Klima in Museen und historischen Gebäuden

Climate in Museums and Historic Buildings. Correct Heating and Ventilation as demanded by the Conservator The material humidities of a room’s shell and the artifacts within it are in equilibrium with the water vapor content of the surrounding air (Fig. 1) and depend on the material’s local temperature. Among other purposes, heating and climate control serve to maintain material humidity within a tolerable range. It is usual to specify this range indirectly by specifying the relative air humidity and to measure this at any point within the room. With conventional heating systems with air circulation (e.g., radiators, full air conditioning systems), however, this approach has two major disadvantages: The surface temperatures of the outer walls are uneven and lower than those of the partition walls. Since the absolute humidity is the same everywhere in the room, the relative air humidity must be higher at the surfaces of cold outer walls and artifacts near them than it is elsewhere in the room. This phenomenon, known as the “Cold Wall Problem” (Ranacher), results in damages to such surfaces due to moisture absorption, mildew, and increased dust adhesion. Thus, in conventionally heated rooms, only climate measurement near objects of interest is valid. Wall tempering (Fig. 2) avoids these disadvantages because it uniformly heats the inside of the building shell and thus the entire room. Additionally, tempering results in the drying out of building walls and elimination of damaging salt problems. If one combines tempering with an optimized building shell (sealing of joints and openings, external shades) and controlled ventilation (necessary for supplying fresh air in museums with a larger numbers of visitors), a sustainable climate control system is achieved with physiological and conservational advantages over conventional methods, and with clearly lower capital, maintenance, and operating costs.