Geothermal Systems

System Types, Applicability and Environmental Impacts

Alex Morris and Andrea Sheets

csd Center for Sustainable Development UTSoA - Seminar in Sustainable Architecture

Geothermal Systems

Alex Morris Andrea Sheets

main picture of presentation

Fig. 01 Currently, is most commonly used to heat homes in extremely cold climates.

Introduction temperatures range from 45 to 75 degrees depending on the elevation. and solar power systems have become part If all geothermal resources were of common knowledge and combined, enough energy would conversation over the past few be produced to provide all of the years. While these provide excellent electricity needs in the United sustainable options of energy States.2 Why then is this option production, geothermal energy employed much less commonly and systems are just as efficient and rarely even involved in sustainable economical. system conversations?

Solar and wind energy collectors Much of this report is based on are site specific. Photo-voltaic information presented by Bruce L. cells will not harness much energy Cutright. Throughout the course in northern locations. The area of his extensive research, he has required to collect wind power can come to the logical conclusion that not be found in large cities. However the capabilities and affordability geothermal systems do not take up of geothermal systems are largely buildable ground level space nor underestimated. A lack of publicly are they location or climate specific. available information is the main The earth has a generally constant reason that these systems are not temperature throughout the year widely used. With improvements which can be used in geothermal in technology and decreases in systems to benefit all sites.1 Figure installation cost, this is now not only 02 shows the average ground a cost-competitive system but could temperatures across the United have a great impact on the future of States. At six feet below the surface, worldwide energy usage.

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Some of the most important yet often underestimated effects of geothermal systems are their environmental impacts beyond energy related matters. Possible consequences to the earth and ecosystem from drilling to such great depths, involving natual water sources into the process, and the activity of heat transfers underground are necessary to understand in order to fully evaluate geothermal systems.

What is Geothermal Heating and Cooling?

Geothermal Heating and Cooling Systems provide space conditioning, and in some cases . These systems Fig. 02 Mean annual earth temperature observations at individual stations, superimposed on well-water temperature contours work by moving heat, rather than by converting chemical energy to heat like in a furnace. A typical system has three major parts: a series of underground pipes (the geothermal loop), a geothermal to move heat between the building and the ground, and a distribution system (a fan and duct work, a radiant floor, etc). When heating the building, the system operates by circulating a fluid through the loop and drawing heat from the soil. The fluid is then pushed through the heat pump inside the building and moved through a . When cooling a building, the process is reversed in order to pull heat out of the building. In open-loop systems, this heat is discharged into the outside air, while in closed-loop systems, the heat is transferred into the soil. This is possible due to the relatively constant temperature a few feet below the earth’s surface, which ranges from between 45º and 70º (data from www.geoexchange.com). In the winter, the earth is used as a heat source, and in the summer, it acts as a heat sink.3

Fig. 03 Amplitude of seasonal soil temerature change as a function of depth below ground surface 2 Geothermal Systems

Energy Sources, Systems and either open- or closed-loop. In most Technological Advances open-loop systems, well water is drawn to the heat exchanger, and The energy for geothermal then discharged into a separate systems may be derived from a well, a field, or a body of water. In number of sources: from magmatic a closed-loop system, the same or hydrothermal areas, from fluid is repeatedly moved through geopressured zones or high-heat a continuous loop of pipes. In flow zones using co-produced fluids either case, the initial capital cost is from active or abandon oil or gas between 30-50% higher than that wells, and from hot dry rocks located of a conventional heating or cooling in deep geologic zones having high system. heat flow. Advances in drilling technology There are two primary types have made 8-10km deep holes of systems: ground source or possible due to polycrystalline source heat exchange diamond compact bits and slim- systems, and enhanced geothermal hole drilling. Advances in controlled systems, or EGS. The system most fracture development have made commonly used today is the ground enhanced geothermal systems source heat exchange system, practical. Advances in Binary-Cycle because while subsurface conditions Heat Exchange Systems have made vary, a viable ground source heat 100 degree Celsius heat sources exchange system can be designed economical.4 for nearly any geologic conditions. Ground source systems can be

Fig. 04 Illustration of geothermal cooling cycle using a closed loop system. 3 UTSoA - Seminar in Sustainable Architecture

Fig. 05 A horizontal loop geothermal system. Loop installers use excavation equipment such as chain trenchers, backhoes and track hoes to dig trenches approximately 6-8 feet deep. Trench lengths range from 100 to 300 feet, depending on the loop design and application.

