Geothermal district heating in Turkey: The Gonen case study

Geothermics 36 (2007) 167–182

Geothermal district heating in Turkey: The Gonen case study Zuhal Oktay a,∗ , Asiye Aslan b a

Department of Mechanical Engineering, Faculty of Engineering and Architecture, Balikesir University, 10100 Cagis-Campus, Balikesir, Turkey b Gonen Vocational College, Balikesir University, Gonen-Balikesir, Turkey Received 10 March 2005; accepted 6 September 2006 Available online 7 November 2006

Abstract The status of geothermal district heating in Turkey and its future prospects are reviewed. A description is given of the Gonen project in Balikesir province, the first system to begin citywide operation in the country. The geology and geothermal resources of the area, the history of the project’s development, the problems encountered, its economic aspects and environmental contributions are all discussed. The results of this and other such systems installed in Turkey have confirmed that, in this country, heating an entire city based on geothermal energy is a significantly cleaner, cheaper option than using fossil fuels or other renewable energy resources. © 2006 CNR. Published by Elsevier Ltd. All rights reserved. Keywords: Geothermal district heating; Energy prices; Gonen; Balikesir; Turkey

1. Introduction The thermal energy content of geothermal fluids has proven to be a reliable, clean, and safe renewable resource, thus explaining its increasing use throughout the world, especially for district heating. It is anticipated that, in countries endowed with abundant such resources, geothermal energy will replace some of the more polluting fossil fuels, mainly because of growing global warming concerns and depleting fossil energy reserves (Hepbasli and Ozgener, 2004; Kaygusuz and Kaygusuz, 2004). Turkey is one of the seven countries richest in geothermal ∗

Corresponding author. Tel.: +90 266 6121194; fax: +90 266 6121257. E-mail address: [email protected] (Z. Oktay).

0375-6505/$30.00 © 2006 CNR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.geothermics.2006.09.001

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Nomenclature c CD DD DT Eres Esmr Etotal Ewtr F H Ncold Ndw Nper Nwarm S Tind Toud Tref Tres Tw Vdw Vres Wdw Wvol Ww

specific heat (kJ/kg ◦ C) interim correction factor for degree-days degree-days (◦ C-days) water temperature depletion (◦ C) thermal energy capacity of the reservoir (kJ) heat requirement for hot water during warmer or summer months (MWh) total annual heat requirements (MWh) heat requirement for colder or winter months (MWh) fuel requirements for the heating season (kg or m3 ) heating value of the energy source (kWh/kg or kWh/m3 ) number of colder (or heating) days number of (average) dwellings number of persons per average dwelling number of warmer or summer days average daily usage of sanitary hot water (kg/(person-day)) design indoor temperature (◦ C) average outdoor temperature (◦ C) reference temperature (◦ C) geothermal reservoir temperature (◦ C) difference in water temperatures (◦ C) volume of average dwelling (m3 ) geothermal reservoir volume (km3 ) total winter heat load for an average dwelling (W) total volumetric heat load for an average dwelling (W/m3 ) total winter heat demand

Greek letters φ porosity ηh average heating system efficiency (%) ρ density (kg/m3 ) Subscripts f fluid (water) r rock

resources, yet so far only 2–3% of this vast potential has been developed (Hepbasli and Ozgener, 2004). Geothermal district heating, with Iceland in the forefront, has been one of the fastest growing segments of the geothermal industry and now accounts for over 75% of all space-heating based on geothermal fluids (Lund et al., 2005). Bloomquist (2003) pointed out that “Turkey is installing new geothermal district heating systems at a fast pace and may soon emerge as a leader in this field”.

