1、116 2008 ASHRAE ABSTRACTIn this study, we investigate the Edremit GeothermalDistrict Heating System (GDHS) in Balikesir, Turkey throughenergetic, exergetic, economic and environmental assess-ments. The actual thermal data taken from the TechnicalDepartment of the GDHS are utilized in the analysis to
2、 deter-mine the exergy destructions in each component of the system,and the overall energy and exergy efficiencies of the system fora reference temperature taken as 13.4C for January 20, 2007.The energy and exergy flow diagrams are clearly drawn toillustrate how much destructions/losses take place i
3、n additionto the inputs and outputs. The average energy and exergy effi-ciencies are found to be 32.69 and 54.26%, respectively. It isobtained from the results that the exergy destructions mainlyoccur in pumps, heat exchangers, transmission pipelinenetwork and discharging sections as 1.66, 6.07, 8.0
4、4, and29.94% respectively. The highest exergy loss occurs in thedischarging section since a large amount of exergy is rejectedinto the river. Some parameters such as energetic and exergeticrenewability and reinjection ratios are defined for varioussystems, particularly for geothermal systems. The en
5、ergeticand exergetic renewability ratios are found to be 0.34 and 0.52,respectively whereas its energetic and exergetic reinjectionratios are determined to be 0.64 and 0.30, respectively. In addi-tion, both quantity and quality values of the other fossil fuelsare studied for comparison purposes for
6、the system. The qual-ity factor for geothermal exergy price of the system is calcu-lated to be 0.178. We finally investigate how much reductionin consumption of traditional fossil fuels and greenhouse gasemissions is possible through the use of the Edremit GDHS.INTRODUCTIONHumans have used geotherma
7、l energy for a variety ofpurposes in a variety of time periods. For centuries theRomans used exothermally heated water in their bathhousesand to treat illnesses and heat homes. In Iceland and NewZealand, many people cooked their food using geothermalheat. Some North American native tribes also used
8、geothermalheat for both comfort and cooking. Most of these early uses ofthe Earths heat were through the exploitation of geothermalvents. Currently, the most common uses of geothermal energyare residential heating and power generation. Heating andcooling buildings using geothermal energy is the prim
9、ary useof the Earths heat energy. Much energy is placed into themoderation of temperature inside buildings, especially duringtimes of extreme cold or heat. Using geothermal energy as away of maintaining temperatures in buildings is one way tocontinue to provide that comfort while reducing the use of
10、energy sources that are more polluting to the Earths atmo-sphere. Geothermal energy can also be used to create electric-ity and supplement the conventional sources available.Space heating is one of the most common and widespreaddirect uses of geothermal resources. District heating networks,and in so
11、me cases district cooling, are employed to providespace heating and/or cooling to multiple consumers from asingle well or from multiple wells or fields. The developmentof geothermal district heating, particularly by the Icelanders,has been one of the fastest growing segments of the geother-mal space
12、 heating industry and now accounts for over 75% ofall space heating provided from geothermal resources world-wide (Lund et al. 2005). Recently, geothermal district heatinghas been successfully implemented in many countries, such asUSA, Canada, Italy, Iceland, and more recently Japan, NewEnergetic, E
13、xergetic and Environmental Assessments of the Edremit Geothermal District Heating SystemZuhal Oktay, PhD Ibrahim Dincer, PhDMember ASHRAEZuhal Oktay is a member of the Mechanical Engineering Department, Faculty of Engineering, Balikesir University, Balikesir, Turkey.Ibrahim Dincer is a professor of
14、mechanical engineering with the Faculty of Engineering and Applied Science, University of Ontario Insti-tute of Technology, Oshawa, Ontario, Canada.NY-08-0172008, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volum
15、e 114, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.ASHRAE Transactions 117Zealand, China and Turkey (Kanoglu 2002, Mertoglu 1995).Turkey has also installed large geothe
16、rmal district heatingsystems. Turkeys share of geothermal energy use worldwideis about 12.1% (Barbier 2002, Hepbasli 2003).As far as geothermal systems are concerned, these studiesmay be classified into five main groups as follows: a. Exergy analysis of geothermal power plants (Kanoglu2002; Ozturk e
17、t al. 2006; Dagdas et al. 2005; Cerci 2003;Kanoglu et al. 1996, 1997, 1998; Kanoglu and Cengel1997; Bettagli and Bidini 1996; DiPippo and Marcille1984; Baba et al. 2006; Cadenas 1999),b. Evaluation of geothermal fields using exergy analysisBaba et al. 2006, Cadenas 1999, Bisio 1998, Bettagli andBidi
