Performance analysis of deep borehole heat exchangers for decarbonization of heating systems

Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector. Heat pumps with deep borehole exchangers are a promising solution to reduce emissions. Here the thermal behavior of deep borehole exchangers (DBHEs) ranging from 1 to 2 km was analyzed for various heat flow profiles. A strong correlation between thermal energy extraction and power output from DBHEs was found, also influenced by the heating profile employed. Longer operating time over the year typically resulted in higher energy production, while shorter one yielded higher average thermal power output, highlighting the importance of the choice of heating strategy and system design for optimal performance of DBHEs. Short breaks in operation for regenerating the borehole, for example, with waste heat, proved to be favorable for the performance yielding an overall heat output close to the same as with continuous extraction of heat. The results demonstrate the usefulness of deep boreholes for dense urban areas with less available space. As the heat production from a single DBHE in Finnish conditions ranges from half up to even a few GWh a year, the technology is best suitable for larger heat loads. To achieve climate change mitigation targets in heating, a transition from fossil to clean fuels is essential. The study explores the thermal behavior of deep borehole exchangers (DBHEs) of 1000-2000 m depth, revealing a correlation between energy extraction, power output, and heating profiles. Longer operating times yield higher energy production, while shorter ones result in higher average thermal power output, emphasizing the significance of heating strategy and system design for optimal performance, particularly in dense urban areas where DBHEs prove beneficial. image Operational strategy affects the performance of deep borehole heat exchanger (DBHE). Correlation between thermal energy extraction and power output. Longer operating time increases thermal energy extraction, shorter thermal power output. Strategic regeneration of DBHE improves performance. DBHE fits urban heating yielding up to a few GWh a year heat per hole in Finland.