Evaluation of geothermal utilization system design factors considering thermo-hydro characteristics of ground

Abstract

This study attempts to evaluate the design factors of geothermal utilization systems considering thermo-hydro characteristics of ground. Depending on the type of geothermal utilization system, different thermal and hydraulic properties of soil should be considered. In addition, as the soil behavior was complex, numerical analysis was mainly employed and on-site experiments were performed for verification. First, this research presents a reliable prediction method for ground temperature variation by spiral coil-type horizontal ground heat exchangers. A new analytical solution for spiral coil-type horizontal ground heat exchanger was derived using Green’s function and validated through on-site thermal response tests. Along with this proposed analytical solution, this study proposed a load sharing ratio model that could be used to consider the effect of outlet pipe in spiral coil-type horizontal ground heat exchangers. Accurate predictions of ground temperature variation, which are essential for the design of ground source heat pump systems, are possible using the proposed analytical solution and load sharing ratio model for cases that employ spiral coil-type horizontal ground heat exchangers. In addition, a scale factor model was provided as an alternative design factor of spiral coil-type horizontal ground heat exchangers. This model was developed using an artificial neural network and linear regression methods, based on the results of parametric studies. This research also attempts to evaluate the thermal properties of the ground for the design of standing column well systems. Using the developed standing column well model, a total of 420 scenarios were simulated by varying the thermal properties, hydraulic properties, operation properties, and bleeding rates to evaluate the effect of each parameter on the enhanced thermal conductivity that was obtained through thermal response tests. The results show that the applicability of thermal response tests in designing standing column well systems is mainly dependent on the magnitude of hydraulic conductivity. Lastly, this research attempts to evaluate the design factors of high-temperature aquifer thermal energy storage systems based on a sensitivity analysis. The reliable sensitivity analysis was conducted for two cases by designing and modeling a computer experiment. The most important input variables were then selected and confirmed to consider the interaction effects for each case. It was confirmed that the key parameters varied depending on the domain of hydraulic and thermal properties of the experiments, as well as the number of input variables.