Accumulator tank in Karlstad

The accumulator holds 35 million litres of hot water, enabling the storage of surplus heat and balancing energy use throughout the day. It is a central component of Karlstad’s district heating system, but also a clear symbol of the city’s energy transition.

From chimney to contemporary marker

Even though the building has an advanced technical purpose, the architecture has been equally important. Beyond designing a building that performs well (of course), our team at Tengbom’s Karlstad studio also wanted to create a building that conveys something about Karlstad’s past and future.

“We wanted to create a building that clearly signals energy, yet respects its setting. Its scale and simple form evoke silos, chimneys and other historic industrial structures in Karlstad. At the same time, it carries an expression that resonates with the present,” says Anki Haasma, lead architect at Tengbom.

Industry as a design language

The design draws on the industrial character of the existing plant. The new tank is clad in an external lattice of vertical aluminium profiles that both accentuate its height and create a rhythmic pattern. This rhythm references the site’s architectural language – the vertical lines of nearby silos and sheet-metal façades – and lends the building a sense of movement and energy.

“The repeated form and the sense of height, what we call verticality, create a clear connection to the site’s character. The building has an elegant lightness despite its massive volume,” Anki explains.

Technology for humanity

At the base of the tank, the expression softens through a wave form inspired by the roof of the CHP plant. The form symbolises a new wave of renewable energy in Karlstad – a gentle movement connecting the technical with the human.

The top and the lattice are equipped with RGB lighting that can change with the season or event. From the blue accent colour that characterises the facility today to light themes for Pride, Christmas or the Pink Ribbon – the lighting makes the building a living part of the city’s pulse, especially after dark.

A building for recognition

We chose materials with long lifespans and minimal maintenance, in line with Karlstad’s climate goals and Tengbom’s local climate contract. When the tank is completed in 2028, it will be an everyday yet hopefully valued part of the city’s energy landscape – a building demonstrating that technical facilities too can evoke feelings and spark discussion.

“This is a building that must operate every day for many years to come, while also serving as a clear and beautiful component of the city’s energy landscape. For us, it is important that technical buildings are also designed with intent. That it is not only about function, but about creating something people can understand, recognise or even grow fond of”.

Anki Haasma