Central A/C in old building

For an example of compressors on the roof, see the Google Maps view of http://streeteasy.com/nyc/building/55-north-moore-street-manhattan. There's one for each of the 12 units.

That was a whole-building rebuild, though, where the power cable and refrigerant piping could be run from each apartment up to the roof.

Just for your own, your co-op or condo isn't likely to let you take roof space for the compressor and tear things up to run the conduit and piping up there.

To stay within the boundaries of your own unit, the compressor needs to be either under a window (like a through-wall AC) or in some spare space with a window. Then you can run power to it, and run the piping from there to the air-handler. The air-handler can be in a room of its own, or up below the ceiling if they're high enough. From there the ducts run to the rooms. You'll also need access to a drain from there, for the condensed humidity.

In Asia you'll see lots of smaller split-system compressors hanging on outside walls and on balconies, but not in NYC.

Do many buildings allow the compressor under a window and does it change the building aesthetics from the outside? Does this end up being loud in the room with the compressor under the window? any ideas on cost? Assume 2000sf apartment

From the outside all you see is a grille, on the same plane as the wall, as with through-wall AC. The building will have standards so that everybody has matching grilles.

I guess the noise in the room would be like three or four air-conditioners. In pre-war co-ops you often see the outer part of a maid's room walled off for the compressor and air-handler, with the rest for laundry room or something.

Don't know about the cost, but $50-100K has been mentioned here before. Somebody in my building was going to do it as part of a renovation, but because of the cost, ductwork, piping, control systems, etc., just went with through-wall AC in each room.

great very helpful thanks

I put central air in my pre-war co-op using a four-zone split system. We carved out a small windowed nook out of a bedroom and put the condenser in there. Air intake is through a typical "through wall" AC grill below the window. The condenser exhausts through the window which was replaced w/ a giant louver. The unit is in a dedicated "closet" behind a solid core door within my son's room. When it's on, you don't even hear it due to the acoustical dampening we installed. From this closet, the refrigerant pipes run to the four zones. I would never have thought it could be done until I met an architect who pulled it off in several other apartments. Works like a champ and should definitely be considered as a viable alternative.