Energy and Buildings 38 (2006) 286–292
www.elsevier.com/locate/enbuild
Performance investigation of two geothermal district
heating systems for building applications: Energy analysis
Leyla Ozgener a,*, Arif Hepbasli b, Ibrahim Dincer c
b
a
P.K. 51, 35040 Bornova, Izmir, Turkey
Department of Mechanical Engineering Faculty of Engineering Ege University, 35100 Bornova, Izmir, Turkey
c
Faculty of Engineering and Applied Science University of Ontario Institute of Technology (UOIT),
2000 Simcoe Street, North Oshawa, Canada ON L1H 7K4
Received 12 February 2005; received in revised form 14 April 2005; accepted 12 June 2005
Abstract
The energetic performance of Balcova geothermal district heating system (BGDHS) and Salihli geothermal district heating system (SGDHS)
installed in Turkey is investigated for building applications in this study. The essential components (e.g., pumps, heat exchangers) of these
geothermal district heating systems are also included in the modeling. The present model is employed for system analysis and energetic
performance evaluation of the geothermal district heating systems. Energy flow diagrams are drawn to exhibit the input and output energies and
losses to the surroundings by using the 2003 and 2004 heating season actual data. In addition, energy efficiencies are studied for comparison
purposes, and are found to be 39.36% for BGDHS and 59.31% for SGDHS, respectively.
# 2005 Elsevier B.V. All rights reserved.
Keywords: District heating; Geothermal energy; Energy; Efficiency; Performance investigation; Renewable energy
1. Introduction
Space heating is one of the most common and widespread
direct uses of geothermal resources. District heating, and in
some cases district cooling, networks are employed to provide
space heating and/or cooling to multiple consumers from a
single well or from multiple wells or fields. The development of
geothermal district heating, particularly by the Icelanders, has
been one of the fastest growing segments of the geothermal
space heating industry and now accounts for over 75% of all
space heating provided from geothermal resources worldwide
[1].
Geothermal energy utilization is generally divided into two
categories, i.e., electric energy production and direct uses for
space heating and cooling, industrial processes and greenhouse
heating. Furthermore practical uses of geothermal energy for
bathing, washing and cooking date back to prehistory. The
earliest residential heating in the world by geothermal water
* Corresponding author. Tel.: +90 232 388 4000x1242;
fax: +90 232 388 6027.
E-mail addresses: leylaozgener@yahoo.com (L. Ozgener),
hepbasli@bornova.ege.edu.tr (A. Hepbasli), Ibrahim.Dincer@uoit.ca
(I. Dincer).
0378-7788/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.enbuild.2005.06.021
was in Chaude Aigues in France in the 14th century. The first
municipal district heating system using geothermal water was
set up in Reykjavik, Iceland in 1930 [2]. Recently, geothermal
district heating has been successfully implemented in many
countries, e.g., USA, Canada, Italy, Iceland and more recently
Japan, New Zealand, China and Turkey [3–5].
Turkey’s share in worldwide geothermal energy use is about
12.0%, and geothermal resources prior to 1960 were only used
spontaneously in bathing and medical treatment in Turkey.
Although some inventorial works and chemical analyses of the
hot springs and mineral waters were first initiated in 1962,
geothermal district heating applications essentially started in
1990 with the heating of 600 residences in Gonen, Balikesir.
Geothermal direct use increased as steeply as 18.5% from 1990
to 1995 and this has brought Turkey to amongst the some
leading countries in the area [6].
