Geothermal district heating for reno, Nevada, U.S.A.

The City of Reno is one of the most obvious candidates for geothermal district heating in the United States. Lying within a helt of major thermal anomalies, it has within its boundaries the Moana Hot Springs geothermal reservoir and probably other reservoirs, and only 14 km to the south is the major reservoir at Steamboat Hot Springs.This paper discusses the alternative heat sources that can be used, and selects Steamboat as the most conservative choice for a “worst-case” analysis of the details and economics of a model district heating system. A closed 16 km transmission loop between Steamboat and downtown Reno is envisaged, carrying 121°C water in the supply line and 65°C in the return line. This loop is isolated by heat exchangers from both the 176°C geothermal fluids at the Steamboat end of the line, and from the Reno user systems at the other. Detailed analysis of thermal demand densities in different parts of the City led to a model distribution network 48 km long, that serves the optimum grouping of zones of concentrated heat users. A large proportion of existing heating systems are hydronic and retrofitting of the selected buildings to the district heating system is relatively straightforward. Total peak load for the proposed system is 138 MJ s⁻¹ (139 MW_t) and annual consumption is 1.1 × 10¹⁵ J. Capital costs total about $55.4 million, in 1981 dollars. The economic analysis shows this system could provide considerable savings relative to the cost of natural gas, if revenue bond financing at 13% is employed for the construction and startup of the system. Even more favorable economic results could be achieved if a geothermal resource could be developed closer to downtown Reno, eliminating the high cost of the 16 km transmission pipeline. Reducing the service area to the most concentrated area of heat use in downtown Reno produces an even more viable system, about half the size of the full system.     

The geothermal exploration of Campanian volcanoes: Historical review and future development

Since Roman time, the heat produced by Neapolitan volcanoes was an appeal for people living in and outside the area, for the fruition of the famous thermal baths. This very large area, which spans from Campi Flegrei and Ischia calderas to Somma-Vesuvius volcano, is characterized by high temperature at shallow depth and intense heat flow, and is yet utilized for the bathing and spa treatment industry, while only in the middle of the 20th century a tentative of geothermal exploitation for energy production was performed. Pioneering researches of geothermal resource were carried out in Campanian region since 1930, until 1985, during which a large amount of geological data were collected. In this paper, we make for the first time a review of the history of geothermal explorations in the active Campanian volcanic area. By the analysis of a great amount of literature data and technical reports we reconstruct the chronology and the main information of the drillings performed since 1930 by the SAFEN Company and successively in the framework of the ENEL-AGIP Joint Venture for geothermal exploration. The available data are utilized to correlate the temperatures measured within the deeper wells with the possible sources of geothermal heat in the shallow crust, down to about 8-10 km of depth. Finally, we assess the geothermal potential of the hottest areas, Ischia Island and Campi Flegrei, which have shown the best data and favorable physical conditions for a reliable, and cost-effective, exploitation for thermal and electric purposes.     

Thermal modeling of the Clear Lake magmatic-hydrothermal system,California, USA

Recent volcanism, high heat flow (4 HFU or 167 mW/m²), and high conductive geothermal gradients (up to 120°C/km) indicate that heat from a shallow silicic intrusion in the Clear Lake region is largely being dissipated by conduction. The Geysers area has the highest heat flow in the region, consistent with the presence of shallow convective heat transport within the vapor-dominated geothermal system. Thermal modeling of the Clear Lake magmatic-hydrothermal system based on petrologic and geophysical constraints provides a test of petrologic models, and yields insight into the relationships between observed thermal gradient and magma chamber size, abundance, and emplacement history in the crust. A user-interactive two-dimensional (2-D) numerical model allowing for complex host rocks and multiple emplacements of magma was developed to simulate conductive and convective heat transport around magma bodies using a finite-difference approach. Conductive models that are broadly consistent with the petrologic history and observed thermal gradients of the Mt. Konocti and Borax Lake areas imply a combination of high background gradients, shallow magma bodies (roofs at 3–4 km), and recent shallow intrusion not represented by eruption. Models that include zones of convective heat transport directly above magma bodies and/or along overlying fault zones allow for deeper magma bodies (roofs at 4–6 km), but do not easily account for the large areal extent of the thermal anomaly in the Clear Lake region. Consideration of the entire Clear Lake magmatic system, including intrusive equivalents, leads us to conclude that: (1) emplacement of numerous small and shallow silicic magma bodies occurred over essentially the entire region of high heat flow (about 750 km²); (2) only a very small fraction (much less than 10%) of the silicic magma emplaced in the upper crust at Clear Lake was erupted; (3) high conductive thermal gradients are enhanced locally by fault-controlled zones of convective heat (geothermal fluid) transport; and (4) except for the Mt. Hannah and possibly the Borax Lake area, most of the silicic magma present in the upper crust has solidified or nearly solidified. These bodies are currently difficult to distinguish from surrounding hot basement rocks dominated by graywacke using geophysical methods. The Clear Lake region north of the Collayomi fault is one of the best prospects for hot dry rock (HDR) geothermal development in the US, but is unlikely to provide significant development opportunities for conventional geothermal power production. Modeling results suggest the possibility that granitic bodies similar to The Geysers felsite may underlie much of the Clear Lake region at shallow depths (3–6 km). This is significant because future HDR reservoirs could potentially be sited in granitoid plutons rather than in structurally complex Franciscan basement rocks.     

