Ground source heat pumps coupled to shallow borehole heat exchanger (BHE) fields represent a low greenhouse gas emission technology to provide space heating and cooling. In district heating applications the resulting multi-source energy systems can be quite complex, which makes numerical system simulation a useful approach for different design stages. Many different BHE models with specific advantages and drawbacks are available, and their limitations are not always clear to the user at first sight. In the present study, we compare different BHE field models that can be used in system simulation (TRNSYS, Modelica) regarding their long and short-term accuracy and limitations, using the example of two residential districts in Darmstadt, Germany. While most models are suitable for an early design stage, accurate short-term results in the range of a few minutes are usually not as straightforward to obtain.

To optimize the performance and sustainability of a borehole heat exchanger (BHE) system, it is critical to accurately estimate the potential of the geothermal source. The focus of this study is to utilize monitoring data to improve the accuracy of geothermal potential estimates for an BHE site in operation. Initially, a numerical model was developed for a specific BHE site based on site characteristics such as geological background, groundwater seepage condition, and surface solar radiation. The model was calibrated based on the monitored energy balance and temperature datasets during BHE operation. To estimate the geothermal potential of the site, we employed Monte Carlo simulations based on assigning various heat loads for the BHE system. Through sensitivity analysis, a robust data-based relationship, also known as a surrogate model, was established between the heat load parameters and the key performance indices of the BHE system. The surrogate model enables efficient calculation of BHE performance indices for a given heat load parameter. This provides the possibility to obtain the optimal heat load strategy to maximize the geothermal potential. Finally, an optimization algorithm was used to obtain an accurate prediction of the site's geothermal potential with an objective function aiming at maximizing heat extraction from BHEs. The innovative approach presented in this study emphasizes the importance of combining monitoring data with advanced numerical modeling techniques. The resulting methodology not only improves the reliability of geothermal potential assessment, but also provides a scalable framework applicable to other BHE sites, facilitating more efficient and sustainable geothermal energy utilization.

Horizontal Ground Heat Exchangers (HGHE) installed by utilizing Horizontal Directional Drilling (HDD) have been proven to be a cost-efficient alternative to install new Ground Heat Exchanger (GHE). A big advantage of this technology is the possibility to install HGHE in places where otherwise space would be a limiting factor.

For this research two HDD drilled boreholes were installed in Saga City, Japan. The boreholes have a diameter of 114,3 mm and a length of 59 m and 56 m as well as a depth of 5 m and 9,5 m respectively. In March 2022 a Thermal Response Test (TRT) was conducted and showed the influence of rain on the system. Bases on this test, the installed HGHE and the geology of the location a numerical model was developed in FEFLOW and validated using the measured temperatures at the turning point and the outlet of the system. The model was then used to conduct long time simulations to show the influence of water injection into the borehole. Furthermore, sensitivity studies have been conducted to investigate the influence of the borehole on the efficiency of water injection and determine optimal well design. The results showed the influence of different well paths, the distance between the boreholes and the long-term effects of water injection on the ground.

As climate change progresses, Europe has been experiencing increasingly severe and frequent summer heat waves, leading to a surge in residential cooling demand. Traditional methods of air conditioning, while effective, contribute to significant energy consumption and greenhouse gas emissions, exacerbating the problem they aim to solve. To address this, alternative and sustainable cooling solutions must be explored and implemented.

One promising solution is shallow geothermal energy, which leverages the earth’s relatively stable subsurface temperatures to provide both heating and cooling. While shallow geothermal systems are well-established for heating applications, their potential for cooling, especially in residential settings, is not yet fully realized or appreciated. This is partly due to the inadequacies of Europe’s historical residential architecture in adapting to modern cooling needs.

Europe’s rich architectural heritage, encompassing medieval, ancient, and old buildings, was not designed with contemporary cooling demands in mind. These structures often lack the insulation and design features necessary for effective temperature regulation, making it difficult to accurately measure and meet the cooling demand. Consequently, the potential of shallow geothermal energy in Europe remains underutilized.

This paper aims to highlight the critical need to redefine geothermal potential to include its cooling capabilities. By understanding the lessons from ancient cooling systems, particularly those in Iran which successfully integrated hydrothermal passive cooling with wind energy, we can better appreciate the diverse applications of geothermal energy. Ultimately, this redefinition will help in realizing the true potential of shallow geothermal energy in meeting Europe’s residential cooling demands amidst changing climate conditions.

Background of the projects:

We calculate the heat pumps exactly according to the desired operating conditions.

These are type-tested series machines that we can combine in various sizes.

This allows us to offer solutions in the output range from approx. 350 kW to 8000 kW per cascade. Larger heat outputs can also be achieved by connecting several cascades in parallel. The specific data depends solely on the respective conditions on the source side and the heating network.

For each project, we offer a customized master control system for the heat pump system with water pumps, control units, measuring equipment, refrigerant monitoring systems and other requirements in order to be able to operate the heat generation system safely and energy-efficiently in the long term.Our factory service offers contracts for the support of the heat pumps and the master control system over the entire service life.

About Carrier

Founded by the inventor of modern air conditioning, Carrier is a world leader in high-technology heating, air-conditioning and refrigeration solutions. Carrier experts provide sustainable solutions, integrating energy-efficient products, building controls and energy services for residential, commercial, retail, transport and food service customers. Carrier is a part of Carrier Global Corporation, global leader in intelligent climate and energy solutions that matter for people and our planet for generations to come. For more information, visit www.carier.com, www.carrier.de.