Fig. 06 A vertical loop geothermal system. A drilling rig is used to bore holes at of depth of 150 to 200 feet. A U-shaped coil of high density pipe is inserted into the bore hole. The holes are then backfilled with a sealing solution.

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Fig. 07 A pond loop geothermal system. The system uses coils of pipe typically 300 to 500 feet in length. The coils are placed in and anchored at the bottom of the body of water.

Fig. 08 An open loop geothermal system. This system can be installed if an abundant supply of high quality well water is avail- able. A proper discharge area such as a river, drainage ditch, field tile, stream, pond, or lake must be present.

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Efficiency

Geothermal systems create positive energy, meaning that they produce higher quantities of energy than they require to operate.

Each kilowatt hour that geothermal heat pump systems consume leads to the production of three to six kilowatt hours of heat. The same efficiency rates apply to groundwater source heat pumps. This is due to the fact that these systems are only using energy to move around fluids and not to generate heat.5 Fig. 09 Installed loop cost per ton of capacity as of 1995. Economics construction processThe are considered Case twenty five tofor fifty years. Geothermal Additionally, Energy easily accessible depths This is the geothermal systems are LEED Overall Cost range of depth where geothermal recognized and Energy Star issues heat pumps are applicable.7 rebates for some of the costs of Geothermal systems have high initial installing a geothermal system. costs. The highest component of Maintenance• costsCost are relatively comparisons low. for generation of electricity this cost is the ground loop. Figure There are fewer mechanical parts Cost Comparison with Alternative 09 lists prices per ton of capacity than traditional heating and cooling Systems for different ground loop types. On systems, and mostover components the are last 30 years average, Ground Source Heat underground and therefore sheltered The initial costs of the systems Pumps cost a total of $2,500 per ton from weather. The piping used in are approximately 30-50% higher 6 of capacity. these systemsCosts ,lasts in Cen tans p eaverager KWhr, for ofPo wer Genthaneratio na f rregularom Hydro caheatrbon pump Source ssystem Upper and Lower Cost Range of Energy for Alternative Energy Sources, Expressed in Cents per KWhr Some of the increased costs can 4 also be attributed to the fact that 140.0 there is limited competition in this 3.5 120.0 market. However, over the past Oil 3 Photovoltaics thirty years, improvements in drilling technology, advancements in binary- Natural Gas 100.0 r 2.5 Concentrating Solar h cycle heat exchange systems and w h K

W

e r Composite Hydrocarbon 80.0 K p advances in controlled fracture 2 r s e t p Wind development have greatly increased en s t C n the affordability of these systems. 1.5 e 60.0 C Geothermal

1 Drilling does add heavily to the 40.0 overall cost. Geothermal systems Coal 0.5 that are installed at depths that are 20.0 no deeper than one hundred meters 0 or what would be part of the normal 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 0.0 Year 1975 1980 1985 1990 1995 2000 2005 2010

Fig. 10 Cost, in Cents per KWhr, for Power Generation from Hydrocarbon Sources.

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Bruce L. Cutright The Case for Geothermal Energy Geothermal Systems

• Cost comparisonswith air conditioning.8 Howeverfor generationconcluded that geothermal of systems electricity and cooling systems on the market.10 throughout the course of operation have the lowest life cycle cost of over the lastand maintenance, 30 years savings can all currently available heating and Geothermal systems positively effect amount to 40% according to the U.S. cooling systems. They consider the environment because they: Environmental Protection Agency. geothermal heat pumps to be the • reduce dependence on foreign most environmentally clean, energy- oil as they are “homegrown” Costs, in Cents per KWhr, for Power Generation from Hydrocarbon Sources Upper and Lower Cost Range of Energy for Alternative Energy Sources, Expressed By using these systems, major in Cents per KWhr 4 conventional equipment is eliminated which reduces cost and size needed 140.0 3.5 in the buiding. The boiler, chiller, complex controls, mechanical room 120.0 Oil Photovoltaics 3 size, added structural roof support, Natural Gas exterior heat exchange system and 100.0 r 2.5 Concentrating Solar h

w roof penetration and access are no h K

W e r Composite Hydrocarbon 80.0

longer needed. Additions include K p 2 r s e t p ground heat exchanger, heat pumps, Wind en s t C n

1.5 large circulation pumps (which are all e 60.0 underground) and possibly larger air C Geothermal 1 9 ducts and partial pipe insulation. 40.0 Coal 0.5 EnvironmentalThe Implications Case for Geothermal Energy 20.0