Use of a probabilistic model to design energy transmission and distribution networks for low enthalpy geothermal multiple use schemes

A probabilistic model is suggested for the design of transmission and distribution network of geothermal energy to potential consumption sites, in cases where the development of various competitive or complementary non-electrical uses is probable, within the broader area of a field. The model can be used to find out (a) the optimum network that may offer the best economic results to the agent who will undertake the development of the field, and (b) the corresponding selling price at which the thermal fluids will be supplied to the end users who are assumed to be other than the above agent. Model input data can be collected in the frame of an appropriate market study, which is roughly specified in this work and commented according to relevant experience from a Greek geothermal field. Finally, applicability of the model is demonstrated through an indicative example.     

油区地热能综合利用方案分析——以福山油田为例*

油田区域地热资源十分丰富,并且存在大量的用热需求。在油田地区综合开发地热能,不仅可以解决油田伴热、社区供暖/制冷等问题,还可以降低环境污染,减少二氧化碳的排放,有利于油田的持续稳定发展。基于海南福山油田的地热资源条件及用能需求,将油田生产伴热、热泵尾水升温和地热驱动吸收式制冷技术相结合,设计了多种油田地热能综合利用方案,并计算比较了各个方案的经济收益,进一步分析了地热水温度和流量对各个方案适用性的影响,研究结果可为其他油田区域地热资源的综合开发利用提供参考。     

Direct uses of earth heat

Potential resources and applications of earth heat in the form of geothermal energy are large. World-wide direct uses amount to 7072 MW thermal above a reference temperature of 35°C. District heating is the major direct use of geothermal energy. Equipment employed in direct use projects is of standard manufacture and includes downhole and circulation pumps, transmission and distribution pipelines, heat exchangers and convectors, heat pumps and chillers. Direct uses of earth heat discussed are district heating and cooling, greenhouse heating and fish farming, process and industrial applications, combined and cascading uses. The economic feasibility of direct use projects is governed by site specific factors such as location of user and resource, resource quality, system load factor and load density, as well as financing. Examples are presented of district heating in Reykjavík, Klamath Falls, Melun l'Amont and Svartsengi. Further developments of direct uses of geothermal energy will depend on matching user needs to the resource, and improving load factors and load density.     

Rapid estimation of geothermal coverage by district-heating systems

An algorithm is developed for the quick estimation of the fraction of annual heat-load that is covered by geothermal energy in district-heating systems. The cases of direct use, heat exchange and heat-pump application are distinguished. The algorithm proved accurate enough for pre-feasibility study purposes and for preliminary considerations with regard to the management of geothermal energy. It is demonstrated that for coverage estimation, detailed heat-supply calculations can be substituted by the use of degree-days, which are quite often available for various base temperatures. Furthermore, the analytic expressions of the algorithm allow the quantitative evaluation of several parameters. Specifically, for low temperature geothermal fluids the coverage is an increasing second-degree function of the temperature of the fluids. Increasing network return temperatures has also a decreasing effect on the coverage. The required geothermal-flow is inversely proportional to the heat exchanger effectiveness, for the same coverage. Application of a heat pump results in a higher coverage that should otherwise require a higher temperature fluid. It is consequently defined as an equivalent geothermal-temperature increase – due to the heat pump – that is proved to be proportional to the compressor capacity. Last, the network supply-temperatures have a rather secondary effect upon the coverage, affecting the flow through the network and so the effectiveness of the heat exchanger.     

