Controlled ventilation of historic buildings: Assessment of impact on the indoor environment via hygrothermal building simulation

Historic buildings, when they are unheated, often face problems of summer condensation. After the cold seasonwarm, humid air enters the building and condenses on the walls, a problem that can occur during the entire warm season. This leads to moisture related problems such as mould or algae growth on building surfaces. High humidity can also damage works of art inside the building. One possibility to lower the level of relative humidity is to ventilate the building every time when the dewpoint outdoors is lower than indoors. On the other hand, the resulting humidity fluctuations may also cause damages on works of art and bringing in cold air will further lower the temperatures of the whole building and its walls thus being counter productive to the drying process. An automatic system for ventilating historic, unheated buildings is assessed using building simulation software (WUFI Plus) on two case studies, the St. Margaretha church in Roggersdorf, near Holzkirchen, Germany and the Gatehall of Lorsch, Germany.