The <str<strong>on</strong>g>12th</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>Symposium</str<strong>on</strong>g> <strong>on</strong> <strong>District</strong> <strong>Heating</strong> <strong>and</strong> <strong>Cooling</strong>,September 5 th to September 7 th , 2010, Tallinn, Est<strong>on</strong>iaTable 3 – Results for the primary energy factor <strong>and</strong> CO 2emissi<strong>on</strong> factor for heat from a geothermal CHP plantSource ofheatHeat,HellisheidiCHP plantHeat,HellisheidiCHP plant,reinjecti<strong>on</strong>DISCUSSIONPrimary energy factors f p[MWh primary energy /MWh produced energy]N<strong>on</strong>-RenewableTotal>0.01 1.78 0.98>0.01 0.69 0.98CO 2producti<strong>on</strong>coeff. K[Kg/MWh]The following discussi<strong>on</strong> highlights the most significantresults from this study:1) By comparing the energy performance indicatorscalculated in this study <strong>and</strong> shown in Table 3 to theindicators given in Table 3 it can be seen that electricityfrom geothermal power plants has the highest total f pfactor while the share of n<strong>on</strong>-renewable energysources is the lowest. The main reas<strong>on</strong> for the high f pfactor is the low c<strong>on</strong>versi<strong>on</strong> efficiency of geothermalpower plants due to low working temperatures <strong>and</strong>pressures. The CO 2 producti<strong>on</strong> coefficient is relativelylow compared to the other energy c<strong>on</strong>versi<strong>on</strong>technologies <strong>and</strong> could be lowered even further ifmeasures are taken to c<strong>on</strong>trol the emissi<strong>on</strong>s from thepower plant. The results for the Hellisheidi geothermalCHP plant cannot be used to represent all geothermalpower plants producing either electricity al<strong>on</strong>e or with acombined producti<strong>on</strong> of electricity <strong>and</strong> heat. Furtherstudies are needed <strong>on</strong> different types of geothermalpower plants, such as single flash <strong>and</strong> organic Rankinecycles, to be able to produce specific or averagefactors representing geothermal utilizati<strong>on</strong>.2) The results for the heat producti<strong>on</strong> at theHellisheidi geothermal CHP plant, given in Table 3,show that the energy performance indicators arerelatively low <strong>and</strong>, in the case of reinjecti<strong>on</strong>, belowunity. This is because the primary energy needed topreheat the DH water is not accounted for in the heatproducti<strong>on</strong> but rather assigned to the electricityproducti<strong>on</strong>. This is due to the fact that the preheating ofthe DH water from 5 °C to 41 °C is d<strong>on</strong>e in thec<strong>on</strong>denser for the high pressure steam turbine as seenin Figure 1 <strong>and</strong> is a necessary step in the electricityproducti<strong>on</strong>, but a beneficial step in the heat producti<strong>on</strong>for the DH system.3) Values for the indicators for both electricity <strong>and</strong>heat are calculated with <strong>and</strong> without reinjecti<strong>on</strong> of thecooled geothermal brine from the energy c<strong>on</strong>versi<strong>on</strong>process. Reinjecti<strong>on</strong> of geothermal brine is recognizedto improve heat mining <strong>and</strong> stabilize the producti<strong>on</strong>capacity of geothermal fields, if successfully carriedout. It can also counteract pressure draw-down in thereservoir by providing an artificial water recharge [18].In this study, reinjecti<strong>on</strong> of the waste stream ismodelled, which decreases the use of primary energyin the energy c<strong>on</strong>versi<strong>on</strong> process, since a part of theprimary energy from the geothermal fluid it is returnedback to the reservoir. Reinjecti<strong>on</strong> is present at theHellisheidi geothermal CHP plant so the values of theenergy performance indicators with reinjecti<strong>on</strong> are validfor the power plant.4) Life cycle assessment is especially useful toevaluate the total impact of geothermal power plantswith respect to their emissi<strong>on</strong> of greenhouse gasses.Figure 3 <strong>and</strong> Figure 4 show how the different phases inthe life cycle of the power plant significantly c<strong>on</strong>tributeto the overall emissi<strong>on</strong> in CO 2 equivalents. If LCA hadnot been carried out for the process, 12% of the CO 2emissi<strong>on</strong>s resulting from the electricity