The central AC unit is a cooling machine big enough to provide the cooling to the whole building. It is installed at one side of the building or roof of the building and cool air is supplied through ducting. Vents are created in several places in the building to supply the cool air to them.

Central AC units are complex and very high energy consuming machines as they have to provide cooling to a significantly larger area than the split A/C units. They are mostly used commercially or in a very large-scale use. Once they are installed there is no need of any split units which cause more separate maintenance and electricity supply chain, while a central A/C alone can take the workload of 4-20 or even more split A/Cs depending on its sizes.

They come in many sizes, most common are mentioned below.

Central AC Unit Common Sizes

  • 5TR
  • 7.5TR
  • 10TR
  • 15TR
  • 25TR

The Central system works as a system rather than a single unit, it contains many units other than the AC unit which works together as a system. To keep things simple and understandable we have divided the central AC unit into these sub-components:

  • Air cooler (Condenser/compressor/two stage evaporative cooler).
  • Air Handling unit.
  • Fan coils.
  • Ducting
  • Insulation Material.
  • Blowers.

All of them if work properly can give the best results. It is also not necessary that a system contains all of them at a time. Some of the components are replacements to each other according to the need environments.

Air Cooler

The air cooler is a unit which takes warm air as input and provides cool air as output. Nowadays there are several different technologies available to perform this job, like (condenser/compressor/Two-stage evaporative cooler). Condenser/compressor are the same things in working but Two-stage evaporative cooling is a new technology and is in its development phase to achieve the efficiency in any type of environment. it is working very effectively in some environments and its research work is moving fast, in the middle-east a few companies are very keen on improving the efficiency of this product most considerable among them is “Windmason“.

They are supplying their product with the name “Supercool”, which saves 80% energy providing temperature less than 17 °C which is a considerable achievement.

Air Handling Unit

The air handling unit also is known as the Terminal unit as the name shows, is a machine which handles air flow, it contains air filter, air blower, dust filter etc. It is a big machine which blows cool air in and sucks warm air out. Big size air handling units may have heating or cooling coils inside them. Some of them are fitted with vibration insulation.

Fan Coils

Fan coil is the very simple device which is used in HVAC systems, which contains heat exchanger for heating or cooling purposes. These could be free-standing and some could be mounted on the ceiling or placed on stands outside the building.


Ducting is usually referred to as a steel squared piping which works as a channel for the supply of cool air to the different events in the building. Ducking helps to distribute air in different areas of desire and its events have on/off capability in case if a vent needs to be closed for a reason. Its vents also have grills to direct the air I different directions as needed.

Insulation Material

The insulation material is used mostly to cover ducts which are outside the building to prevent the cool supply air from temperature rise. The ducts outside the building are exposed to direct sunlight and hot air and inside the building, the duct may heat up due to the heat sources inside the building like Burner. To prevent this heat up which causes cooling loss, ducts are insulated with insulation material. It may be in the form of foam or Powder or spray or just aluminum foils. This increases the efficiency of the Central AC unit.


The last but not the least part of the Central AC unit is the blower. Blowers are used to increasing the air throw in the building. As the ducts become longer and bend come in the way, the air throw speed decreases which are again increased by the blowers. Usually, AHUs and Fan Coils also contain blowers to throw the cool air gently into the building.

These are the components which make up a system of Central Air Conditioners. One system may contain some of the units and some may use other units, it all depends on the configuration of the system.