EAp2

Air-cooled chiller is an option. I see lots of project in Argentina achieving LEED certifications with these. Although Air-cooled will probably have less efficiency than water cooled systems this is not always the case, and you can find extremely efficient air-cooled chillers that will perform better than ASHRAE minimum. Also have in mind that you can achieve energy savings in many other ways, for example by reducing cooling demand, reducing installed lighting power, installing efficient AC, etc. Did I answer your question?

Baseline HVAC system for non-residential building with 19000 m² of conditioned floor area, is System 8 or 7 (depending on what heating source you have). In either case Baseline system is water-cooled chillers. - The Baseline number, type and size of chillers should be acording to TABLE G3.1.3.7. - Chillers COP depends on chiller size and type, you should reference TABLE 6.8.1C Water Chilling Packages–Minimum Efficiency Requirements, either 'Water cooled, electrically operated, positive displacement (rotary screw and scroll)' or 'Water cooled, electrically operated, centrifugal'. - Maximum COP for baseline's chillers, is 5.50 (screw) and 6.40 centrifugal, again this could be lower depending on size. For your actual building design, you can choose which ever system you like as long as the efficiency is better than 90.1 Section 6.4 and Tables 6.8.1 and you achieve greater savings than 10% over baseline.

I am not aware of any exceptions for using air cooled systems instead of water cooled when it is a system 7 or 8. If there is an efficiency loss you simply have to make it up elsewhere to meet the minimum % savings.