Air Conditioning Options: Central, Ductless, or Through-the-Wall?
My first choice for energy efficiency, as well overall comfort, would be to install a central air conditioning system. These systems can be “zoned” so they will only cool one floor of the home and not both. However, you certainly should plan on both and discuss that with your contractor as it may be less costly to install some of the ducting to “get ready” for cooling the second floor at some point in the future.
Another option might be to install a through-the-wall air conditioning unit. Many of the larger units are available with wall mounted sleeves. To install, you’d need to cut a hole in the exterior wall and frame it out the same way you’d frame an opening for a window or door. It is very important to do this correctly, as you will be impacting the structural integrity of the house. Also, this type of system will very likely cause a heat loss in the winter as it is very difficult to seal it to prevent cold air leaking in.
A better option, which cost-wise will be in between the cost of a central system and a through-the-wall mounted portable, might be ductless air conditioning. I have Fujitsu ductless air conditioning system like this in my office and the ductless air conditioning system works extremely well as a supplement to my central system, which doesn’t fully extend into the office space. With ductless air conditioning, you have a wall blower that hangs on the inside wall of your home. This is connected via a refrigerant line to a small compressor which sits outside, just like a central system. The compressor supplies chilled refrigerant to the blower inside, which circulates the cooled air.
Given the above, my choice would be (1) central; (2) ductless; (3) through-the-wall.
Regardless of what you ultimately decide, you should be certain to choose the most energy efficient air conditioning unit possible.