Applying Variable Speed Drive Compressors In Multiple Compressor Applications

By Neil Mehltretter

Variable speed control for all types of industrial equipment is readily available on the market with competitive pricing to non-variable speed controlled alternatives, including in the air compressor industry. With the advent of prescriptive rebate programs for variable speed compressors and other equipment, the demand for these types of controls has increased. General wisdom would recommend a variable speed compressor for all applications, or multiple variable speed compressors within each system. There are significant benefits for systems where the demand changes rapidly to be served by variable speed compressors; by varying the frequency of the input electricity to the motor, a variable speed compressor can speed up and slow down to match supply output to the customer’s demand while maintaining a stable operating pressure within the system. However, many factors should be considered when selecting new air compressors – especially for multiple compressor systems. This paper will provide guidance on the design of variable speed compressors, how they can operate most efficiently with existing compressors, explain the tools necessary to consider when applying variable speed compressors to multiple compressor stations (or any compressors within a system), and provide examples of systems which required improvement as well as systems which were well optimized.