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Geothermal

About Geothermal Energy

Definitions

Korean government pushes forward the supply of renewable energy to prepare for high oil prices and to cope against global warming, in view of finding alternative energy resources to fossil energy; where geothermal energy is one of the most popular energy sources.

Geothermal energy is normally defined as the energy from the heat of magma inside the earth which is held by the ground (soil, ground water, surface water, etc.). Geothermal energy is classified according to temperature; either low to medium temperature (10~90℃) or high temperature (over 120℃).

Geothermal energy technologies are classified into direct use and indirect use according to their final product. The final product of direct use is heat, whereas the final product of indirect use is electricity.
Typical type of direct use technology is GHP (Geothermal Heat Pump system) which uses the low temperature (10~30℃) efficiently. This system relatively uses the lower temperature compared to other technologies but it can maintain the temperature constantly all year around and has no geographical limitation.
Indirect use technology refers to geothermal power generation that produces electricity by operating the plant using hot water or vapor (120~350℃) which is extracted from the ground.

Ground source heat pump releases the heat absorbed from indoor through the ground heat exchanger during the cooling period. During the heating period, the ground heat exchanger absorbs heat from the ground and provides such heat to the indoor. One of its advantages is having very high performance by keeping the temperature more stable compared to the use of air source heat pump. In other words, it has the advantages of high efficiency and economic feasibility owing to its low power consumption, simple structure, long life, and easy maintenance and operation. Specially, it is very applicable to Korea where the seasons of summer and winter are clearly defined.

The superiority of ground source heat pump is demonstrated by the many studies done in the United States and other developed countries where the commercialization has been promoted since the 1940s. U.S. EPA (Environment Protection Agency) introduces that the most energy efficient, environment friendly and cost-effective air conditioning system technology is the ground source heat pump. Actually, this system can reduce the energy consumption to 44% compared to the use of air source heat pump and 72% compared to the use of air conditioner and electric heater. The efficiency of ground source heat pump is the best of air-conditioner in the daily modern use. For this reason, the report says that installation of ground source heat pumps in the United States and Europe has been increased annually by about 12% for the past ten years. About 550 thousand units of 12kW ground source heat pumps are installed and currently in operation, and about 66 thousand units are newly installed every year.

Characteristics

About Geothermal Energy

Cooling cycle

When the ground source heat pump works as a cooling cycle, it absorbs the heat from indoors and the heat is released through the ground heat exchanger. High temperature and high pressure refrigerant is sprayed as superheated steam from the compressor and is drawn into the condenser through a 4-way valve. In the condenser, high temperature steam refrigerant exchanges the heat with the circulating fluid (water or antifreeze) of the ground heat exchanger which has relatively low temperature.

In this process, the temperature of antifreeze is rising and steam refrigerant is condensed (phase change) from vapor to liquid. High temperature antifreeze is circulating in the ground heat exchanger and then the heat is released into the ground. High temperature refrigerant reaches low temperature and low pressure by moving the expansion valve. Low temperature and low pressure liquid refrigerant exchanges the heat with the indoor air through the evaporator.

At this point, liquid refrigerant is condensed (phase change) from liquid to vapor as the indoor air flowing into the evaporator is being cooled. Low temperature and low pressure liquid refrigerant from the evaporator goes into the compressor through the 4-way valve and after compression process it becomes the high temperature and high pressure steam refrigerant again. Meanwhile, in a typical system, EWT (Entering Water Temperature) is about 15℃ and LWT (Leaving Water Temperature) is raised to about 5~6℃ by absorbing the heat from the refrigerant of the heat pump.

Temperature risen antifreeze becomes the set EWT by exchanging with the soil of 12℃ through the circulation in the pipe of the ground heat exchanger. The specification of ground heat exchanger is determined by considering the temperature differential between EWT and LWT, antifreeze flow, heat capacity of soil, load of indoor heating and cooling, performance of heat pump, and so on.
There are two types of ground source heat pump, namely, Water-to-Air and Water-to-Water

Heating cycle

Geothermal is used for heating energy source, opposite to the cooling cycle.
High temperature and high pressure refrigerant steam which is released from the compressor is drawn into condenser through the 4-way valve.
High temperature refrigerant steam released from the condenser is changed to liquid by the heat exchange with indoor circulation air (Water-to-Air) or water (Water-to-Water).
At this point, the temperature of the air or water which is circulating indoors is raised by the heat in refrigerant and then heating. Hot water is provided through the forced circulation of the temperature risen air or water by the distributor unit.

Temperature and pressure of condensed refrigerant from condenser is decreased by passing the expansion valve and the condensed refrigerant is entered into the evaporator.
Refrigerant that entered into evaporator is evaporated by the high temperature antifreeze that is circulating in the heat exchanger and then it is drawn into the compressor.

