If you were to take a window air conditioner, and bandsaw off the front 2", you have a mini-split system.
The part that mounts in the room is about 2" thick, surface mounts, and requires three things - plumbing (in and out), 120V from a junction box, and control cable which is the same stuff as furnace control cable. Three small holes in the wall rather than a huge vent/duct hole.
The condensor/compressor unit is much like central air conditioning systems, is a big round thing with vents, and mounts outside on a concrete pad. If sized correctly, you can support multiple room units. Generally, you mount the room units above the windows in the room so the cold air comes out across the ceiling and starts an airflow cycle that way.
Since each room unit has it's own control cable, and it's own thermostat (and some have timers, etc), you can program the ones in your bedroom to kick on an hour before you go to bed, the ones in the living spaces to be on during the day, etc, to different temperatures if you like. The ones I was looking at have all that plus a TV-remote shaped remote for controlling from across the room. No need to stand on a short stool to adjust the temperature
This also allows me to keep the studio at a constant temperature, and the rest of the house can be adjusted individually based on whoever is in which room. I prefer rooms a little cooler, whereas my wife doesn't mind blistering heat and humidity. Ack!
They can be ordered with fans, or without, and the without fans obviously are dead quiet but take a little longer to cool a room. I've heard the fan-based units before and they aren't all that loud, probably no louder than a PC buried under your console table with stuff in front of it - you barely notice it - this is because the compressor part is outside somewhere, like i said above. The compressor and the electric motor to drive it, is what makes all the noise and vibration.
The other advantage I see is it is by far easier to bury plumbing in outside walls, whereas ductwork would take up all the space between studs, not allowing for insulation to be put back in. This way in the winter the wall is warmer. Plumbing is far easier to snake around tight spaces especially in older construction, and I don't have to give up attic space with large 4"x8" ducts or those big 12" flexiducts being draped all over.
Since its not forced air, the filters are easier to replace, though each unit has its own filter. Units you run a lot you replace the filters more often, the units that you rarely use you can ignore longer. They are maintanence free and use the same refrigerant as commercial and home central air systems - nothing special and any AC service company can recharge the system and service the compressor/condensor as its like every other central air system on that end.
The plastic shells of the wall mount parts can be lightly sanded, painted with automotive primer, followed with automotive paint. Its the same type of plastic used in automobiles, probably to resist cracking due to temperature changes. So you can make them any color you want if White, Beige, Gray isn't acceptable to your decor.
I like these systems a lot, and will be installing such in my house eventually.
