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 are 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, more or less, is to pump up cold water in the summer to cool buildings above ground. This makes the water temperature rise a small amount. This water is then pumped back down into the ground and stored until next winter, when it can be used for heating buildings. In total, this process generates about three or four times as much energy than what is required for pumping the water up and down.
Vasakronan – a large property company – hopes to be able to use this technology in one of the big high-rise buildings by Stockholm’s main square, Sergels Torg. According to Vasakronan’s head of development and environment, using such a system can save energy equivalent to that consumed by 450 detached houses.
It might seem 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 underground without losing the heat, but in a recent article about aquifers in Swedish construction journal Byggindustrin, Olle Andersson – professor in energy storage at the University of Lund – stated that scientists have yet to find any disadvantages with this technology.