So called “Phase-Change-Material” (PCM) is able to store temperature through change of their physical condition from solid to liquid without heating-up. If outside temperature drops to a certain limit the stored heat will be emitted again. The storing effect of PCM is comparable to implementing thermal mass like concrete or brick walls in building. In order to enable the effect of phase change a significant difference of maximum daytime and minimum night-time temperature is required. The Chilean climate of the central valley does fit perfectly since the average temperature difference between day- and night-time in Santiago range from 11 (15/4 in July) up to 16 degrees (29/13 in February). The use of PCM in the central part of Chile could be an energy-efficient and economical way of passive cooling of buildings. If special façade elements with PCM will be developed that do allow a direct connection to the inside and outside climate, the storing capacity of PCM could be highly amplified. The night-cooling effect could enhance the “recharging” of the PCM. A prototype of a PCM-based building concept of the author will be introduced illustrating this possible principle.