0 Positive Environmental Effects 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 0.0 Year 1975 1980 1985 1990 1995 2000 2005 2010 A study conducted by the U.S. E.P.A. Fig. 11 Upper and Lower Cost Range of Energy for Alternative Energy Sources, in Cents per KWhr

Levelized Cost of Electricity Analysis (Source: Credit Low Suisse 2009) High Case Base Case Case Minimum

Solar Photovoltaic (crystalline) $201 $153 $119 $119

Bruce L. Cutright Solar Photovoltaic (Thin Film) $180 $140 $110 $110

Fuel Cell $117 $90 $72 $72

Solar Thermal $126 $90 $69 $69

Coal $66 $55 $46 $46

Natural Gas (CCGT) $64 $52 $40 $40

Nuclear $64 $62 $35 $35

Wind $61 $43 $29 $29

Geothermal $59 $36 $22 $22

Conservation/Efficiency $30 $15 $0 $0

(figures in dollars per MWhr)

Fig. 12 Cost, in dollars per MWhr, for varying power generation systems

Bruce L. Cutright 7 UTSoA - Seminar in Sustainable Architecture

efficient, and cost-effective heating depleting substance, until recently. deep drilling and draw their water • provide a consant source of This product is now being phased from a well may contribute to energy twenty four hours a day out in favor of a non-toxic fluid. the depletion of acquifers, water • can be obtained without burning shortages, contamination of any fossil fuels Depending on the soil and rock groundwater and soil errosion conditions of a specific location, issues. In Germany, the town of Negative Environmental Effects the pumping of fluids can cause Staufen im Breisgau has been tensile or shear failure in the rock experiencing considerable ground Although geothermal systems leading to seismic activity. In level shifts since the Fall of 2007 produce zero emissions locally, Basel, Switzerland (an earthquake when deep drilling was conducted to the electricity needed to run them prone zone), enhanced geothermal accommodate a geothermal system. often contributes to harmful carbon systems lead to a eathquake with At first the town sank by a couple of emissions. Therefore their true a magnitude of 3.4 during the centimeters, and by 2008 it had risen impact on the environment needs beginning of 2007. It has been by about five inches. Research has to be evaluated with the inclusion argued that these occurances can be concluded that the official cause of of the sourse of their electric greatly reduced through predictive these rapid level changes is from suppply. Also, the fluid used to run siting techniques. the mineral anhydrite transforming through theThe closed loops Case contained for Geothermalinto .Energy This happens when chlorodifluoromethane, an ozone Open-loopWhy the systems Hyperbole? which require anhydrite comes into contact with

Estimated U. S. Geothermal Resource Base to 10km Depth by Category (Modified from "The Future of Geothermal Energy, MIT 2006) Thermal Energy, in ExaJoules Thermal Energy in Barrels of (1EJ = 1018 J) Oil Equivalent Category of Resource High-Low Range High-Low Range Hydrothermal 2.40E+03 9.60E+03 4.13E+11 1.65E+12 Co-Produced Fluids 9.44E-02 4.51E-01 1.62E+07 7.76E+07 Geopressured Systems 7.10E+04 1.70E+05 1.22E+13 2.92E+13 US Annual Primary Energy 94.14 1.81E+10 Consumption (2008)

COMPARISON OF FOSSIL FUEL EXTRACTABLE RESERVES TO GEOTHERMAL GEOPRESSURED/CO-PRODUCED FLUIDS EQUIVALENT ENERGY RESERVES Source Estimate of Extractable Reserves Reference Canadian Tar Sands 300 billion barrels of oil equivalent Edwards, 1997 Orinoco Heavy Oils 267 BBLSOE Edwards, 1997 Green River Shales 139 BBLSOE Edwards, 1997 U. S. Proven Reserves of Crude Oil 21.3 BBLSOE EIA 2008

