TECHNICAL FEATURE
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Industrial Refrigeration Systems
Sequencing & Control
Of Compressors
BY DOUGLAS T. REINDL, PH.D., P.E., FELLOW ASHRAE
Virtually every built-up refrigeration system used in commercial or industrial
applications has multiple compressors available for operation to meet loads.
One of the challenges in designing and operating a system with multiple
compressors is deciding how best to sequence their controls to meet variable
refrigeration loads while avoiding inefficient compressor performance at
part-load to maintain high system efficiency.
This article discusses typical part-load efficiency characteristics for screw and reciprocating compressors
commonly found in built-up industrial refrigeration
systems. It includes recommendations for sequencing and control strategies that enable efficient system
operation.
Introduction
Industrial refrigeration systems come in all different
sizes, configurations, and arrangements. The nature
of the food production and storage facilities this technology most frequently calls “home” are quite varied,
and nearly all of the refrigeration systems installed in
these applications are custom-engineered to meet the
specific thermal requirements of loads within the facility. Individual owners establish specific requirements
for their refrigeration infrastructure, and the relative
importance of these requirements vary on a plant-byplant basis. The requirements can be grouped into two
categories “non-negotiable” and “negotiable.”
Non-negotiable requirements dictate that the refrigeration system must be: safe and able to meet the magnitude and temperature requirements of coincident
load(s). Safety is achieved by ensuring the systems are
designed, constructed, and operated in accordance with
the latest applicable standards, codes, regulations, and
industry best practices. Guaranteeing the refrigeration
system can reliably meet its loads requires appropriate sizing of key components including compressors. In
some cases, achieving the ability to reliably meet loads
may necessitate redundant compressors. Negotiable
requirements can include capital cost, operating costs,
ABOUT THE AUTHOR Douglas T. Reindl, Ph.D., P.E., is a professor and director at the University of Wisconsin-Madison’s Industrial Refrigeration Consortium in Madison, Wis.
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