The potential of district heating using geothermal energy. A case study, Greece

The purpose of this study is to investigate the possibility of using low-enthalpy geothermal energy from the geothermal field of Sousaki in the province of Korinthos, Greece, to cover the thermal needs of the nearby town of Ag. Theodori. The possibility of developing a system of district heating was examined based on a proposed town model. Total thermal demands were calculated on the basis of a model dwelling and prevailing weather conditions in the area. Subsequently, a heat transfer circuit is proposed, including the distribution network, the heat exchanger, the production and reinjection pumps, and the pumping station. Finally, energy indices are presented, such as demand in tons of equivalent oil and CO₂ emissions.     

Geothermal energy utilization in Turkey

This paper investigates the status of geothermal development in Turkey as of the end of 1999. Turkey is one of the countries with significant potential in geothermal energy. Resource assessments have been made many times by the Mineral Research and Exploration Directorate (MTA) of Turkey. The main uses of geothermal energy are mostly moderate‐ and low‐temperature applications such as space heating and domestic hot water supply, greenhouse heating, swimming and balneology, industrial processes, heat pumps and electricity generation. The data accumulated since 1962 show that the estimated geothermal power and direct use potential are about 4500 MW_e and 31 500 MW_t, respectively. The direct use capacity in thermal applications is in total 640 MW_t representing only 2 per cent of its total potential. Since 1990, space heating and greenhouse developments have exhibited a significant progress. The total area of greenhouses heated by geothermal energy reached up to about 31 ha with a heating capacity of 69.61 MW_t. A geothermal power plant with a capacity of 20.4 MW_e and a CO₂ factory with a capacity of 40000 ton yr^?1 have been operated in the Denizli‐Kizildere field since 1984 and 1986, respectively. Ground source heat pumps have been used in residential buildings for heating and cooling for approximately 2 years. Present applications have shown that geothermal energy in Turkey is clean and much cheaper compared to the other energy sources like fossil fuels and therefore is a promising alternative. As the projects are recognized by the public, the progress will continue. Copyright © 2001 John Wiley & Sons, Ltd.     

Current status of ground source heat pumps and underground thermal energy storage in Europe

Geothermal Heat Pumps, or Ground Coupled Heat Pumps (GCHP), are systems combining a heat pump with a ground heat exchanger (closed loop systems), or fed by ground water from a well (open loop systems). They use the earth as a heat source when operating in heating mode, with a fluid (usually water or a water–antifreeze mixture) as the medium that transfers the heat from the earth to the evaporator of the heat pump, thus utilising geothermal energy. In cooling mode, they use the earth as a heat sink. With Borehole Heat Exchangers (BHE), geothermal heat pumps can offer both heating and cooling at virtually any location, with great flexibility to meet any demands. More than 20 years of R&D focusing on BHE in Europe has resulted in a well-established concept of sustainability for this technology, as well as sound design and installation criteria. Recent developments are the Thermal Response Test, which allows in-situ-determination of ground thermal properties for design purposes, and thermally enhanced grouting materials to reduce borehole thermal resistance. For cooling purposes, but also for the storage of solar or waste heat, the concept of underground thermal energy storage (UTES) could prove successful. Systems can be either open (aquifer storage) or can use BHE (borehole storage). Whereas cold storage is already established on the market, heat storage, and, in particular, high temperature heat storage (> 50 °C) is still in the demonstration phase. Despite the fact that geothermal heat pumps have been in use for over 50 years now (the first were in the USA), market penetration of this technology is still in its infancy, with fossil fuels dominating the space heating market and air-to-air heat pumps that of space cooling. In Germany, Switzerland, Austria, Sweden, Denmark, Norway, France and the USA, large numbers of geothermal heat pumps are already operational, and installation guidelines, quality control and contractor certification are now major issues of debate.     