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2. Geothermal district heating in Turkey Approximately 25–30% of the total energy consumed annually in Turkey is used in heating buildings (Bulut et al., 2003). In the cities, people usually live in apartments heated by boiler–radiator systems serving individual dwellings or entire buildings. The heating systems in Turkey, other than geothermal, are typically designed for a 90–70 ◦ C temperature range, and use local or imported coal, oil or natural gas as fuel. The price of these fossil fuels is dictated by the international market and passed on to the consumers. Because of the high cost of imported fuels, several cities located near dependable geothermal resources, such as Balikesir, Izmir, Denizli and Kirsehir, have switched to geothermal district heating, gradually replacing their conventional fossil-fuelled systems (Mertoglu et al., 2003; Kaygusuz and Kaygusuz, 2004). Turkey is one of the top five countries for geothermal direct applications (Lund et al., 2005) because of its large number of geothermal district heating systems (Table 1). The first such system was installed in the Gonen field, Balikesir province, in 1987. That year, 600 residences were heated by the system (Fig. 1). 3. Gonen geothermal district heating system 3.1. Potential of the Gonen geothermal area The Gonen geothermal field (GGF) is located in northwestern Anatolia, 140 km north of the city of Balikesir, and extends over an area of more than 1.5 km2 (Fig. 1). The field has been the subject of geophysical and geochemical surveys, including radon gas measurements (Ozen, 1995). The effective thickness of the geothermal reservoir is between about 200 and 400 m; in our calculations, we assumed it to be 300 m, resulting in a reservoir volume (Vres ) of 0.45 km3 . The waters in the Gonen geothermal field are of the Na > Ca > Mg and SO4 > HCO3 > Cl type (Table 2). Silica geothermometry indicates a reservoir temperature (Tres ) of about 110 ◦ C. Based on this information, the thermal energy capacity of the geothermal reservoir (Eres ) can be calculated (Barylo, 2000) as follows: Eres = Vres (Tres − Tref )[ρr cr (1 − φ) + ρf cf φ]

(1)

where ρr is rock density (2600 kg/m3 ), ρf the water density (1000 kg/m3 ), cr the rock specific heat (0.807 kJ/kg ◦ C), cf the water specific heat (4.18 kJ/kg ◦ C), φ the rock porosity (10%), and Tref is the reference temperature (local mean annual temperature; i.e. 7.66 ◦ C), so that: Eres = 4.5 × 108 × (110 − 7.66) × [2600 × 0.807 × (1 − 0.1) + 1000 × 4.18 × 0.1] = 1.06 × 1014 kJ

(1a)

Eq. (1) reflects the fact that some of the heat is stored in the rock matrix of the geothermal reservoir and some in its pore water. Only a fraction of the thermal energy contained in the geothermal system can be brought to the surface and used or transformed. The recoverable energy can be estimated by applying a geothermal recovery factor to the geothermal resource base, which depends on the proposed production mechanism, the effective porosity of the rock and the reduction in water temperature (i.e. the difference between the wellhead fluid temperature and the reinjection temperature at the end of the application).

170

Table 1 Geothermal district heating systems installed in Turkey (Hepbasli and Canakci, 2003; Erdogmus et al., 2006) Province Capacity (MWt )

Gonen

Balikesir

32

Simav

Kutahya

25

Kirsehirc Kizilcahamam Balcova (Narlidere) Kozakli Afyon Sandiklid

Kirsehir Ankara Izmir

18 25 72

Nevsehir Afyon Afyon

11.2 40 45

Diyadinc Salihli

Agri Manisa

Saraykoy

Denizli

a

42 142 10.8

Commissioning date

Average temperature of inlet/outlet water (◦ C)a

Maximum capacity/actually connected to the system (in number of dwellings)

Type of pipes used in the distribution linesb

June 1987

75/45

4500/2985

120

October 1991

100/50

6500/3200

54–57 80 115

March 1994 November 1995 October 1996

54/49 70/42 118/60

1800/1800 2500/2500 20,000/6849 (758)

Fiberglass-reinforced polyester system with two loops Fiberglass-reinforced polyester system with two loops is replaced by steel-pipe system with three loops Steel-pipe system with two loops Steel-pipe system with two loops Steel-pipe system with three loops

90 95 70

November 1996 October 1996 March 1998

92/52 90/45 70/42

1250/1000 10,000/4000 5000/1700

78 94

September 1998 November 2002

86/73 98/40

2000/1037 24,000/7000

97

December 2002

97/50

5000/2000

Geothermal fluid temperatures (◦ C) 60–80

Steel-pipe system with two loops Steel-pipe system with three loops Two loops, geothermal loop made of fiberglass-reinforced polyester; district heating loop made of steel-pipe Steel-pipe system with three loops Fiberglass-reinforced polyester system with three loops Steel-pipe system with three loops

Inlet and outlet temperatures of geothermal fluid in primary heat exchangers. In a system with two loops, a heat exchanger is used between the geothermal fluid and the district heating water, while in a three-loop system, there is a primary heat exchanger between the geothermal fluid and the district heating water, and a secondary one between the district heating water and building substation. c This is an integrated geothermal direct application that includes district heating, agriculture (greenhouse heating), bathing and balneology (thermal spa hotel), aquaculture (fish pond) and industrial processes (liquefied carbon dioxide and precipitated calcium carbonate production). d A peak-load boiler is used. b

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Town or district

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Fig. 1. Location of the Gonen geothermal area, Turkey.

