Groundwater interference modelling between different low temperature ATES systems in urban context

Abstract

Aquifer Thermal Energy Storage (ATES) is a relatively new heating and cooling technique. Heat and cold are stored in an aquifer, allowing energy and CO2 savings. However, thermal plumes are created and these plumes can migrate in the subsurface. When ATES systems are located close to each other, interference phenomena can occur and affect their efficiency. Understanding how the plumes develop and behave in the aquifer is therefore of major importance for optimal operation of ATES systems. A numerical model was built in FEFLOW® to simulate groundwater flow and heat transport in a study area including two ATES systems. These latter have been operating for several years in adjacent buildings and some operational data have been recorded. The model was calibrated for groundwater flow and partially for heat transport. Several scenarios were then considered to determine if the two systems were interfering. The results showed that a significant imbalance between the injection of warm and cold water in the first ATES system led to the creation of a heat plume which has spread over the years. This plume developed until it 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 operation of the second ATES system was taken into account, the 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 its first two years of operation. Finally, a longer simulation pointed out that in the long term, if the operation of the two ATES systems was not adapted to balance the quantity of warm and cold water injected in the subsurface, the temperature would increase in the warm and cold wells of the two systems. The heat plumes of the two systems would spread out year after year at the expense of the cold storage and the efficiency of the two systems.