The article compares decentralized air conditioning systems for individual rooms. Particular interest is taken in decentralized individual air conditioning units with blower convectors. These systems have a marked advantage especially if rooms are used for different purposes. Energy is supplied at low cost by circulating water. If rooms or parts of a building are not used at a given moment, the systems can be shut off in order to minimize costs. Ambient air can be pretreated and supplied to the blower convector via a primary air processing unit; alternatively, primary air can be taken in by the blower convector directly through the outer wall. The second alternative provides partial air conditioning at very low cost.