A summer surplus of heat can be used in the winter for heating. Conversely, winter cold can supply cooling in the summer. A storage medium for this thermal energy is available everywhere: the underground. Underground Thermal Energy Storage (UTES) systems relies on the principle that below a certain depth, the subsurface has the ability to store thermal energy for a substantial period of time. UTES system can be classified into Aquifer Thermal Energy Storage and Borehole Thermal Energy Storage systems. With the implementation of a UTES system, the primary energy consumption and associated CO2 emissions can be reduced up to an 80%.