These regulations stress the necessity of light control in museums, concerning daylight as well as artificial light.
For the orientation of visitors a general room illumination is needed, which can be object lighting simultaneously. Daylight openings should allow the visitors a view to the outside.
Daylighting is applied in many museums, as it is characterized by good colour reproduction, natural lighting conditions, contin- uous spectral distribution, and energy efficiency. Although integral part of the architectural design lighting experts should be consulted. For illumination purposes skylights are more efficient than vertical windows. Transmission of direct sunlight must be avoided because of glare. For cooling situations solar heat gains must be minimized. This can be done
by fixed or movable shading devices. Solar control glass without additional shading or light diffusion cannot be used, as glare is bound to occur. Movable shading devices, e.g. lamellas, havea high adaptabilityand allowfor an accurate daylight control and, may be, for thermal control as well as total light black-out. Fig. 9 shows the annual illumination of an exhibition room with a skylight and fixed shading devices,which is designed to guarantee a maximum illumination of 400 luxunder maximum external illumination. For poor daylight condi-tions inwinter and under covered sky the room illumination is very poor and (power consuming) artificial light has to be switched on.
A movable shading device with variable light transmission, as shown in Fig. 10, can offer controlled daylighting for a significantlonger time of the year. Fig. 10 shows an example of a skylight constructionwith light control (positions from top down): External glazing (ventilated), movable solar and glare control (lamellas),highly insulated glazing, conditioned air gap, artificial lighting, light diffusing ceiling.
Fig. 11. Light diffusing ceiling for daylighting from glazed faced facade and artificial lighting from clear storey. Kunshaus Bregenz, A., Architect: Peter Zumthor.
As shown in Fig.10 daylight and artificial light systems are often integrated the same building elements, e.g. skylights. A good example is the Kunsthaus (art house) in Bregenz with a suspended light diffusing ceiling and a clear storey above, distributing daylight from the glazed facades and artificial light sources (Fig. 11).
Artificial light will vary a lot depending on the kind of museum room and exhibit, and accordingly the energy consumption will. The installed capacity can range from 10 W/m2(general room illumination) to 100 W/m2. The annual electricity consumption will be influenced strongly by the daylight facilities and the automatic control of artificial light (dimming and switching). 3. Conclusions
Museum buildings can be highly energy efficient although the performance requirements for comfort and object conservation are ambitious. Advanced passive and active means of temperature and light control were developed, which are predestined for utilization of geothermal energy and daylight. Energy consumption can be reduced to less than one tenth compared to traditional museum buildings with standard air conditioning. Comfort and conservation of exhibits are improved and lifecycle economy is given. To achieve this result forenergyefficient museum buildings, an integral design process of architects, engineers and experts and the application of
simulation tools are necessary. References
[1] Von Naredi-Rainer P, editor. Entwurfsatlas Museumsbau. Basel, Berlin, Boston:
Birkh?user e Verlag für Architektur; 2004. [2] www.Kolumba.de. [3] www.esmh.de.
[4] Müller HFO, Schmitz H-J. Lighting design for museums. In: Von Naredi-Rainer P,editor. Entwurfsatlas Museumsbau. Basel, Berlin, Boston: Birkh?user e Verlag für Architektur; 2004.