Receiver Compressor Start Control Using Bypass Valve Flow Modeling
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Solution Overview
Problem
Existing vapor compression systems face challenges in determining the optimal time to start and stop the receiver compressor due to variable operating conditions, leading to inefficient energy use and excessive wear from repeated starts and stops.
Innovation Solution
A method that measures the pressure difference across the bypass valve and derives the mass flow rate of refrigerant through it using a fluid model, comparing it to the minimum mass flow rate required for stable operation of the receiver compressor, 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 experiences excessive wear from repeated starts and stops
Solution Approach 1:
The controller performs preliminary assessment of gaseous refrigerant flow conditions before starting the receiver compressor. By evaluating flow rate thresholds and system conditions in advance, the controller prevents premature starts that would cause instability and excessive wear, while still capturing energy-saving opportunities when conditions are favorable.
Solution Approach 2:
The system continuously monitors gaseous refrigerant flow conditions and uses this feedback to make real-time decisions about receiver compressor operation. The controller adjusts compressor start/stop commands based on current flow rates and system state, optimizing the balance between energy efficiency and compressor reliability.
2Reliability
If the receiver compressor is kept stopped to avoid repeated starts and stops, then compressor wear is reduced, but energy efficiency deteriorates
Solution Approach 1:
The system dynamically adjusts receiver compressor operation based on real-time gaseous refrigerant flow conditions. Rather than a fixed on/off strategy, the controller continuously evaluates flow rates and system conditions, adapting compressor operation to match actual demand while maintaining stability thresholds to prevent excessive cycling.
3Reliability
If the switching decision is made conservatively to ensure stable operation, then compressor reliability is improved, but energy efficiency is compromised due to delayed switching
Solution Approach 1:
The system uses multiple parameters (gaseous flow rate, pressure differential, temperature conditions) to make switching decisions rather than relying on a single conservative threshold. By evaluating multiple parameters simultaneously, the controller can make more accurate and timely decisions about when to start or stop the receiver compressor, reducing unnecessary delays while maintaining stability.
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 precise determination of the switch point for the receiver compressor, preventing unnecessary starts and stops, ensuring stable operation and optimizing energy efficiency regardless of operating conditions.
Implementation Method 1
A pressure difference across the bypass valve is measured or derived
Implementation Method 2
a mass flow rate of refrigerant through the bypass valve is derived, based at least on the pressure difference across the bypass valve, and using a fluid model
Implementation Method 3
In the receiver, the refrigerant is separated into a gaseous part and a liquid part
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
Implementation Method 5
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 6
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 7
Refrigerant flowing in the refrigerant path is thereby compressed by the compressor(s) of the compressor unit
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 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.