In actually, we can find the thermal energy commonly around us. It is enough that if some mass can keep in some specific temperature. We call this kind of mass to ‘heat source’. In generally, we can see river, lake, sea and ground. Ground is suitable for building or house. What is the geothermal system? Geothermal system is the system for house warming by using of thermal energy of ground. For example, in hot summer, you might feel cool before in the place such as inside of cave. Even, the temperature of inside does not change easily in winter. Because many huge of rocks surrounded work as thermal mass that can store thermal energies in the ground. Thus, they can absorb almost infinite thermal energy. Geothermal system is applied by this kind of effect. When we look for the structure of geothermal energy, it is the form of a huge cycle contained heat pumps, water heater, air coils and earth loop-horizontal, vertical, pond(or well water), etc. Most important part of geothermal energy is heat pump in the cycles. It influence the main idea geothermal system. In first, we penetrate the ground to put pipes. And then, we circulate the heat sources as air through the pipes by heat pumps. For example, the cold air above the ground recovers to the specific temperature, the warm air of underground in winter. It can be applied backward in the case of summer. Thus, the air can get suitable temperature in each seasons. It also require the electrical energy to operate the pump. The electrical energy convert the kinetic energy in the pumps. And then, the kinetic energy affects the air circulated in pump. So, the air had thermal energy from underground move up by kinetic energy. This process also contains the sound energy in the pipes or pumps. The efficiency of geothermal system is pretty high by researching. The high efficiency of geothermal energy are on the average 48 percent more efficient than gas furnaces, 75 percent more efficient than oil furnaces, and 43 percent more efficient when in the cooling mode. However, it has the high efficiency in energy parts, we have to consider about cost. At first, it required the pretty big cost for installing it. It include the penetrating of ground, set the cycle with pipe, and connecting the heat pump. It is too much burden for people lived in house. But after setting of it, its equipments work for long terms because, it isn’t broke easily. Its environmental benefits are pretty work for the environments. It just consume the electrical energy. Because of this part, we can not say that it is perfectly work for environments. It is applied by scientific environmental phenomenons. Thus, it also doesn’t make the any pollutions(air, or water), because it doesn’t use fossil fuels. It also gives the good quality of indoor air.