Numerical modeling of the interference of thermally unbalanced Aquifer Thermal Energy Storage systems in Brussels (Belgium)

A numerical model was built using FEFLOW® to simulate groundwater flow and heat
transport in a confined aquifer in Brussels where two Aquifer Thermal Energy Storage (ATES)
systems were installed. These systems are operating in adjacent buildings and exploit the same
aquifer made up of mixed sandy and silty sublayers. The model was calibrated for groundwater
flow and partially for heat transport. Several scenarios were considered to determine if the two
ATES systems were interfering. The results showed that a significant imbalance between the injection
of warm and cold water in the first installed ATES system led to the occurrence of a heat plume
spreading more and more over the years. This plume eventually reached the cold wells of the same
installation. The temperature, therefore, increased in warm and cold wells and the efficiency of the
building’s cooling system decreased. When the second ATES system began to be operational, the
simulated results showed that, even if the heat plumes of the two systems had come into contact,
the influence of the second system on the first one was negligible during the first two years of joint
operation. For a longer modeled period, simulated results pointed out that the joint operation of the
two ATES systems was not adapted to balance, in the long term, the quantity of warm and cold water
injected in the aquifer. The groundwater temperature would rise inexorably in the warm and cold
wells of both systems. The heat plumes would spread more and more over the years at the expense of
the efficiency of both systems, especially concerning building’s cooling with stored cold groundwater.