Modelling of heat transport in aquifers. Application to the analysis of efficiency of ground heat exchangers in the city of Barcelona

Groundwater can be used for cooling buildings. In summer, groundwater is cooler than the temperature of the atmosphere. Then, this water can be either circulated through heat exchangers. This is an enviromenally friendly system that may also be reserved and use groundwater for heating purposes during winter.Basic principles governing heat transport in aquifers are well known. It is widely accepted that heat is transported by advection and conduction. One would expect dispersion to be also a relevant mechanism for heat transport. Surprisingly, this mechanism is rarely accounted for in cooling studies. This may reflect uncertainties in how to represent dispersion, which is known to grow with the scale of the problem. If one adopts a large dispersivity (typical of large scale problems), then unrealistically too much heat is dispersed into the aquifer. On the other hand, if dispersion is neglected then one would not simulate accurately heat dissipation