Efficiency Increase of Soil Heat Exchangers due to Groundwater Flow and Air Injection Wells

Abstract

Geothermal Energy is available all over the world and plays an increasingly important role in the supply of renewable energy, especially in the heating and cooling sector. In order to collect geothermal energy, various soil heat exchanger systems have been established and developed in recent years. Thermal activated piles (energy piles) are one of the most efficient systems, since the cost of production can be reduced due to dual utilization. The heat production of energy piles depends on various factors. In soils with moving groundwater heat propagates much faster than without groundwater flow. However, the impact of groundwater on the heat output of energy piles has not yet been studied thoroughly. A numerical approach was utilized to simulate conductive and convective heat transfer between heat carrying fluid and the surrounding materials (tube, concrete, soil and groundwater). In addition to the investigation of groundwater impact, a patented optimization method for borehole heat exchangers – the air injection well -- is presented. It has been simulated numerically, in order to obtain an estimate of the theoretical efficiency.