Scroll Compressor Shutdown Control for Stable Pressure Differential
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Solution Overview
Problem
Existing cooling systems with tandem scroll compressors face issues of undirected unloading, leading to reduced cooling capacity and temperature control instability due to low-pressure differences, especially at low outdoor ambient temperatures and high evaporator pressures.
Innovation Solution
Implementing a method that determines and maintains pressure differences across scroll compressors above a predetermined level by adjusting parameters such as condenser fan speeds, compressor operation, and evaporator fan speeds using PID control and hysteresis-based adjustments to prevent undirected unloading, ensuring stable compressor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the pressure difference of the compressor is reduced to increase operating efficiencies, then energy consumption is reduced, but the stationary scrolls separate from the orbiting scrolls causing undirected unloading which reduces cooling capacity and temperature control stability
Solution Approach 1:
The control system continuously monitors the pressure difference across the compressor and dynamically adjusts the PWM duty cycle to maintain the pressure difference within an optimal range. This feedback mechanism prevents undirected unloading while optimizing energy consumption by avoiding excessive pressure differences.
Solution Approach 2:
The system changes the operating parameters by adjusting the PWM duty cycle of the compressor motor based on the measured pressure difference. When the pressure difference approaches the threshold for undirected unloading, the duty cycle is reduced to maintain stable operation and cooling capacity.
2Use of energy by moving object
If the lag compressor is turned off to reduce energy consumption, then energy efficiency is improved, but the pressure difference drops causing undirected unloading of the lead compressor
Solution Approach 1:
Before turning off the lag compressor, the control system performs preliminary actions by adjusting the lead compressor's PWM duty cycle and modifying condenser fan speed to compensate for the upcoming loss of compression capacity. This prevents the pressure difference from dropping below the threshold that would cause undirected unloading.
Solution Approach 2:
The system dynamically adjusts the operation of the lead compressor and condenser fan based on the status of the lag compressor. When the lag compressor is turned off, the lead compressor's duty cycle is increased and fan speed is adjusted to maintain the pressure difference within the optimal range, ensuring continuous stable operation.
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, maintains cooling capacity, and enhances temperature control stability by maintaining pressure differences above the threshold, thereby improving the efficiency and reliability of cooling systems.
Implementation Method 1
A condenser fan may be controlled at a first speed according to a proportional integral derivative (PID) method
Implementation Method 2
An evaporator fan may be controlled at a first speed according to a proportional integral derivative (PID) method
Implementation Method 3
The compressor 58 circulates the cooling fluid through the condenser 60, the expansion valve 62, the evaporator 54 and back to the compressor 58
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. A system including the lag compressor module and the lead compressor module.