generati<strong>on</strong>would not have been accounted for <strong>and</strong> no emissi<strong>on</strong>swould have been found for the heat producti<strong>on</strong>, sincethe emissi<strong>on</strong>s from drilling, c<strong>on</strong>structi<strong>on</strong> of buildings,<strong>and</strong> manufacture of comp<strong>on</strong>ents had not beenaccounted for.ACKNOWLEDGMENTSSpecial thanks are given to the following partners:Nordic Energy Research (NER) for funding the study<strong>and</strong> the Energy Research Fund of L<strong>and</strong>svirkjun for theirsupport. To Orkuveita Reykjavíkur for providing data forHellisheidi Power plant, to Mannvit engineering fordiscussi<strong>on</strong> <strong>and</strong> data provisi<strong>on</strong> <strong>and</strong> to Ragnar Gylfas<strong>on</strong>for his c<strong>on</strong>tributi<strong>on</strong> in the data gathering phase.REFERENCES[1] EU. (2003, January 4). Directive 2002/91/EC ofthe European Parliament <strong>and</strong> of the Council of 16December 2002 <strong>on</strong> the energy performance ofbuildings. Official Journal of the EuropeanCommunities .[2] Bertani, R. (2010). Geothermal Power Generati<strong>on</strong>in the World 2005 – 2010 Update Report.Proceedings World Geothermal C<strong>on</strong>gress 2010,(April), 25-29.[3] Lund, J. W., Freest<strong>on</strong>, D. H., & Boyd, T. L. (2010).Direct Utilizati<strong>on</strong> of Geothermal Energy 2010Worldwide Review. Proceedings World GeothermalC<strong>on</strong>gress 2010, (April), 25-29.[4] EN 15603:2008. Energy performance of buildings.Overall energy use <strong>and</strong> definiti<strong>on</strong> of energy ratings.191
The <str<strong>on</strong>g>12th</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>Symposium</str<strong>on</strong>g> <strong>on</strong> <strong>District</strong> <strong>Heating</strong> <strong>and</strong> <strong>Cooling</strong>,September 5 th to September 7 th , 2010, Tallinn, Est<strong>on</strong>iaGeneva: <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> Organisati<strong>on</strong> forSt<strong>and</strong>ardisati<strong>on</strong> (ISO).[5] Helisheidi Geothermal Plant. (2009). RetrievedMay 2009, from http://www.or.is/English/Projects/HellisheidiGeothermalPlant/[6] H. Douglas Lightfoot. (2007). Underst<strong>and</strong> the threedifferent scales for measuring primary energy <strong>and</strong>avoid errors. Energy, 32, 1478-1483.[7] Segers, R. (2008). Three opti<strong>on</strong>s to calculate thepercentage renewable energy: An example for aEU policy debate. Energy Policy , 36 (9), 3243-3248.[8] IEA. (2004). Energy Statistics Manual.<str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> Energy Agency (IEA). Paris:OECD/IEA.[9] ISO 2533:1975. St<strong>and</strong>ard atmosphere.<str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> Organizati<strong>on</strong> for St<strong>and</strong>ardizati<strong>on</strong>,Geneva, Switzerl<strong>and</strong>.[10] Russell, A., Ekvall, T., & Baumann, H. (2005). Lifecycle assessment - introducti<strong>on</strong> <strong>and</strong> overview.Journal of Cleaner Producti<strong>on</strong> , 13 (13-14), 1207-1210.[11] Baumann, H., & Tillman, A.-M. (2004). The HitchHiker's Guide to LCA. Lund, Sweden:Studentlitteratur AB.[12] PRéC<strong>on</strong>sultants. (2009, September 6). SimaProLCA software. Retrieved October 14, 2009, fromSimaPro LCA software: http://www.ecoinvent.ch/[13] Ecoinvent. (2009, August 13). Home. RetrievedOctober 14, 2009, from Home:http://www.ecoinvent.ch/[14] DiPippo, R. (2008). Geothermal Power Plants –Principles, Applicati<strong>on</strong>s, Case Studies <strong>and</strong>Envir<strong>on</strong>mental Impact (2nd editi<strong>on</strong> ed.). Oxford:Butterworth-Heinemann.[15] Klöpffer, W. (1997). In defense of the cumulativeenergy dem<strong>and</strong> (editorial). <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> Journal ofLife Cycle Assessment , 2, 61.[16] PRéC<strong>on</strong>sultants. (2009, September 6). Methods.Retrieved October 14, 2009, from SimaPro LCAsoftware:http://www.pre.nl/simapro/impact_assessment_methods.htm#CML2[17] Gunnlaugss<strong>on</strong>, E., & Oddsdóttir, A. L. (2009).Helisheidi - Gufuborholur 2008 (Hellisheidi - Steamwells 2008). Reykjavík: Orkuveita Reykjavíkur.[18] Stefanss<strong>on</strong>, V. Geothermal reinjecti<strong>on</strong> experience.Geothermics, 26, (1997), 99–130.192
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