- This system uses the thermal difference of eth water, underground water, and underground heat, etc. for heating/cooling.
- About 47% of the sun heat is stored underground through the ground surface and the underground temperature of the ground
.. which absorbed solar heat is 10℃∼20℃ near to the ground surface although the temperature is different by topographical
.. feature and this temperature may be used in the heating/cooling systems equipped with heat pumps.