Geothermal Resources 29,200 BBLSOE (29.2 x 1012 BLSOE) Blackwell, 2006

Fig.B r13u c Charte L. Cudisplayingtrigh efficiencyt of geothermal systems

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water. The common belief is that was installed under a completely Teachers and students reported drilling broke into a layer of high paved area as a retrofit project, and satisfaction with the system and pressure groundwater and exposed energy savings are still estimated at appreciate the individual control each stata of the earth to water that were 25%. room has over the temperature.12 not originally in contact with the element.11 The installation costs for Pease Conclusion Elementary are as follows: Case Studies • Heat Pumps: $92,000 Although geothermal systems • Loop Wells: $96,000 still do not draw the same level Austin, Texas Schools • Other/Installation: $86,170 of attention as do solar and wind • Utility Rebate: $5,470 energy systems, their use is The Austin Independent School ($2,000 per kW on heat pump increasing for multiple reasons. District was the very first school nameplate) Rapidly improving efficiency caused district in the nation to install • Total: $268,700 by technological advances in drilling GeoExchange geothermal systems and heat exchange have expanded on a broad scale. Since 1989 almost Besides savings in energy, AISD the area in which these systems can all new heating and cooling system has also noticed an improvement be used, along with how well they installations in Austin schools have in maintenance. With a little over perform. Meanwhile, heightened been GeoExchange. Total estimated one hundred schools in the district, awareness of their benefits through savings were around 25% in energy stocking parts like chillers, boilers recognition in programs like LEED costs according to a report from and convectors for traditional and Energy Star have demonstrated 1997. Figure 14 shows energy systems was quite a difficult task. the reduced environmental impacts savings for four AISD schools. By standardizing the GeoExchange of the systems, as well as their units, maintenance was majorly low maintenance costs and high In all cases, the system has reduced. Replacement and repair return values. As additional high- improved energy performance. This can be done classroom by classroom profile examples of geothermal is regardless of the school size, as each room’s unit is individually systems – such as that of the Austin the previous type of system, or the connected to a well system. Independent School District – are individual conditions surrounding However this method did add to the built, the use of these systems installation and operation. At Pease installation cost. should only increase. Elementary, for instance, the system

School Pease Elementary Brooke Elementary Govalle Elementary Bailey Middle

New/Retrofit Retrofit Retrofit Retrofit New

Square feet 39,162 51,605 89,319 approx. 200,000

Old System Roof Packaged not available Chiller, gas none

Capacity 90 tons approx. 150 tons approx. 230 tons 512 tons

Est. $ Savings 25% 25% 20% not available

kWh/sq ft 8.3 9.6 8.5 not available

Students 298 346 626 1614

Year Installed 1994 1993 1994 1992

Fig. 14 Installation and cost information for four AISD schools.

