Air conditioning your offices and homes using solar or gas fired systems

Ammonia doesn't power the system; it's the refrigerant (heat transfer fluid). It works, but is toxic, so leaks can be dangerous. Newer refrigerants are non-toxic, non flammable, and ozone friendly.

http://en.wikipedia.org/wiki/Refrigerant

As far as using gas/solar power to cool the building, it's being done: http://www.scusolar.org/technology.thermal

An absorption chiller, like an external combustion engine, doesn't care what the heat source is.