Performance of a sedimentation tank for standing column wells coupled with geothermal heat pump systems

Abstract

Ground heat exchangers used with heat pumps have the potential to lower energy consumption and reduce greenhouse gas emissions of buildings. In particular, standing column wells that directly use groundwater have a significant potential in dense urban areas. However, recirculation of groundwater in the well may induce a sediment load that tends to reduce the flow rate of the injection wells, leading to efficiency loss. To avoid this problem, the use of a sedimentation tank placed before the injection well is investigated numerically in this work. To assess the feasibility of this solution, a fully coupled numerical model has been developed based on typical operating conditions and on laboratory analyses performed on sediments. The multiphysics model developed integrates the fluid dynamics and settling processes inside the tank. The capacity of the tank to collect sediments has been investigated for different flow rates and tank geometries. Results obtained show that a commercially-available sedimentation tank can reduce the sediment load in the groundwater returned to the injection well for different flow rate conditions. Indeed, with tank efficiencies ranging from 46.8% to 85% and a capacity to recover 100% of the largest particles, use of intermediate sedimentation tank has a real potential for reducing clogging phenomena. Results also show that for the typical conditions used in the study, usage of inlet baffles enhance tank efficiency and reduce the inlet kinetic energy of the flow, allowing use of tanks having a lower footprint.