Receiver Compressor Control Using Bypass Valve Pressure Difference
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Solution Overview
Problem
Existing vapour compression systems face challenges in determining the optimal time to start or stop a receiver compressor due to variable ambient conditions, leading to inefficient energy use and excessive wear from repeated starts and stops.
Innovation Solution
A method that measures pressure difference across a bypass valve, derives mass flow rate using a fluid model, and compares it with a minimum mass flow rate required for stable compressor operation, ensuring accurate switching between bypass valve and receiver compressor operation based on prevailing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the receiver compressor is started whenever gaseous refrigerant is available, then energy efficiency is improved, but the compressor suffers from excessive wear due to repeated starts and stops
Solution Approach 1:
The controller performs preliminary assessment of gaseous refrigerant availability by measuring pressure difference across the bypass valve and deriving mass flow rate before deciding to start the receiver compressor. This preliminary action ensures that the compressor is only started when sufficient refrigerant flow is guaranteed, preventing repeated starts and stops while maintaining energy efficiency.
2Reliability
If the receiver compressor is stopped when gaseous refrigerant flow is low, then compressor stability is improved, but energy efficiency deteriorates
Solution Approach 1:
The controller continuously monitors the pressure difference across the bypass valve and derives the mass flow rate of gaseous refrigerant in real-time. This feedback mechanism allows the system to accurately determine when sufficient refrigerant flow is available to support stable compressor operation, enabling the compressor to run continuously when conditions permit, thereby improving energy efficiency while maintaining stability.
3Device complexity
If simple pressure-based control is used, then device complexity is reduced, but measurement precision is insufficient to accurately determine switch points
Solution Approach 1:
The controller uses the bypass valve as an intermediary element to indirectly measure gaseous refrigerant flow characteristics. By measuring the pressure difference across the bypass valve and using this information to derive mass flow rate, the system achieves accurate determination of switch points without requiring direct flow measurement devices, thus maintaining control system simplicity while improving measurement precision.
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
Ensures efficient and stable operation of the receiver compressor by accurately determining the switch point, preventing repeated starts and stops, and optimizing energy use.
Implementation Method 1
measuring or deriving a pressure difference across the bypass valve
Implementation Method 2
In the receiver, the refrigerant is separated into a gaseous part and a liquid part
Implementation Method 3
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 4
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 5
The refrigerant then passes through the expansion device, where it undergoes expansion
Data Source
AI summary
A vapour compression system (1) including a compressor unit (2) having 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 includes a bypass valve (12) fluidly interconnecting the gaseous outlet (10) of the receiver (7) and the main compressor(s) (3). A pressure difference across the bypass valve (12) is measured or derived, and a mass flow rate of refrigerant through the bypass valve (12) is derived, based at least on the pressure difference across the bypass valve (12), and using a fluid model. A minimum mass flow rate of refrigerant required to operate the receiver compressor (4) is derived, based on a minimum displacement volume of the receiver compressor (4) and using a fluid model taking prevailing operating conditions into account. In the case that the derived mass flow rate of refrigerant through the bypass valve (12) exceeds the derived minimum mass flow rate of refrigerant required to operate the receiver compressor (4), the receiver compressor (4) is started and the bypass valve (12) is closed.