My project is an addition to an existing facility, so the CHW and HHW comes from a district plant.  I am modeling the plant as cost neutral, purchased CHW and HHW in baseline and proposed.  My proposed design has 2 ORs that are designed to a 55F setpoint using an air-cool glycol sub-cooling chiller that is dedicated to this addition.  I am using G3.1.1 exception b to put those two ORs on their own system 3s.  Should I make the cooling source for the system 3s DX or put them on the purchased CHW loop?  Technically the purchased CHW loop doesn't make cold enough water to sub-cool the OR to 55F, and their cooling source is not part of the district loop (the first stage is in reality).