Scroll compressor differential pressure control techniques
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Solution Overview
Problem
Existing cooling systems face issues with undirected unloading of scroll compressors due to low pressure differences, leading to reduced cooling capacity and temperature control instability, particularly at varying ambient temperatures.
Innovation Solution
A method is implemented to maintain pressure differences across scroll compressors above a predetermined level by adjusting parameters such as head pressure set points and evaporator fan speeds, using proportional integral derivative (PID) control and hysteresis values to prevent unloading, and managing compressor operation through lead and lag compressor activation strategies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the pressure difference across the scroll compressor is reduced to increase operating efficiency, then energy consumption is minimized, but the stationary scrolls separate from the orbiting scrolls causing undirected unloading and reduced cooling capacity
Solution Approach 1:
The control system continuously monitors the pressure difference across the scroll compressor and provides feedback to the controller. When the pressure difference falls below a predetermined threshold, the controller activates the condenser fan to increase head pressure and restore the pressure difference to acceptable levels, preventing undirected unloading while maintaining energy efficiency during normal operation
Solution Approach 2:
The system dynamically adjusts operating parameters based on conditions: the condenser fan speed is modified in response to pressure difference measurements, and the expansion valve position is adjusted to control refrigerant flow. This allows the system to operate at low pressure differences for energy efficiency while maintaining sufficient pressure difference thresholds to prevent compressor unloading
2Loss of energy
If the pressure difference across the scroll compressor is reduced to improve efficiency, then operating cost decreases, but temperature control stability deteriorates due to compressor unloading
Solution Approach 1:
The system uses continuous feedback from pressure sensors to monitor the pressure difference across the compressor. When the pressure difference approaches levels that could cause unloading, the controller responds by adjusting the condenser fan speed to maintain stable head pressure, thereby ensuring consistent cooling performance and temperature control stability
Solution Approach 2:
The control system takes preliminary action by monitoring the pressure difference trend and activating the condenser fan before actual unloading occurs. This proactive approach prevents the separation of scrolls and maintains stable compressor operation, ensuring continuous temperature control stability
3Reliability
If the condenser fan speed is increased to maintain head pressure, then the pressure difference is maintained above minimum levels, but energy consumption increases
Solution Approach 1:
The condenser fan operates dynamically with variable speed control rather than at constant high speed. The fan speed is adjusted in real-time based on the measured pressure difference and cooling load conditions, allowing the system to consume minimal energy during low-load operation while maintaining sufficient speed to preserve the pressure difference threshold when needed
Solution Approach 2:
The system changes the condenser fan speed parameter in response to operating conditions. During high cooling demands or when pressure difference approaches minimum levels, the fan speed increases to maintain head pressure. During low-demand periods, the fan speed reduces to minimize energy consumption while still preventing compressor unloading
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 prevents undirected unloading of compressors, ensuring stable cooling capacity and temperature control across varying conditions, thereby enhancing the efficiency and reliability of cooling systems.
Implementation Method 1
The cooling fluid is received at an inlet of the scroll compressor, trapped between the offset spiral disks, compressed, and discharged at a center (or outlet) towards the condenser 60
Implementation Method 2
The condenser 60 may be a micro-channel condenser that cools the cooling fluid received from the compressor 58
Implementation Method 3
The expansion valve 62 may be an electronic expansion valve and expand the cooling fluid out of the condenser 60 from, for example, a liquid to a vapor
Implementation Method 4
The evaporator 54 receives the cooling fluid and cools air passing through openings in evaporator 54
Data Source
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AI summary
A method includes determining a pressure difference across a scroll compressor of a cooling system. The pressure difference is compared to a minimum differential pressure value. Pressure differences across the scroll compressor that are less than the minimum differential pressure value are associated with unloading the scroll compressor. Parameters including a pressure set point value and an absolute minimum pressure value are increased when the pressure difference is less than the minimum differential pressure value. Subsequent to the increasing of the parameters, the parameters are decreased when the pressure difference is greater than a sum of the minimum differential pressure value and a hysteresis value.