Method for controlling a vapour compression system with a bypass valve
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Solution Overview
Problem
Existing vapour compression systems face challenges in maintaining receiver pressure efficiently, leading to excessive wear on compressors, conflicts between receiver compressors and bypass valves, and unnecessary over-dimensioning of compressor capacity.
Innovation Solution
A method for controlling vapour compression systems by defining first and second pressure setpoints, using a bypass valve to regulate receiver pressure based on load demand, and employing a 'half-side hysteresis' control strategy to minimize conflicts and ensure efficient operation without over-dimensioning.
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 compressor wear increases due to repeated stops and starts when gaseous refrigerant flow is low
Solution Approach 1:
The bypass valve acts as an intermediary device to regulate receiver pressure when gaseous refrigerant flow is insufficient for stable receiver compressor operation. This allows the receiver compressor to avoid repeated stops and starts, reducing wear while maintaining energy efficiency during normal operation.
Solution Approach 2:
The control strategy dynamically switches between using the receiver compressor and the bypass valve based on the flow of gaseous refrigerant. When flow is sufficient, the receiver compressor is used; when flow is low, the bypass valve takes over, optimizing both energy efficiency and reliability under varying conditions.
2Reliability
If the receiver compressor capacity is dimensioned for high load conditions, then pressure regulation under high load is improved, but manufacturing costs increase due to over-dimensioning
Solution Approach 1:
The bypass valve is integrated into the system to handle high load conditions, allowing the receiver compressor to be dimensioned for normal operation rather than peak demand. This multi-functional approach (receiver compressor for normal operation, bypass valve for high load) reduces manufacturing costs while maintaining the ability to regulate pressure under all load conditions.
3Adaptability or versatility
If both receiver compressor and bypass valve are used to control receiver pressure, then pressure regulation flexibility is improved, but control conflicts arise between the two devices
Solution Approach 1:
The control system dynamically determines when to use the receiver compressor versus the bypass valve based on real-time conditions such as gaseous refrigerant flow and load demand. This dynamic control strategy provides flexibility in pressure regulation while avoiding conflicts by ensuring only one device is active at a time based on predefined criteria.
4Reliability
If the bypass valve is used to regulate receiver pressure, then compressor wear is reduced, but energy efficiency deteriorates due to introduced pressure drop
Solution Approach 1:
The system dynamically switches between the receiver compressor and bypass valve based on operating conditions. The bypass valve is used only when necessary (low gaseous flow, high load) to protect the compressor, while the receiver compressor handles normal operation for optimal energy efficiency. This dynamic allocation minimizes the overall energy penalty while protecting compressor reliability.
Data Source
AI summary
The vapour compression system includes a compressor unit having at least one main compressor and at least one receiver compressor, a heat rejecting heat exchanger, a receiver, an expansion device and an evaporator being arranged in a refrigerant path. The vapour compression system further includes a bypass valve fluidly interconnecting the gaseous outlet of the receiver and the main compressor(s). An opening degree of the bypass valve is controlled to regulate the pressure prevailing in the receiver in accordance with a first pressure setpoint when a load demand of the vapour compression system exceeds a maximum capacity of the receiver compressor(s). The opening degree of the bypass valve is controlled to regulate the pressure prevailing in the receiver in accordance with a second pressure setpoint when the receiver compressor(s) is/are operating and the load demand of the vapour compression system is below the maximum capacity of the receiver compressor(s).