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Notes 12. Geothermal Heat Pump Consortium, Figure 12: Bruce L. Cutright, “The Case for “Austin Independent School District, 1997”, Geothermal Energy” (Presentation for the 1.Geo4VA, “Seasonal Temperature Cycles”, GeoExchange, http://www.geoexchange.org, Meadows Seminar at the University of Texas Virginia Tech, http://www.geo4va.vt.edu/A1/ accessed November 2009. in Austin, Texas, October 29, 2009). A1.htm, accessed November 2009. Figure 13: Bruce L. Cutright, “The Case for 2. Bruce L. Cutright, “The Case for Geother- Figures Geothermal Energy” (Presentation for the mal Energy” (Presentation for the Meadows Meadows Seminar at the University of Texas Seminar at the University of Texas in Austin, Figure 01: About My Planet, “Geothermal En- in Austin, Texas, October 29, 2009). Texas, October 29, 2009). ergy”, AmpBlogs Network, http://www.about- myplanet.com/alternative-energy/geothermal- Figure 14:Geothermal Heat Pump Consor 3. Geothermal Heat Pump Consortium “Com- energy/2009, accessed November 2009. tium, “Austin Independent School District, mon Questions.” 2006. http://www.geoex- 1997”, GeoExchange, http://www.geoex- Figure 02: Geo4VA, “Seasonal Temperature change.org/resources/common-questions. change.org, accessed November 2009. html, accessed November, 2009. Cycles”, Virginia Tech, http://www.geo4va. vt.edu/A1/A1.htm, accessed November 2009. 4. Bruce L. Cutright, “The Case for Geother- References mal Energy” (Presentation for the Meadows Figure 03: Geo4VA, “Seasonal Temperature Seminar at the University of Texas in Austin, Cycles”, Virginia Tech, http://www.geo4va. Reference 01 Kavanaugh, Steve, Christopher Texas, October 29, 2009). vt.edu/A1/A1.htm, accessed November 2009. Gilbreath, and Joseph Kilpatrick. 1995. Cost Containment for Ground-Source Heat Pumps. 5. Consumer Energy Center, “Geothermal Figure 04: GeoComfort. Illustration of geother- Final Report submitted to the Alabama Heat Pumps”, California Energy Commission, mal cooling cycle, 2008. http://geocomfort. Universities-TVA Research Consortium and http://www.consumerenergycenter.org/home/ publishpath.com/geothermal-technology (ac- the Tennessee Valley Authority, December. heating_cooling/geothermal.html, accessed cessed November, 2009). November 2009. Reference 02 Hughes, Patrick J. 2008. Figure 05: GeoComfort. Illustration of hori- Geothermal (Ground Source) Heat Pumps: 6. Steve Kavanaugh et al., “Cost Containment zontal closed-loop geothermal system, 2008. Market Status, Barriers to Adoption, and for Ground-Source Heat Pumps” (Final Report http://geocomfort.publishpath.com/geother- Actions to Overcome Barriers. Sponsered by submitted to the Alabama Universities-TVA mal-technology (accessed November, 2009). EERE Geothermal Technologies Program and Research Consortium and the Tennessee Val- the U.S. Department of Energy, December. ley Authority, December 1995). Figure 06: GeoComfort. Illustration of vertical closed-loop geothermal system, 2008. http:// Reference 03 Geothermal Heat Pump 7. Bruce L. Cutright, “The Case for Geother- geocomfort.publishpath.com/geothermal-tech- Consortium. Austin Independent School mal Energy” (Presentation for the Meadows nology (accessed November, 2009). District, 1997. GeoExchange. http://www. Seminar at the University of Texas in Austin, geoexchange.org. Accessed November 2009. Texas, October 29, 2009). Figure 07: GeoComfort. Illustration of pond loop geothermal system, 2008. http://geocom- Reference 04 Doherty, P.S., S. Al-Huthaili, 8. Steve Kavanaugh et al., “Cost Containment fort.publishpath.com/geothermal-technology S.B. Riffat and N. Abodahab. November for Ground-Source Heat Pumps” (Final Report (accessed November, 2009). 2003. - submitted to the Alabama Universities-TVA Description and Preliminary Results of the Research Consortium and the Tennessee Val- Figure 08: GeoComfort. Illustration of open Eco House System. School of the Built ley Authority, December 1995). loop geothermal system, 2008. http://geocom- Environment, Institute of Building Technology, fort.publishpath.com/geothermal-technology University of Nottingham. 9. Consumer Energy Center, “Geothermal (accessed November, 2009). Heat Pumps”, California Energy Commission, Reference 05 Geo4VA. Seasonal Temperature http://www.consumerenergycenter.org/home/ Figure 09: Steve Kavanaugh et al., “Cost Cycles. Virginia Tech. http://www.geo4va. heating_cooling/geothermal.html, accessed Containment for Ground-Source Heat Pumps” vt.edu/A1/A1.htm. Accessed November 2009. November 2009. (Final Report submitted to the Alabama Universities-TVA Research Consortium and Reference 06 Bruce L. Cutright. The Case 10. Energy Star, “Geothermal Heat Pumps”. the Tennessee Valley Authority, December for Geothermal Energy. Presentation for the U.S. EPA, http://www.energystar.gov/index. 1995). Meadows Seminar at the University of Texas cfm?c=geo_heat.pr_geo_heat_pumps, ac- in Austin, Texas, October 29, 2009. cessed November 2009. Figure 10: Bruce L. Cutright, “The Case for Geothermal Energy” (Presentation for the Reference 07 Consumer Energy Center. 11.SwissInfo with Agencies, “Man-Made Trem- Meadows Seminar at the University of Texas Geothermal Heat Pumps. California Energy or Shakes Swiss City of Basel” SwissInfo, in Austin, Texas, October 29, 2009). Commission. http://www.consumerenergycen- http://www.swissinfo.ch/eng/Man-made_trem- ter.org/home/heating_cooling/geothermal.html. or_shakes_Basel.html?cid=46232, accessed Figure 11: Bruce L. Cutright, “The Case for Accessed November 2009. November 2009. Geothermal Energy” (Presentation for the Meadows Seminar at the University of Texas Reference 08 Energy Star. Geothermal Heat in Austin, Texas, October 29, 2009). Pumps. U.S. EPA. http://www.energystar.gov/

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index.cfm?c=geo_heat.pr_geo_heat_pumps. Accessed November 2009.

Reference 09 Geothermal Heat Pump Con- sortium. Common Questions. 2006. http:// www.geoexchange.org/resources/common- questions.html. Accessed November, 2009.

Reference 10 SwissInfo with Agencies. Man- Made Tremor Shakes Swiss City of Basel. SwissInfo. http://www.swissinfo.ch/eng/Man- made_tremor_shakes_Basel.html?cid=46232. Accessed November 2009.

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