Turning the Building Pit into an Energy Store: A Major Relief for the Power Grid
A large share of electricity consumption in Norwegian buildings goes to heating. By harnessing a building's foundation as a thermal energy store, developers can dramatically reduce the need for grid-supplied power.
The building pit at Campus Ullevål, where workers have built Norway's first energy wall into the foundation. The walls will store and reuse heat from the ground beneath NGI's new headquarters at Sognsveien 72. ( Photo: NGI)
In recent years, high electricity prices and grid capacity challenges have pushed energy use to the top of the agenda. Norway relies heavily on electric power for heating buildings and water. For larger commercial and office buildings, one solution rarely gets mentioned: using the foundation itself as an energy store.
The principle is called energy geostructures. Workers install pipe loops in the building pit to extract heat from the ground in winter and store surplus heat in summer. This turns the foundation into both a load-bearing structure and an energy source.
"In practice, it works as a seasonal heat store. We store heat in the ground during summer and retrieve it when the heating demand peaks in winter," says Habibollah Sadeghi, Project Engineer at the Norwegian Geotechnical Institute (NGI).
The government's recent energy efficiency action plan paints the same picture: the building sector accounts for a large share of the country's energy use. The plan calls for greater local energy flexibility to relieve pressure on the power grid, especially in winter. Yet it makes no mention of solutions that builders can integrate directly into the foundation at the start of a construction project.
New pile joint solves practical problem
Norway commonly uses prefabricated concrete piles joined together in segments. This has made it challenging to run pipes through the piles without weakening them or causing leaks. During his doctoral research at NTNU, Sadeghi developed a new joint that solves this problem.
"We had to find a solution that could withstand impact, pressure, and Norwegian ground conditions, while still being easy to install," he says.
With the new joint, crews can assemble the piles and drive them into the ground as usual. Tests show that the system remains watertight even in challenging soils such as quick clay.
Using energy to remove energy
Today's energy system often suffers from a mismatch between when we have energy and when we need it. In summer, many commercial buildings and data centres face significant cooling demands.
"At NTNU, for example, data centres produce a lot of heat. In summer, cooling systems consume electricity to dump that heat into the air. In other words, we use energy to get rid of energy," says Sadeghi.
Energy piles offer an alternative: they send surplus heat down into the ground and retrieve it through heat pumps when winter arrives. The system also delivers high efficiency — for every unit of electricity fed into the heat pump, it returns four to five units of heat.
Traditional ground-source heating requires dedicated energy wells, which can cost up to NOK 200,000 each. Energy piles make use of structures that builders must construct anyway to support the building.
"Converting a standard concrete pile into an energy source adds roughly 20 per cent to the cost. And once the foundation is in place, the energy store lasts at least 100 years. It is an extremely energy-efficient solution," says Sadeghi.
Norway's first energy wall
The technology is widely adopted internationally. Google used around 2,500 energy piles when it built its new headquarters in California in 2022. These covered 95 per cent of the building's cooling demand and 100 per cent of its heating demand.
In Norway, the technology has been implemented at Campus Ullevål in Oslo, which will house the research institutes NGI, NIVA, CICERO, NORCE, and NIBIO, among others. Here, workers have installed Norway's first energy wall. The steel walls around the building pit carry more than 2,100 metres of collector piping.
"The goal is to store and reuse 250,000 kWh of heat annually from the clay surrounding the building," says Sadeghi.
If everything goes according to plan, the Campus Ullevål system will reach regular operation around mid-2026. NGI moves into the building in June. Campus Ullevål stands as a pioneering project that demonstrates the solution works even in demanding Norwegian ground conditions.
"If you wait to integrate the collector pipes, the opportunity is lost. Retrofitting a completed foundation is impossible. This is a rare chance to make one smart decision and reap the benefits for generations," Sadeghi concludes.
Habibollah Sadeghi
Engineer/Researcher Offshore Geotechnical Design habibollah.sadeghi@ngi.no+4741348194