The authors have recently conducted various studies on the
energy and exergy analysis of geothermal district heating
systems for system analysis, parametric studies of various
aspects (e.g., efficiency), etc. [3–5]. In the present paper we
undertake a further study to analyze the thermodynamic aspects
of both Balcova geothermal district heating system (BGDHS)
and Salihli geothermal district heating system (SGDHS) and
compare their energetic performances through efficiency
L. Ozgener et al. / Energy and Buildings 38 (2006) 286–292
Nomenclature
Ė
EPLL
ETR
h
ṁ
P
Q̇
s
T
TEI
Ẇ
energy rate (kW)
rate of energy loss due to water leaks in the
distribution network (kW)
rate of energy loss due to thermal re-injection
(kW)
specific enthalpy (kJ/kg)
mass flow rate (kg/s)
pressure (kPa)
rate of heat (kW)
specific entropy (kJ/kg K)
temperature (8C or K)
rate of total energy input (kW)
work rate (or power) (kW)
Greek letters
h
energy efficiency (%)
Subscripts
d
natural direct discharge
HE
heat exchanger
i
successive number of elements
in
inlet
out
outlet
r
re-injected thermal water
tot
total
w
well-head
0
reference state
analysis. The present study differs from the previous studies as
follows: (i) It includes an analysis depending on the various
reference temperature values, namely the different actual
outside temperatures of each geothermal district heating
system considered and a common design temperature value
selected using the whether design data determined by [7]
according to ASHRAE [8], and (ii) It makes a detailed
comparison between two geothermal district heating systems
studied in terms of energy analyses as well as potential for
possible improvements. A model to evaluate the contribution
of geothermal energy sources for improving the heating
performance of district heating systems is also proposed. As
two case studies, the model is applied to the Balcova
geothermal district heating system (BGDHS) in Izmir and
Salihli geothermal district heating system (SGDHS) in
Manisa, Turkey.
2. Description of the Balcova and Salihli geothermal
district heating systems
2.1. Balcova geothermal district heating system (BGDHS)
The Izmir–Balcova geothermal field covers a total area of
about 3.5 km2 with an average thickness of the aquifer horizon
of 150 m. Assume that no feeding occurs, and 25% of the fluid
contained in the reservoir is utilized. The field has a maximum
287
yield of 810 m3/h at a reservoir temperature of 118 8C. This
district heating system consists of the Izmir–Balcova geothermal district heating system (IBGDHS) and the Izmir–Narlidere
geothermal district heating system (INGDHS). The design
heating capacity of the IBGDHS is equivalent to 7500
residences. The INGDHS was designed for 1500 residence
equivalence but has a sufficient infrastructure to allow a
capacity growth to 5000 residence equivalence. The outdoor
and indoor design temperatures for the two systems are taken as
0 and 22 8C, respectively [10]. Both IBGDHS and INGDHS are
essentially investigated here under BGDHS (for more details,
see Refs. [2,3,9,10]). The BGDHS is presently run by a
governmental body under the governorship of Izmir and is
utilized only for district heating purposes.
Fig. 1 shows a schematic diagram of the BGDHS where
hotels and official buildings heated by geothermal energy are
also included. The BGDHS consists mainly of three cycles,
such as: (a) energy production cycle through geothermal well
loop and geothermal heating center loop, (b) energy distribution cycle through district heating distribution network and (c)
energy consumption cycle through building substations.
As of the end of the year 2001, there were 14 wells ranging in
depth from 48 to 1100 m in the IBGF, while 9 wells were
working at the date studied. Of these, eight wells (designated as
BD2, BD3, BD4, BD5, BD7, B1, B4 and B5) and one well
(BD8) are production and re-injection wells, respectively. B10
well was not operated on 1 December 2003, but the well is
included in Fig. 1. The well-head temperatures of the
production wells vary from 95 to 140 8C, while the volumetric
flow rates of the wells range from 30 to 150 m3/h, respectively.
The thermal water is then sent to two primary plate type heat
exchangers and is cooled to about 60–62 8C, as its heat is
transferred to secondary fluid. The primary thermal water is reinjected into the well BD8 after extracting enthalpy, internal
energy, entropy, etc., while the secondary fluid is utilized to
heat the buildings through the substation heat exchangers. The
average conversion temperatures obtained during the operation
of the BGDHS are 80 8C/57 8C for the district heating
distribution network and 60 8C/45 8C for the building circuit.
Using the control valves for flow rate and temperature at the
building substations, the required amount of water is sent to
each housing unit to achieve the heat balance of the system
[3,4,11].
2.2. Salihli geothermal district heating system (SGDHS)
The Salihli geothermal field is about 7 km far from the
Centrum of the town Salihli and has a maximal yield of 87 l/s at
an average reservoir temperature of 95 8C, with a minimal
capacity 838 MW. Although it was initially designed for 20,000
residences equivalence, 2400 residences were heated by
geothermal energy as of February 2004. The outdoor and
indoor design temperatures for the system are taken as 4 and
22 8C, respectively.
