Important properties of the indoor air quality are temperature and humidity. Very often in new and oldbuildings the temperature is too high or varies too strongly. A suspended ceiling with phase changematerials has a good influence to avoid too high indoor air temperatures. An additional heat exchangerat the outside of the building can increase the efficiency of the system by working in the night andcooling down the phase change material, so that after this cooling the full heat storage capacity isattainable. Further a great heat storage capacity of phase change materials decreases the heatingenergy demand of buildings.