18、ni 1996, Oszuszky and Szeless 1980, Quijano 2000,Haenel et al. 1988, Dickson and Fanelli 1990),c. Classification of geothermal resources by exergy (Etemo-glu and Can 2007, Lee 2001, Muffler and Cataldi 1978,Hochstein 1990),d. Energy and exergy analysis geothermal district heatingsystems (GDHSs) (Ozg
19、ener et al. 2007; Ozgener et al.2007a, 2007b, 2007c; Erdogmus et al. 2006; Ozgener etal. 2005a, 2005b, 2005c; Hepbasli 2005; Ozgener et al.2004; Ozgener et al. in press) ande. Exergoeconomic analysis with cost accounting aspects ofGDHSs (Ozgener et al. 2007, Benderitter and Cormy1990).The main objec
20、tive of this paper is to conduct an energy andexergy analysis of the Edremit GDHS, to introduce some newparameters as energetic renewability ratio, exergetic renewabil-ity ratio, energetic reinjection ratio, and exergetic reinjectionratio for the geothermal systems and apply to the EdremitGDHS, and
21、to discuss performance improvement opportunities.It is also aimed to investigate how much reduction in consump-tion of traditional fossil fuels and greenhouse gas emissions ispossible through the use of the Edremit GDHS.CASE STUDY: THE EDREMIT GEOTHERMAL DISTRICT HEATING SYSTEM Geothermal district h
22、eating systems are divided into twomain groups depending on whether the geothermal water isused directly in the house systems (secondary system) or indi-rectly by transferring the geothermal heat to the secondarysystem via the use of heat exchangers. It is generally acceptedthat hot water at tempera
23、tures ranging from 60 to 125C hasbeen used for space heating and a primary fluid temperature of60C is minimum practicable for direct geothermal heatinguse (Piatti et al. 1992).Many systems in Turkey have been operating using theprinciple of the indirect use of the geothermal fluid. On thecontrary, E
24、dremit GDHS operates on the principle of directuse and geothermal water is piped directly to the users with atransmission pipeline, like in Iceland.The Edremit geothermal field is located 87 km in the westof the city of Balikesir in Turkey, knows as the northwest Anato-lia. There is a 3 to 4 km dist
25、ance between geothermal source andthe center of the Edremit. As of January 2006; there were sevenwells in geothermal field, with depths ranging from 195 to 496m. Information for the wells opened is shown in Table 1. Threewells (ED-1. ED-3, EDJ-3) were in use for production. One well(ED-2) was closed
26、 because of the insufficient mass flow rate.Other three (EDJ-4, ED-5, EDJ-7) wells had a pump, but not yetconnected to system. The wellhead production temperature was60C. The mass flow rates of operating wells chance from 18 to86 kg/s (EGEI 2007). The Edremit GDHS wells extend over ofnearly 0.3 km2.
27、 As of January 2007, the number of dwellings forthe Edremit GDHS was 1650.Generally, heating systems become operational when theoutdoor temperature falls below 15C. On this temperaturebasis, there are 190 “colder” (or heat-requiring) days annuallyin the Edremit area. In summer or warmer season, duri
28、ng anaverage of 175 days, only domestic hot water is supplied fromEdremit GDHS. In designated period, outdoor design temper-ature, while determining the heat demand of a dwelling, hadbeen chosen to be 3C by project engineers. However thelowest outdoor temperature is about 4.9C when consideringthe av
29、erage outdoor temperature. Energy is generated fromgeothermal energy when the outdoor temperature is over 5C.Under 5C, the auxiliary system, which uses the fuel-oil as afuel, is activated.The Edremit geothermal district heating system (EdremitGDHS) was designed for 3 stages with the total capacity u
30、lti-mately corresponding to 7500 dwelling equivalences. In thefirst stage, heat demand was compensated to 1650 dwellingequivalence. In the second stage, 5000 and in the last stage,7500 dwelling equivalences will be constructed. In Figure.1,a schematic diagram of the system is shown. On January 20,20
31、07, Edremit GDHS supplied the heat requirement of onereligious facility, one dormitory, one college, two hospitalsand 1345 residences. Equivalent dwelling values of these utili-zations are given in Table 2.The components of the Edremit GDHS are pumps, heatexchangers, constructed under the each build
32、ing, and a peak-ing station. Peaking station is activated in case of emergencyheat requirements for low outdoor temperatures, when there isTable 1. Explanation of the WellsNameTotal Depth (m)Wellhead Temperature(C)Flow Rate (kg/s) Type/ConditionED-1 195.60 60.00 75 Production/OperatingED-2 496.50 55
33、.00 2 ClosedED-3 495.00 59.00 18 Production/OperatingEDJ-3 266.00 60.00 86 Production/OperatingEDJ-4 296.00 49.00 86 Production/Out of serviceEDJ-5 216.00 58.70 45 Production/Out of serviceEDJ-7 246.00 58.30 30 Production/Out of service118 ASHRAE Transactionsa problem in the energy demand of the sys
34、tem. The system isdesigned to have one heat exchanger for each building. Sonow, each building has a heat exchanger to supply its heatrequirement. There are 62 buildings which have 1650 equiv-alent dwellings in the system. In calculations, it is very diffi-cult to take a value for each heat exchanger
