Waste heat generated by a tram depot to be recycled in the new Laajasalo hybrid block

Sweco is participating in the development of Laajasalo with a large team of experts. Sweco railway engineers are contributing to the construction of a tram connection in the Crown Bridges project, while the company’s building services engineering and structural engineering experts are designing energy-efficient solutions for the new hybrid block’s tram depot. Everything is being steered by Helsinki’s carbon neutrality objectives.

Helsinki City Transport (HKL) wanted to integrate energy assessments into the new tram depot’s HVACE engineering from the very beginning. 

“The City strategy requires us to systematically monitor the environmental impacts of projects,” says HKL Project Manager Leena Mätäsniemi. “From the perspective of the environment, promoting the best options means improving the energy efficiency of both transports and buildings.” 

With this in mind, Laajasalo features many solutions that will enable people to lead more sustainable lives. The area combines functional public transport connections with urban living close to nature, and the new bridges and city bike stations make Laajasalo highly accessible by bike as well. The heart of the hybrid block is the tram depot. 

“This type of hybrid project sets many demands for all engineers, but cooperation and coordination is made easier by the fact that so many of the experts involved are provided by the same company,” states Mätäsniemi. Sweco is providing both structural and HVACE engineers for the design of the depot. 

“Cooperation has been the keyword from the very beginning, both internally and between different operators,” says Lifecycle Design Project Manager Niina Laasonen from Sweco. “Even the hybrid project’s energy solutions are being developed in collaboration with HKL, Anttinen Oiva Architects and the energy company Helen.” 

Energy recycling cuts emissions and energy consumption in half 

Assessing the tram depot’s energy consumption was a challenging task for engineers since the planning of the hybrid block is still in its early stages. The area plan is expected to be completed in 2022, and the construction of the depot will be complete in approximately 2026. 

“There are still a lot of variables, but it was important to prepare a target energy calculation as early as possible to support planning,” says Laasonen. To this end, energy experts had to consider things like the depot’s energy flows and heating and cooling solutions. 

“For example, the depot hall’s tramway electricity transformers and ventilation system generate large amounts of waste heat,” Laasonen states. According to calculations, the depot generates more waste heat than it can utilise by itself. “With heat pump technology, the energy could be recycled for the benefit of not only the depot but the apartment buildings to be constructed in the area as well.” 

The heating of buildings is one of the largest sources of global carbon dioxide emissions, and In Finland, heating accounts for approximately 30% of the country’s total emissions. Recycling the tram depot’s waste heat results in greater savings than could be achieved by improving insulation, for example. What’s more, recycling waste heat also reduces emissions, energy consumption and operating costs. 

“Calculated business models show that recovering and recycling the depot hall’s waste heat to heat nearby buildings is economically viable,” Laasonen says. “Recycling and selling the energy back to the district heating network would reduce the depot’s CO2 emissions and energy consumption by 50% compared to the depot only being heated with district heating, based on current emission factors.” 

The depot is an important precedent in heat recovery 

Waste heat has traditionally been recovered from industrial properties and data centres, for example. The depot project shows that there is plenty of potential elsewhere as well. 

“In the future, advancements such as rapidly developing heat pump technology will improve the possibilities of heat recovery in different types of properties,” Laasonen says. 

For HKL, the energy solutions of the Laajasalo depot are an important step towards Helsinki’s goal of becoming carbon neutral by 2035. The possibility of simultaneously reducing both energy consumption and carbon dioxide emissions has convinced the energy company as well. 

“With Sweco’s help, we are currently conducting contract negotiations with Helen on how the depot’s waste energy could be supplied back to the energy company’s district heating network and utilised in the residential buildings of Laajasalo. Expert help is very important to us in negotiating such major contracts,” Mätäsniemi says. The decisions on the depot’s heating solutions will be made in 2020.