Energy

Two different sources

Low enthalpy geothermics therefore uses two distinct layers of the subsoil:
-the first layer is from 50 – 150 m to about 350 m deep, where deep geothermal heat from inside the Earth is exploited: here temperatures are constant all year round, and similar all around the planet, due to the effect of the regional geothermal gradient (on average about 12°C at a depth of 100 m, between 14 and 20°C at a depth of 150 – 300 m, with the exception of the geothermal fields, where the values are much higher);
-the second layer, instead, is superficial, from few metres to 50 – 60 cm deep (just below the layer of the Earth which can freeze during winter) and exploits the heat stored by the Earth by effect of solar radiation in the warmer months, and thermal inertia of the ground in returning the energy received: in winter the soil slowly releases the heat stored in the summer months, and will therefore be warmer on the surface, instead it will be fresher in the summer.