Fig. 2 illustrates a schematic of the SGDHS where two
hospitals and official buildings heated by geothermal energy
were also included. The SGDHS consists mainly of three
288
L. Ozgener et al. / Energy and Buildings 38 (2006) 286–292
Fig. 1. A schematic diagram of the BGDHS [3].
cycles, such as: (a) energy production cycle (geothermal well
loop and geothermal heating center loop), (b) energy
distribution cycle (district heating distribution network) and
(c) energy consumption cycle (building substations). At the
beginning of the year 2004, there were seven wells ranging in
depth from 70 to 262 m in the SGDHS. Of these, five wells were
in operation at the date studied and two wells (K5 and K6) were
out of operation. Four wells (designated as K2, K3, K4 and K7)
and one well (K1) are production and balneology wells,
respectively. The well-head temperatures of the production
wells vary from 56 to 115 8C, while the volumetric flow rates of
the wells range from 2 to 20 l/s. Thermal water is sent to two
primary plate type heat exchangers and is cooled to about
45 8C, as its heat is transferred to secondary. The thermal water
is discharged via natural direct discharge, no recharge to the
Salihli geothermal field production, but re-injection studies will
be completed in the near future. The average temperatures
obtained during the operation of the SGDHS are 98 8C/45 8C
for the district heating distribution network and 62 8C/42 8C for
the building circuit. By using the control valves for flow rate
and temperature at the building main station, the needed
amount of water is sent to each housing unit and the heat
balance of the system is achieved. Thermal water, collected
from the four production wells at an average well heat
temperature of 91.75 8C, is pumped to the inlet of the head
exchanger mixing tank later a main collector (from four
production wells) with a total mass flow rate of about 44.39 kg/s
on 1 January 2004.
In the present case study on the BGDHS and SGDHS, the
hourly recorded experimental thermal data of various parameters (e.g., temperatures, pressures and volumetric flow rates)
were taken directly from the system technical staff, who
conducted
the measurements of pressures and temperatures
of fluids (inclu- ding water and geothermal) through the
Fig. 2. A schematic diagram of the SGDHS [5].
L. Ozgener et al. / Energy and Buildings 38 (2006) 286–292
Bourdon-tube pressure gauges and fluid-expansion thermometers, respectively.
3. Energy modeling
where ṁ is the mass flow rate, and the subscript ‘‘in’’ stands for
inlet and ‘‘out’’ for outlet.
For the both geothermal district heating systems studied, the
mass balance equations are written as follows:
n
X
ṁw;tot ṁr ṁd ¼ 0
(2a)
i¼1
and
n
X
ṁw;tot ṁd ¼ 0
(2b)
i¼1
where ṁw;tot is the total mass flow rate at wellhead, ṁr the flow
rate of the re-injected thermal water and ṁd is the mass flow rate
of the natural direct discharge.
The general energy balance can be expressed below as the
total energy input equal to total energy output (Ėin ¼ Ėout ), with
all energy terms as follows:
Q̇ þ
X
ṁin hin ¼ Ẇ þ
Basically, the energy efficiency of the system can be defined as
the ratio of total energy output to total energy input:
h¼
The balance equations are written for mass and energy
flows for the BGDHS and SGDHS and their components
under steady-state steady-flow control volume conditions.
Neglected are the pressure drops due to the liquid flow friction,
and thermal water of intermingling molecules of different
species through molecular diffusion in this study. The average ambient temperatures for the BGDHS and SGDHS are
taken to be 12 and 9.7 8C, based on the measurements obtained on site.
For a general steady-state, steady-flow process, the two
balance equations, namely mass, energy balance equations, are
employed to find the heat input, and the energy efficiencies.
In general, the mass balance equation can be expressed in the
rate form as:
X
X
ṁin ¼
ṁout
(1)
X
ṁout hout
(3)
where Q̇ ¼ Q̇net;in ¼ Q̇in Q̇out is the rate of net heat input,
Ẇ ¼ Ẇnet;out ¼ Ẇout Ẇin the rate of net work output and h is
the specific enthalpy.
