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Compressed air storage is an important, but often misunderstood, component of compressed air systems. This paper discusses methods to properly size compressed air storage in load-unload systems to avoid short cycling and reduce system energy use. First, key equations relating storage, pressure, and compressed air flow are derived using fundamental thermodynamic relations. Next, these relations are used to calculate the relation between volume of storage and cycle time in load-unload compressors. It is shown that cycle time is minimized when compressed air demand is 50% of compressor capacity. The effect of pressure drop between compressor system and storage on cycle time is discussed. These relations are used to develop guidelines for compressed air storage that minimize energy consumption. These methods are demonstrated in two case study examples.

The cooling of equipment and products is an integral part of many manufacturing processes. This paper describes typical process cooling systems used in manufacturing and the approximate cost of cooling for each system. The paper then describes the inside out approach to energy efficiency, which recommends sequential evaluation of end use, distribution and primary energy conversion systems, as it relates to process cooling. General methods for improving the energy efficiency of cooling processes, organized according to the inside-out approach, are described. These methods include adding insulation and heat exchangers, improving process control, avoiding mixing, employing variable-speed and low friction pumping systems, and using cooling towers in place of chillers. The fundamental equations for estimating savings, and examples, are presented for these methods.