Solar Energy System of the Month:

Sun, Light and Heat: Light Control and Optimizing Energy
in Offices and Other Buildings

Daylight is solar energy. This is a trivial statement but comes lightly to the background when speaking of solar energy use. Photovoltaic modules and solar collectors make the sun's energy usable, but technologies that provide for optimal light efficiency in buildings and that make "living and working with the sun" enjoyable also use solar energy.


Sun installation in the German Museum of Technology in Berlin

Measures taken to save electricity for lighting or conserving energy for heating are activities - a fact that the president of EUROSOLAR, Herman Scheer, does not tire of stressing. And in fact it seems as though the concept of passive solar energy use or of a "passive building" veils everything that is done here: effective daylight use and control as well as energy optimizing are the characteristics of three buildings that we present in cooperation with the BINE Information Service (BINE Informationsdienst).

Sun installation in the German Museum of Technology in Berlin. A fascinating play of light and shadow - but also an intelligent solution for transporting light: Collector mirrors and reflectors project sunlight into a tunnel that one passes through when entering the exhibit hall. Photo: BINE Information Service BINE-logo

The Institute for Solar Technologies (Institut für Solartechnologien) in Frankfurt/Oder, Germany, an office building in Weilheim/Teck and the German Museum of Technology in Berlin are examples of an energy concept in which sunlight and heat play central roles. Daylight technology (systems that control and transport sunlight) and the protection of exhibit pieces against radiation as well as favorable room climate are central for the museum building. That spaces with cozy qualities and considerable energy conservation potential are also possible in buildings that aren't used for dwelling is shown by projects sponsored by the Federal Ministry for Economy and Technology (Bundesministerium für Wirtschaft und Technologie (BMWi)) for the research of "solar building".

High Work Place Quality - Low Costs for Lighting and Heat

Many factors influence how well someone feels at work-therefore also influencing job performance output. Among these are a comfortable temperature, good air quality, and the most natural and glare-free light possible. For the Solar Center in Frankfurt/Oder, an energy-optimized building both was realized that offers: year-round comfortable work conditions and low energy demand. The modularly constructed façade system replaces the outside wall and at the same time guarantees the best possible supply of daylight and fresh air. In effect, this synergy façade combines the function of the building's walls with the tasks of household technology.

Solar Center in Frankfurt/Oder

The windows are equipped with outside blinds over which a rigid daylight control system is installed-artificial light is only activated by a light detector when needed.


Modular façade system on the south side of the Solar Center in Frankfurt/Oder. Photo: BINE Information Service

Integrated in the balustrade area of the façade are thermal air collectors and a photovoltaic system. Behind that is a heating, air-conditioning and ventilating machine with a heat exchanger.

Schematic diagram of the façade with air ventilation

This pence of equipment is connected to the active flow of air via a connection canal between the window's two panes of glass (gap between the conventional pane and the heat-insulating pane). In winter the incoming air is heated over the air collector and then led to the heat exchanger. There, another rise in temperature follows due to the heat energy absorbed from the used air. Afterwards the pre-heated outside air comes to a convection heater in the room.

Schematic diagram of the façade with air ventilation (winter operation). Graphic: BINE Information Service.

This is then simultaneously supplied with fresh air and heated. On sunny days the output from collectors and the heat gain for the room's heating system are both adequate, and the used air is then led outside through the space between the windowpanes. Over the course of a year the photovoltaic system delivers the needed energy for the operation of the ventilation system. The collectors are turned off in the summer via a summer-winter circuit because the warm outside air comes in direct contact with the heat exchanger and there the cooler inside air can cool it. On very hot days cold water from an underground reservoir flows through the heaters, turning the heating system into a cooling system. Soil serves as the cold source.

The concept fulfills the planners' expectations: The thermal heating and ventilation heating demands for the technology area are around 58 kilowatt hours per square meter and year and meet the requirements of the Energy Conservation Act (Energieeinsparverordnung (EnEV)). The energy demand for lighting and office technology was more than halved compared to a conventional building. And those working in the rooms are content: The lighting conditions are experienced as pleasant and adequate, and even during the summer rooms don't become overheated.

Energy Efficiency without Extra Costs: Office Building as a Passive Building with Solar Heat and Solar Electricity

The first passive office building in the German state of Baden-Wuerttemberg has been standing in Weilheim/Teck since the beginning of 2000. Its ecological design concept, the corresponding architecture and the economical aspects are convincing: Despite the difficult requirements for building ecology and the considerable energy conservation, one square meter of office area costs less than 1,000 € (ca. $ 900) - no more than a conventionally constructed building.

Office building "Lamparter"

The building uses the sun's energy both actively and passively. By avoiding transmission and ventilation heat losses the energy demand for heating was reduced to under 15 kilowatt hours per square meter and year-making a conventional heating system as unnecessary as active air conditioning.

Office building "Lamparter" as seen from the west. Photo: BINE Information Service

Passive cooling during the summer is achieved by a variety of methods including shadow elements, ground soil heat exchangers and night ventilation. Elements in place for lighting control minimized the need for artificial lighting, which is at just 7.2 kWh/m² per year. Strict cost controls even made it possible to use funds from the budget to provide for solar heating and solar power systems.

