Typical operation of some of the ventilation strategies is depicted here for a building with heavy thermal mass and high insulation, subject to 20 W/m2 internal gains, in urban situation and for a normal summer of type 2004 (fig. 3). Analysis is given in terms of overheating duration (number of hours of occupation above 26.5°C), which should not exceed 100 h according to Swiss comfort regulation [6]:

• Limited to diurnal occupation, mere base ventilation (Base) yields a building response way above ambient. Overheating extends over more than 1000 h, of which 500 h above 30°C.

• With a twice more important airflow, limited to the fresh hours, direct night cooling (Direct) considerably reduces the diurnal building temperature. Overheating now reduces to 240 h, with a summer peak slightly below 30°C.

• By dampening of he day/night oscillation, buried pipes of 20 m length used in single-mode (Pipe20m-Sgl) allow for continuous over-ventilation of the building, whereas the 12 h phase — shifting device (Shift12h-Sgl) moves night ventilation onto the day period. Overheating now extends over 200 h, respectively 180 h, with a summer peak slightly below 29°C.

• Not depicted here, setup of these systems with alternative direct night cooling allows to reduce overheating below the 100 h limit.

• The strongest cooling potential however goes for evaporative cooling. Except for base ventilation, all the configurations with increased flow (direct ventilation, buried pipes, phase — shifting, in single or alternate mode) allow to remain below the 26.5°C threshold, hence largely respecting the Swiss comfort regulation.