Geothermal Direct Use


Geo-Heat Center, Oregon Institute of Technology Klamath Falls, Oregon, United States

1. Utilization

2. Equipment

3. Economic Considerations

4. Future Developments


agribusiness application Agriculture and aquaculture de­velopments; in this article, it includes the heating of the various applications, such as greenhouses and fish ponds. aquaculture pond/raceway heating Heat energy provided to ponds and raceway in order to optimize the growing of fish, shrimp, alligators, or other aquatic species. balneology The use of mineral waters for therapeutic purposes.

direct use The use of the heat energy rather than its conversion to other forms such as electricity; for example, a furnace used for space heating. district heating Energy provided to a group of buildings or even to an entire community, generally in the form of hot water or steam supplied from a central plant to customers through a pipeline distribution system. energy cascading The multiple use of an energy source by various applications, with each successive one using an increasingly lower temperature in order to maximize the efficiency of the system.

geothermal energy Energy that can be extracted from the earth’s internal heat. The heat is produced by the radioactive decay of thorium, potassium, and uranium that exist in the earth’s molten core. greenhouse heating Heat energy provide to a glass or plastic enclosure in order to optimize the growing of tree seedlings, flowers, and vegetables. heat pumps A device used to transfer heat from a low- temperature resource to a high-temperature reservoir, thus providing the higher temperature for space heating. The process can be reversed to provide space cooling. industrial application Manufacturing, machining, assem­bling, and producing products for consumption; in this article, it includes the heating of the various applications. space heating Energy provided to a room and building for heating purposes.

Direct or nonelectric utilization of geothermal energy refers to the immediate use of the heat energy rather than to its conversion to some other form such as electrical energy. The primary forms of direct heat use are for swimming, bathing, and balneology (thera­peutic use); space heating and cooling, including district heating; agriculture (mainly greenhouse heat­ing and some animal husbandry), aquaculture (mainly fish pond and raceway heating), and indus­trial processes; and heat pumps (for both heating and cooling). In general, the geothermal fluid tempera­tures required for direct heat use are lower than those for economic electric power generation.

Most direct use applications use geothermal fluids in the low to moderate temperature range between 50 and 150°C, and in general, the reservoir can be exploited by conventional water well drilling equip­ment. Low-temperature systems are also more wide­spread than high-temperature systems (above 150°C), so they are more likely to be located near potential users. In the United States, for example, of the 1350 known or identified geothermal systems, only 5% are higher than 150°C; whereas 85% are lower than 90°C. In fact, almost every country in the world has some low-temperature systems, whereas only a few have accessible high-temperature systems.


Traditionally, direct use of geothermal energy has been on a small scale by individuals. Recent developments involve large-scale projects, such as district heating (Iceland and France), greenhouse complexes (Hungary and Russia), or major industrial use (New Zealand and the United States). Heat exchangers are also becoming more efficient and better adapted to geothermal projects, allowing use of lower temperature water and highly saline fluids. Heat pumps utilizing very low-temperature fluids have extended geothermal developments into

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traditionally nongeothermal countries, such as France, Switzerland, and Sweden, as well as areas of the midwestern and eastern United States. Most equipment used in these projects is of standard, off – the-shelf design and needs only slight modifications to handle geothermal fluids.

Worldwide in 2002, the installed capacity of direct geothermal utilization was 15,145 MWt and the energy use was approximately 190,699 TJ/year (52,976 GWh/year) utilizing at least 52,746 kg/s of fluid distributed among 58 countries. A summary by region is presented in Table I. This amounts to saving an equivalent of 13.5 million tonnes of fuel oil per year (TOE). The distribution of the energy use among the various types of use is shown in Fig. 1 for the world, and for comparison that of the United States is shown in Fig. 2. The installed capacity in the United States (2000) is 4000 MWt and the annual energy use is 20,300 TJ (5640 GWh), saving 3.94 million TOE. Internationally, the largest uses are for space heating (37%) (three-fourths of which is due to district heating) and for swimming, bathing, and balneology (22%), whereas in the United States the largest use is for geothermal heat pumps (59%). In comparison, Iceland’s largest geothermal energy use (77%) is for space heating [15,600 TJ/year (4,334 GWh/year)], primarily with district heating systems.