The use of natural gas and geothermal energy in school units. Greece: A case study

The ever-increasing degradation of the environment along with high demands for energy consumption in buildings has prompted many countries to use other energy sources such as natural gas and geothermal energy instead of oil.This study refers to the use of natural gas in school units in Greece. More specifically, it focuses on school units that are connected to the natural gas network and on the economic and environmental benefits arising from this.In this context, the advantages and disadvantages in using natural gas are compared with those resulting from the use of geothermal energy. In areas which have a significant geothermal potential, the choice of geothermal heating and cooling of large school units is the best solution, but this however does not apply to all areas. Clearly, the development of geothermal energy in school units is still in pilot stage.However, the use of natural gas in school units has been rising over the last decade and it has already contributed to some extent towards the reduction of carbon dioxide and towards saving natural resources. Thus, the survey shows clear advantages in using natural gas and in plans to extend its use to other school units.     

Geothermal resources in the shallow, unsaturated zone of the Wiesbaden spa district, Germany

The geothermal energy potential of the Wiesbaden spa district continues to be largely untapped. Although the thermal water is being utilized, any other activity liable to disturb the hydraulic regime of the thermal springs is prohibited. The geothermal potential of the unsaturated zone in the spa district has been mapped, although the zone must be regarded as a thermal insulator rather than a good conductor. The results of the mapping revealed the presence of a number of heat anomalies that could be exploited in the future; further economic benefits could be gained from installing the heat transfer units during road works. The modelling studies considered two possible scenarios: direct heating and heat pump usage. The results indicate that heat pumps are the more efficient option, yielding a thermal capacity of approximately 100 W/m².     

Geothermal reservoir potential of volcaniclastic settings: The Valley of Mexico,Central Mexico

The geothermal potential of the Valley of Mexico has not been addressed in the past, although volcaniclastic settings in other parts of the world contain promising target reservoir formations. An outcrop analogue study of the thermophysical rock properties of the Neogene rocks within the Valley of Mexico was conducted to assess the geothermal potential of this area. Permeability and thermal conductivity are key parameters in geothermal reservoir characterization and the values gained from outcrop samples serve as a sufficient database for further assessment. The mainly low permeable lithofacies types may be operated as stimulated systems, depending on the fracture porosity in the deeper subsurface. In some areas also auto-convective thermal water circulation might be expected and direct heat use without artificial stimulation becomes reasonable. Thermophysical properties of tuffs and siliciclastic rocks qualify them as target horizons for future utilization of deep geothermal reservoirs.     

Background, present state and future prospects of geothermal development

After a brief review of the nature, origin and occurrence of geothermal energy, the various conceptual models of geothermal systems are described.Subsequently the different utilizations of terrestrial heat (direct, indirect and combined) are described and the related production technologies are briefly illustrated.Following a historical overview of the development of geothermal energy, the current situation is presented (4719 MW electric and 12,000 MW thermal) and a projection for the end of the century is made (20,000–40,000 MWe and 19,000–33,000 MWt).A breakdown of geothermal projects and a block diagram of the costs and various activities is then presented and an average expenditure value is given.Finally, the role of geothermal energy in the overall energy context is discussed, as well as the main problems, both technical and non-technical, that will have to be faced in the future.     

An investigation of the technical and economical feasibility of using low temperature geothermal sources in Colorado

A preliminary feasibility study of utilizing low temperature geothermal sources in Colorado to heat buildings has been completed. It is concluded that the technology for using geothermal sources to heat building exists and that the cost of heat will be between $2 and 5 per million Btu delivered. Although geothermal heating is more expensive than heating with natural gas at current prices, it is considerably less expensive than heating by means of current solar thermal conversion methods. It is, therefore, recommended that an exploratory well be drilled in a place such as Glenwood Springs, Colorado, to define the thermal, chemical, and geological characteristics of a geothermal source in detail as a first step toward utilization of geothermal energy on a commercial scale in Colorado.     

Geothermal energy in Phrao Basin, Chiang Mai, Thailand

Phrao Basin is famous for its geothermal and seismic activities. There are five geothermal manifestations along the western margin of the basin. These geothermal sites are probably controlled by the major fault extending northward from the Sankamphaeng geothermal field. Geological, geochemical and geophysical studies, along with 2 boreholes of 150 m depth, were aimed at investigating the potential of this area. The results indicated that the intermediate depth of the geothermal reservoir may produce enough hot fluids for various uses, albeit on a small-scale. Several industries that could be attracted to Phrao Basin by development of these geothermal areas have been identified.     

