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for the owner. So despite the potential technical difficulties, several manufactures are offering retrofit programs that replace HFC-134a in some screw compressor products using a lower GWP refrigerant, namely R-450A or R-513A. 9.4.2 Centrifugal/axial turbo chillers Centrifugal and axial-turbo compressors by nature must be designed specifically for a particular refrigerant and a particular set of operating conditions for the refrigerant cycle in which they are used. Direct refrigerant substitution in these chillers can be made only in cases where the properties of the substitute refrigerant are nearly the same as those of the refrigerant for which the equipment was designed, or when the impeller speed and/or impeller geometry can be changed easily. In the past this has been accomplished by gear changes in open drive chillers and with variable speed drives in both open and hermetic compressor chillers. The compressor surge margin must be checked using the properties of the substitute refrigerant. However, centrifugal and axial-turbo chiller installations can represent a very large capital investment for the owner. So despite the possible technical difficulties, several manufacturers are offering chiller retrofits using a lower GWP refrigerants, namely R-450A, R-513A and R-514A. 9.5 9.6 Concluding remarks ChillersusinglowGWPrefrigerantshavebeencommercialisedandareemerginginthe market. This comes after years of research and screening of alternative refrigerant candidates. It is expected that the transition to low GWP refrigerants will take some years owing to the high investment and the large product development effort to convert the huge array of product types and sizes. It is also noted that non-fluorinated refrigerants are available in some chiller types, albeit in select sizes, rather than broad, complete product lines. The refrigerants that are being commercialised may not be the final choices. Chemical producers and chiller manufacturers will continue to focus their efforts on refrigerant candidates that provide energy efficiencies that are equal to or better than the refrigerants being replaced and reduce product development cost and time. Global warming effects from chillers are dominated by their energy use during their operating life, rather than direct emissions. The direct global warming impact from refrigerant emissions are minimal, because emissions have been significantly reduced in recent years through lower charge systems, low-leak designs, manufacturing and testing improvements, and improved service practices. Customers and regulators alike are interested in less energy consumption, which results in lower climate impact. There continues to be consumer and regulatory pressure to improve full and part load or seasonal energy consumption which will have a positive climate impact. Various application and control strategies exist, especially those involving larger multiple chillers. Since chillers are a major user of energy, the additional benefits of lower energy cost, and potentially lower power production and transmission infrastructure are also noteworthy. References AHRI, 2018. Standard 550/590(I-P)-2018: Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle, 2018. Air-Conditioning, Heating, and Refrigeration Institute (AHRI), Arlington VA, USA ASHRAE 15. 2016. ANSI/ASHRAE Standard 15-2016, Safety Standard for Refrigeration 182 2018 TOC Refrigeration, A/C and Heat Pumps Assessment ReportPDF Image | Heat Pumps Technical Options
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