** It is possible to install multiple smaller systems as suggested by Dan in the attic and basement of the house **
The system I was speaking of has evaporator units in each room needed to be cooled and several of those would be connected to a single outdoor condensing unit. There could be several of these installations in the same house depending on how many rooms needed to be cooled. Only the refrigerant and drain line goes through the wall to the outdoor condenser unit.
You can read a bit about that system at the following link or at the URLs Jay gave.