An air conditioning system is the most complicated service utility in the building sector, because it enables the complete control of the internal climatic conditions, by means of heating, cooling, wetting and drying the air.

The use of air conditioning has become popular in Europe since the seventies, in sharp contrast to the USA, where it has been widespread since the twenties. One justification for the propagation of air conditioning in Europe is the significant changes in the urban micro-climate, combined with the increase of the prevailing noise level and the atmospheric pollution, which made natural ventilation no longer possible. At the same time thermal comfort demands, on behalf of the users, have risen steadily whilst the initial cost of air conditioning systems has dropped.

There are many different A/C systems available and the choice depends on the function of the building, its architectural lay-out, the heating and cooling demand and of course the financial restrictions.