Multi-Compressor Chiller Capacity Control With Modular Inverters
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Solution Overview
Problem
Existing multiple compressor chiller systems face challenges in efficiently controlling capacity, particularly during high ambient air temperature conditions, and suffer from increased costs and reliability issues due to the use of separate variable speed drives for each compressor and the risk of disabling all compressors if one motor fails.
Innovation Solution
A method and system utilizing a variable speed drive with multiple inverters to power compressors, allowing for dynamic adjustment of compressor speed and number based on monitored conditions, including ambient temperature, to maintain optimal capacity and efficiency, with a high ambient air temperature capacity control program to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single variable speed drive is used to power multiple compressor motors in parallel, then the overall system cost is reduced, but a fault in one motor may disable the variable speed drive and prevent other motors from operating
Solution Approach 1:
The variable speed drive is segmented into multiple independent inverter modules, each capable of powering one or more compressor motors. This modular architecture allows individual inverters to be isolated in case of fault, preventing system-wide shutdown while maintaining cost efficiency through shared control infrastructure.
Solution Approach 2:
A control system acts as an intermediary between the segmented inverter modules and compressor motors, managing power distribution and fault isolation. The control system enables selective engagement of inverters and motors, ensuring that a failure in one motor does not propagate to disable the entire drive system.
2Reliability
If separate variable speed drives are used for each compressor motor, then system reliability is improved by isolating faults, but the overall system cost increases
Solution Approach 1:
Multiple inverter modules are electrically connected in parallel within a single variable speed drive housing, sharing common control electronics and power processing circuitry. This merging approach provides fault isolation equivalent to separate drives while reducing overall system cost through component sharing and integration.
3Ease of operation
If compressors are operated sequentially to meet system load, then the control process is simplified, but system efficiency is reduced during high ambient temperature conditions
Solution Approach 1:
The system dynamically adjusts compressor operation modes based on ambient temperature conditions. During high ambient temperature conditions, the control system enables parallel operation of multiple compressors with independent inverter control, allowing continuous capacity adjustment and improved efficiency while maintaining simplified control through automated decision-making algorithms.
Data Source
AI summary
A capacity control algorithm for a multiple compressor liquid chiller system is provided wherein the speed and number of compressors in operation are controlled in order to obtain a leaving liquid temperature setpoint. In response to an increase in the load in the chiller system, the algorithm determines if a compressor should be started and adjusts the operating speed of all operating compressors when an additional compressor is started. In response to a decrease in the load in the chiller system with multiple compressors operating, the algorithm determines if a compressor should be de-energized and adjusts the operating speed of all remaining operating compressors when a compressor is de-energized.