Green Lighthouse, Denmark's first CO2-neutral building

In Denmark’s capital, the VELUX Group joined forces with engineering, architectural and environmental experts to conduct an innovative experiment in optimising renewable energy. The project aimed to demonstrate that green building concepts need not conflict with architectural and functional values, nor jeopardise a good indoor climate.

An innovative building for the University of Copenhagen

Now one of the best-known buildings in Copenhagen, the Green Lighthouse – Denmark’s first CO₂-neutral building, completed in 2009 – is recognised for its visionary architecture and use of cutting-edge, earth-friendly technology. It is home to meeting facilities, faculty offices and student services for the University of Copenhagen’s Faculty of Science, and was endorsed by the European Commission’s Sustainable Energy Europe Campaign. 

The building’s sculptural construction was inspired by the sundial and the movement of the sun around the building, with the distinctive cylindrical shape reflecting the sun’s dominant role as the main energy provider. As sustainable as it is healthy, the Green Lighthouse makes use of Copenhagen’s efficient district heating system, solar cells, solar heating and cooling, seasonal hot water storage and innovative architectural features to create a visually and conceptually striking environment.

The design reduces energy consumption by 70% via renewable energy, natural ventilation and light – and results in a minimal environmental footprint. Every element was chosen for its energy efficiency and ability to enhance the well being of those working in and visiting the facility. Open, inviting, and spacious, the Green Lighthouse stands out amongst the traditional buildings in the neighbourhood.

Photos: Adam Mørk

Key design elements and achievements

Ample daylight

In the Green Lighthouse, the sun is the primary source of light. Thanks to numerous façade and roof windows, all permanent workplaces have a daylight factor of 3% or more, while corridors have a factor of at least 2%, keeping artificial lighting to a minimum and enhancing energy efficiency. Roof windows deliver high levels of daylight to the second floor lounge area, creating a healthy indoor environment and offering views of the skies.

The roof windows also raise daylight levels on the lower floors via the bright atrium space, resulting in much better daylight distribution over the first floor’s office area. Daylight invites people on the ground floor towards the stairwell and upper floors.

Shading and sun screening also play an essential role in creating an optimal indoor environment. Dynamic sun screening enables users to control their immediate work spaces through external Venetian blinds with variable settings, meaning one can block direct sunlight while allowing daylight to penetrate deep into the building through louvers, which are painted white to optimise the light effect.

Renewable energy

The Green Lighthouse’s main energy source is the sun, with 76 m² of roof solar cells powering the building’s LED lighting, hybrid ventilation and pumps. In fact, the total need for hot water and electricity is covered by solar panels and solar cells. Here, an angled roof plays an active role, serving as a power plant by capturing the sun’s energy via solar panels and solar cells. Efficient windows also contribute to the energy profile, minimising heat loss and maximising passive solar gain.

To generate power and heat, the building relies on 35% solar energy from the roof solar collectors and solar heat that is stored underground via a heat pump, and 65% eco-friendly district heating, with a 30% increase in utilisation due to the heat pump.

The heat pump heats the building in the winter (including via a floor heating system) and cools it in the summer. If the building runs out of solar heat, it can use district heating instead of electricity to power the heat pump. This innovative solution, developed by COWI, a Denmark-based multi-disciplinary engineering and planning firm, further reduces the building’s CO₂ impact.

The Green Lighthouse project marked the first time such an energy experiment was applied in Denmark. In the long term, this energy solution could be used in the construction of office and industrial buildings in most parts of Europe and will undoubtedly be used when planning the energy supply of future CO₂-neutral constructions.

Intelligent materials

The building’s façade is made from Swissfiber, an extremely light and strong composite materials made of 30% glass and 70% polymer. The façade weighs only six tonnes, while a similar solution in tile would have weighed over 175 tonnes and been considerably thicker. Also worth noting are the building’s concrete floors, which help absorb excess heat in warmer months.

Hybrid ventilation for great air quality

In the Green Lighthouse – like in all carbon-neutral homes – natural ventilation is key to achieving a comfortable indoor climate. In colder months, a back-up mechanical ventilation system brings in fresh air from outside. The hybrid ventilation system also allows the building to recover heat for days when weather conditions do not permit natural ventilation.

Most of year, however, the façade windows provide sufficient natural ventilation. During the warm season, automated roof windows in a wide configuration cool the space naturally, with fresh air from the sides of the building moving through the central space before exiting through the roof windows.

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