Assuming no changes in kinetic and potential energies with
no heat or work transfers, the energy balance given in Eq. (3)
can be simplified to flow enthalpies only:
X
X
ṁin hin ¼
ṁout hout
(4)
The geothermal brine energy inputs from the production
field of the both systems investigated are calculated from the
following equation:
Ėbrine ¼ ṁw ðhbrine h0 Þ
(5)
289
Ėoutput
Ėinput
(6a)
where in most cases ‘‘output’’ refers to ‘‘useful’’ one.
Based upon Eq. (6a), the energy efficiency of the two
systems can be calculated from:
hsystem ¼
Ėuseful;HE
Ėbrine
(6b)
4. Results
The temperature, pressure and mass flow rate data for both
thermal water and water are given in accordance with their
state numbers as specified in Figs. 1 and 2. The energy rates
are calculated for each state and listed in Tables 1 and 2. Note
that state 0 stands for ambient conditions for the thermal
water and water. For thermal water the thermodynamic
properties of water are used. By doing so, any possible effects
of salts and non-condensable gases that might be present in
the geothermal brine are neglected (e.g., [3–5,11–13]). The
thermodynamic properties of water are obtained from the
general thermodynamic tables and software. The number of
the wells in operation in the Balcova and Salihli geothermal
fields may vary depending on the heating days and operating
strategy.
4.1. The performance evaluation results of the BGDHS
Using Eq. (2a), the total geothermal re-injection fluid (the
thermal water re-injected into the well BD8) mass flow rate is
99.72 kg/s at an average temperature of 64 8C and the total
production well mass flow rate is 170.7 kg/s, and the natural
direct discharge of the system is then calculated to be
70.98 kg/s on 1 December 2003. It is observed that the
distribution pipeline losses in the geothermal scheme are quite
large and account for 32.28% of the total production well
mass flow rate, due to the fact that the pipelines of the
distribution network are old resulting in high flow losses
(and leakages). In this regard, replacement of some pipelines
and proper control of the flow are required for possible
improvements.
To cover some leaks, the water was added by a pump (using a
pressurized water tank) to this network up to the date studied,
while recently, this application has been changed, and carbon
steel pipes are being changed with glass reinforced plastics)
pipes currently.
Using the values given in Table 1 and Eq. (6a) or (6b), the
energy efficiency of the BGDHS is determined to be 39.36%.
The energy balance diagram is illustrated in Fig. 3. The thermal
re-injection accounts for 28.36% of the total energy input,
while the natural direct discharge of the system amounts to
32.28%.
290
L. Ozgener et al. / Energy and Buildings 38 (2006) 286–292
Table 1
Energy rates and other thermodynamic properties of the states as shown in Fig. 1 for the BGDHS (based on the measurements taken on 1 December 2003)
