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| Photos: Adam Mørk |
Brian Edwards visits the Green Lighthouse at the University of Copenhagen, a demonstration project that sets a new benchmark for energy-efficient buildings in Denmark.
With its claim to be the first carbon neutral public building in Denmark, the Green Lighthouse at the University of Copenhagen pushes at the frontiers of energy-efficient architecture. Using a mixture of super-insulation, thermal solar collectors, hybrid ventilation with heat recovery, geothermal heat storage, phase-change materials, photovoltaic cells and district heating, the building is of interest in the way it integrates various old and new technologies. Parts function like a rechargeable battery, others breathe like a lung, yet the whole operates smoothly as a light and airy science faculty centre for Denmark’s premier university.
The cylindrical shape and sloping roof betrays much of the strategic thinking behind the design by the relatively young practice of Christensen & Co Arkitekter. The sun is a key force in driving the building’s technologies and in providing bright teaching and seminar rooms. The levels of daylight and insulation are automatically controlled using solar powered thermal venetian blinds with windows prioritised towards the south. Ventilation is mainly natural through a generous atrium with electrically operated perimeter and roof windows. Since the diameter of the building is only 22 metres, the relationship between perimeter and core is lively. Hence the meeting and cafe spaces inside are animated by the environmental and climatic discourses taking place.
Particular attention is paid to U values, which are 0.095 in the outer walls, 0.084 in the roof and 0.085 in the floor slab. Wall windows have a U-value of 0.93 (0.72 for the pane) and the angled roof windows 1.1 and 0.6 respectively. The g-value (solar gain) of the Velfac windows is 0.5 making the annual balance between heat loss and solar gain roughly equal
About 35 per cent of the thermal demand of the Green Lighthouse is met by solar energy with the remainder satisfied by district heating which itself uses 35 per cent renewable energy (mainly waste and wind). The heat pump increases the utilisation of the district heating by 30 per cent. The 74 square metres of photovoltaic solar cells cover, in a typical year, the base demand for lighting, ventilation and pumps.
The large south-facing roof is angled at 15 degrees. This provides good conditions for solar heat gain, night-time cooling, generation of electricity, and penetration of daylight. The latter is deflected deep into the building using broad light-reflecting window surrounds. From above, the building has an active roof which is arguably of more interest than the restrained curved facades. These are formed from varied shades of green glass panels which have a matt or gloss finish and windows with integral external sun screening blinds. Both the roof and the walls change their appearance according to climatic conditions, lending the building a dynamic character. But as much of the technology is within the thickness of the walls, on the roof and underground, the Green Lighthouse carries its sustainability with a light touch.
One notable innovation consists of seasonal storage of heat below the building. Solar panels allow summer heat to be pumped deep underground (using PV electricity) with the stored heat trapped in water for ground slab heating in the winter. As such the floor slabs act as the only radiators in the building and, by using heat pumps and ground water thermal storage, the total heating demand is about 25 per cent that of a typical faculty building in Denmark.
Taking the total primary energy load at 30kWh/m2/year, the building can generate 27kWh/m2/year, resulting in a building which under ideal conditions only requires 3kWh/m2/year to run. Since much depends upon user behaviour, the Green Lighthouse contains display screens which record at any particular time the level of energy and other resource use. As such the building is itself a teaching tool, raising awareness of the interactions between science and environmental design for students, faculty staff and visitors.
One role of university buildings is to test new technologies and to present a vision for the future for the students who will be tomorrow’s decision-makers. Built by the Danish University and Property Agency (Denmark’s largest public building owner) in collaboration with the University of Copenhagen, Municipality of Copenhagen, Velux and Velfac, the Green Lighthouse has significance beyond national boundaries. Although Velux window and Velfac facade systems and solar technologies are widely used in the building, this is more than a showhouse. To create a carbon neutral building on this scale requires considerable design and engineering expertise, innovation in materials and their assembly, and a client willing to take risk. It is reassuring to note that the performance of the building will be monitored so that others can learn from the experience.
Brian Edwards is a professor in the architecture school at the Royal Danish Academy of Fine Arts in Copenhagen. He is author of a number of books on sustainable design, and corresponding member of the RIBA Sustainable Futures Group.
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