According to Barylo (2000), the recovery factor is given by a linear equation as 1.25φ, where φ is porosity. The following equation applies for converting the estimated energy reserve into “usable thermal power”: Usable thermal power =

Energy available × Recovery factor × Efficiency factor Load factor × Lifetime

(2)

where the efficiency factor is 50–90% for space-heating and the load factor indicates the percentage of time the plant (or system) is in operation. For the Gonen geothermal area, the direct use potential

172

Temperature (◦ C)

pH

K+ (mg/L)

Na+ (mg/L)

Ca2+ (mg/L)

Mg2+ (mg/L)

Fe2+ (mg/L)

HCO3 − (mg/L)

SO4 2− (mg/L)

PO4 2− (mg/L)

Cl− (mg/L)

F− (mg/L)

CO2 (dissolved) (mg/L)

82

7.2

22

440

49

1.6

0.1

394

491

0.3

270

4.3

33.8

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Table 2 Chemical composition of typical geothermal water from the Gonen geothermal field (from Erzeno˘glu and Ulusahin, 1990)

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for a 25-year period is then estimated to be about 25.8 MWt , i.e.: Usable thermal power =

1.06 × 1017 J × (1.25 × 0.1) × 0.46 = 25.8 MW 0.3 × (25 × 365 × 24 × 3600) s

(2a)

According to Ozgener et al. (2005), the energy efficiency factor for the Gonen geothermal district heating system (GGDHS) is 0.64, its load factor is 0.3, and its energy efficiency is 0.46. 3.2. Geothermal wells in the Gonen geothermal field As of April 2006, there were 17 wells in the GGF, with depths ranging from 133 to 800 m. Nine wells are used for production and three as injection wells; five have been taken out of operation (Table 3). Wellhead production temperatures vary from 53 to 94 ◦ C, and the volumetric well flow rates from 18 to 90 m3 /h. The district heating scheme used at Gonen is divided into three subsections as shown in Fig. 2. On the left of the figure are the systems related to fluid production (A), including production and injection wells, pumps, thermometers and pressure gauges; in the middle are the district energy transmission systems (B), including plate heat exchangers, and on the right are the end-user loads (C), including users’ heating devices. Geothermal fluid, collected from the nine production wells at an average wellhead temperature of 67 ◦ C, is pumped to a mixing chamber. The fluid is then piped to six primary plate-type heat exchangers and cooled to 43–44 ◦ C, as its heat is transferred to the secondary fluid (clean water). The heat-depleted geothermal fluid is injected back into the reservoir; no pumps are needed. The heated secondary fluid is transferred to the heating grid and the buildings connected to it. For the district heating grid the average conversion temperatures during operation of the Gonen geothermal district heating system (GGDHS) range between 44 and 55 ◦ C. Flow rate and temperature-control valves at the substations are used to allocate the required amount of heat to each building, and to achieve thermal balance in the system (BGGI, 2006). Table 3 Wells in the Gonen geothermal field (as of 3 April 2006) Name

Year of completion

Total depth (m)

Depth to water level (m)

Wellhead temp. (◦ C)

Flow rate (m3 /h)

Type of well/condition

G1 G2 G3 G4 G5 G6 G7 G8 G9 G10 G11 G12 G13 G14 G15 G16 G17

1976 1976 1987 1990 1991 1997 1997 1998 1999 1999 2002 2002 2002 2002 2003 2003 2003

133 534 308 432 332 385 380 280 560 265 800 250 350 250 188 230 240

– – – – – 58 33 34 60 55 55 – 33 – – 55 34

– – – – – 80 53 59 94 66 78 – 68 – – 79 62

– – – – – 18 72 72 28.8 72 28.8 – 72 – – 90 72

Out of service Out of service Reinjection Out of service Out of service Production Production Production Production Production Production Out of service Production Reinjection Reinjection Production Production

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Fig. 2. Schematic diagram of the Gonen geothermal district heating system.

