Air conditioning series – part 1

Air conditioning series – part 1

24 Nov 2023

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This informal CPD article, ‘Air conditioning series – part 1', was provided by Institute of Refrigeration (IOR), who exists to promote the advancement of refrigeration in all its applications in relation both to the perfection of its methods and to the extension of its services to the community.

This series of articles covers the fundamental principles of comfort and close control air conditioning, applications, design, equipment, components and systems and is intended for experienced personnel as well as newcomers to our industry.

What Is Air Conditioning?

Full air conditioning implies the control of temperature and humidity levels within a conditioned space. Control of pressure is occasionally required for special applications. Air conditioning equipment will always include the ability to reduce the temperature and humidity level of the air being processed. Most equipment will offer the option of heating to raise air temperature and more specialised equipment has an optional humidification facility to raise air humidity levels. Air conditioning also includes the control of motion of the air and the regulation of purity levels.

The above can be summarised as follows:


Air temperature is controlled by the removal (cooling) or addition (heating) of sensible heat energy. 


Air humidity level is determined by the moisture content. Air humidity is controlled by the removal (dehumidification) or addition (humidification) of latent heat energy. 


Air purity is a measure of cleanliness or air quality and is controlled by filtration and/or ventilation. Ventilation is the controlled introduction of outside (ambient) fresh air into the conditioned space to dilute the concentration level of contaminants. 


Motion or air movement covers the distribution and velocity of air introduced to the condition space. This is controlled by the air conditioning unit(s) or an air distribution system (ductwork and grilles). 


Sound or noise control may be required to attenuate (reduce) the noise generated by the air-conditioning equipment and distribution system.

Air conditioning is normally applied to maintain the comfort and working efficiency of people or to manufacturing, industrial and scientific processes. The combination of the elements above has generated the term HVAC but an air conditioning system need not include all these elements.

For thousands of years mankind relied upon fires for heating and cool water for relief in high temperatures. The Romans conceived an effective form of radiant heating in certain buildings by circulating heated air through hollow walls and floors. In the warmer climates of the Middle and Far East, wet mats suspended in open doorways provided evaporative cooling. The incredible Leonardo da Vinci designed and built an enormous evaporative cooler in the fifteenth century. This machine consisted of a large drum rotated by waterpower (or by slaves when available!) which drew in air and supplied this to the conditioned space after washing and cooling the air inside the drum.

Only within the last hundred years has air conditioning become established and during this time the technology has developed to very advanced levels. Air conditioning is now a major industry throughout the world worth billions of pounds annually.

Human Comfort

The objective of all comfort air conditioning installations and systems is to ensure the comfort of individuals in the conditioned zone and this is achieved by control of temperature and percentage saturation levels within prescribed limits. Following studies by American National Standards Institute (ANSI) and American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), which measured the effects of temperature, humidity (percentage saturation), air motion and clothing on human comfort, the ANSI/ASHRAE Standard 55-1981 was developed.

Whilst internal design conditions must be based on the comfort requirements of the occupants, the energy consumption, equipment costs and other factors need to be considered. These factors will be covered later in the series. Air Conditioning Technology Part 2 will provide basic definitions and principles of key terms.

We hope this article was helpful. For more information from Institute of Refrigeration, please visit their CPD Member Directory page. Alternatively, you can go to the CPD Industry Hubs for more articles, courses and events relevant to your Continuing Professional Development requirements.

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Institute of Refrigeration

Institute of Refrigeration

For more information from Institute of Refrigeration, please visit their CPD Member Directory page. Alternatively please visit the CPD Industry Hubs for more CPD articles, courses and events relevant to your Continuing Professional Development requirements.

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