Following calculations of potential energy savings, several types of earth-air heat exchangers have been coupled to buildings in novel concepts for passive heating and cooling of ventilation air. For the first time this technology was used in the Belgian climate. In a first case one short plastic tube is coupled to the HVAC system of an office building, to preheat/precool the fresh ventilation air. Measurements are presented on this system and it is shown that performance could have been improved by more concern during the design stage. A second case involves four large concrete tubes coupled to the basement of an exhibition space. The low velocity hybrid ventilation system relies solely on control of pulsion and extraction grids and mechanical extraction in sanitary rooms. In winter, ventilation air is only preheated by the earth-air heat exchanger. A last case study discusses the dimensioning and the construction of a prefabricated PE tube system for air intake. Simulations and measurements show the importance of correct sizing and taking into account the conditions of the soil. Two calculation models are compared: one with CAPSOL, the other one developed at the Ghent University. It can be noticed that, for the Belgian climate, air can sufficiently be controlled by an earth-air heat exchanger and preheating equipment in ventilation systems can be avoided.