Scroll compressor differential pressure control during compressor shutdown transitions
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Solution Overview
Problem
Existing cooling systems face inefficiencies due to undirected unloading of scroll compressors, which reduces cooling capacity and stability, particularly at varying ambient temperatures and pressure differences.
Innovation Solution
Implementing a method to maintain pressure differences across scroll compressors above a predetermined level by adjusting condenser fan speeds and compressor operation using PID control and hysteresis-based parameter adjustments, ensuring continuous operation and preventing unloading.
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 reduced, but the compressor enters an unloaded condition causing undirected unloading and reduced cooling capacity
Solution Approach 1:
The control system performs preliminary action by detecting when the pressure difference approaches the minimum threshold before the compressor actually unloads. It proactively adjusts the condenser fan speed to maintain the pressure difference above the minimum level, preventing undirected unloading from occurring in the first place
Solution Approach 2:
The system implements feedback control by continuously monitoring the pressure difference across the compressor and using this information to dynamically adjust the condenser fan speed. This closed-loop control ensures the pressure difference remains within the optimal range, preventing compressor unloading while maintaining energy efficiency
2Reliability
If the condenser fan speed is increased to maintain pressure difference, then compressor unloading is prevented, but energy consumption increases
Solution Approach 1:
The system applies dynamics by making the condenser fan speed adjustable and variable rather than fixed. The fan speed dynamically adapts to changing operating conditions, increasing only when necessary to maintain the minimum pressure difference and decreasing when the pressure difference is sufficient, optimizing the balance between reliability and energy consumption
Solution Approach 2:
The control system changes the operational parameters of the condenser fan based on real-time pressure difference measurements. By adjusting the fan speed parameter in response to pressure conditions, the system maintains compressor stability while minimizing unnecessary energy consumption during periods when high fan speed is not required
3Loss of energy
If the compressor operates at minimum pressure difference for extended periods, then energy efficiency is improved, but the stationary scrolls separate from orbiting scrolls causing unpredictable unloading
Solution Approach 1:
The control system applies preliminary anti-action by taking preventive measures before compressor unloading occurs. It monitors the pressure difference and adjusts the condenser fan speed in advance to counteract the tendency toward unloading, preventing the separation of stationary and orbiting scrolls before it can happen
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 enhances cooling system efficiency and stability by maintaining optimal pressure ratios, preventing compressor unloading and ensuring consistent cooling capacity across different operating conditions.
Implementation Method 1
The condenser fan speed is reduced below the speed that would otherwise be selected to maintain a head pressure
Implementation Method 2
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
Implementation Method 3
The evaporator 54 receives the cooling fluid and cools air passing through openings in evaporator 54
Data Source
AI summary
A method including determining whether an OFF criterion is satisfied for a lag compressor of a tandem set of scroll compressors. The tandem set of scroll compressors includes a lead compressor. The method further includes: initiating at least one process when the OFF criterion is satisfied; and maintaining the lag compressor in an ON state for a predetermined period subsequent to the OFF criterion being satisfied. The at least one process includes at least one of: operating the lead compressor at a maximum level; overriding a motor overload protection method, wherein the motor overload protection method protects motors of the lead compressor and the lag compressor; and overriding a proportional integral derivative (PID) method to reduce a speed of a condenser fan. The PID method controls the speed of the condenser fan.