Solar domestic water heating in Turkey

Energy 24 (1999) 363–374

Solar domestic water heating in Turkey

B.G. Akinoglua,*, A.M. Shariahb, A. Ecevita

aPhysics Department, Middle East Technical University, Ankara, TurkeybPhysics Department, Jordan University of Science and Technology, Irbid, Jordan

Received 10 October 1998

Abstract

In this report we discuss the present situation of solar water heating for domestic supplies in Turkeyand give the results of a computer analysis for nine distinct regions. The analyses are carried out for fourtypical days of the four seasons and also on a monthly base. The results show that detailed initial workmust be carried out before installing the system to determine the optimized collector area. Such analysiscan provide efficient using of the Sun’s energy as well as economical benefits in the initial investmentsand long term utilization. 1999 Elsevier Science Ltd. All rights reserved.

Nomenclature

Ac collector areaCp specific heatf monthly solar contributionFRUL slope of the collector efficiency curveFR(ta)n intercept of the collector efficiency curveF9 collector efficiency factorIT incident solar radiation on the collector surfaceQaux energy input to tank from the auxiliaryQl energy delivered to loadQu useful energy collectionmc collector flow rateNc number of equal sized collector nodes

* Corresponding author. Tel.:1 00-312-210-50-64; fax:1 00-312-210-12-81; e-mail: [email protected]

0360-5442/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved.PII: S0360-5442(99)00004-3

364 B.G. Akinogˇlu et al. /Energy 24 (1999) 363–374

Ta ambient air temperatureTi collector inlet temperatureTk temperature of nodek in the collectorUL collector loss coefficientDt time periodh efficiency of the collector

1. Introduction

Although solar energy is the most important renewable energy source it has not yet becomewidely commercial even in nations with high solar potential such as Turkey. There are limitedapplications and most of them are inefficient both in terms of energy use and economical benefits.The economical feasibility of a solar energy system is mainly determined by its initial cost andlong term efficiency. The cost of the conventional energy replaced by solar means is, of course,another important parameter. Therefore, in the use of solar energy systems careful considerationis vital to find out the system capacity for optimum useful energy collection at the installation site.

Thermosyphon-type flat plate collectors have been used in Turkey since 1950, and at presentabout 30% of the installed systems are still of this type. However, the installations are mostly bytrial and error. There are quite a large number of different manufacturers producing collectorswith varying types and performances.

Although the performance of solar water heating systems largely depends on the design para-meters [1–10], such as hot water consumption rate [1,11,12] and climatic data [1,11–13], systemsare installed without prior determination of the optimum system size and capacity.

In this study, the TRNSYS computer simulation model [14] is used. It is a computer simulationprogram in which the mathematical models of the components of the system make up the wholesystem so that any subsystem can be inserted into the system or can be completely ignored. Thismodel was used by Shariah et al. [15] who conducted a study on the optimization of the designparameters of a system installed in Los Angles. Shariah and Shalabi [13] used the TRNSYS tooptimize the design parameters for a thermosyphon solar water heater in Amman and Aqaba,representing mild and hot climates in Jordan. Shariah and Lo¨f used TRNSYS to optimize thetank volume to collector area ratio [16].

The aim of the present study is to compare two collectors having high and low performances,for two values of water consumption and three values of collector area. The analyses are carriedout for nine cities in Turkey (Table 1), ranging in altitude from 3 to 1283 m and in latitude from36° 379 N to 42° 029 N. We believe that these locations reflect all different types of climatesoccurring in Turkey.

2. Description of the thermosyphon system and the model

A diagram of the solar water heating thermosyphon system is shown in Fig. 1 [13]. It consistsof a flat plate collector, a vertical storage tank, a flow mixer to mix the water from the mains attimes when the water from the tank is above the desired load temperature, an electric heater to

365B.G. Akinogˇlu et al. /Energy 24 (1999) 363–374

Table 1Geographical parameters of the locations

Location Latitude Longitude Altitude (m) Tambient (°C) Region

Iskenderun 36° 379 N 36° 079 E 3 20.2 MediterraneanDalaman 36° 459 N 28° 479 E 9 18.1 MediterraneanIzmir 38° 249 N 27° 109 E 25 17.6 MediterraneanIstanbul 40° 599 N 28° 489 E 36 13.7 Black SeaSinop 42° 029 N 35° 109 E 32 14.0 Black SeaRize 41° 029 N 40° 309 E 4 14.1 Black SeaKayseri 38° 439 N 35° 299 E 1068 10.8 M&E Anatol.Mardin 37° 189 N 40° 449 E 1080 15.8 M&E Anatol.Mus 38° 449 N 41° 319 E 1283 9.7 M&E Anatol.

