If you are building a new house, or you live in a house or flat without air conditioning and you want the benefits of a cooling system without having to install a central air (ducted) system, there are several options on the market to satisfy your desire for AC that can save you money.
Ductless Split System AC -- A ductless split system AC unit is similar to a window unit, but it can be mounted on a wall or ceiling. The ductless unit is installed with an outdoor condenser and an indoor cooling unit, which makes it impractical for an apartment because of space considerations for the outside condenser. However, split system AC units are perfect for houses, especially if you want to save money on installation. Contractors install wires and cables that connect the indoor unit with the outdoor condenser, and they can run these wires and cables through your floor or inside a wall to disguise their presence. They run quieter than window units or portable units because the condenser is installed outdoors. You can also buy a zone split system AC, which comes with additional indoor units that can be programmed on a different cooling setting so that one room is colder than another room that isn't used as often.
Portable AC -- A portable AC unit, also known as a moveable unit, is a self-contained cooling unit that you can move from one room to another as long as you vent the back of the unit through a window. Portable AC units are ideal if you live in a flat in which you are not allowed to mount a window unit. They are small, upright devices that you can select with a range of BTU power. BTU stands for British Thermal Unit and is the way AC cooling power is measured, with a higher BTU providing you with more cooling power. Portable units feature exhaust holes in the back of the unit that pipe warm air out of a window. You can also buy them with accessories such as a dehumidifier to reduce the amount of humidity in a room on sweltering days.
Window Unit AC -- As the name implies, these AC units are mounted on a window and typically jut out so that the back of the unit is exposed and visible to the outside world. For that reason and for some safety concerns in multi-story apartment buildings, many superintendents do not allow renters on the second floor or higher to install window units, though contractor-installed window units are safe, secure and required to adhere to the Australian Standard for installed cooling devices. Window unit ACs are ideal if you have a smaller space and don't want the cooling system taking away valuable real estate. They have features similar to central AC systems, including a thermostat and a timer. Window units tend to be a bit noisier than portable units, and because they aren't moveable, you have to choose their location carefully to maximise cooling space.