Utilization of low-grade thermal energy for residential applications: A review of the existing and potential technologies

To address the current energy-related crisis that leads to environmental and economic concerns as well, new policies and actions must be taken in different areas, one of which is to utilize low-temperature sources for heating instead of conventionally burning fossil fuels. The current work aims to review the present-day condition of this subject, which covers “providing low-grade heat for low-temperature demand in the residential sector”, including individual and district heating (DH) networks. Here, the existing sources, like solar thermal energy and geothermal sources, and storage methods (mostly sensible seasonal storage) are demonstrated with relevant statistics and real-world operating cases for them as well. Also, their current challenges and potential for improvement are reviewed. Furthermore, this study encompasses new trends and several possible technologies that will potentially form the body of this research and development area in the near future. Briefly, it is concluded that the shift towards low-grade heating for the residential sector has successfully taken initial steps, especially in Europe. However, it is anticipated that with the faster development in related technologies (like latent heat storage systems or using the available heat from the data centers) and the policies and regulations imposed by the governments, a more significant movement will take place all over the world.