The General Standards Committee of theAir-Conditioning and Refrigeration Institute(ARI, Arlington, VA) has approved and released an addendum to ARI Standard 550/590-1998 "Standard for Water Chilling Packages Using the Vapor Compression Cycle." Standard 550/590-98 combines two previously separate standards: ARI Standard 550-92, "Centrifugal and Rotary Screw Water Chilling Packages," and ARI Standard 590-92, "Positive Displacement Compressor Water Chilling Packages." The standard and addendum can be downloaded for free at www.ari.org.