Energy-positive houses - This is what CO2 reduction of the future looks like

Interview with Rune Grasdal und Bjørn Jenssen

Global CO2 emissions have again reached a record level in 2019 despite a smaller increase. According to a study by the international research association Global Carbon Project, global emissions amounted to 37 billion tons. One of the main reasons for the slower increase is primarily the weaker economic growth last year. In an international comparison, Germany even recorded a 6.3 percent reduction in CO2 emissions in 2019. In absolute figures, this amounts to 54 million tonnes.

As a study by the World Resources Institute shows, buildings are responsible for a third of global energy consumption and a quarter of all CO2 emissions. This is largely due to the lack of energy efficiency in many existing buildings that still rely on fossil fuels. But what can buildings of the future look like that are both climate-neutral and produce renewable energy themselves? The Powerhouse project from Norway provides the answer.

The Powerhouse concept is to take a new approach to planning, construction, power supply and deconstruction with energy-positive buildings. The focus is on the efficient use and distribution of energy. This means that energy positive houses produce more renewable energy than is consumed by their construction and existence.

To learn more about Powerhouse, we spoke to Rune Grasdal and Bjørn Jenssen from Snøhetta and Skanska, the companies involved in the project.

How did Powerhouse collaboration come about and what are its goals?

Snohetta: Powerhouse represents a research, design and engineering collaboration of industry partners in the development of energy-positive buildings, and consists of the property company Entra, the entrepreneur Skanska, the environmental organization ZERO, the design and architecture firm Snøhetta, and the consulting company Asplan Viak.

The Powerhouse collaboration originally defined an energy-positive building as a building that will produce more clean and renewable energy throughout its lifespan than it uses in the production of building materials, construction, operation and demolition.

Powerhouse was established in 2011 and is responsible for several plus house projects, including Norway’s first plus house, the world’s first rehabilitated plus house at Kjørbo in Sandvika, Norway. The latter was completed in 2014.

Skanska: The Powerhouse Collaboration is all about changing buildings from being part of the problem to become part of the solution to the major environmental problems in the world.

What does each member of Powerhouse bring to the collaboration to ensure it meets its goals?

Snohetta: Snøhetta is the architectural and design party in the collaboration. Building energy positive buildings is an extremely challenging task. No architectural practice, entrepreneur or developer could handle this individually. It is due to the Powerhouse collaboration that we are able to compose such strong teams with exceptional knowledge and experience of how we can build more sustainable buildings. This is truly a team effort.

Skanska: Skanska is both a contractor and project developer, and we aim to be a leader when it comes to green and sustainability. We are responsible for managing the project and construction of the building, but we also have a number of experts within engineering, energy and concrete. My colleagues and I serve as in-house consultants and play an important role in developing and selecting solutions and materials that allow the building to meet the strict criteria of the Powerhouse definition. Skanska has been heavily involved from the design phase and until the building was handed over to the client.

How has the collaboration evolved in its short history and how, in any way, has this changed the future course of Powerhouse?

Snohetta: In the autumn of 2019, Powerhouse launched a new standard for future-proof buildings, called Powerhouse Paris Proof. The standard is based on the Paris Agreement’s 1.5-degree objective and sets a cap for total greenhouse gas emissions for a building throughout its lifespan. Another underlying requirement is that the building must be constructed as an energy-positive building.

Skanska: The Powerhouse pilot projects has triggered innovation. Solutions have been developed through integrated energy and environmental design processes, and implementation has proven successful through monitoring during the first years of operation.

This provides a sound basis for increasing volume and the further development of Powerhouse solutions, continuously aiming at even more ambitious goals. Achieving the Powerhouse Paris Proof standard will require zero-emission construction sites, climate-friendly materials, recycling and reuse as part of the solution, in addition to renewable energy production and energy efficiency.

© Ivan Kvaal

How does the process of a Powerhouse project compare to other more traditional projects, particularly in regards to collaboration with the contractor?

Snohetta: One of the key aspects of the Powerhouse alliance is that we are able to compose such strong teams with exceptional knowledge and experience of how we can build more sustainable buildings. The objective of the Powerhouse collaboration is to be the most climate-ambitious player in the construction sector. Powerhouse is both the name of the collaboration and the buildings we conceive together. To achieve the Powerhouse standard, we need to also have a very sustainable building process. There will be a need for a very detailed construction management process to have a sustainable building phase as well.

What characteristics do you look for in collaborators that you work with on your projects, especially those geared to sustainability?

Snohetta: We’re part of a very strong collaboration that will make this project possible. We hope more people will be inspired by the project and take on similar, ambitious tasks in the future. I believe that to meet future environmental requirements, clients, architects and contractors need to be ambitious and bold – both when it comes to function, but also when it comes to form.

At what point in the design process do you like to involve collaborators for unique applications such as the solar panels on this project?

Snohetta: On this particular project, Skanska was already involved since they are part of the Powerhouse alliance and have been a part of the collaboration since the beginning.

At what point in the design process are you normally called upon to work on a project?

Skanska: Skanska is a property owner and project developer, with comprehensive inhouse expertise in all fields of engineering. Often we develop projects from start together with our customers, but more often we participate in a competitive bidding based on a more or less detailed tender description. Our main target is to create value for our customers. We are at our best when we can work together with our clients and partners towards agreed objectives with high degree of liberty, rather than starting off from a detailed and often sub-optimized design. The Powerhouse cooperation is a very good example of a successful approach to reach ambitious targets.

