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Green Lighthouse: Denmark’s first public carbon-neutral building

A Subliniat Caz September 2015
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​Green Lighthouse is Denmark’s first public carbon-neutral building. The building has been built in less than a year in a close public/private partnership.
It is a round, sculptural building with high ceilings and an open, spacious floorplan. It is designed in a way that reduces energy consumption by 70% utilising renewable energy, natural ventilation and light – and with a highly efficient climate envelope.

The sun is the building’s main energy source, providing passive solar gain, hot water and electricity. Efficient windows minimise the heat loss while maximising passive solar gain. Green Lighthouse’s angled roof plays an active role in the building’s energy profile. It acts as a power plant, capturing the sun’s energy using both solar panels and solar cells.

As sustainable as it is healthy, the two-storey public building relies on district heating, solar cells, solar heating and cooling, seasonal storage and innovative architecture to create a gorgeous, CO2-neutral building.


Main energy efficiency features

Daylight design: From an architectural point of view, the design is inspired by the sundial and movement of the sun around the building. The house is circular and has an internal core, which simultaneously holds the central staircase, provides ventilation through the natural stack effect and draws a lot of daylight down through the house from the roof windows. The integration of this daylight with building components and materials is the main reason for the very low energy consumption obtained in this building.

Energy concept: The purpose of the Green Lighthouse energy concept was to make the building CO2-neutral. Green Lighthouse is a completely new experiment, with energy supply being a combination of district heating, solar cells, solar heating and cooling, and seasonal storage. It means that the building takes advantage of renewable sources of energy by using the sun to cool the building in the summer and improve the efficiency of the heat pump during winter. Solar energy is also used in the building’s floor heating, and the excess energy can even be stored. A heat pump that uses solar and geothermal energy can both heat and cool the building. If the building runs out of solar heat, the building can use district heating instead of electricity to power the heat pump. This innovative solution developed by COWI further reduces the building’s CO2 impact.

Indoor climate: Shading and sunscreening is essential to obtain an optimum indoor climate. Dynamic sunscreening enables the user to influence his or her direct working environment in Green Lighthouse via external Venetian blinds. The blinds have variable settings, which means that direct sunlight can be blocked, while the louvers still transport daylight deep into the building. The louvers are painted white to optimise this effect. Natural ventilation is also a key component in achieving a comfortable indoor climate. During the colder months, a back-up mechanical ventilation system can bring in fresh air from the outside, but façade windows provide the building with natural ventilation most of the year. In the Green Lighthouse building, fresh air from the sides of the building moves through the central space before exiting through the roof windows at the top of the atrium.



The Green Lighthouse is located at the Faculty of Science at the University of Copenhagen (Tagensvej 16, Copenhagen).


Project management (public-private partnership-PPP)

Building owners: University of Copenhagen and the Danish University and Property Agency (UBST),

Strategic partners: VELFAC and the VELUX Group (private companies) and the City of Copenhagen.




-Architects: Christensen & Co Architects a/s

-Energy design: COWI

-Turn-key contractor: Hellerup Byg a/s

Client advisors: Ramboll and Grontmij / Carl Bro.

Components and materials: WindowMaster, Faber, Knauf Danogips, Veksø and Rockwool.


Project planning, delivery and controls

Preparation and definition of partnership strategy: From December 2007

Design (bidding process): March – July 2008

Construction: October 2008 – May 2009

Delivery and inauguration: October 2009


Surface areas / building use

Total Ground Floor Area (GFA): 950m2

2-storey public building for students of the Faculty of Science.

  • Ground and first floor:  Administration/Orientation offices where students can be assisted with all issues ranging from career planning to deadlines and exams.
  • Second floor:  Faculty Lounge for meetings with researchers and other people from the campus.


Construction costs

Building cost: ca. 5 M€ (DKK 37 M):

-ca. 470.00 € in building components and technologies from WindowMaster, Faber, VELFAC & VELUX.

-ca. 67.000 € in materials from Rockwool, Veksø, Knauf Danogips.

-Payment made by University of Copenhagen for use of the building (unknown amount).

-Innovative fund received by UBST for the construction of this building in view if gathering experience and being used as a learning study case (unknown amount).


Energy consumption

Primary energy consumptions (estimated values are accounted according to the Danish Energy Calculation tool BE 06):

-Consumption calculated without considering renewable production: 30 kWh PE/m2.year

-Consumption with ST and PV systems: 3 kWh PE/m2.year (ST and PV systems)

-Consumption for standard building: 60 kWh PE/m2.year

Breakdown for energy consumption (estimated values are accounted according to the Danish Energy Calculation tool BE 06):

-Building energy need: 14 kWh PE/m2.year for heating; 7 kWh PE/m2.year for lighting; 3 kWh PE/m2.year for ventilation; 4 kWh PE/m2.year for hot water; 2 kWh PE/m2.year for building installations.

-Renewable energy production: 20 kWh PE/m2.year from PV (solar cells); 7 kWh PE/m2.year from ST (Heat pump, seasonal storage and thermal solar heat).

-Efficient fossil energy production: 3 kWh PE/m2.year from urban network.