3.3. Development of the Gonen geothermal field The history of the development of the GGF between 1963 and 2006 is summarized in Table 4. The first space-heating application of geothermal energy in Turkey was at the Gonen Park Hotel in 1964. As of April 2006, the number of subscribers to the GGDHS had reached 2985 equivalent dwellings (BGGI, 2006): residences (80.3%; i.e. a total of 2397 residences), hotels (13.4%), office buildings (4.39%), tanneries (1.5%), mosques (0.24%) and schools (0.17%). Table 4 Development milestones for the GGDHS between 1963 and 2006 (BGGI, 2006) Year

Main activity or development

1963 1964 1964 1976 1979 1981 1987 1992 1995 1999 2000 2002 2004 April 2006

Geophysical studies by MTA Heating of Gonen Park Hotel (first geothermal space-heating project in Turkey) Shallow wells put into operation (they stopped operating in 1976) Drilling of geothermal wells G1 and G2 Heating of Yildiz Hotel Heating of Derman Hotel Geothermal district heating system for 600 residences (first network) began operation First reinjection well came on-line Capacity of the geothermal district system increased to 1600 residences (second network) Heating of Sun Hotel Number of (equivalent) residences connected to the geothermal district system reached 2400 Heating of Green Hotel Number of (equivalent) residences connected to the geothermal district system increased to 2928 Number of (equivalent) residences connected to the geothermal district system increased to 2985

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3.4. Heat requirements per average dwelling in Gonen conditions Heat load calculations in Turkey are generally based on the climate design data provided by the Turkish Chamber of Mechanical Engineers (MMO, 1997), which lists the heating dry-bulb design temperatures for 590 locations in Turkey, including smaller towns. The volumetric heat load requirement for a dwelling is taken as 19.97 W/m3 , assuming outdoor and indoor temperatures of 0 and 20 ◦ C, respectively; the rationale behind this requirement is explained in Mertoglu (1995). When calculating the total value, the heat load of the hot water used is added to the unit volume heat load, leading to a total volumetric heat load for an average (or equivalent) dwelling of: Wvol = 19.97 W/m3 (1 + 0.15) = 22.97 W/m3

(3)

Note that the 0.15 value used in Eq. (3) is a space-dependent coefficient (Mertoglu, 1995). As the average area and height of an average dwelling are assumed to be 100 m2 and 2.8 m, respectively [i.e. residence volume (Vdw ) = 280 m3 ], the total heat load for such a dwelling during the cold season (Wdw ) is given by: Wdw = Wvol × Vdw = 6431.6 W

(4)

3.5. Calculation of the annual number of degree-days Data from the Turkish State Meteorological Service are used to determine the degree-day (DD) requirements for a given project. Generally, heating systems are operated when the design outdoor temperature falls below 12 ◦ C. On this temperature basis, there are 150 “colder” (or heatrequiring) days (Ncold ) annually in the Gonen area. In our study, however, we assume the average outdoor temperature (Toud ) to be equal to Tref (7.66 ◦ C), so that Ncold becomes 200 days. If we use an indoor design temperature (Tind ) of 20 ◦ C, the annual number of degree-days (DD) for Gonen is given by: DD = Ncold × (Tind − Toud ) = 2468 ◦ C-day

(5)

3.6. Average total residential heat consumption Total winter heat demand [sanitary hot water + heating proper] is expressed as: Ww = Wdw × Ndw

(6)

where Ndw is the number of average dwellings, and Wdw is the winter heat load for an average (or equivalent) dwelling. Given 2397 residences and a maximum load of 6431.6 W per residence, the overall winter heat load would amount to about 15.42 MW. Table 5 shows the monthly heat demand breakdown for the colder months. In the summer, or warmer season (when there is no need to heat the dwellings), during an average of 165 days (i.e. 365–200), only sanitary hot water is supplied to the residences. The total sanitary hot water load over the summer season (Qs ) is given by: Esmr = Ndw × Nwarm × Nper × S × Tw × cf

(7)

where Nwarm is the number of warmer days per year (165), Nper the average number of persons per average dwelling (i.e. 4), S the average daily usage of sanitary hot water [50 L/(person-day

