Aquifers can be used to store thermal energy, either produced as waste heat or captured during cooling in summer. This thermal energy can be used for heating in the winter via a heat pump system. Typically, such a system will have an injection and an extraction well, and the flow is reversed seasonally as the system changes from heat storage to heat supply.

In this article, we present a simplified model to examine the controls on (i) the temperature contrast which develops between the two wells and also (ii) the drift in the temperature of the system if, over a series of years, the heat supply does not match the heat load on the system. We consider t he implications of these results in practice.