Modelling and monitoring of Aquifer Thermal Energy Storage : impacts of soil heterogeneity, thermal interference and bioremediation

Modelling and monitoring of Aquifer Thermal Energy Storage Impacts of heterogeneity, thermal interference and bioremediation Wijbrand Sommer PhD thesis, Wageningen University, Wageningen, NL (2015) ISBN 978-94-6257-294-2 Abstract Aquifer thermal energy storage (ATES) is applied world-wide to provide heating and cooling to buildings. Application of ATES, instead of traditional heating and cooling installations, reduces primary energy consumption and related CO2 emissions. Intensified use of the subsurface for thermal applications requires more accurate methods to measure and predict the development of thermal plumes in the subsurface related to thermal interference between systems and address issues concerning subsurface urban planning and wide spread presence of contaminants in urban groundwater systems. In this thesis, subsurface heat transport in ATES and the associated influence on storage performance for thermal energy was assessed. Detailed monitoring of subsurface temperature development around the wells of an existing system was achieved by a unique application of Distributed Temperature Sensing (DTS) using glass fibre optical cables. The measurements reveal unequal distribution of flow rate over different parts of the well screen and preferential flow due to aquifer heterogeneity. Heat transport modelling shows that heterogeneity causes preferential flow paths that can affect thermal interference between systems, mainly depending on well-to-well distance and hydrogeological conditions. At present, design rules are applied in such way that all negative interference is avoided. However, this limits the number of ATES systems that can be realized in a specific area, especially as these systems generally use only 60% of their permitted capacity. To optimize the use of available aquifer volume, the amount of thermal interference that is acceptable from an economical and environmental perspective was studied for different zonation patterns and well-to-well distances. Selecting the hydrogeological conditions of Amsterdam, the Netherlands, as a case study, this method shows that it is cost-effective to allow a limited amount of thermal interference, such that 30–40% more energy can be provided than compared to the case in which all negative thermal interference is avoided. Because many urbanized areas deal with contaminated soil and groundwater, ambitions to increase the number of ATES systems are confronted with the presence of groundwater contaminants. This is of concern, because groundwater movement induced by the ATES system can result in increased mobility and spreading of these contaminants. However, the combination between ATES and soil and groundwater remediation could be a promising integrated technique, both for improving groundwater quality and development of ATES. Opportunities to use ATES as a continuous biostimulation tool for enhanced reductive dechlorination (ERD) have been explored with a reactive transport model.