In order to mitigate the adverse effects of Global Climate Change, harnessing Green Energy has become the focus of the scientific community. To fulfill this demand, the research described in this book addresses utilizing geothermal energy through Ground Source Heat Pump for space cooling and heating applications. To maximize the efficiency of heat transfer, nanofluids are considered, which are novel fluids due to their improved heat transfer capability over the base fluid. This book presents different types of nanofluids and heat pumps and reviews the latest literature available in these two areas. A chapter is devoted to the thermophysical properties of this new type of fluid, which are prepared by dispersing nanoparticles in base fluids. Analytical and computational models are presented to perform the thermal design of such heat pump systems. The analyses conclude the superior thermal performance of nanofluids by comparing their performances. The readers will gain knowledge on how to design heat pumps that can successfully employ nanofluids.