Normally, temperature of antifreeze which is circulating in the ground heat exchanger dropped to about 5~6℃ after vaporization of the refrigerant in the evaporator. The entering water temperature of evaporator is about 10℃.
Temperature dropped antifreeze is became the set EWT by exchanging with the soil through the circulation in the pipe of the ground heat exchanger.

About Geothermal Energy

GSHP (Ground Source Heat Pump) is classified as GCHP (Ground Coupled Heat Pump), GWHP (Ground Water Heat Pump), SWHP (Surface Water Heat Pump), HGSHP (Hybrid Ground Source Heat Pump), and so on depending on the type of heat source.

Introduction to Research Methods Resources

  • Collect the city (Si) and district (Gun, Gu) owned borehole data of the country and analyze the geothermal gradient.
  • Collect the borehole data or rock samples around it, and measure the thermal property and build the database.
  • Data analysis (Geothermal gradient, thermal conductivities of rocks, geothermal heat flow)
  • Analysis of the geological and geophysical correlation.
  • Modification of the Digital geological map (1:250,000) and forming of the thematic map using the spatial database.

Domestic Status

When the ground source heat pump works as a cooling cycle, it absorbs the heat from indoors and the heat is released through the ground heat exchanger. High temperature and high pressure refrigerant is sprayed as superheated steam from the compressor and is drawn into the condenser through the 4-way valve. In the condenser, high temperature steam refrigerant exchanges the heat with the circulating fluid (water or antifreeze) of the ground heat exchanger which has relatively low temperature. In this process, the temperature of antifreeze is rising and steam refrigerant is condensed (phase change) from vapor to liquid. High temperature antifreeze is circulating in the ground heat exchanger and then the heat is released into the ground.

High temperature refrigerant reaches low temperature and low pressure by moving the expansion valve. Low temperature and low pressure liquid refrigerant exchanges the heat with indoor air through the evaporator. In this process, liquid refrigerant is condensed (phase change) from liquid to vapor as the indoor air flowing into evaporator is being cooled. Low temperature and low pressure liquid refrigerant from evaporator goes into the compressor through the 4-way valve and after the compression process, it becomes the high temperature, high pressure steam refrigerant again.

  • Development of geothermal heat pump cooling and heating system and technologies for efficiency of ground heat exchanger is in progress to secure the economic feasibility.
  • Studies on the application of the geothermal-use building are actively conducted, so after 2011 when the studies are concluded, the sales will be predicted for a large-scale building, apartment, and so on.
  • In 2010, the development of direct circulating ground source heat pump systems and decentralized geothermal system is gaining support.

Renewable energy supply plan by the 3rd general plan

(Unit: Thousand TOE)

Field 2008 2010 2015 2020 2030 08~30
Annual Growth Rate
Geothermal 9 (0.1) 43 (0.6) 280 (2.4) 544 (3.1) 1,261(3.8) (25.5)

Korea Energy Management Corporation –New & Renewable Energy 2010

Renewable energy supply portion of the total electricity production by the 2nd general plan

(Unit: MWh)

Field 2008 2010 2015 2020 2030
Geothermal - 70,080 744,600 1,401,600 2,803,200

Korea Energy Management Corporation –New & Renewable Energy 2010

Specific plans (Promotion of strategic technology development)

Field Key areas General areas in the short-term Future areas in the long-term
Geothermal Geothermal heating and cooling technologies for reducing the prices Geothermal heat pump system Geothermal power generation technologies

Korea Energy Management Corporation –New & Renewable Energy 2010

Note)
  • Key areas : Priority areas of considering urgency, technology influence, marketability, need for execution of budget
  • General areas in the short-term : Predictable main technical areas after five to ten years
  • Future areas in the long-term : Blue ocean areas in the long-term

The amount of potential

We made the estimation standards for the geothermal potential of Korea in 2008. The following are the analysis results in the initial stage; in this extent, we need to conduct in-depth survey and analysis for calculating the more exact potential.

Natural potential Nationwide natural potential of geothermal energy in 5km depth
Available potential Natural potential in development area (about 6.81% of the size of South Korea)
Select the area above 125℃
Consider the power plant location
Limit to the height of less than 200m
Technical potential Apply the heat recovery rate as 2%, generating efficiency as a maximum of 10% in 125℃, and operation rate as 73% to estimate the potential based on the present technological level

Deep geothermal potential estimated overview

The natural potential for 5km of depth in Korea is 235,225 million TOE, and available potential is 16,013 million TOE which is 6.81% of natural potential by considering the power plant location requirement as the area above 125℃, less than 200m of height, and other requirements.

The technical potential is estimated as 23.4 million TOE by applying of heat recovery rate as 2%, generating efficiency as a maximum of 10% in 125℃, and operation rate as 73% which was surveyed by WEC in 2007.