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I've looked at all the E+ examples files, and whenever SetpointManager:FollowOutdorAirTemperature is used to do condenser water reset, the Offset Temperature Difference (deltaC) is set to 0.

I think this is potentially a misleading choice, because then the CT is basically controlled to deliver an unachievable approach of 0°F, and therefore you get high fan energy consumption that isn't compensated by a reduced lift on the chiller, as @Lincoln pointed out.

Here's total energy versus offset temp for the example file 2ZoneDataCenterHVAC_wEconomizer.idf, using chicago weather file. energy in Joules, offset temp in C.

foat offset