Water chiller with oil-free centrifugal compressors.

This paper deals with energy performances of a 440-kW (125-ton) air-conditioning factory-assembled water chiller with totally oil-free, variable speed centrifugal compressors and air-cooled condensers. The prototype was installed in Montreal (Eastern Canada) in a retrofit building with telecommunication equipment, process computers and other similar cooling charges. The non-standard part load values (NPLV) are calculated during a typical summer Canadian weather period. This study demonstrates that magnetic bearings, variable-speed compression and digital electronic controls achieve high compressor efficiencies with air-cooled water chillers. For the retrofit system having a very constant process cooling charge, the average seasonal NPLV is 49% lower as compared to previous existing conventional air-cooled chillers. The mechanical room noise is also significantly diminished, while the simple pay-back period is estimated at 3.5 years (without subsides) for a technical life of 25 year.