Mechanical Air Conditioners - Part I - Operating Principle

Summary

Mechanical air conditioners form the largest population of AC in this world. This article will go through the simple operating principles of this AC type. Additionally, we'll also go through other AC types used in commercial world. Namely, these are gas absorption, steam based, and thermoelectric units.


By TS Mohamed Rasied

Common ACs, that we see almost everywhere on this globe, is actually, the mechanical type of AC unit. If we were to be very meticulous in the naming structure, we would have called it Mechanical ACs.

However, we just name it as air conditioner, or ACs, and everyone understands it.

One should not confuse the term between, air conditioning, and AC. Air conditioning means altering temperature, humidity, air filtration, movement and mixing. Whilst ACs are the equipment used to alter the temperature and humidity - in one package.

There are four types of air conditioners available for us. The,

  • gas absorption AC,

  • steam based AC,

  • thermoelectric AC, and

  • the mechanical AC

The first three AC types are mainly (if not totally) used in industrial applications. We'll go through the air conditioner operation, briefly, before concentrating on mechanical air conditioners.


Gas absorption AC

Uses, water as its refrigerant. The system uses the principle of vacuum, to encourage boiling of water at very low temperature. The water will be passed through cooling coil, for producing cool air.

Lithium bromide will be used as the absorption (or recovery) medium, once the water has passed through the cooling coil.


Steam based ACs

Is similar to gas absorption units, but it uses the brute power of steam, and venturi, to reduce the pressure of water (which is the refrigerant).

Water at low pressure will boil at low temperature, and becomes a refrigerant.


Thermoelectric AC

This AC uses the principle of thermocouple to attain heating and cooling effects at the same time. The beauty of this system lies in its simplicity of construction.

It uses electrical power, and thermocouple. As the electricity flows through the circuit, you'll get a hot region, and a cold region. Talk about killing two birds with one stone.

However, the major limitation of this concept is that, it can only produce a small cooling or heating effect, compared to other air conditioners.


Mechanical Air Conditioners

It is named mechanical, as it requires the continuous act of refrigerant compression for cooling, or heating effect. This concept was thought by Willis Haviland Carrier, when he created the first mechanical air conditioner.

Special refrigerant are used in order to achieve this. These are known as CFCs (already banned), HCFCs and, HFCs. Why use these? Because of very low boiling temperatures, at ambient pressure.

Details of this air conditioner operation,

  • a compression process is required to raise the pressure of refrigerant. When this happens, you can liquefy the refrigerant (through condensation) easily,

  • this is followed by refrigerant condensation. Condensation happens through heat exchange between refrigerant, and air (or water),

  • an expansion device (or valve) will be placed after the condenser. This is a device to allow for pressure build up from compressor. This is also, the place where refrigerant will evaporate into low pressure region.

    When this happens refrigerant will start to boil at very low temperatures,

  • finally, the refrigerant will be passed through another heat exchanger - to complete the boiling process. Heat exchange happens between air and refrigerant

  • this process repeats at the compression side

Those are the processes involved in achieving cool air, through mechanical air conditioners - through continuous "supply" of refrigerant at low temperatures.

Part II is coming soon...



TS Mohamed Rasied,
Provides information on air conditioners and air conditioning in her site,
http://www.air-conditioner-selection.com/
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