35、. Since, those 62heat exchangers were considered as one heat exchanger whichwas represented by HE in Figure. 1. Same model plate-typeheat exchangers are used throughout the system. Inlet andoutlet heat exchanger liquid temperatures were measured forboth water and geothermal water. Temperature values
36、 weretaken from the farthest building. This building is taken as acritical point. The difference between critical point andgeothermal field is not much, so the effect of elevation isconsidered negligible in the calculations.The temperature and pressure data of the system wererecorded on January 20,
37、2007. Geothermal fluid collectedfrom three production wells, at an average wellhead temper-ature of 60C, is pumped to heat exchangers constructed underthe buildings after passing the peaking station. Geothermalfluid enters the heat exchanger at an average temperature of 58to 59C and here, heat is tr
38、ansferred to the fresh water in thoseheat exchangers At this point used geothermal fluid isdischarged to Edremit river at 40 to 42C. No pump is neededon the main distribution pipeline or discharge section. Thepressure supplied from well pumps is enough for circulation.In Table 3, some general charac
39、teristic properties of theEdremit GDHS are shown.ANALYSISBalance EquationsThe balance equations are written in this paper for mass,energy and exergy flows in the systems which act like thesteady-state and steady-flow system. Energy and exergy effi-ciency equations are also written for performance ev
40、aluationof the overall system and its components.The mass balance equation for the overall geothermalsystem can be written as(1)The geothermal water energy and exergy are calculatedfrom the following equations:(2)(3)Here h0and s0depend on the reference (environment) temper-ature and are considered t
41、o be variable for each day.The exergy destructions in the heat exchanger, pump andsystem itself are calculated using the following equations:(4)(5)Table 2. Distribution of theGeothermal Energy UsageUsers Residences Equivalence %Religious facilities 6 0.36Dormitory 9 0.55College 72 4.36Hospitals 65 3
42、.94Residences 1498 90.79Figure 1 Flow chart of the Edremit GDHS.Table 3. General Characteristic Properties of the Edremit GDHSEdremit GDHSTown Edremit (Turkey)Wellhead Temperature (C) 60Capacity (MWt) 11,32Commissioning date 2003Average inlet/outlet temperature for geothermal water59/40-42Average in
43、let/outlet temperature for fresh water58/38-40Actually connected to system/Maximum capacity1650/7500Type of pipes used in the distribution lines.Fiberglass-reinforced polyester system.mini=1nmouti=1n=Egwmgwhgwh0()=Exgwmgwhgwh0()T0sgws0()=mgw i,hih0()T0sis0()i=1n=3Exdest HE,ExinExout=Exdest Pump,Wpum
44、pExoutExin()=ASHRAE Transactions 119(6)(7)The energy efficiency of the GDHS system is calculatedfrom(8)The exergy efficiency of the system heat exchanger isdetermined by the increase in the exergy of the cold streamdivided by the decrease in the exergy of the hot stream as(9)with the flow exergy ()
45、as = (h h0) T0(s s0)(10)The exergy efficiency of the system is calculated fromfollowing equation:(11)Many researchers use the specific exergy index as a kindof exergetic rating to classify the geothermal resources asinitially introduced by (Lee 2001) in the following form:1. SExI 0.05 represents the
46、 low quality geothermalresources,2. 0.05 SExI 0.5 represents the medium-quality geother-mal resources, and3. 0.5 SExI represents the high quality geothermalresources.This index is written as follows as applied commonly(Quijano 2000; Lee 2001):(12)where 1192 is the reference specific exergy as identi
47、fied by theresearcher (Lee 2001). Therefore, the specific exergy indexfor any geothermal resource is determined as the ratio of thespecific exergy of the geothermal system considered to thereference specific exergy content. The following is thespecific geothermal enthalpy equation as required for th
48、eabove equation:(13)which is based on the flow energy balance for an adiabaticmixing process since there are three wells to receive geother-mal waters and mix them for the system.The following is the specific geothermal entropy equationas required for Equation (12):(14)which is based on the flow ent
49、ropy balance for an adiabaticmixing process (with negligible entropy generation term)since there are three wells to receive geothermal waters andmix them for the system.Furthermore, the rate-basis improvement potential, IP,developed by Hammond and Stapleton (2001) is alsoemployed to show how much improvement potential exists forthe system. Here the IP value for the heat exchanger is(15)Geothermal sources, apart from fossil fuels, are renew-able. In this section we introduce four new parameters, namelyenergetic renewability ratio, exe
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