Before I retired I installed quite a few of the mini-splits, I'm not sure on how much they save but I do know they are VERY efficient. They are a little difficult to install as they are so compact sometimes its hard to get your hands in the inside wall unit to make it up. The fan motor and the compressor ramp up and down in speed depending on what the requirements are at any given time, and they are super quit. They are fairly inexpensive and easy to install as there is no duct work, just refrigerant lines and a power cable (supplied with unit). The AC power from the building is ran to the outside unit and the supplied cable is ran from the outside unit to the inside wall unit, the inside unit gets its power from the outside unit and is DC power. The outside unit comes pre-charged with freon so all you need to do is install the refrigerent line set, pull a vacuum and open the valves releasing the freon. If I were to air condition my garage I would defiantly install one of these units.