Energy Efficient Museum Buildings

Transcription

1 Energy Efficient Museum Buildings Helmut F.O. Mueller 1 * 1 Department of Environmental Architecture, Faculty of Building Sciences, Technische Universität (TU) Dortmund, Dortmund, Germany, Green Building R&D, 4greenarchitecture, Duesseldorf, Germany * Corresponding author: helmut.mueller@tu-dortmund.de Abstract Museum buildings perform ambitious demands for sound conditions of exhibits and comfort of visitors. There is a narrow allowance for room temperature and relative humidity, which has to be maintained for varying situations of weather and occupancy. Lighting has to assure an excellent visual performance but to avoid deterioration of exhibits. Energy consumption can be kept extremely low contrariwise. Several high quality and low energy museum buildings could be realised recently by utilisation of energy efficient measures and renewable energies. Outstanding pieces of architecture, e.g. Kolumba Art Museum, Cologne (architect P. Zumthor), Emil-Schumacher-Museum, Hagen (architect M. Lindemann), are presented and integrated advanced technologies like thermal active room surfaces, low air change ventilation, geothermal heating and cooling, and controlled daylighting are explained. Keywords: Museum buildings, energy efficiency, conservation of exhibits, comfort, thermal conditioning, lighting 1. Introduction There is a basic conflict between conservation and exposure of exhibits for museums. On the one hand minimal fluctuations of room temperature (21 C +/ 3 C), relative humidity (55 % +/ 5%), and air flow throughout the year as well as low irradiation of light and ultraviolet radiation are required in order to reduce ageing of samples to a minimum. On the other hand visitors and staff demand excellent thermal comfort, air quality, room illumination, and visual perception of objects. The erection and operation of museum buildings with such high performance standards nowadays has to be energy efficient with a minimum output of green house gases over the life cycle. This means a low embodied energy in the building materials and construction, a low energy demand for heating, cooling, ventilation and lighting as well as a utilization of renewable instead of fossil energies. Last not least economical conditions have to be fulfilled. While building investments often tend to be increased by measures of energy efficiency, the operation costs for energy and maintenance will be reduced. Overall life cycle costs must clearly account for sustainability. This ambitious and complex task of high quality as well as ecologically and economically sustainable museum buildings can only be realized by a comprehensive design approach of architects, engineers and experts utilizing the latest knowledge about passive and active means of architecture and technology. This challenge has created new principles of design, which differ a lot from the traditional and fully air conditioned museum building, as advanced examples show [1]. 2. Principles of energy efficient museum buildings 2.1 Thermal control The narrow bands of room temperature and relative humidity are traditionally aimed at by complete air conditioning with heating, cooling, dehumidification, humidification of air and varying air change rates for exhibition rooms. The ideal climate supposed to be created by these means provokes some doubts: The ac plants, which have to adjust by measurement and control technology to the ever- Please put the session title here, e.g. LEA: Low Energy Architecture 1

2 changing influences of number and local concentration of visitors as well external climate factors, cannot warrant stable climate condition in spite of their technical and financial input. The large volumes of heated and cooled air, which have to be transported under peak loads (2 to 3 and up to 6 air changes per hour), make it difficult to avoid negative effects of draft and raised dust. For the case of failure redundant back-up systems have to be installed or exhibits have to be removed. The energy efficiency of completely air conditioned museums can be improved by passive means like geometry, thermal insulation, thermal capacity of room surfaces, orientation and solar control of windows as well as by advanced systems and components, but the new principles of climate control, which are shown in table 1, allow for higher efficiency and performance: Table 1 Disturbances and means of climate control of museum buildings Disturbances of Climate Factor Effect Means of Stabilization/Control Passive Active Ambient temperature Heat transmittance Thermal Capacity Surface Temperature Control Wind Infiltration Airtight Joints, Air Locks Solar Radiation Heat Gain Solar Control (glass, shading device) Lighting Heat Gain Visitors Heat and Humidity Gain Sorption Surface Temperature Control Ventilation + Surface Temperature Control Ventilation Thermal capacity of indoor room surfaces in combination with chilled / heated ceilings, floors and walls are the basic principals of a stable climate control. The room surfaces maintain the required temperature for exhibits by embedded water pipes (fig. 1and 2). Thus all conventional heat or cold distributers like radiators or convectors can be omitted with regard to conservatory reasons. The materials used are concrete (ceilings, walls), screed (floors), plaster with cement, lime, gypsum or clay binder (ceilings, walls) or masonry (walls). Clay plaster has a relatively high sorption rate, which allows for storing excess humidity (e.g. for times of high visitor frequency). Components of the building envelope are characterized by air tightness and thermal insulation in addition to the described surface temperature control. The ventilation system can be reduced in comparison to complete air conditioning, as air change rates are mainly based on loads of occupants and lighting. The design of advanced ventilation and surface control systems requires dynamical simulations of the thermal behaviour and the air flow (fig.3 and 4). 1 2 Figure 1 and 2 Kolumba Art Museum in Cologne, D. Architect: Peter Zumthor, Energy concept: Kahlert Eng. and 4greenarchitecture. [2]. Exhibition room with surface temperature control of ceilings, floors and walls (1). Water pipes for heating and cooling embedded in building components (2). Please put the session title here, e.g. LEA: Low Energy Architecture 2

