I am trying to model a data center space that uses a fluid cooler for its first stage of cooling and then an air cooled chiller for its second stage when the fluid cooler can not handle the entire load. I have tried modeling the fluid cooler as a chiller of type "waterside economizer", and putting this chiller on the primary CHW loop. How exactly should the waterside economizer CW loop be modeled? Since it technically doesn't have a condensing water loop, I didn't think I should add a fluid cooler to this loop or anything, so I left the CW loop at its default. Should the air cooled chiller be on a secondary loop or on the same primary loop? I have tried both ways and have gotten errors. Any help would be much appreciated. Thanks.

Brian Goldsmith, LEED(r) AP