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2.8 System Design for Efficient Low-Load Cooling

This part of the Energy Efficiency Manual presents energy conservation measures that improve the efficiency of cooling during periods of time when the cooling load is low. In most applications, the average cooling load is much lower than the peak load for most of the cooling season. To achieve good efficiency under all load conditions, you need chillers that are sized so that no chiller is forced to linger at an inefficiently low load. In addition, you may want a chiller of a separate type to satisfy low loads.

Unfortunately, the types of chillers that are most efficient at full load (centrifugal and screw compressor types) suffer serious loss of efficiency at reduced loads. While modern versions of these chiller types have greatly improved part-load performance, many machines that are presently installed have poor part-load efficiency.

This Subsection provides design improvements to central cooling systems and chiller plants that increase cooling efficiency at low cooling loads. Here you will learn how to balance the characteristics of the machines in your chiller plant for efficient operation under all load conditions.