## 6 Conclusions  
This study presents the development and implementation of Type 1410, a new TRNSYS module that incorporates the integral exponential function through its series expansion. This function is fundamental in subsurface heat transfer modeling but was not previously included in TRNSYS predefined modules. By implementing this function, the Type 1410 module improves the accuracy of geothermal system simulations, particularly in evaluating the thermal interference effects between boreholes. The model's accuracy was validated using experimental data from two shallow geothermal boreholes (Q-Thermie-Uniovi 1 and Q-Thermie-Uniovi 2), located in Asturias, Spain, and separated by 7.3 m. A thermal response test (TRT) was performed, where thermal injection in Q-Thermie-Uniovi 1 led to a measurable temperature response in Q-Thermie-Uniovi 2. These experimental measurements served as a benchmark for assessing the reliability of the TRNSYS simulations. While the current application focuses on a pair of boreholes located in Asturias (Spain), the developed Type 1410 is designed to be fully generalizable. It allows users to define input parameters such as borehole depth, spacing, thermal conductivity, and diffusivity, as well as the number of terms in the exponential integral series. This makes the module applicable to a wide range of shallow geothermal configurations, regardless of geographic location. The Q-Thermie-Uniovi system served as a controlled experimental validation platform, but the modeling approach is not site-specific and is suitable for broader use in research, system design, and optimization tasks. Regarding applicability, the developed Type 1410 allows the user to define all relevant input parameters, including the following:  
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* Borehole depth and spacing;
* Thermal conductivity and diffusivity of the soil;
* Heating power and test duration;
* The number of terms in the exponential integral series. This makes it compatible with a wide range of geological conditions (e.g., varying diffusivities or stratified layers, provided these are averaged or estimated at the sensor depth) and borehole configurations, as long as the borehole can be modeled as a line source. The results demonstrate that increasing the number of terms in the series expansion of the integral exponential function significantly improves the accuracy of the model, aligning the simulated results more closely with experimental data. This finding underscores the importance of correctly approximating the integral exponential function when modeling subsurface heat transfer, as well as the effectiveness of Type 1410 in capturing geothermal borehole behavior. By integrating Type 1410 into TRNSYS, researchers and engineers can achieve more precise and reliable simulations of subsurface heat transfer processes. The module provides a valuable tool for optimizing borehole configurations, minimizing thermal interference effects, and ultimately enhancing the efficiency of geothermal energy systems. Additionally, it enables improved decision-making in borehole spacing and system design, ensuring the better long-term performance of shallow geothermal systems. The Type 1410 module was developed to solve heat conduction problems governed by the exponential integral function. It provides a customizable, semi-analytical solution to the radial Fourier heat conduction equation from a line source in a homogeneous and isotropic medium. Therefore, the module is applicable to any system configuration in which this mathematical formulation is appropriate; not only geothermal boreholes but also other thermal conduction problems in porous or solid media. The implementation of this function within TRNSYS allows users to simulate long-term heat transfer by conduction in contexts where traditional borehole models may not apply or may oversimplify the underlying physics. As such, the Type 1410 module expands the modeling capabilities of TRNSYS in all situations where the exponential integral function is required.