Evaporative Chiller in EAp2?

The basic rule is that if the standard does not regulate it, it is the same in both baseline and proposed case models, i.e. both get the proposed case equipment. In my SI Version of 90.1-2007, Table 6.8.1C lists Water Chilling Packages-Minimum Efficience Requirements for Equipment Type "Air colled, with condenser, electrically operated" as 2.80 COP and 3.05 IPLV (as long as the chilled water temp is more than 4.4ºC). The size category says "All capacities", so that covers your 50RT. If your chiller has a seperate conderser unit, then you're looking at tables 6.8.1H,I,J for the chiller TOGETHER WITH 6.8.1G for the condenser unit (Heat Rejection Equipment). You'll have to figure out if 50RT is IP or SI units and get the match in the tables. If it's not there, then it's not regulated.

90.1-2013 added significantly more systems so you could check there to see if your system is covered. As Jean said you are not held to a minimum efficiency if the system is not covered under 90.1-2007 but if you are looking for a minimum to use you might find it in the newer version.