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A chiller control algorithm for multiple variable-speed centrifugal compressors.

Number: pap. 1435

Author(s) : CABALLERO P., ORDONEZ J., SHIH C., et al.

Summary

Capacity control of a chiller with multiple variable-speed centrifugal compressors running in parallel between a common evaporator and condenser under reduced load conditions can be achieved by speed variation and/or adjusting the number of compressors in operation. Quite often there is not a unique solution for a specific part-load condition in terms of the number of compressors required and the speed of each of these compressors. These different capacity control schemes can result in substantial differences in chiller performance under part-load conditions. The decision in selecting the optimum number of operational compressors to reach a desired part-load capacity depends not only on the required partial load but also on the required pressure ratio at that part-load condition. To illustrate the control dilemma, the paper will start with an example that shows the need for a different control strategy for two different chiller pressure ratios at equal part-load capacity. This difference in partial load control can be planned by observing the location of the efficiency islands on the variable-speed centrifugal compressor map. For a given refrigerant the efficiency of a compressor is a function of only two process variables: head (isentropic enthalpy rise) and volumetric flow rate. With that information a multiple compressor control algorithm has been developed that can estimate optimum chiller performance for any head/flow combination the chiller with multiple compressors might encounter. The improvement in chiller part-load performance using this algorithm can be substantial as will be illustrated in the paper for a two compressor chiller configuration.

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Pages: 8 p.

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Details

  • Original title: A chiller control algorithm for multiple variable-speed centrifugal compressors.
  • Record ID : 30012811
  • Languages: English
  • Source: 2014 Purdue Conferences. 22nd International Compressor Engineering Conference at Purdue.
  • Publication date: 2014/07/14

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