Pumping Heat

“What is this wild looking thing?” Larry King asked his guest, futurologist Jaque Fresco in a 1974 interview. Fresco produced a drawing of a shining metallic circle of pipes and valves, lava spurting up in the background, and replied, “this is clean sources of power. By utilising the natural heat of the Earth, that is volcanic energy… we can get enough power to electrify the world. It’s easy to tap, it’s clean and available.”

A couple of decades on, the picturesque peaks that split the surface of the city of Grenoble are home to just such an enterprise. “We have to build around 800,000 square metres of buildings,” explains Franck Izoard, director of Innovia, the company behind this feat of engineering. “We want to heat them well, but we have to reduce the energy. We have to push the construction to have a very good consumption level. Our buildings will use 16% of the carbon energy that they could according to regulations. Because we want to be ahead, we can have real change right now, not in 20 or 30 years.”

Lava-free heat

There is no lava spurting from Grenoble’s snow-capped inclines, so how can the city achieve this remarkable aim? Well, Izoard explains, you don’t need a volcano – in fact, it’s the relatively moderate underground temperatures that make this system work so well, and that allow it to provide not only heating during the winter, but also cooling during the summer months. The temperature of the groundwater shifts around much less than the air temperature, so in the winter, the groundwater will be warmer than the air – perfect for heating homes – while in the summer, the groundwater will be cooler than the air – perfect for creating a refreshing indoor environment.

The sheer scale of this project, almost one million square metres of buildings, may seem like a challenge, but according to Izoard, it is actually one of the conditions of success. “We have been convinced that it is not just playing with the buildings that you can reduce consumption. When you change the scale you can do more than just changing the percentages.” Because the city can include so many buildings in the one project, it can take advantage of enormous economies of scale.


The basic idea here is not new, but there is one major innovation which is responsible for a huge increase in the efficacy of the system. “Basically it’s a very simple project. We use a heating pump for each building, and instead of having the pump pumping the groundwater, doing its job and reinjecting into the groundwater, which is what we have been doing for half a century and is not working very well, we will reinject elsewhere.” Formerly, one enormous intake would have pumped the water into the system and then each of the buildings would have drawn water from and returned it to the same supply.

The problem is obvious: after the water had been used for heating the first building, it would have less heat energy left for the second one, and so on: “When the first is doing its job, the second one just behind has less quality, the fourth one is worse, and the fifth can’t do anything. In French we call it ‘cannibalisation’ – too many things trying to do the same thing at the same time with the same resources.”

Equal for everyone

Grenoble’s solution may sound counterintuitive: you create a more efficient system if each building has its own little system, rather than one large system that tries to serve the whole area. “We have tested how the groundwater can support what we want it to do. The solution that we have found is for each building to have its own little system, then the water is collected by a big pipe and brought out to the river. That means that nobody will have the water that has been used by somebody else, so everyone will have the same quality of groundwater. This is a way that guarantees that the groundwater is the same for everybody, so the performance of the heating pump will be the same for everybody,” Izoard declares proudly.


In an age when the fragility of natural ecosystems is becoming ever more apparent, is there any concern that interfering with the water system on this enormous scale will have spillover effects that are harmful for the city? According to Izoard, there will be such effects, but rather than causing harm, they will actually make the city safer. “Four kilometres below the site we have a dam. We have to be very careful in Grenoble to protect ourselves from flooding. We have big pumps that pump the groundwater just to keep the water level stable, but now in this project we take the water from that pump and we use it.” In this way, by taking some pressure out of this system, the project can save even more energy than it would otherwise.

“You get exactly what you need”

Izoard’s advice for other cities? “If you want to reduce your impact, never use a big pump, use lots of little ones. Then you get exactly what you need in the place that you need it.” Now Grenoble is working to share the message of geothermal power with other cities, using projects like the EU-funded ‘City-zen’ to let other cities know that you don’t need a volcano to heat your home – a river will do just fine.

Anthony Colclough Eurocities Writer