What are the ideas and concepts that architects come to you with? How often do their ideas require custom solutions?

Skanska: The question misses the whole point. It’s not the architect that “comes with the ideas” in an integrated design process.

"Form follows environment" is a natural consequence of creating energy-positive buildings in the most efficient way possible. The key success in order to arrive at the most optimal form of the building lies in an integrated approach that involves the whole team. This requires interaction, expertise and holistic thinking. "Less is more" is a well-known concept, but to achieve more with less requires interdisciplinary knowledge. For example, an important point of knowledge about technology is not to use more technical equipment, but to use less — and often more building integrated technical solutions to achieve an even better result.

In this creative process team members are encouraged to bring all ideas to the table, and not only ideas related to their specific field of knowledge. I.e., architects can propose technical solutions and engineers can propose solutions related to architecture. Our experience is that the best ideas not necessarily comes from where you’d expect. They often suddenly appear as a result of the integrated design process.

What characteristics do you appreciate most with architects?

Skanska: The same as characteristics with engineers, developers, leaders, controllers and other team members: Expertise in their field, curiosity, dedication, creativity, open minded knowledge-sharing and knowledge searching attitude.

© Ivar Kvaal

Was the site a given for the building or was it selected? And how does the building design respond to different site conditions (culture, climate, social, etc.)?

Snohetta: The building’s site was carefully chosen to ensure maximum exposure to the sun throughout the day and seasons. Its skewed, pentagonal roof and the upper part of the façade is clad with almost 3 000 m^2 of solar panels, strategically placed to harvest as much solar energy as possible.

The building is located in Trondheim, Norway, 63° north of the Earth’s equator, where sunlight varies greatly between the seasons. This presents a unique opportunity to explore how to harvest and store solar energy under challenging conditions. The 18 000 m2 office building is situated by the harbor and connects to Trondheim Central Station via a pedestrian bridge on the rear end of the building. The waterfront façade is the slimmest face of the building, allowing the project to be read at a similar scale with its neighbors. Clad with black aluminum and solar panels, the façade is reflected in the adjacent Trondheim Fjord.

Skanska: For a Powerhouse the shape of the building must be determined by the natural environment surrounding it. In order to be able to construct a building that meets the strict energy criteria of Powerhouse this far north, you must have a holistic approach. All the partners involved and other external stakeholders, such as the municipality, have to be willing to make compromises in order to reach the energy targets. The shape, height and size of the building was changed a number of times and a source of much debate. In order to meet the targets in the Paris agreement we need to be able to transform existing buildings and construct new ones into energy positive buildings that are “Paris Proof” with respect to total lifecycle emissions, regardless of where they are or will be located.

How did you determine that solar energy would be the primary means of achieving an energy-positive building?

Snohetta: The production of energy of a Powerhouse can be seen through two different angles. Firstly, and because it is a Powerhouse building, the building will generate more renewable energy in a 60-year period than the total amount of energy that would be required to sustain daily operations and to build, produce materials and demolish the building.

Secondly, the building produces more electricity than it uses in a year, thanks to the solar panels integrated on the roof of the building. The building geometry is optimized to harvest solar energy specific to the location and excess electricity produced by the solar panels will be sold to the electricity grid. Over a year, this amounts to a total of about 500 000 kWh with clean, renewable energy.

Solar panels are an integral part of all the Powerhouse projects that have been realized or that are in the pipeline now.

Skanska: It is sort of misleading that solar energy is the primary means of achieving an energy positive building. The most “environmental” energy is the energy that you don’t use. Powerhouse Brattørkaia requires about 220.000 kwh/year, which is 80% less energy to cover the need for heating, cooling, ventilation and lighting compared to a typical new office building in Trondheim. The energy needed to produce all the materials, transport and construction process is equally important. Broken down to yearly electricity, embodied energy corresponds to about 255.000 kWh/year. The reduced demand both regard to operational and embodied energy is what makes it possible to balance the whole demand by solar power. The building design with integrated PV is key to maximize PV production, while at the same time providing good daylight conditions and view for the users. Calculated yearly production is slightly above 460.000 kWh/year.

What was the main design problem with the solar panels that cover the roof and the façades, and how did you arrive at the solution?

Snohetta: One of the challenges was to create safe access to the roof and required access for fire fighters. Another challenge was to secure the roof to avoid ice and snow fallout. Rainwater management was also a challenge.

Skanska: In addition, secure attachment of both the PV’s in the frames, and the frame system itself is essential, due to the extreme wind exposure at the northwest ridge along the top of the building.

Were there any aspects of the solar panels that required special attention both in design and construction?

Snohetta: The standardized size of the solar panels made it challenging to optimize the amount of m2 of panels on the roof.

How did the project change from its initial design to its realization?

Snohetta: The angle of the roof was somewhat reduced due to building regulations, and the façade ended up with a slightly simpler geometry. The windows were also adjusted somewhat to allow for optimized daylight penetration.

Thank you very much for the interview, Mr. Grasdal and Mr. Jenssen.

Published: 20.10.2020

Interview by: John Hill,