Fig. 1. Schematic diagram of the system.

heat the water in the tank when the solar contribution from the collector is insufficient, a checkvalve to prevent reverse flow at times of low or no radiation and the necessary piping. The bottomof the tank is levelled with the top of the collector. The values of the parameters used in thecalculations are given in Table 2 and Ref. [13].

The collector is simulated as having 20 nodes in the flow direction whereas the storage tankis considered to be a stratified tank with variable number of nodes depending on the collector size,load rate, auxiliary input, loses and the simulation time step. The connecting pipes are modeled asa single node due to small thermal losses and surface areas.

The Hottel–Whiller equation for the collector characterizing the total useful energy gain by thecollector is given by [17]:

Qu 5 rAcDt[FR(ta)nIT 2 FRUL(Ti 2 Ta)] (1)


Table 2The parameters of the collectors used in the analysis

Area (m2) FR(ta) FRUL (kJ/hm2C) LoadVl (lt)

2 0.8 16 1202 0.8 16 1802 0.6 30 1202 0.6 30 1803 0.8 16 1203 0.8 16 1803 0.6 30 1203 0.6 30 1804 0.8 16 1204 0.8 16 1804 0.6 30 1204 0.6 30 180

wherer is a modification coefficient correcting theFR(ta) andFRUL, and is presented as:

r 5F mcCp

AcF9ULS1 2 expS 2 AcF9UL

mcCpDDG

use

F mcCp

AcF9ULS1 2 expS 2 AcF9UL

mcCpDDG

test

(2)

In Ref. [17] the temperature at the midpoint of any nodek in the collector is given as:

Tk 5 Ta 1ITFR(ta)

FRUL

1 STI 2 Ta 2ITFR(ta)

FRULDexpS 2

F9ULAc(k 2 1/2)mcCpNc

D (3)

whereF9UL are

F9UL 5 2mcCp

Ac

lnS1 2FRULAc

mcCpD (4)

The monthly efficiencyh and monthly solar fractionf are given by:

h 5Qu

AcSIT

(5)

f 5Ql 2 Qaux

Ql

(6)

representing the thermal performance of the solar system, and the annual values are denoted askhl and kfl.


The hourly simulation is performed on the 15th of four months representing the months March,June, September and December. The dry bulb temperature is obtained from the State Meteorologi-cal Institute of Turkey [18] and the solar radiation is estimated using Ref. [19]. Daily loads of120 and 180 l are used with the assumption of Rand hot water use profile [20]. The auxiliaryheater in the tank is activated at times when the water temperature in the tank is below 55°C.Two types of collectors having two differentFR(ta) and FRUL values (low efficiency: 0.6,30 kJ/hm2 K and, high efficiency: 0.8, 16 kJ/hm2 K) are compared and the analyses cover collectorareas of 2, 3 and 4 m2. In this article only monthly and annual results are presented.

3. Results and discussions

The results of this study show that Turkey can be divided into three separate regions: Mediter-ranean, Black Sea Coasts, and Middle and East Anatolia. The groups and cities together with thelatitudes and altitudes are given in Table 1.

Monthly solar fractions (f) and efficiency (h) are shown in Figs. 2–4 for a hot water supplyof 120 l/day, with collector areas of 2, 3 and 4 m2, for the low-efficient system. Fig. 2 is for theMediterranean (Iskenderun, Dalaman, Izmir), Fig. 3 is for the Black Sea Coasts (Istanbul, Sinop,Rize) and Fig. 4 is for the Middle and East Anatolia (Kayseri, Mus, Mardin). It is evident fromFig. 2 that thef for the summer months in the Mediterranean region is very close to 100%. Inthis region,f values for the winter months are also quite high and only for about 3 months arethey below 50%. For the low-efficient system with a 2 m2 collector area,f values are quite high,close to those obtained for the system with 3 and 4 m2.

