Ground-Source Heat Pumps and Thermal Energy Storage Systems—Energy for the Future

Dear Colleagues,

Heat pumps (HPs) are a cornerstone technology in the worldwide shift toward secure and sustainable heating of buildings. According to a recent IEA Report (“Future of Heat Pumps”, a specialised report within the IEA's World Energy Outlook series), heat pumps in 2021 had already met 10% of the global demand for space heating, but their installation is gaining momentum swiftly, marked by record-breaking sales, despite the challenges that are still present along the direction to the progressive substitution of fuel-based heating systems in future cities.

Heat pumps, which operate using electricity with low emissions, serve as the cornerstone technology in the worldwide shift toward secure and sustainable heating. "The Future of Heat Pumps," a specialised report within the IEA's World Energy Outlook series, presents a forward-looking perspective on heat pumps. It not only identifies crucial opportunities to expedite their adoption but also sheds light on the principal challenges and policy solutions. Additionally, the report delves into the repercussions of an accelerated integration of heat pumps, touching upon energy security, consumers' energy expenditures, employment, and endeavours to combat climate change. Again, according to the IEA, financial incentives for heat pumps are already accessible in more than 30 countries, encompassing over 70% of today's heating demand. According to IEA estimates, heat pumps possess the potential to curtail global carbon dioxide (CO₂) emissions by at least 500 million tonnes in 2030, an amount equivalent to the yearly CO₂ emissions produced by all the cars circulating in Europe during the year 2021.

As is well known, HPs offer a method for generating heat without direct combustion, and they can be successfully employed in both residential and industrial sectors. These systems exhibit exceptional efficiency by utilising electrical energy, resulting in a significant reduction in local environmental pollution and global CO₂ emissions, even in countries where electricity production using renewable resources is still a small fraction of the overall amount. The utilisation of electricity, which is partly derived from renewable sources, combined with a coefficient of performance (COP) that can reach values as high as four or more, implies that HPs have the potential to become nearly carbon neutral; hence, HPs contribute to the goal of zero emissions by the year 2050.

The appropriate selection of a heat source and the careful design of heat exchangers are essential for achieving high HP efficiencies. This can encompass various approaches, including Ground-Source Heat Pumps (GSHPs), where the lower temperature heat source can be the ground or open waters and aquifers. Heat exchangers in GSHP applications play a pivotal role in heat pump performance, and enhancing their performance contributes significantly to the overall system's effectiveness. Furthermore, different from air-source heat pumps, the ground-coupled ones can perform energy storage in the ground (or water), thus providing an additional benefit to clean heating strategies.

Many studies have been devoted to ground heat pumps, from ground heat exchanger design, to heat pump component engineering, to proper refrigerant selection, to the correct modelling and monitoring of the entire building and heat pump system. Optimal control of the HPs as well as best matching with the hourly electricity production are other fundamental fields of research. A multidisciplinary approach to analysis is imperative in the GSHP sector. The present Special Issue is addressed to this aim.

Prof. Dr. Marco Fossa
Dr. Antonella Priarone
Prof. Dr. Stefano Morchio
Guest Editors

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