Single-Package Central Air - Single package central air conditioners are most commonly used in industrial applications. All of the components are mounted into one "package" which is typically mounted on the roof of a building although occasionally on a wall.
Split System Central Air Conditioning (ducted A/C) - This is what people most commonly think of when they speak of wanting air conditioning. Split central air allows you to place the noisy portion or your cooling unit outside where it will be less noticeable. Split central air requires that your house have ducting to the various rooms in your home (usually the same ducting you use for your central heat). Central air allows you to cool all parts of a house evenly and quietly.
Ductless Air Conditioning - For homes that do not have ducting already in place there have been real advancements in ductless air conditioning units. While you are not typically able to cool an entire home if you have a very open floor plan this allows you to once again keep the noisy parts of the process outside while you cool the area that surrounds the ductless A/C unit.
Portable Air Conditioning- For those on a budget or if you just have a room that refuses to cool as well as the rest of the house a portable unit is an economical option. It will be noisier, allow some warm outside air into the house, and have a more limited cooling area but it will make a significant difference on the temperature of your room.
Evaporation coolers - Also known as "swamp coolers" evaporation coolers pull air through damp pads cooling it as the air evaporates the water that becomes attached to it.