The Lindal diagram, named after Baldur Lindal, the Icelandic engineer who first proposed it, indicates the temperature range suitable for various direct use activities (Fig. 3). Typically, agricultural and aquacultural uses require the lowest temperatures, from 25 to 90°C. The amounts and types of chemicals in the geothermal water, such as arsenic and dissolved gases such as boron, are a major problem with regard to plants and animals; thus, heat exchangers are often necessary. Space heating requires temperatures in the range of 50-100°C, with 40°C useful in some marginal cases and ground-source heat pumps extending the range to 4°C. Cooling and industrial processing normally requires temperatures higher than 100°C. In terms of market penetration, the leading user of geothermal energy is Iceland, where more than 86% of the population enjoys geothermal heat in their homes from 26 municipal district heating services and 50% of the country’s total energy use is supplied by direct heat and electrical energy derived from geothermal resources.

1.1 Historical Development

Although the direct use of geothermal energy has a much longer history than that of electric power generation, the data on utilization has been under

reported. In fact, it is difficult to compare installed capacity and annual use due to the inclusion or exclusion of bathing, swimming, and balneology data. This has not been consistent; in the past, this use was not included, but in current reports it is included but not in a consistent manner. Also, values prior to 1970 were not summarized and up to 1980 could only be estimated from country descriptions in rapporteur reports. The early reports did not include China, a large user of geothermal energy for direct use, due to the political situation at the time, and they also did not include the United States even though a geothermal district heating system had been installed in Boise, Idaho, in 1892 and individual wells had been utilized in Klamath Falls, Oregon, since the 1930s for home heating. Finally, since many direct uses are small and not concentrated in one place, they are often overlooked by researchers reporting on their own country.

As a result, the 1961 United Nations (UN) conference in Rome reported only developments in Iceland, New Zealand, Italy, Japan, and Kenya. This report described district heating of 45,000 houses in Reykjavik; use of 1000 wells in Rotorua, New Zealand, for space heating; heating of 95,000 m2 of
greenhouses in Iceland; production of 21,000 tons/ year of salt in Japan; the pulp and paper plant at Kawerau, New Zealand; the chemical industry at Larderello, Italy; pig raising in New Zealand; and chicken hatching in Kenya. The 1970 report of the UN meeting in Pisa included descriptions from Hungary, Iceland, Italy, Japan, New Zealand, and the USSR. As mentioned previously, China and the United States were not included. The data in Table II are based on information from the 1970 UN conference in Pisa, a report by Lawrence Livermore Laboratory in 1975, the second UN conference in San Francisco, papers by Lund in 1979 and 1982, and reports from the Geothermal Resources Council (GRC) annual meetings in 1985 and 1990, the 1995 World Geothermal Congress in Italy, and the 2000 World Geothermal Congress in Japan. Starting in 1995, geothermal heat pumps (ground-source heat pumps) were included in the reports and now comprise a significant percentage of the totals.

The large increase in installed capacity between 1980 and 1985 is due to the inclusion of pool heating at spas in Japan (onsen) and the first available data from China. The annual growth rate (based on MWt) from 1970 to 1980 was 9.3%, from 1980 to

1990 it was 15.2% (which was strongly influenced by data from Japan and China), and from 1990 to 2000 it was 6.5%. The overall growth rate during the past 30 years has averaged 10.3% annually. The large increases from 1970 to 1990 (average annual increase of 12.2%) and the reduction from 1990 to present were influenced by the availability of cheap fossil fuels and the economic slowdown in Southeast Asia.

Updated: March 12, 2016 — 10:46 pm