementation Method 3
the work required in order to compress the refrigerant can therefore be reduced
Data Source
AI summary
A method for controlling a vapour compression system (1) is disclosed, the vapour compression system (1) comprising at least one expansion device (8) and at least one evaporator (9). For each expansion device (8), an opening degree of the expansion device (8) is obtained, and a representative opening degree, ODrep, is identified based on the obtained opening degree(s) of the expansion device(s) (8). The representative opening degree could be a maximum opening degree, ODmax, being the largest among the obtained opening degrees. The representative opening degree, ODrep, is compared to a predefined target opening degree, ODtarget, and a minimum setpoint value, SPrec, for a pressure prevailing inside a receiver (7), is calculated or adjusted, based on the comparison. The vapour compression system (1) is controlled to obtain a pressure inside the receiver (7) which is equal to or higher than the calculated or adjusted minimum setpoint value, SPrec.