State
no.
Fluid
type
Temperature,
T (8C)
Pressure,
P (kPa)
Specific enthalpy,
h (kJ/kg)
Specific entropy,
s (kJ/kg K)
Mass flow
rate, ṁ (kg/s)
Energy
rate, Ė (kW)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21a
210 a
22
220
23
230
24
240
25
26
27
28
29
30
31
310
32
320
33
330
34
340
35
350
36
360
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
W
TW
TWR
W
W
TW
TWR
W
W
TW
TWR
W
W
TW
TWR
W
W
TW
TWR
W
W
TW
TW
TW
TW
TW
TW
TW
TW
TW
TW
TW
W
W
W
W
W
TW
TW
TW
TW
TW
TW
TW
TW
TW
TW
TW
TWR
W
W
TW
TWR
W
W
TW
TWR
W
W
TW
TWR
W
W
12
105
80
55
50
105
80
55
50
90
57
85
55
90
57
85
55
75
60
70
50
–
–
107
106.7
102
101.7
101
100.7
112.5
112.8
64.4
90.9
63.7
63.9
15
14.7
132
131.7
130
129.7
136
135.7
120
119.7
116.7
116.4
90
57
85
55
105
65
80
60
107.3
78.7
80
61.7
110
50
65
36.6
101.32
222.11
117.05
148.67
113.65
222.11
117.05
148.67
113.65
171.42
118.62
159.11
117.05
171.42
118.62
159.11
117.05
139.86
121.23
132.47
113.65
–
–
354.63
229.4
405.3
208.94
403.27
205.2
257.05
506.62
486.36
628.21
468.12
709.27
250
200
400.23
385.49
506.62
369.05
506.62
420.84
496.49
297.99
455.96
278.25
171.42
118.62
159.11
117.05
222.11
126.32
148.67
121.24
486.36
303.97
162.12
212.78
486.36
113.65
263.44
273.57
51.01
439.95
230.02
334.71
209.13
439.95
230.02
334.71
209.13
376.73
238.38
355.71
230.02
376.73
238.38
355.71
230.02
313.74
250.93
292.78
209.13
–
–
448.57
447.14
427.51
426.02
423.29
421.8
471.68
473.2
269.7
380.93
266.76
267.79
63.64
62.34
554.67
553.32
546.22
544.78
571.82
570.42
503.7
502.21
489.68
488.21
376.73
238.38
355.71
230.02
439.95
271.85
334.72
250.93
449.94
327.76
334.78
258.18
461.35
209.13
272.02
153.52
0.1804
1.3623
0.7671
1.0744
0.703
1.3623
0.7671
1.0744
0.703
1.1917
0.7925
1.1334
0.7671
1.1917
0.7925
1.1334
0.7671
1.0146
0.8303
0.954
0.703
–
–
1.3846
1.3813
1.3287
1.3253
1.3174
1.314
1.4454
1.4487
0.8851
1.2021
0.8764
0.8789
0.2244
0.22
1.6549
1.6517
1.6338
1.6306
1.6968
1.6937
1.527
1.5238
1.4913
1.488
1.1917
0.7925
1.1334
0.7671
1.3623
0.8925
1.0744
0.8303
1.388
1.0541
1.0744
0.8515
1.4179
0.703
0.8925
0.5264
–
11.2
11.2
18.71
18.71
5.82
5.82
9.72
9.72
4.88
4.88
5.37
5.37
5.42
5.42
5.97
5.97
21.89
21.89
16.44
16.44
–
–
30.45
30.45
12.23
12.23
25.28
25.28
58.68
58.68
58.68
105.76
99.83
105.76
5.93
5.93
9.58
9.58
19.99
19.99
36.92
36.92
18.47
18.47
17.78
17.78
3.66
3.66
4.02
4.02
38.34
38.34
76.67
76.67
1.32
1.32
2.09
2.09
0.2
0.2
0.43
0.43
–
581.52
131.18
538.40
170.27
302.18
68.17
279.70
88.46
182.26
62.61
176.95
62.90
202.43
69.54
196.72
69.92
544.14
319.62
348.17
149.61
–
–
1649.85
1634.96
600.03
593.67
1215.07
1201.91
3518.17
3552.15
1041.26
4080.46
1725.62
1861.66
0.49
0.23
797.12
792.93
1614.65
1604.11
3264.04
3244.99
1269.02
1258.35
1153.33
1143.93
136.69
46.96
132.47
47.08
1990.66
681.86
2207.01
1119.46
72.05
36.45
60.29
33.03
11.49
1.82
7.72
1.65
L. Ozgener et al. / Energy and Buildings 38 (2006) 286–292
291
Table 1 (Continued )
State
no.