3 3 4 Figure 3 and 4 CFD simulations for distribution of air temperature (3) and air velocity (4) in exhibition rooms. Kolumba Art Museum in Cologne, D. [2]. Geothermal energy is predestined for heating (in combination with a heat pump) and cooling (free cooling) of room surfaces in Middle Europe. Boreholes of a depth until 100 m with heat exchangers are used for the basic loads of water systems. Horizontal earth air heat exchangers are applied for preheating / -cooling of fresh air (fig. 5 to 7). 5 6 Figure 5 and 6 Geothermal heating and cooling of Emil-Schumacher-Museum, Hagen, D. Architect: M. Lindemann. Energy concept: Kahlert Eng. and 4greenarchitecture [3]. Earth tube with heat exchangers (5). Vertical section of building with earth tubes and heat pump for surface temperature control (6). wa rm e Aussenluft Figure 7 Geothermal pre-cooling of air by earth ducts. Emil-Schumacher-Museum, Hagen, D. Please put the session title here, e.g. LEA: Low Energy Architecture 3

4 Three examples of out a larger number of museums using these principles (compare ) are shown here, Kolumba Art Museum in Cologne and Emil-Schumacher-Museum in Hagen (ESMH), and Kunsthaus Bregenz. A comparison of energy consumption with traditional buildings could be demonstrated in Hagen, where the existing Osthaus-Museum (OMH) is located directly beside the new Emil-Schumacher-Museum, which was opened Fig. 8 shows, that the annual energy costs of the ESMH could be reduced to /m²a by means of energy efficiency and to 2.71 /m²a in addition by renewable energies in comparison to /m²a of the OHM. In terms of energy the classification of consumers and renewable sources is given in table 2. Osthaus-Museum ESMH without ESMH with renewable energy renewable energy Figure 8 Comparison of annual energy costs [ /(m²a)] for Osthaus-Museum (OMH) and Emil-Schumacher-Museum (ESMH) Table 2 Annual energy demand of consumers and renewable energies for Emil-Schumacher-Museum (gross floor area 2,600 m²) Energy Demand [kwh/a] Renewable Energies [kwh/a] Lighting 38,000 Photovoltaics 30,000 Heating 104,000 Geothermal heating + cooling Cooling 104, ,000 Ventilation 58,000 Earth air heat exchangers 9, Light control There are three tasks for the lighting in museums, visibility of objects, conservation of objects, and illumination of rooms, which can be realized by daylight and/or artificial light. A good visibility of objects needs a minimum brightness, good contrasts without cast shadows, good colour reproduction, and avoidance of glare. Depending on the kind of objects, e.g. two-dimensional pictures with micro structures on the surface, three dimensional sculptures or large exhibits like building monuments, the object lighting will differ a lot, especially as the replacement of exhibitions requires a certain variety. For a true colour reproduction of artwork it is highly important whether daylight or artificial light sources are used and which colour rendering is applied on the room surfaces. Please put the session title here, e.g. LEA: Low Energy Architecture 4

5 The conservation of objects often is in contradiction to good visibility, which increases with the brightness. The energy of absorbed light damages the object. The shorter the wavelength the higher the destructive energy of radiation is, thus UV or blue light has a higher damage factor than green or red. This means that a dark (absorbing) surface will be damaged more than a light one, and a red surface more than a blue one. In addition the sensitivity highly depends on the kind of material, e.g. paper is more sensitive than metal. Finally the ageing of a material is influenced by the time of illumination. Because of these reasons maximum values for the energetic exposure to light are defined. As 50 lux is the lowest value for good visibility, this illumination often is defined as maximum value for sensitive objects of paper or fabric, while 150 lux are defined for paintings on canvas. This regulation is vulnerable from the scientific point of view, as it does not consider the spectral component and the time of illumination. Therefore many museums try to define the conservation of objects by [4]: - Definition of varying maximum illumination depending on light source - Limitation of maximum duration of exhibition - Absolute protection against UV and blacking-out before/after visiting hours - Individual classification of artwork in light sensitivity categories. 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, continuous 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 minimised. 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, have a high adaptability and allow for 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 lux under maximum external illumination. For poor daylight conditions in winter and under covered sky the room illumination is very poor and (power consuming) artificial light has to be switched on Beleuchtungsstärke Raummitte Außenbeleuchtungsstärke Figure 9 Annual distribution of horizontal outside (light blue) and inside illumination (dark blue), calculated for a room with skylight and fixed shading device for all solar positions Figure 10 Skylight with movable shading devices (Emil-Schumacher-Museum in Hagen) Please put the session title here, e.g. LEA: Low Energy Architecture 5

6 A movable shading device with variable light transmission, as shown in fig. 10, can offer controlled daylighting for a significant longer time of the year. Fig. 10 shows an example of a skylight construction with 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. 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). Figure 11 Light diffusing ceiling for daylighting from glazed faced facade and artificial lighting from clear storey. Kunshaus Bregenz, A., Architect: Peter Zumthor. 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 for energy efficient museum buildings, an integral design process of architects, engineers and experts and the application of simulation tools are necessary. 5. References [1] P. Von Naredi-Rainer (ed.) (2004) Entwurfsatlas Museumsbau, Birkhäuser Verlag für Architektur, Basel, Berlin, Boston. [2] [3] [4] H.F.O. Müller, H.-J. Schmitz (2004) Lighting Design for Museums, P. Von Naredi-Rainer (ed.) Entwurfsatlas Museumsbau, Birkhäuser Verlag für Architektur, Basel, Berlin, Boston. Please put the session title here, e.g. LEA: Low Energy Architecture 6