Aquifers to Heat and Cool City Buildings?

It sounds unlikely, big developers in Sweden are reportedly set to use aquifers from underneath the streets of Stockholm to heat and cool the buildings above them. As “This Big City” website reports: "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."