Real energy billing costs (2010)

-Energy costs: ca. 2.000 €/year (Source: Construction 21)

-Real final energy consumption: 44 kWh FE/m2.year (Source: Construction 21)


Envelope performance

U-Value total average is 0.08 W/m2.K

Details of individual elements:

Roof windows

Angle 90º

Angle 15° (South)

Uw (Heat loss U-­value window)

1.0 W/m2.K

1.1 W/m2.K

Ug (Heat loss U-­value panel)

0.5 W/m2.K

0.7 W/m2.K

g (Heat gain g-­value)



Tau (Light transmittance)




External awning blinds

Angle 15° (South)

Uw (Heat loss U­-value window)

1.1 W/m2.K

g (Heat gain g-­value)


Tau (Light transmittance)



Façade windows

Angle 90º

Uw (Heat loss U-­value window)

0.93 W/m2.K

Ug (Heat loss U-­value panel)

0.72 W/m2.K

g (Heat gain g-­value)



U-value outer walls (Heat loss U­-value): 0.095 W/m2.K

The external skin façade is covered with Swissfiber panels that are made of a composite fibreglass material of 30% glass and 70% polymer that is extremely light and strong. In fact, the entire façade weighs only six tonnes. By comparison, a similar solution in tile would have weighed more than 175 tonnes and been considerably thicker.

U-value roof (Heat loss U-­value): 0.084 W/m2.K

U-value floor slab, with thermo active capacity in ground and 1st floor (Heat loss U­value): 0.084 W/m2.K

U-value roof terrace (Heat loss U-­value): 0.13 W/m2K

U-value corbel at entrance (Heat loss U-­value): 0.106 W/m2K


Indoor performance

The architectural concept of the house is a sundial; the house follows the sun. This is also applied in the window design where the facade windows and exterior sunscreening follow the path of the sun. The users can follow the changing seasons and adapt to the indoor climate accordingly. The house is flooded with daylight on all floors and there is a "cathedral effect" coming from the central atrium where users benefit from a more than 2500 lux experience which adds to the user´s indoor comfort, general well-being and productivity.

Some other minor specifications:

-Calculated indoor CO2 concentration: 700 ppm

-Measured indoor CO2 concentration: 650 ppm on average

-Calculated thermal comfort: Class 2 in EN 15251

-Daylight Factor (DF): Average is 5% with at least 3% in all working stations and a minimum of 2% in hallways


Energy performance

The Green Lighthouse building relies on the following sources for energy performance:

-35% solar energy from solar collectors on the roof and stored solar heat in the ground via a heat pump

-65% eco-friendly district heating, with a 30 percent increase in utilisation due to the heat pump

-100% power of the building’s lighting, ventilation and pumps covered with PV solar cells on the roof

An innovative building installation based on a centralized heat pump is able to supply energy-building needs through heat received from 90% renewable energy production):

-Seasonal storage (located in earth warming tubes) from 22 Solar Thermal panels (ST system).

-Power electricity from 76m2 of PV panels (PV system).

-Only in Winter, Urban District Heating (35% share of renewable energy),


Energy systems

-Heating and DHW system are fed with heat from solar thermal (ST) system and District Heating.

-Cooling and Ventilation systems are fed from ST system and a special SorTech’s Adseoprtion Chiller Aggregate to turn heat into cold by fluid-fluid flow in an efficient process. Furthermore, ventilation can be provided naturally or with heat recovery for days when the weather conditions do not allow natural ventilation.

-Power and lighting system are only fed from PV system.

-BMS: A classic building management system integrated with shading and sunscreening of windows. Based on the relative comfort principle, according to EN 15 251. The user is connected to the outdoors visually, and also in terms of comfort. During winter, the Indoor Air Quality (IAQ) is stable based on mechanical ventilation and heat exchange, during summer the users enjoy natural ventilation, combined with night cooling.


Awards and recognitions


  • Winner in the Green Good Design Award 2010, selected from thousands of submissions from over 46 countries. (
  • Municipality of Copenhagen award for Excellent and Beautiful Buildings in 2010.
  • Confederation of Danish Industries Building Materials Award 2009 for Innovative Collaboration.


  • The Danish Light Award 2010
  • Education & Learning category at the World Architecture Festival in Barcelona 2010
  • Climate Cup Partnership Award at the World Climate Solutions Conference in 2010
  • In 2011, the European Commission endorsed the building as an Official Partner in spreading.


  • Green Buildings Pay, 2012, Routledge
  • Frugtbare Partnerskaber (Fruitful Partnership), 2011, Gyldendal
  • Arkitektur og Energi (Architecture and Energy) – towards a 2020 low-energy strategy, 2011, Statens Byggeforsknings Institut (Danish Building Research Institute)
  • Ny Arkitektur i Hovedstaden (New Architecture in the Capital), 2011, Dansk Arkitektur Center (Danish Architecture Centre)
  • Reference in technical theme of indoor climate, Arkitekten (The Architect)
  • Energi + Arkitektur, 2011 (Energy + Architecture) Arkitektens Forlag (The Danish Architectural Press)
  • Exhibition New Nordic at Louisiana, 2012, − model, photos and drawings
  • Exhibition Ecobuild in London, 2013 − model
  • White Book on sustainability in building, 2013



Additional information

Video explannation:

Time-lapse video of the construction process:

Video animation of the building concept and elements:

Lessons learnt report/Three year status Green Lighthouse, April 2013:



Original source Construction21 (C21)

Lessons learnt

Green Lighthouse is an energy-efficient building of great architectural merit, with a high influx of daylight. Its energy concept plays a role in science as a real study case of the sun in buildings and this is the first time it is applied in Denmark. In the long term, this solution could be used in construction of office and industrial buildings in most parts of Europe. The energy concept will undoubtedly be used when planning the energy supply of CO2-neutral constructions in the future. See more information about learning points and user experiences in the 3-Year Status Green Lighthouse report located on the Constructuion21 website or above under Additional information.

Award labels

Additional documents

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