Environmental Compliant Planning of Shallow Geothermal District Heating Using Numerical Groundwater Models

Abstract

The direct usage of shallow groundwater resources in open loop systems for district heating is attractive due to the higher coefficients of performance of the heat pump which can be achieved compared to closed loop systems. Groundwater coupled heat pumps are well established on the growing market for renewable energy but they require more detailed planning due to the environmental impact of the pumping and injection process. Typically, the systems are popular on household scale, but recently pilot concepts for district heating have been started in Germany. Advantages are low construction and operating costs and absence of circulating potentially harmful fluids. However, abstraction and injection rates may reach more than 1000 m³/day, thus requiring environmental impact assessment in the planning process. The paper explores the use of numerical groundwater models for optimizing the well positions as well as for avoiding potential conflicts of interest with other groundwater users. Based on three pilot studies, it is demonstrated how shallow groundwater sources can be utilized for district heating. Existing analytical solutions for the spreading of cold water plumes in aquifers are compared to numerical solution using finite elements. The numerical models can also serve to study seasonally changing directions of the open loop systems, thus actively using the aquifer as heat storage during summer time operation.