Innovative energy solutions in plus-energy buildings

Stockholmshem (one of the municipal housing companies) built two plus-energy buildings in Stockholm Royal Seaport and tenants moved in during 2019. The two buildings, with 43 rental apartments designed to be net producers of energy with the help of solar panels, geothermal heat, efficient insulation and ventilation, as well as recycling of excess heat from wastewater. Design features – such as balconies built into the facade and angled roofs to use the sun as an energy source – are unique. This project of engineering excellence innovatively combines some 20 new energy solutions.

Land allocation competitions are one of the innovation-driving tools used to achieve sustainability goals for Stockholm Royal Seaport. In 2014, a competition was held for the Brofästet phase with the specific aim of constructing plus-energy buildings with smart energy solutions and functional architecture. Of the 16 competing housing companies, Stockholmshem scored the highest number of points thanks to “a holistic approach for energy efficiency and good living environments with interesting and exciting architectural expression”.

Building energy-efficient multiple-dwelling buildings that also produce a large proportion of, or more than their energy requirement is a unique challenge. This is why it is important that experiences from this project can be shared to help others develop future projects.

External walls of the buildings are straight without bays or angles. The roof ridges of the buildings have been rotated to create straight south-facing roof areas, optimised to catch the sun’s rays. The roof angle of 30 degrees is within the optimal span for highly efficient solar panels with silicon technology.

Plus-energy building in phase Brofästet.

The opposite side of the roof is covered in sedum to delay the path of stormwater to Husarviken via so-called raingardens – a shallow recess in the ground fitted with a drainage system and a filter material covered in foliage. Sun-facing gable facades are fitted with solar panels with a less shadow-sensitive thin film technology. North-facing gable facades are equipped with grid panels to encourage growth of climbing plants.

Space-efficient apartments have been an integral part of efforts to maximise the efficiency of internal heat loads. This has resulted in highly space-optimised two-, three-, and four-bedroom apartments. Active heated living areas are minimised and complemented with unheated living spaces as glazed balconies along the longer facades of the building. This creates compact, well-functioning homes during the winter, with substantially increased space that is heated naturally in the summer. By using sun shades as blinds along the outside of balconies, heat can be released in the winter and stored in balconies’ concrete frames but reflected away in the summer.

Compact design, a tight building envelope, and the implementation of a raft of energy technology solutions have been key factors in ensuring that the plus-energy buildings achieve energy targets. Together with a wastewater heat exchanger and geothermal heating, the buildings become a functioning whole.

Optimised airflow, and thereby reduced volume of air to heat, makes it easier to use internal heat sources. Energy calculations show that the building uses around 14.8 kWh/m² per year, heating, building electricity and hotwater included. Energy produced by solar panels is calculated at around 16 kWh/m² per year. This means that over the course of a year, the building generates excess energy. Around 30 per cent of energy produced by solar panels can be used directly to meet the properties’ power needs for lighting, heat pumps, and fans.

Excess electricity production is sold to the grid and balanced against purchased electricity during colder periods. Over the course of the year, solar panels produce more energy than the properties need.

Technology and service providers
Developer: Stockholmshems website >
Architect: DinellJohanssons website >
Energy, electricity, and ventilation: Incoords website >
Landscape architects: Tema, numera del av PE teknik & arkitektur website >
LCA and environmental buildings: Tyréns website >
Constructor: Kåver & Mellins  
Brand consultancy: Debrand
General contractor: Skanska Sverige website >