ExistingChiller requires cost to not be sized

[adfarth]

Currently, you need to add a cost to the existing chiller to have it not be sized in the optimal case if no other new cooling techs are sized (for some reason, it looks like you don’t have to do this for the Existing Boiler and maybe don’t have to do this if a GHP max ton is included?).

In this run, GHP is not cost-optimal but the Existing Chiller size is included (and increased) in the optimal case