Thermodynamic Analysis of Geothermal Energy Systems With Forced Recovery From Aquifers

A thermodynamic analysis of forced geoheat recovery from aquifers has been accomplished. The system investigated consists of a single recharging-discharging well pair, in a horizontally extensive aquifer, with either power generation or space heating as the surface application. The space heating systems investigated are (i) direct heating, (ii) heat pumps, and (iii) a combination of direct heating and heat pumps. The thermodynamic performance parameters considered are the effectiveness and fossil fuel savings. Due to the interaction between the surface and subsurface systems, the load conditions and geologic conditions play important roles in determining the thermodynamic optimum operation. For high temperature resources (higher than about 435 K), power generation yields the best performance and is therefore recommended. The relative desirability of the combination (direct heating and heat pumps) requires consideration of the load condition, resource temperature and other geologic conditions. Such evaluations for these automatically determine the appropriate ranges of direct heating. The thermodynamic optimum operation of each system is also dependent on these same parameters, as well as on the injection temperature.