AHRI Standard 550-590, Standard for Performance Rating of Water–Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle, has recently undergone updates. The new version of this standard includes heat pump water heaters, expands the testing options for air-cooled chillers by including a barometric pressure adjustment and witness test labrequirements and provides an expanded discussion of the purpose and use of IPLV.