What is the difference between split air conditioner, central air conditioning and window air conditioner?

Split AC

It consists of two main parts – the indoor and the outdoor unit. Outdoor is placed/ installed near or on the wall outside of the room that is to be cooled. Outdoor unit consists of the compressor, condenser, and the expansion valve. Indoor units consist of the evaporator or cooling coil and the cooling fan. It does not need major installation as it does not require duct work. Instead the indoor and outdoor units relate to a set of electrical wires and tubing. This adds to the aesthetics of the room.

Advantages –

· In this you can opt for a multi-split system to include more than one indoor unit connected to a single outdoor unit.

· It is easy to install and maintain, even for longer period.

· It is cost-effective and simple to operate.

· They are available in attractive designs

Popular brands of split air conditioner available in the market include Hitachi, Godrej, LG, Whirlpool, Voltas ,... Etc. 

WINDOW AC

Window air conditioning units are made to fit right inside a window and will usually cool one to two rooms. These units save both energy and money. Due to the ease of installation, these units only require a few minutes to set up. You can find them available for single or double-hung window styles, as well as for other types of windows.

Through the wall units are similar to window units, except that they are placed within a precut space within a wall. Also like window units, these are perfect for cooling down one to two room's worth of space. Because of their placement, they do require a little bit more work for installation purposes than a window unit. You will have to cut a hole in one of your exterior walls, use a sleeve, and insert the wall unit. 

Central AC

Compressor condenser outside, far away from the room to be cooled.

Imagine there's just one BIG outdoor unit (like in split AC but of much larger capacity) with multiple ducts (outlet openings) which are connected to multiple indoor units. These indoor units can be of different types. See above few pictures of different indoor units which you see in offices and CCDs or multiplexes.

                         Is central air conditioning more efficient than window units?. 

central air conditioning is overall more efficient than a window unit. The main benefits are a more efficient fan, a more efficient chiller compressor, and more advanced energy-saving features. You really shouldn't have more than 10% duct losses in a typical office building.

There are also several different kinds of central air conditioning. Full fresh air AC is not very efficient, however when used as a displacement ventilation system with economisers it can be extremely efficient. Then you have fan coils or chilled beams, where a small amount of unconditioned air is supplied to a room equipped to a fan coil or chilled beam which uses chilled water to deliver cooling, and the air is either passively or actively moved around in the room, that also can be really efficient.

You also have mixed-mode AC where the chiller is only used in peak cooling cases, otherwise people are free to open windows to passively cool down rooms. Finally you also have night ventilation, where you use the cool night air to completely chill down the building and rely on the structure's thermal inertia to maintain that temperature well into the day.

None of these energy-saving features are possible with window units.

Please comment for more doubts. 

Thanks.