Geothermal systems classification, coupling, and hybridization: A recent comprehensive review

Fossil fuels have been heavily used to meet the rising global energy demand brought on by population growth, which has resulted in negative environmental effects such pollution, deteriorating air quality, and climate change. Heating, Ventilating, and Air Conditioning (HVAC) systems make up a large amount of this demand. In response, renewable energy sources (RES) have drawn significant attention as a solution to problems brought on by the use of fossil fuels. Notably, geothermal energy stands out as a strong option, providing both heating and cooling needs with special benefits including consistent availability and cost-effective operation. This paper offers a comprehensive short recent review of the geothermal energy landscape, delving into geothermal systems classification, coupling to HVAC and heat recovery systems, geothermal energy piles, and various hybrid systems. Furthermore, the application of nanotechnology to closed geothermal heat pumps, the use of Phase Change Materials (PCM) to stabilise geothermal-powered HVAC systems, and the investigation of energy heaps as a potential alternative energy source are notable studies in this field. This study is unique because it takes a methodical approach to classifying and evaluating various geothermal concepts. It also considers how these concepts are coupled with other systems and hybridized, all of which have a substantial impact on the advancement of geothermal energy approaches.