A method for controlling a vapour compression system with a variable receiver pressure setpoint
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Solution Overview
Problem
Vapour compression systems face inefficiencies at low ambient temperatures due to high pressure inside the receiver, which limits the amount of gaseous refrigerant available for compressors and increases energy consumption.
Innovation Solution
A method to control the vapour compression system by adjusting the minimum setpoint pressure in the receiver based on the opening degree of expansion devices, allowing the pressure to decrease while ensuring sufficient refrigerant supply to evaporators, thereby optimizing energy efficiency and compressor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
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 gaseous refrigerant available for compressors decreases and more liquid refrigerant is present
Solution Approach 1:
The patent applies dynamics by making the receiver pressure setpoint variable rather than fixed. The control system dynamically adjusts the minimum receiver pressure setpoint based on operating conditions (ambient temperature, evaporator demand). This allows the system to optimize between compressor work and gaseous refrigerant availability in real-time, resolving the contradiction by adapting pressure levels to current system needs rather than maintaining a constant high pressure.
Solution Approach 2:
The patent changes the pressure parameter dynamically. Instead of maintaining a fixed high receiver pressure, the system varies the minimum pressure setpoint based on ambient temperature and evaporator requirements. At low ambient temperatures, the minimum pressure setpoint is reduced to increase gaseous refrigerant availability, while at higher temperatures, the setpoint is increased to reduce compressor work, thus resolving the contradiction through parameter adaptation.
2Loss of energy
If the pressure inside the heat rejecting heat exchanger is kept relatively low, then the efficiency of the vapour compression system is improved at low ambient temperatures, but the system may not maintain adequate refrigerant supply
Solution Approach 1:
The patent implements feedback control by continuously monitoring evaporator refrigerant demand and ambient temperature conditions, then adjusting the receiver pressure setpoint accordingly. The control system uses feedback from system performance and operating conditions to maintain optimal pressure levels that ensure both efficiency and reliable refrigerant supply, resolving the contradiction between low-pressure efficiency gains and supply reliability.
Solution Approach 2:
The system dynamically adjusts receiver pressure based on real-time operating conditions. At low ambient temperatures where low pressure improves efficiency, the system maintains lower minimum pressure setpoints. However, when evaporator demand requires adequate refrigerant supply, the system dynamically increases the pressure setpoint to ensure sufficient liquid refrigerant availability, thus maintaining both efficiency and reliability through dynamic adaptation.
3Loss of energy
If the receiver pressure setpoint is reduced to increase gaseous refrigerant availability, then energy efficiency improves, but the pressure may drop below levels needed for adequate refrigerant supply
Solution Approach 1:
The patent resolves this contradiction by making the receiver pressure setpoint dynamic rather than static. The control system continuously adjusts the minimum pressure setpoint based on evaporator demand and ambient temperature. When energy efficiency is the priority and evaporator demand is met, the system allows lower pressure setpoints to increase gaseous refrigerant availability. When refrigerant supply adequacy becomes critical, the system dynamically raises the minimum pressure setpoint to ensure sufficient supply, thus balancing both objectives through real-time adaptation.
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 enhances energy conservation by increasing the available gaseous refrigerant and improving the system's ability to operate at lower ambient temperatures, reducing energy consumption and maintaining adequate refrigerant supply.
Implementation Method 1
an expansion device arranged to control a supply of refrigerant to an evaporator... the pressure of refrigerant is thereby reduced
Implementation Method 2
an evaporator arranged to absorb heat from a space to be cooled
Implementation Method 3
the evaporator... absorbs heat from the surrounding environment
Implementation Method 4
a compressor unit... refrigerant leaving the evaporator is compressed by the compressor unit
Implementation Method 5
a heat rejecting heat exchanger... heat is rejected from the refrigerant flowing through the heat rejecting heat exchanger
Implementation Method 6
the refrigerant is at least partly condensed when passing through the heat rejecting heat exchanger
Implementation Method 7
In the receiver, liquid refrigerant is separated from gaseous refrigerant
Data Source
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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.