Economizer Location Optimization for a Centrifugal Compressor With Refrigerant as Working Fluid

In a typical HVAC chiller, centrifugal compressors are used to compress the refrigerant. These compressors are of single or multi-stage cycles that can be configured for a reinjection between cycles. This reinjection introduces cascade cycle options while improving the Coefficient of Performance (COP). One cascade cycle option that has become industry standard is an economizer cycle. During this process, the goal becomes to reinject flow back into the compressor between stages while the remaining flow continues through the cycle. The exact location of the economizer where its benefit would be at a maximum has yet to be determined. This paper develops a high-fidelity full compressor model where an economizer may be simply added into any location. A thermodynamic cycle analysis is used to highlight the locations where an economizer may be most beneficial thus limiting the number of locations to investigate. Initially, three different full compressor models are developed with increased model complexity for model validation. The most complex agreed with experimental results with high-accuracy and was used for further economizer testing. The most complex compressor model is investigated under 100% the design speed without the added economizer where a baseline is achieved. The thermodynamic cycle analysis is then implemented to identify the optimal economizer location based on the interstage pressure. Four locations are determined to fit the criteria. Two economizer locations were found to exhibit improved performance when compared to the remaining locations, increasing the aerodynamic efficiency of the base model by 10%.