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Table 5 GGDHS heat requirements for the colder or winter season Month

Average outdoor temperature, a (◦ C)

Heat load ratio, b

Number of heating days, c

October November December January February March April

15.2 11.0 6.9 4.7 5.7 7.7 12.5

0.185 0.346 0.504 0.588 0.550 0.473 0.288

20 30 31 31 29 31 28

Heat requirement for the winter months (Ewtr )

Total heat for the month, d = Ww bc24 h (MWh) 1369.3 3841.4 5782.2 6745.8 5902.8 5426.5 2984.3 32,052.3

Note: Ww = 15.42 MW (see Section 3.6); b = [20 − (a)]/26 (Mertoglu, 1995); c: number of heating days.

or 50 kg/(person-day)], and Tw is the difference in temperature between that of the sanitary hot water (60 ◦ C) and that of the water from the city distribution network (10 ◦ C). Thus: Esmr = (2397 × 165 × 4 × 50)kg/year × 50 ◦ C × 4.18 kJ/kg ◦ C = 1.65 × 1013 Joules/year = 4588 MWh/year

(7a)

The total annual heat requirement (Etotal ) is the sum of what is needed in the winter (Ewtr ) and summer (Esmr ) seasons: Etotal = Ewtr + Esmr = 32, 052 MWh/year (see Table 5) + 4588 MWh/year = 36, 640 MWh/year

(8)

4. Economic evaluation 4.1. Investment, operation and billing Geothermal projects are characterized by their high initial investments and relatively low operation and maintenance costs. For example, the cost of drilling and developing production and injection wells varies from US$ 500 to 4000 per kW (Kanoglu and Cengel, 1999; BGGI, 2006). Under the conditions prevailing in Turkey, the pipeline network represents about 70% of the investment cost of a geothermal district heating project, followed by the wells (10%), building modifications (10%), construction of the heating center (5%), and engineering design (5%) (Hepbasli and Ozgener, 2004). With appropriate design and implementation, the investment per residence for a GDHS is in the range US$ 1500–2500, excluding radiator installation. In Turkey, the payback time for investment in a geothermal district heating project ranges from 5 to 8 years (Mertoglu et al., 2003). The monthly geothermally-based heating fee for the 2004–2005 heating season was set by Balikesir-Gonen Geothermal Inc. at 57 New Turkish Lira (about US$ 38 at that time). System connection fees and monthly payments for GGDHS are given in Table 6 (BGGI, 2006).

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Table 6 System connection fees and monthly payments for GGDHS for 2000–2006 Season

System connection fee (in TRY)

2000–2001 2001–2002 2002–2003 2003–2004 2004–2005 2005–2006

2710 3360 2920 2960 2680 3000

Monthly payment/user (in TRY) Residences (per 100 m2 )

Office buildings (per 100 m2 )

Tannery (per 100 m3 of space)

25 35 39.75 45 50 57

17 24 25 28 32 36.5

1 14 18 20 22 24

Note: One (new) Turkish lira (TRY) is equivalent to about US$ 0.66 and D 0.52 (as of August 2006).

4.2. Fuel cost considerations The general equation for calculating fuel requirements for the heating season (F), using the degree-day procedure, is that given by Hepbasli and Canakci (2003): F=

0.024(DD)CD Wdw ηh (DT)H

(9)

where F is in kg or m3 , CD the interim correction factor for degree-days based on various outdoor design temperatures (set at 0.8 to account for the values given by Lund and Lienau, 1997), H the heating value of the energy source (expressed in kWh per kg or m3 ), and ηh is the average heating efficiency. For Gonen, DD equals 2468 ◦ C-day (see Section 3.5). Based on design conditions, the heat load for an equivalent dwelling was estimated to be 6.384 kW (Toksoy and Canakci, 2001) and 6.15 kW (Agioutantis and Bekas, 2000) when assuming temperature depletions (DT) of 22 and 20 ◦ C, respectively. For the GGDHS, the heat load per dwelling was estimated at 6.43 kW; this number was obtained using Eq. (3) and assuming that the DT was 20 ◦ C. The cost (as of April 2006) of using different energy sources to heat one “equivalent residence” connected to the GGDHS is given in Table 7. 4.3. Environmental considerations All heating projects have some impact on the environment, but the degree or extent will depend on the technology used (Rybach, 2003). The emission of air pollutants such as nitrogen oxides, sulfur dioxide and particulates, and carbon dioxide, will be greatly reduced if we manage to limit our consumption of fossil fuels. The environmental benefits of exploiting the Gonen geothermal resources for district heating can be quantified by calculating the reduction in pollutant emissions compared to fossil fuels. We assumed the following parameters for the Gonen geothermal district heating system (GGDHS): (a) Total equivalent dwellings: 2985, which includes hotels, public buildings, schools, tanneries and mosques. (b) The share of coal-fired heating systems (stoves and boilers) in the total dwelling heat load is 60% (i.e. 1791 dwellings), followed by the systems using fuel oil at 40% (i.e. 1194 dwellings).

