Thermal Conductivity Estimation From Subsurface Data For The Dimensioning of Borehole Heat Exchangers: The Effect of Database Selection

Ground-source heat pumps with borehole heat exchangers are an efficient and sustainable option to heat and cool buildings. Knowledge of subsurface parameters, most importantly the thermal conductivity, are crucial for the design of ground-source heat pumps, but also for their long-term efficient operation. Before drilling, subsurface parameters can only be inferred from existing data. Results of such estimates are published as maps, thus providing a decision base for planners and homeowners. Such estimates have high but rarely quantified uncertainty. In addition, thermal conductivity maps of different regions are not comparable, because the approaches applied to obtain them differ. To provide a consistent planning base for shallow geothermal installations, we present a geoportal that allows the estimation of thermal conductivity and its uncertainty. The method for estimating the thermal conductivity is solely based on publicly available subsurface data which are available as Open-Web-Services. A web-based geodata infrastructure connects data provision and thermal conductivity estimation. A geoportal visualizes input data and results and is responsible for storing and providing the calculation results. Thus, the approach does not only provide an estimate of thermal conductivity that is always up-to-date, but also automatizes the cumbersome step of subsurface data aggregation. The resulting estimate of thermal conductivity and uncertainty can be used as a planning base for ground-source heat pump installations. In a further step, the estimate can be updated with data obtained from a thermal response test and last but not least with operation data from a monitoring system. We demonstrate the approach using data from the federal state of Hamburg and compare the results to another thermal conductivity map, published by the Geological Survey of Hamburg. The results highlight the importance of considering and communicating uncertainty in geothermal potential estimates.