We don’t often think about what’s under our feet when walking around in the middle of a city, but in the centre of Stockholm there is actually several aquifers – large underground layers of water-bearing rock or gravel – that can be of great use. Since water has an ability to store heat or cold, these aquifers work a bit like a thermos.
The idea is more or less to pump up the cold water at summer to cool buildings above ground. This makes the water temperature rise a bit. Then the water is pumped back down into the ground and stored until next winter, when it can be used for heating buildings. This gives about three or four times more energy than what is used for pumping the water up and down.
Vasakronan, which is a large property company, hopes to be able to use this technology for example in one of the big high-rise buildings just by Stockholms main square, Sergels Torg. According to Vasakronan’s head of development and environment, this system can save energy equivalent to the energy use of 450 detached houses.
I must confess that to me it’s a bit of a mystery how only a few centigrades of difference in the water’s heat can make this big a difference, and how it can spend several months under ground without losing the heat… But in an article about aquifers in the construction industry journal Byggindustrin, Olle Andersson who is a professor in energy storage at the University of Lund stated that this is actually a technology where scientists actually have failed to find any disadvantages.