Warm Water and Electricity from the Sun

In the entire building there are no heaters - the job of distributing heat is taken over by the ventilation system. With the help of temperature gauges warm air can be separately led to the top floor, or the north or south side. Used air is vented out from the common areas (conference rooms, stairways) of every floor, led to a heat exchanger and finally vented outside. In this way about 85 % of its heat can be absorbed by incoming air. Additionally, on cold days the outside air's temperature can be raised by an average of 4.6 Kelvin by using an earth-to-air heat exchanger. A connected bivalent condensing boiler provides the remaining needed heat. At 10.6 kWh/m², the actual heating energy demand is even lower than the planned value.

Passive office building "Lamparter": Energy supply system

 

Passive office building "Lamparter": Energy supply system. Graphic: BINE Information Service

Contributing to the electric current supply is a 67 square meter photovoltaic system that is mounted on the flat roof and pent roof of the building. The estimated 6 to 7 megawatt hours (MWh) produced yearly correspond to 6.5 kWh/m² of electricity based on the net heated floor area. By heating potable water, a solar thermal system supports the gas heating system with 1.5 kWh/m² per year, and because the demand for this water is very low at just 2.6 liters per person per day, water heating can be up to 93 % covered by solar means. Outside the main heating period the water heating system runs for just one hour per day. Therefore it is accepted that the water temperature fluctuates. Overall, solar energy provides 20.9 kWh/m² of the needed primary energy with solar-produced electricity covering about half of the energy used for lighting and the ventilation system.

Comparison of primary energy requirements for building technology
Comparison of primary energy requirements for building technology in kilowatt-hours per square meter per year (kWh/m²). Graphic: BINE Information Service

Controlling and Transporting Light - The German Museum of Technology in Berlin

With a usable floor area of 20,000 square meters, the expansion building of the German Museum of Technology is subdivided into departments for air and sea travel as well as accommodations for a library, workshops, a lounge and catering areas. In order to protect exhibit pieces from direct solar radiation, they were placed on the north side. The additional accommodations open towards the south and are characterized by a transparent façade design.

With an energy concept, which meanwhile the museum is presenting in multimedia to bring visitors closer to the rising energy-efficient technology, it was also possible to reach a low energy standard here.

Berlin Institute for Construction, Environment and Solar Research Ltd

The Berlin Institute for Construction, Environment and Solar Research Ltd. (Berliner Institut für Bau, Umwelt und Solarforschung GmbH (IBUS)) and the Fraunhofer Institute for Building Physics (Fraunhofer Institut für Bauphysik) in Stuttgart conducted the project's implementation over many years.

Expansion building of the German Museum of Technology in Berlin, right of the exhibit hall with a hanging C-47 "Skytrain" and sometimes affectionately referred to as the "Gooney Bird". Photo: BINE Information Service

Despite demanding requirements it was still possible to get by without air-conditioning and the high energy needs associated with it. Planners stabilized the inside humidity (important for a museum) through the use of hygroscopic materials (the expanded clay in walls and wood-block paving on floors attract and absorb moisture and therefore dry the air in the museum).

Light and Shadow

The overhead light layout and the implementation of the daylight systems were optimized in detailed studies under an artificial sky. On the east façade, for example, it was effective to develop a daylight system that obtains the attractive city view, yet at the same time is able to fulfill its function of a visor against the sun and additionally has light-controlling qualities. Here the planners installed large lamellas at every story of the building. An inner transparent lamella wing was installed with an outer wing made of perforated metal. Depending on the angle of the lamella the degree of daylight screening can be varied without reducing the illumination.

The floor areas of the museum that are further in and cannot be supplied with daylight by the facades led to the idea of installing a daylight transportation system along the paths that visitors take in the exhibit areas. Using three systems, planners bring sunlight into the building.

Sun-tracking Fresnel lenses collect daylight that is then led all the way to the foyer in the second floor via fluid light tubes. There, four daylight tubes are supplied with sunlight by this transport system.

Light collectors (tracking Fresnel lenses) Light tubes as a transportation system
Left: Light collectors (tracking Fresnel lenses). Right: Light tubes as a transportation system in further-in parts of the museum. Photos: BINE Information Service

A so-called sun installation throws sunlight into a well, which one walks through when entering the exhibit area. This occurs with the use of a mirror system that is composed of a single-axis sun tracking collector mirror (heliostat) and a stationary reflector.

Heliostat The systems fulfill the lighting needs The systems fulfill the lighting needs
Left: Heliostat. Right: The systems fulfill the lighting needs of the further-in interior parts of the building. Photos: BINE Information Service

A concave mirror (heliostat) with a surface area of about 14 square meters together with lighting reflectors supplies the interior of the museum with sunlight. With this modifiable system the various lighting tasks in the exhibit area can be met.

Material and pictures BINE: www.bine.info (project information 7-9/01….in German) / Solarserver editor: Rolf Hug

Further Information in English:

German Museum of Technology Berlin: www.dtmb.de/index_en.html

Further Solar Energy Systems of the Month:

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