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Energy source used for space-heating

Heating value of energy source, a1

Unit price, b2

Average efficiency, c (%)

Annual cost increase, d3 (%)

Fuel cost, e = [100b/ac] (in US$/kWh)

Fuel requirements for the heating season [F in Eq. (9)], f

Cost of fuel over the heating season, g = bf (in US$)

Domestic coal Natural gas LPG4

4.74 kWh/kg 9.59 kWh/m3 12.79 kWh/kg

US$ 0.144 kg−1 US$ 0.345 m−3 US$ 1.805 kg−1

60 90 90

40 26 20

0.0506 0.0400 0.1568

5356.7 kg 1765.08 m3 1323.47 kg

771.36 608.95 2388.86

Furnace oil Electricity

11.48 kWh/kg 1 kWh/kWh

US$ 0.946 kg−1 US$ 0.105 kWh−1

80 99

13 0

0.1030 0.1061

1658.80 kg 15,388.35 kWh

1569.22 1615.78

Notes: For geothermal, the annual cost of fuel (i.e. hot water) is only US$ 456 per dwelling. 1 Heating value is taken from Turkish cogeneration website (http://www.kojenerasyon.com). 2 Assuming l US$ = 1.5 (new) Turkish Lira (TRY) (as of August 2006) (note that the table refers to April 2006 prices). 3 Based on cost in TRY given at http://www.kojenerasyon.com. 4 LPG: Liquid Propane Gas.

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Table 7 Cost comparisons for different energy sources used to heat an equivalent Gonen dwelling over the heating season based on April 2006 prices)

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(c) The sulfur contents in coal and fuel oil are taken as 1.25 and 1.0 wt%, respectively; the actual values for fuel oil range between 1.0 and 1.5%, and for coal between 1.25 and 4.0% (EIE, 1997). The quality of the coal used at Gonen is regulated by the local Environmental Council at the beginning of every winter period, to prevent the burning of low-grade coals. We have taken this into account in our calculations, by using the lowest sulfur values. Our analysis will therefore give the minimum emission rates. Using the values for heating systems burning coal, fuel oil and diesel oil over the heating season (Table 7), the local emissions of SO2 and CO2 have been reduced annually by about 280 and 29,000 tonnes/year, respectively, when geothermal energy is used instead. This represents average values per equivalent dwelling of about 93.5 kg of SO2 and 9743 kg of CO2 , respectively, as shown in Table 8. 5. Problems encountered in the GDHS Wastewater disposal and calcite scaling are the main technical problems encountered in the operation of the Gonen geothermal district heating system. Another difficulty is the lack of adequate and relevant geothermal energy laws and regulations in Turkey. 5.1. Wastewater disposal and thermal pollution The spent Gonen geothermal brines contain salts that could contaminate ground and surface water, the main problem being their salinity and boron content. Chlorides, ammonia and other dissolved salts could also be regarded as potential pollutants. Three (see Section 3.2) injection wells have been drilled to solve the wastewater disposal problem, while insulation of the pipes carrying the hot fluids has controlled thermal pollution. 5.2. Scaling and corrosion These phenomena are a consequence of lowering the pressures and temperatures of geothermal fluids. Chemical inhibitors, pressure control and heat exchanger systems are used at Gonen to reduce the severe calcite-scaling problem. In the district heating system the mineral scales are mechanically scrubbed away. Since the Gonen geothermal waters are corrosive, fiberglass pipes and titanium plate heat exchangers are used. 5.3. Pollution High noise levels (i.e. noise pollution) in and around the GGDHS heating center affected the densely populated area surrounding the heating center (or plant). Sound-proofing of different parts of the center has substantially reduced this impact. Gas emissions have been discussed in detail in Section 4.3. The environmental impact of using geothermal energy is much smaller than when fossil fuels are burned for heating dwellings. 5.4. Laws and regulations One of the most important problems in the exploration, development and operation of geothermal district systems in Turkey is the lack of appropriate laws and regulations. Existing legislation

