The objective of this article is to develop and test a simplified method to compute the savings in building cooling demand by use of passive cooling systems based on ventilation (direct night ventilation, air-soil heat exchangers, controlled thermal phaseshifting, evaporative cooling, as well as possible combinations thereof). The systems are characterized in terms of a climatic cooling potential, independently of any building, which is then compared to the cooling load of a particular building. The method is tested against an extensive numerical simulation campaign, combining diverse passive cooling systems and sizes with diverse constructive and operational modes for an administrative building situated in Geneva. The key point of the simplified method is to choose an appropriate time resolution, for taking into account the building thermal inertia. Although best results are obtained with a daily resolution, good results are also obtained with monthly data, where an overestimation of the passive cooling fraction remains less than 20% in half of the cases. This opens way for using the method for first assessing the potential of these passive cooling techniques on a large spatiotemporal scale, for which integrated building and system simulation becomes prohibitive.