To evaluate the impact of the natural ventilation of the air cavity in the prototype of the glazing system being studied in the frame of the project SOLVENT, funded in part by the Commission of the European Union, a prototype of a reversible naturally ventilated glazing system. The system consists of a double (clear and tinted) glazing. In the summer position the tinted glazing is in the outer position and the cavity is open to the outside air at both top and bottom extremes. The heat gains are reduced by the fact that the air flowing cools the inner glazing and the reduced transmissivity of the tinted glass. In the winter position the system is reversed making the tinted glass in the inner position. So when the radiation impinges the glazing it heats the tinted pane which is now open to the inside air making the air movement to increase the heat gains of the system.