Mini-split AC systems are designed to cool several rooms with different air-handling units or... just a room or part of the house. All that without ducts and the distribution loss of ducted systems.
The difference between ductless mini-splits and central AC systems
Many central air conditioners are “packaged” systems. They have the evaporator, condenser and compressor housed in a single outdoor box, connected to ducts that run throughout the building.
Ducted central AC split-systems are another type of ducted AC. In this case there is an outdoor unit (with the condenser) and an indoor unit (the evaporator and blower), both connected to the ductwork.
Ductless mini-split systems, like central AC split-systems, have an outdoor and an indoor unit, but they do not involve ductwork: they use a conduit to carry the refrigerant to the indoor air handlers (ceiling suspended or mounted in a wall).
Though sometimes classified as central AC systems, many mini-split systems have just one indoor air handler and can be designed to cool just one room or small part of the house.
Recommended or not?
Most American contractors do not like or do not recommend mini-split ductless AC systems. They prefer the more conventional AC central systems, or window-room units. But that doesn't mean much. Ductless units can be a good alternative to other types of AC as attested by their popularity in Europe and Asia.
The difference between ductless mini-Split systems and Window-Room AC units
Mini-splits with a one-indoor air handler are similar to window air conditioners, in the sense that both are duct-free and designed to cool a room or part of the house...
But unlike window air-conditioners, mini-splits are mounted on the wall (or on the ceiling) and have an outdoor unit. And, most of all, they can have several indoor units, serving different rooms or parts of the house, and may also use the heat pump technology to provide heating (besides cooling) during the winter months...
Mini-split systems are a tested and versatile technology, able to provide a flexible air-conditioning solution for single and multi-room applications. They are very easy to install and reliable.
They haven't the large capacity of many central AC systems, but - compared to typical central AC systems - they are a very cost-effective solution for low and moderate cooling needs. They haven't the distribution losses of ducted systems which make them a lot less expensive to run.
Besides they can be used in zoning strategies (to cool just the room you are in), for energy improvements and savings; and they can also be used for heating, when equipped with the heat-pump technology, even in cold climates, in homes with very high levels of insulation and good passive house techniques.
There are now cold-climate heat pumps (mini-splits), able to meet the heating needs of very energy efficient homes, even in freezing temperatures (besides being able to meet the cooling requirements). They are the "cold-climate" heat pumps. (see, on these issue: Ductless Heat Pumps).
Though less expensive than central AC, ductless AC systems can be expensive to run and very questionable from an environmental standpoint.
You should consider other cooling alternatives before investing in any type of mechanical air conditioning if you are going to build a new home. Properly designed, insulated and sealed homes, with a proper landscaping, may not need air conditioning, even in hot climates.
Room air conditioners have the lowest prices, often around $250-$350. A good central AC equipment can cost, say, $3.000. But installation costs can double or triple the costs of central AC equipment...
Prices and reviews
Panasonic has inexpensive single air-handling models: est. $300-$350. But prices are mostly in the range $500-$1.000.
2-4 air-handlers units providing both cooling and heating come at higher prices: $1.000-$2.000.
See, for Online prices and customer reviews in Amazon.com: Mini-split AC