Numerical simulation of a sedimentation tank applied to an open loop Ground Heat Exchanger system

Ground Heat Exchanger (GHE) used with heat pumps have the potential to lower energy consumption and greenhouse gas emissions. In particular, Standing Column Well (SCW), which is a category of GHE that uses groundwater has the heat transfer medium, is more compact and less expensive than conventional closed-loop GHEs. SCWs are usually coupled with an injection well to enhance the advection process and the overall efficiency during peak power period. Due to the sediment load present in groundwater, water reinjection tends to clog the aquifer, making it less permeable, and in the worst case, leading to undesirable overflows. To avoid this problem, the use of a sedimentation tank placed before the injection well is investigated. To assess the feasibility of this solution, a fully coupled numerical model has been developed based on standard SCW conditions and on laboratory analysis performed on sediments. The fluid dynamics and settling processes have been coupled and simulated with the Mixture model at a constant temperature. Results show that a conventional sedimentation tank can reduce the sediment concentration in the groundwater returned to the aquifer for different flow rate conditions. As the temperature has a major impact on the sedimentation process, a coupled Heat transfer Mixture model simulation was developed to analyse the response of the tank efficiency for a range of typical SCW operating conditions.