12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaAnnual cost ($)$2,500,000$2,400,000$2,300,000$2,200,000$2,100,000$2,000,000$1,900,000$1,800,000$1,700,000$1,600,0000.60 0.62 0.64 0.66 0.68 0.70 0.72 0.74 0.76 0.78 0.80 0.82No carbon taxf-factor (-)Carbon tax $30/tCO2Fig.5. Relation between f-factor and annual cost crossflowheat exchanger system, with and without carbon tax.From the foregoing, it is clear that useful comparisonscan be made using this methodology. The results fromexergoeconomic analyses can significantly deviatefrom those obtained with a classical analysis. Which ofthe two is the more relevant one will depend on thesituation. For non-integrated systems, the classicalanalysis may be the one to follow, but for integratedenergy systems, which are expected to become moreand more important, the temperature level of heatbecomes important, and the exergoeconomic analysisseems more appropriate. Using the f-factor will help infinding optimum solutions, especially for exergoeconomicanalyses.Variations in external factors, such as fuel costs orGovernment / utility incentives could change the shapeof the curves to make the minimum more pronounced.CONCLUSION AND SUGGESTIONS FOR FURTHERWORKFrom the results of testing the methodology ofexergoeconomic optimization using the f-factor, it isclear that it is a useful tool to determine the effects ofdifferent heating technologies and heat transfer surfacesizes of these technologies on the annual overalloperational costs. This is especially true if the heatingsystem is integrated with other energy systems. It isalso true if the temperature level of the heat isimportant for another reason. The methodology can beused to make informed choices regarding technologiesto be used for heating homes or buildings andregarding the size of these technologies.To continue this development work, it is recommendedthat more practical considerations will be incorporatedinto the models and analyses. Increasing temperaturesdo not just cost more in terms of exergy but also inmore expensive materials, and steam based districtheating systems are considerably more expensive thanhot water based systems. Heat losses from the pipelinewere small but may need to be considered in a followupstudy. Including passive heating of houses by solarradiation, plug loads and occupancy gains will alsoimprove model predictions. Also mixed systemscombining heating technologies and possibly includingother technologies such as under-floor heating providefurther opportunities to optimize system cost.In addition, the application of the methodologydeveloped in this study should be applied to a heatpump, where the variations in COP with supplytemperature would be included. This would result in theability to match the heating equipment to the heatpump, resulting in an optimum operation.ACKNOWLEDGEMENTDuring this work the authors have had very fruitfulconversations with many colleagues: Mikhail Sorin,Evgueniy Entchev, Libing Yang, Ibrahim Dincer, HajoRibberink and Kirby Wittich. These discussions helpedfocus the work and stimulated further thinking in thisinteresting area of science. This is to thank all thosewho spent their valuable time listening and providingvaluable comments.REFERENCES[1] G. Wall, ―Exergy and Morals‖, in Second lawanalysis of energy systems: towards the 21stcentury, E. Sciubba, M.J. Moran Eds, Circus,Roma (1995), ISBN 88-86662-0-9, pp. 21-29.[2] D. Schmidt, ―Design of Low Exergy Buildings –Method and a Pre-Design Tool‖, in <strong>International</strong>Journal of Low Exergy and Sustainable Buildings,Vol. 3 (2003), pp. 120-126.[3] A. Valero, L. Serra & J. Uche, ―Fundamentals ofExergy Cost Accounting and Thermoeconomics.Part I: Theory‖, in Journal of Energy ResourcesTechnology, Vol. 128 (2006), pp. 1-8.[4] G. Tsatsaronis, ―Application of Thermoeconomicsto the Design and Synthesis of Energy Plants‖, inExergy, Energy System Analysis, andOptimization, [ed. Christos A. Frongopoulos], inEncyclopedia of Life Support Systems (EOLSS),developed under auspices of the Unesco, EolssPublishers, Oxford, UK (2007).[5] G. Temir, D. Bilge, ―Thermoeconomic analysis of atrigeneration system‖ in Applied ThermalEngineering, Vol. 24 (2004), pp. 2689-2699.[6] Clean Energy Project Analysis – RETScreenEngineering & Cases Textbook, 3 rd edition,RETScreen <strong>International</strong>, Natural ResourcesCanada, Varennes (2005).52