Free cooling techniques are usefully used in buildings where internal heat gain is high enough to need cooling also when outside air temperature is lower than the set inside air temperature. They are all founded on the possibility of varying the outside air flow treated by the Air Handling Unit (AHU), from the minimum (ventilation air flow Gvent) to the whole inlet air flow GI. This can surely be achieved in Variable Air Volume (VAV) HVAC plants (where the cooling load is faced by a fixed inlet air temperature, varying the air flow), but in Constant Air Volume (CAV) plants as well (where the cooling load is faced by a fixed air flow, varying the inlet air temperature). These characteristics allow to realize economizer cycles (outside air flow is controlled to reduce the building cooling load). Wet bulb economizer cycles use evaporative cooling potentials, whereas dry bulb economizer cycles do not. The former (worth of a special attention because they allow to obtain greater energetic savings against a more critical control logic) can be classified into Direct Evaporative Cooling (DEC) techniques and Indirect Evaporative Cooling (IEC) techniques. The possible energy savings using such techniques are here evaluated in four different European typical climates. The analysis is based on hourly meteorological data (Typical Meteorological Year), evaluating each technique from the point of view both of energy and money savings.