Fluid
type
Temperature,
T (8C)
Pressure,
P (kPa)
Specific enthalpy,
h (kJ/kg)
Specific entropy,
s (kJ/kg K)
53
54
55
56
57
58
59
60
61 a
610 a
62
63
630
64
65
66
67
TW
TWR
W
W
TW
W
W
W
W
W
TWR
TW
TW
TWR
W
W
TWR
111.6
80
81
57.7
118
76.7
51.3
51.6
–
–
57.4
57.4
57.1
40
47
37
64
486.36
148.67
303.97
364.77
344.5
483.32
388.07
628.21
–
–
324.24
324.24
118.71
108.69
111.93
107.6
263.44
460.11
334.71
339.09
241.59
495.11
319.94
214.89
216.35
–
–
240.31
240.31
238.8
167.37
196.6
154.85
267.84
1.4355
1.0744
1.0863
0.8014
1.5054
1.0314
0.7198
0.7236
–
–
0.7975
0.7975
0.7937
0.572
0.6642
0.5319
0.8801
Mass flow
rate, ṁ (kg/s)
9.4
9.4
12.83
12.83
9.98
24.57
24.57
24.57
–
–
9.98
9.98
9.98
9.98
17.43
17.43
99.72
Energy
rate, Ė (kW)
481.36
270.49
381.85
173.23
661.44
645.39
247.42
256.67
–
–
133.07
133.07
128.82
46.86
133.07
62.92
1726.21
Note: The phase of the reference state is liquid. W: water; TW: thermal water; TWR: thermal water re-injection.
a
Not operational on the day the experimental data were taken.
Table 2
Energy rates and other thermodynamic properties of the states for the SGDHS as shown in Fig. 2 (on 1 January 2004)
State
no.
Fluid
type
Temperature,
T (8C)
Pressure,
P (kPa)
Specific enthalpy,
h (kJ/kg)
Specific entropy,
s (kJ/kg K)
Mass flow
rate, ṁ (kg/s)
Energy rate,
Ė (kW)
0
1
10
2
20
3
30
4
40
5
6
7
8
9
10
W
TW
TW
TW
TW
TW
TW
TW
TW
TW
TW
TWR
W
W
W
9.7
56
55.3
98
97.3
98
97.3
115
114.3
95
95.7
44.8
62
42.8
43.5
101.32
117.83
117.29
195.62
193.26
195.62
193.26
270.39
266.56
185.83
435.7
395.17
445.83
109.86
354.64
41.43
234.2
231.28
410.42
407.46
410.42
407.46
482.27
479.3
397.78
400.98
187.8
259.63
179.07
182.34
1.46E01
0.7798
0.7709
1.2835
1.2755
1.2835
1.2755
1.4728
1.4651
1.2493
1.2573
0.6354
0.8553
0.6091
0.6183
–
–
6.3
6.3
9.18
9.18
19.18
19.18
9.73
9.73
44.39
44.39
44.39
120.82
116.49
120.82
85.05
82.51
433.74
427.34
906.22
892.85
637.85
630.14
1965.66
2007.26
352.60
2123.35
774.91
884.40
Note: The phase of the reference state is liquid. W: water; TW: thermal water; TWR: thermal water re-injection.
Fig. 3. Energy flow diagram of the BGDHS at an average temperature of 12 8C.
292
L. Ozgener et al. / Energy and Buildings 38 (2006) 286–292
Fig. 4. Energy flow diagram of the SGDHS at an average temperature of 9.7 8C.
4.2. The performance evaluation results of the SGDHS
References
The total geothermal natural direct discharge fluid mass flow
rate is about equal to the production wells total mass flow rate in
the SGDHS. This flow rate value was measured as 44.39 kg/s at
an average temperature of 44.8 8C. This clearly indicates that in
the SGDHS, there is a significant amount of water lost in the
natural direct discharge. If water losses measured in the district
heating distribution network are above 5 m3/h, the water is
added via a pump (using a pressurized water tank) to this
network for covering these leaks. However, the water losses
were neglected in this study, as these losses were less than 5 m3/
h at the date studied. As can be seen from the energy balance
diagram illustrated in Fig. 4, the natural direct discharge (pipe
line losses) of the system accounts for 40.69% of the total
energy input. Using the values given in Eq. (6a) or (6b), the
energy efficiency of the SGDHS is determined to be 59.31%.
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5. Conclusions
The energetic performance of the BGDHS and SGDHS,
along with their essential system components, such as pumps
and heat exchanger, has been evaluated through a comprehensive energy analysis. In this regard, modeling for an energy
analysis of a geothermal district heating system uses mass and
energy balance equations. The values for energy efficiencies
of the SGDHS in Salihli, Manisa are also compared to those
of the BGDHS installed in Balcova, Izmir. The SGDHS has
higher energy efficiency than the BGDHS. The energy recovery
is crucial and should be implemented with more effective/
efficient re-injection.