180

Type of heating system

Number of (equivalent) dwellings, a

Amount of fuel used over the heating season per equivalent dwelling (from Table 7), b

Total amount of fuel used over the heating season, c = ab (tons/year)

Content of S in the fuel, d (% by mass)

Tons SO2 / tons S, e

Tons SO2 / year or tons SO2 /heating season, f = cde/100

Content of C in fuel (% by mass, g

Tons CO2 / tons C, h

Tons CO2 / year or tons CO2 /heating season, i = cgh/100

Coal-fired heating systems Furnace-oil fired systems Total Average (per dwelling)

1791 (i.e. 60%)

5356.7

9593.8

1.25

1.998

239.6

65.0

3.664

22,849

1194 (i.e. 40%)

1658.8

1980.6

1.0

1.998

39.6

85.9

3.664

6,234

2985

279.2

29,083

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Table 8 Distribution of values for local emissions of sulfur dioxide and carbon dioxide associated with fossil combustion

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was created for mining, groundwater and mineral water operations, and cannot be readily applied to geothermal energy resources. Geothermal laws are currently being discussed and drafted. If adopted, they will significantly facilitate the exploration and development of geothermal resources. 6. Conclusions The estimated geothermal power and direct use potential for Turkey stand at about 500 MWe and 31,500 MWt , respectively (MTA, 2003). At present, the installed capacity of all space-heating projects (including district systems) using geothermal energy amounts to 827 MWt , representing only 2.6% of the total estimated potential for the country (Lund et al., 2005). There are a total of 38 geothermal space-heating systems in Turkey, but only eleven are municipal district heating systems (Table 1), the Gonen system being the first. Geothermal energy is more economically attractive to the Turkish consumer than fossil fueldriven schemes, particularly because the cost of geothermal heat is kept constant over the entire year. Moreover, since the monthly cost (or fee) is set in Turkish lira, it is not affected by currency exchange rates. The cost of heating a typical 100 m2 residence hooked to a geothermal district heating system (GDHS), including hot sanitary water, varies between US$ 17 and 72/month in Turkey (Erdogmus et al., 2006). Heating systems have been retrofitted and integrated into the GDHS. Existing radiator models, designed for 70–90 ◦ C temperatures, work fine when used with lower temperature ranges (i.e. 40–80, 50–70, and 40–60 ◦ C), indicating that the radiators in conventional heating systems were over-designed originally. Water temperatures are kept constant to prevent damage to pipes. To save electricity, full automatic control of the variable-speed drivers must be incorporated for the pumps in the system. Geothermal district heating systems require relatively high initial investments, but their operation and maintenance costs are low compared to fossil fuel-driven systems (Table 7). To reduce GDHS costs, remote-controlled energy or flow meters should be installed at every dwelling. These meters could be monitored using real-time data acquisition systems. The information that is collected could be used to study the operation of the GDHS, and to reduce the number of personnel needed to monitor the system, bill customers, update databases, etc. The district heating system at Gonen shows that geothermal energy is not only cheaper, but also cleaner than fossil fuels. A countrywide database for Turkey should be set up to monitor the advantages of geothermal district heating systems in the long-term. The number of geothermal direct applications is expected to increase significantly in Turkey once geothermal laws and regulations have been ratified. It is hoped that these will be approved and implemented in the near future. Acknowledgments The authors are grateful for the support provided by Balikesir-Gonen Geothermal Inc. (BGGI) and the Governorship of Balikesir, Turkey. The valuable comments of the reviewers, the Associate Editors M. Dickson and S. Bellani, and the Editor-in-Chief M.J. Lippmann are also greatly appreciated. References Agioutantis, Z., Bekas, A., 2000. The potential of district heating using geothermal energy. A case study, Greece. Geothermics 29, 51–64.

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