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Heat from the ground, it's there for the taking

Before sinking the foundation into the ground, pipes are integrated into the frame for the concrete

(epfl)

To heat a building using the least energy possible, simply use its foundations to draw heat from the earth. It’s an idea gaining traction thanks to a Swiss laboratory.

In April, Lyesse Laloui, head of the Laboratory of Soil Mechanics at the Federal Institute of Technology in Lausanne (EPFL) will host a meeting of world specialists in “energy geostructures” for a workshop that has the support of the American National Science Foundation.

EPFL were the first to test in real conditions the behaviour of heat transfer pipes integrated into the foundations of buildings.

Humans live on a furnace, and although the exact temperature of the centre of the earth is unknown, 99 per cent of the earth’s mass beneath our feet is cooking away at 1,000 degrees centigrade. The more we dig, the more the temperature increases.

Given that even the most unimportant construction needs foundations buried in the earth, it is possible to integrate them with tubes containing a liquid which can transport heat and thus recover thermal energy via heat pumps.

It’s a system which works equally well in foundations for large buildings, pylons for bridges, in walls of tunnels or basements of houses. In urban environments where there is little space to run heating coils in the ground, it’s an ideal solution.

Near surface geothermal energy takes heat from a field from up to 100 metres below the earth’s surface. At these depths, the temperature remains stable at about 10 or 12 degrees Celsius all year round. It’s not much, but a good heat pump is pretty much all that is needed to heat a building from the earth. The process can also function in the reverse – cooling the building in the summer.

It is a different concept to that of deep geothermal energy in which steam needed to power electric turbines is gathered from up to five kilometres into the earth’s crust. And energy geostructures remove the risk of causing an earthquake as happened in Basel in 2006, when tests for the Deep Heat Mining project caused an earthquake that measured 3.4 on the Richter scale.

Centre of excellence

The idea of integrating heat transfer pipes into the foundations of buildings is as old as the heat pumps which make it possible to exploit these few degrees.

“We’ve been doing it for the last 30 years,” Laloui told swissinfo.ch. “But it is being done in an empirical manner. Here at the EPFL, we were the first to test the behaviour of such foundations in real conditions.”

“What you have to consider is that you’re going to heat and cool the foundations and the earth around them, so the materials will expand and contract,” Laloui said. “If the building is constructed on clay, the soil will shrink when it is heated but will not revert to its original size when cooled.”

To measure these kinds of movements, the EPFL drilled the first energy stakes in the world entirely dedicated to tests more than a decade ago.

“We are the only ones to have developed software for architects and engineers to measure this kind of thing,” added Laloui.

With this expertise, the EPFL is hoping to have geothermal heat transfer systems incorporated into the foundations of the planned Museum of Fine Arts in Lausanne and the Riviera-Chablais hospital in Rennaz.

In the first case, the desire to find ecological solutions for energy supply is stipulated in the  tender process. In the second, the EPFL is counting on its vice-president Francis-Luc Perret, a member of the establishment committee for the planned hospital, to push the idea.

Way of the future

For the moment however, neither architects nor developers are flocking to still largely misunderstood technology, preferring to stick with established solutions for heating and cooling.

“If they have to gamble on economising energy consumption over the next 50 years, but compromise their chances of getting the project because the technology is more expensive, then it doesn’t seem to them to be a most fundamental [need],” said Laloui.

“It’s up to political leaders to provide the impetus,” he said. “The Federal Energy Office has made a lot of effort, but now it’s up to the cantons and local councils to promote this technology. But I think we’re heading in the right direction.”

Taking the example of Britain, the number of buildings which draw energy from the earth through the foundations has increased over the last five years from a few hundred buildings to more than 5,000.

And it’s not just by chance that it’s happened – the mayor of London has issued a recommendation that all new public buildings should be built on foundations equipped with heat transfer systems.

Again, the challenge is significant. Around half of all the energy consumed in Switzerland is used to heat buildings and produce hot water. 

Although there is no statistical study on the subject, it is not hard to imagine the potential such technology has to significantly reduce energy consumption and carbon dioxide emissions.

The green terminal

Inaugurated in 2003, terminal E of Zurich Airport is the most famous example among the around 40 buildings in Switzerland which use energy producing foundations.

500 metres long and 30 metres wide, it rests on 350 concrete piles driven 30 metres into the earth, including 306 which are equipped with cooling pipes.

In the summer, the cold drawn from the ground enables the building to be air-conditioned without the need of a heat pump.

The heat that is injected into the ground is retrieved in winter and increased to 30-40 degrees by a heat pump.

In total, 75 per cent of the energy used for heating and cooling the terminal comes from the foundations.

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Geothermal energy in Switzerland

2640 gigawatt hours (GWh) is the total heat production from the ground in Switzerland in 2010.

It is 19 per cent more than in 2009, but still a fraction of the energy produced and consumed each year.

Source: Swiss Geothermal Society

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(Translated from French by Sophie Douez), swissinfo.ch

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