The basic rules that have to be followed when designing an A/C system deal with the following parameters:

a) The desired internal climatic conditions have to be achieved under any external climatic conditions. The designer has therefore to consider, apart from the heat losses and gains through the building's shell, the latent and the internal thermal loads

b) The minimum required air exchange rate has to be established, in order to maintain a good air quality.

c) Noise from the A/C system has to be kept at a minimum level, particular in air-air systems.

d) The cleanness of the re-circulated air has to be maintained by using the appropriate filters.

e) The system has to respond in reasonable time to changes of the weather.

f) Energy losses have to be minimised.

g) The initial construction cost and the operational expenses have to be kept at the lowest possible level.