For the Black Sea Coasts,f values hardly reach 100% for Istanbul and are below 90% forSinop and Rize (Fig. 3). For the winter months the solar contribution drops down almost to zerosuggesting the use of high-efficient collectors for this region as seen in Fig. 5 which shows theresults for a high-efficient collector system for the location Sinop in the Black Sea region. Whena high-efficient collector is used in this region thef values are high and even for a 3 m2 systemthe solar contribution is above 90% for most months.

For the Middle and East Anatolia region, althoughf for the summer months is close to 100%,for around five or six months of the year the solar fraction is below 40%. For a low-efficientcollector for Mus, three of the months havef values of 0%. Fig. 6 shows the results for Mus fora high-efficient collector. As can be seen from this figure, two or three of the winter months stillhave lowf values (below 40%) while the summer months are better than the low-efficient collectorsystem. This suggests that a different tilt angle must be preferred for the collector system to attainoptimized f values, at least for some of the locations in Middle and East Anatolia.

Sample results for low-efficient collectors with a load of 180 l/day are presented in Fig. 7 forthree typical cities representing the three regions. The figure suggests that a 1 m2 increase in thecollector area may be enough to compensate for the 60 l increase in the load, the result being inagreement with the optimum load-collector area ratio as proposed by Shariah et al. [15].

For the Mediterranean region, the use of the collectors is mostly during the summer monthssince the families in big cities usually move to their residences at the Mediterranean Coasts forholidays during the summer months. Therefore, for this region, even for a low efficient system,the load can be increased without increasing the area, just by proper orientation of the collectortilt for use only in the summer months.


Fig. 2. Monthly efficiency and solar heating fraction for the Mediterranean region, low-efficient collector.


Fig. 3. Monthly efficiency and solar heating fraction for the Black Sea region, low-efficient collector.


Fig. 4. Monthly efficiency and solar heating fraction for the Middle and East Anatolian region, low-efficient collector.


Fig. 5. Monthly efficiency and solar heating fraction for Sinop, high-efficient collector.

Fig. 6. Monthly efficiency and solar heating fraction for Mus, high-efficient collector.

Table 3 shows the annual average of the solar heating fractions for the three sample locations(namely, Dalaman, Sinop and Mus) for three different collector areas, for two types of collectorsand for 120 l/day. Thekfl values for the low-efficient collector in the Mediterranean are the sameas thekfl values for the high-efficient collector in the Black Sea Coast and Middle and EastAnatolia regions. Therefore, for these regions letter collectors should be preferred and a furtheroptimization should be consider for the orientation and economy of the systems.

4. Conclusion

It is concluded that Turkey can be divided into three different regions in terms of solar domestichot water applications. The best region is Mediterranean and it is enough to use a 2 m2 high-


Fig. 7. Monthly efficiency and solar heating fraction for Dalaman, Sinop and Mus, low-efficient collector, 180 l/day.


Table 3The annual performances of the collectors for three locations

Low efficiency

2 m2 3 m2 4 m2

khl kfl khl kfl khl kfl

Dal. 0.35 0.67 0.29 0.77 0.24 0.83Sin. 0.31 0.44 0.26 0.53 0.23 0.60Mus 0.30 0.46 0.25 0.54 0.21 0.59

High efficiency

2 m2 3 m2 4 m2

khl kfl khl kfl khl kfl

Dal. 0.51 0.86 0.40 0.94 0.34 0.98Sin. 0.50 0.68 0.42 0.78 0.36 0.85Mus 0.47 0.69 0.38 0.77 0.32 0.82

efficient collector system or 3 m2 low-efficient system, even for a load of 180 l. The presentinstallations in this region usually have a 4 m2 collector area (most of them have low efficiencies)which seems more than necessary to supply hot water during the summer months.

For the Black Sea and Middle and East Anatolia regions, low-efficient collectors seem to haveproblems in supplying the hot water for all months of the year. For the Black Sea Coast this isprobably due to the large number of rainy months and for Middle and East Anatolia it may bedue to the very cold and cloudy winter months. Therefore, for these two regions high-efficientcollectors with 3 or at most 4 m2 collector areas should be preferred.

References

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Solar domestic water heating in Turkey