Bypass Valve Control for Receiver Pressure in Vapour Compression
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Solution Overview
Problem
Vapour compression systems face challenges in maintaining desired pressure in the receiver efficiently, leading to excessive wear on compressors, conflicts between compressor and bypass valve control, and over-dimensioning of receiver compressors due to varying load demands and inefficient energy use.
Innovation Solution
A method involving a vapour compression system with two compressors, a heat rejecting heat exchanger, a receiver, and a bypass valve, where pressure in the receiver is regulated by defining two pressure setpoints and controlling the bypass valve and receiver compressor based on load demand, ensuring efficient operation without over-dimensioning the compressor capacity and minimizing control conflicts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the receiver compressor is used to regulate receiver pressure, then energy efficiency is improved, but the compressor experiences excessive wear when gaseous refrigerant flow is low causing repeated stops and starts
Solution Approach 1:
A bypass valve is introduced as an intermediary device to regulate receiver pressure by diverting gaseous refrigerant from the receiver to the suction line. This allows pressure control without requiring the receiver compressor to operate during low-flow conditions, preventing excessive wear and operational instability while maintaining energy efficiency during normal operation.
Solution Approach 2:
The control system dynamically switches between using the receiver compressor and the bypass valve based on real-time assessment of gaseous refrigerant flow conditions. When flow is sufficient, the receiver compressor is used for energy-efficient pressure regulation; when flow is low, the bypass valve takes over to ensure stable operation, creating a dynamic adaptation to varying system conditions.
2Productivity
If the receiver compressor capacity is increased to handle exceptionally high load demands, then the system can meet peak loads, but the compressor becomes over-dimensioned and costs increase
Solution Approach 1:
The system merges the pressure regulation functions of the receiver compressor and the bypass valve, allowing them to work together during high-load conditions. The receiver compressor handles the majority of the load while the bypass valve provides supplementary pressure control, enabling the receiver compressor to be sized for normal operation rather than peak demand, thus avoiding over-dimensioning and reducing manufacturing costs.
Solution Approach 2:
During exceptionally high load demands, the bypass valve is opened to provide additional pressure control capacity beyond what the normally-sized receiver compressor can provide alone. This partial use of the bypass valve during peak loads allows the system to handle maximum demands without requiring the receiver compressor to be permanently oversized for these rare conditions.
3Adaptability or versatility
If both the receiver compressor and bypass valve are used to control receiver pressure, then pressure regulation flexibility is improved, but control conflicts may arise between the two devices
Solution Approach 1:
The control system continuously monitors receiver pressure and gaseous refrigerant flow conditions, using this feedback to intelligently determine when to use the receiver compressor and when to use the bypass valve. This feedback-based control prevents simultaneous operation that could cause conflicts while maintaining the flexibility to use either device based on real-time system conditions.
Solution Approach 2:
The pressure control function is segmented into two distinct operational modes: one where the receiver compressor is the primary control device during normal and high-flow conditions, and another where the bypass valve becomes the primary control device during low-flow conditions. This segmentation of control responsibilities eliminates conflicts by ensuring that only one device is actively regulating pressure at any given time based on flow conditions.
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 regulation of receiver pressure under varying load conditions, reducing compressor wear and energy costs, while preventing conflicts between compressor and bypass valve control, ensuring stable operation without over-dimensioning the receiver compressor capacity.
Implementation Method 1
the gaseous refrigerant may be supplied directly to a dedicated receiver compressor, which does not receive refrigerant from the evaporator
Implementation Method 2
Supplying the gaseous refrigerant to a receiver compressor is more energy efficient than supplying it to the suction line, via a bypass valve, or supplying it to the expansion device, because thereby a pressure drop is not introduced
Implementation Method 3
When passing through the heat rejecting heat exchanger, heat exchange takes place between the refrigerant and the ambient or a secondary fluid flowing across the heat rejecting heat exchanger, in such a manner that heat is rejected from the refrigerant
Implementation Method 4
When passing through the evaporator, the liquid part of the refrigerant is evaporated, while heat exchange takes place between the refrigerant and the ambient or a secondary fluid flow across the evaporator, in such a manner that heat is absorbed by the refrigerant
Implementation Method 5
The refrigerant then passes through the expansion device, where it undergoes expansion, before being supplied to the evaporator
Data Source
Figure 1
Figure 2
AI summary
A method for controlling a vapour compression system (1) is disclosed. The vapour compression system (1) comprises a compressor unit (2) comprising at least one main compressor (3) and at least one receiver compressor (4), a heat rejecting heat exchanger (5), a receiver (7), an expansion device (8) and an evaporator (9) being arranged in a refrigerant path. The vapour compression system (1) further comprises a bypass valve (12) fluidly interconnecting the gaseous outlet (10) of the receiver (7) and the main compressor(s) (3). A first pressure setpoint for a pressure prevailing in the receiver (7) and a second pressure setpoint for the pressure prevailing in the receiver (7) are defined, the second pressure setpoint being higher than the first pressure setpoint. An opening degree of the bypass valve (12) is controlled in order to regulate the pressure prevailing in the receiver (7) in accordance with the first pressure setpoint in the case that a load demand of the vapour compression system (1) exceeds a maximum capacity of the receiver compressor(s) (4). The opening degree of the bypass valve (12) is controlled in order to regulate the pressure prevailing in the receiver (7) in accordance with the second pressure setpoint in the case that the receiver compressor(s) (4) is/are operating and the load demand of the vapour compression system (1) is below the maximum capacity of the receiver compressor(s) (4).