Comparing completion design in hydrocarbon and geothermal wells: The need to evaluate the integrity of casing connections subject to thermal stresses

Tapping for geothermal energy very often requires deep drilling in order to access high-temperature resources. This type of drilling is expensive and is financed by the operator with a long period of debt service before costs can be recovered from the energy sale (heat, electricity or a combination of both). Drilling costs are only a part of the total well expenditure. Tubulars can double the total well cost, especially when complex well completions are required. Together, drilling and well completions can account for more than half of the capital cost for a geothermal power project. A comparison is made of the different completions used for oil, gas and geothermal wells, and geothermal well completion requirements are discussed. Special attention is given to the thermal stresses induced by temperature variations in the casing string of a geothermal well. When the induced thermal stresses exceed the yield strength of the casing material, the fatigue behavior of the latter can be defined as low-cycle fatigue (LCF). The connection threads in the casing body amplify the local stresses and lower the LCF resistance. A theoretical approach is presented to evaluate that parameter, and calculations are compared with preliminary results from experiments on large-diameter Buttress connections, which are commonly used in geothermal well completions. It is shown that under extreme loads the LCF resistance of the Buttress thread connection can be as low as 10 cycles.     

Three-dimensional imaging of a geothermal system using temperature and geological models derived from a well-log dataset

The accurate imaging of geothermal systems from the ground surface down to great depths is an interdisciplinary problem common to geothermal resource exploration and development. Rocks can be characterized mainly in terms of their lithology, mineralogy, fracture distribution, permeability, thermal conductivity and porosity, and similarly the geothermal fluid (and its circulation) by its geochemistry, flow pattern, velocity, temperature and pressure. Some of these data are obtained by well logging and from laboratory tests conducted on drillhole cores. In general, the distribution of geothermal wells is not random, and well data are limited in terms of quantity and depth range. Accordingly, a sophisticated spatial modeling technique is indispensable in the three-dimensional imaging of geothermal systems. We describe a versatile 3-D modeling method that can be used to determine the temperature, flow velocity, and distribution of geological units within a geothermal field based on well log data. The model results for the Hohi geothermal area, Japan, provide plausible estimates of temperature, flow velocity, and geology to a depth of 3000 m. Superimposition of the three spatial models we obtained shows that, at Hohi, two geothermal reservoirs are localized near highly fractured fault zones that provide paths for the ascent of thermal fluids from depth.     

Enel activity in the research, exploration and exploitation of geothermal energy in Italy

In Italy the utilization of geothermal resources for industrial purposes began about 150 years ago. Prior to 1913, geothermal fluids were utilized both as a source of heat and chemical products; from 1913 to 1965, combined chemical and electric production was achieved; from 1965 on, power generation prevailed over chemical production, which was abandoned immediately thereafter; between 1975 and 1984, geothermal energy was mostly used for generating electricity, but a number of thermal projects were also started.An overview is given of Italian geothermal development after 1975, including electric production and direct applications of geothermal heat.More in particular, the research and development activity in the period 1975–1985 is first presented, and the criteria, programmes and development objectives through 1995 are then illustrated.     

Development of a radial-flow multiple magnetically coupled fan system with one piezoelectric actuator

In recent years, piezoelectric fans and their feasibility for use in cooling electronic devices have been widely studied. However, there are few studies that address using a single piezoelectric actuator to generate radial air flow. In this study, a radial-flow multiple fan system (RMFS) was developed for the thermal management of high power LEDs. This system only used one piezoelectric actuator and a magnetic repulsive force to activate up to 20 fans, which featured low power consumption and a large cooling area. The RMFS was mounted in a circular heat sink to evaluate its thermal performance. To find the optimal design for the RMFS, the influence of some geometric parameters was investigated. The performance of different designs was compared with a commercially available axial fan. The results showed that design E had the best thermal performance among the designs because of its relatively large frequency and amplitude. The thermal resistance and percentage improvement under a 35 W heat flux were 0.86 K/W and 36.9%, respectively. In addition, a coefficient of performance (COP) was defined. The COP of design E was approximately 3.7 times that of the rotary fan. For the power consumption aspect, the RMFS is more efficient than the rotary fan.