GeoStar systems: Advancements in borehole heat exchanger technology for urban heat transitions - monitoring and future developments

Since its first deployment and commissioning in 2013, the GeoStar technology has emerged as a significant solution for addressing the challenges associated with urban heating systems within spatially constrained environments. We are giving a detailed overview of the GeoStar projects located in Bochum, focusing mainly on their energetic behavior and sustained performance, innovative drilling methodologies, and forthcoming operational strategies. GeoStar systems represent an innovative approach to borehole heat exchanger (BHE) technology, designed to optimize thermal energy supply in densely populated urban areas with limited surface area. This methodology involves the drilling of multiple inclined BHEs arranged in a star-shaped configuration from a central drill pad. This approach facilitates efficient extraction and storage of thermal energy beneath existing urban infrastructure, addressing challenges encountered with traditional vertical BHEs. Our presentation includes an analysis of the long-term performance data from the initial GeoStar 1 installation at the Fraunhofer IEG Campus in Bochum. Comprising 17 BHEs supporting four heat pumps for campus heating and cooling, this installation serves as a compelling case study. Furthermore, GeoStar 2, situated at Hochschule Bochum, demonstrates advancements achieved through the integration of advanced borehole drilling techniques, enhancing precision and system efficiency. Both installations are equipped with heat and cooling meters, temperature sensors, and optical fiber technology for distributed in-situ temperature sensing, providing insights into system efficiency and thermal budget management. Looking ahead, our research aims to integrate the operation of heat pump systems with the electricity market. Preliminary work has been initiated, laying the foundation for a more adaptive and market-responsive operation. This forward-thinking approach not only promises to enhance system efficiency but also aligns energy production with market dynamics and renewable energy availability. These advancements offer valuable insights into sustainable urban heating and cooling, providing a model adaptable to similar urban contexts.