When studying improvements on room by room air conditioning appliances (RAC), it is necessary to know for how long these appliances function and which is their effectiveness - EER - on average (or Seasonal) known as SEER. A method was developed for Europe, taking into account the cycling losses, the fouling losses and the variations due to outside temperature and humidity. Further to this the load was represented by an equivalent number of hours at full load. Practically a user can just multiply the electric input called in nominal conditions (T1 of testing standard ISO 5151) by a number of hours which integrates the number of operating hours in ideal behaviour and the SEER effects listed previously. The results make it possible to define the total cost (LCC) of appliances and to find rapidly the minimum LCC appliance.