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PROCEEDINGS, Thirty-Eighth Workshop on Geothermal Reservoir EngineeringStanford University, Stanford, California, February 11-13, 2013SGP-TR-198

THREE HEATING SEASONS MONITORING OF USAGE OF LOW ENTHALPYGEOTHERMAL RESOURCES: EXERGETIC PERFORMANCE ANALYSIS OF AN EAHE

ASSISTED AGRICULTURAL BUILDING

Onder Ozgener1 , , Leyla Ozgener2, , , Jefferson W. Tester3

1Solar Energy Institute, Ege University, TR 35100 Bornova, Izmir, Turkey2Department of Mechanical Engineering Faculty of Engineering,

Celal Bayar University, TR45140 Muradiye, Manisa, Turkey3Cornell Energy Institute, Cornell University, 2160 Snee Hall, Ithaca, NY, 14853 USA

e-mail:[email protected],[email protected]

ABSTRACT

The study experimentally investigated the exergetic

performance (efficiency) of a closed loop Earth(geothermal) to Air Heat Exchanger (EAHE) in theheating mode. EAHE systems are used as a techniquefrom ancient times for heating and cooling purposes,and they make it possible to evaluate low enthalpygeothermal resources. The experimental system wascommissioned in June 2009 and experimental datacollection has been conducted since then. The data,consisting of hourly thermodynamic records for

heating over a three year period from 2009-2012,were measured by the Solar Energy Institute of theBornova Campus at Ege University. At the presenttime, the database contains more than 30000 recordsof measurements. Exergetic efficiencies based on the

heat exchanger for an air-conditioned building havebeen evaluated for both winter and summer byAscione et al. (2011). By means of dynamic building

energy performance simulation codes, the energyrequirements of the systems have been analysed fordifferent Italian climates, as a function of the mainboundary conditions (such as the typology of soil,tube material, tube length and depth, velocity of theair crossing the tube, ventilation airflow rates, controlmodes) by Ascione et al. (2011). The implementationof thermal design method and a simple pneumaticwas made for the EAHE of a large passive house(PH) built near Bucharest in Romania by Badescu

and Isvoranu (2011). Year round hourly performanceanalysis of integrated EAHE- evaporative coolingsystem using multiphase CFD modeling forinvestigating performance enhancement was carriedout using a simplifed EAHE system developed by
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]

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g out using a simplifed EAHE system developed by

elements method) allows analysis of energyperformance dependence on a wide range ofparameters including air-ground heat exchanger

geometrical configuration, mode of operation andenvironmental factors (Trzski and Zawada, 2011).The earth-to-air heat exchanger has shown thehighest efficiency for cold climates both in winterand summer (Ascione et al. , 2011). Nayak andTiwari (2010) carried out to evaluate the annualthermal and exergy performance of a photo-voltaic/thermal (PV/T) and earth air heat exchanger(EAHE) system, integrated with a greenhouse,

located at IIT Delhi, India, for different climaticconditions of Srinagar, Mumbai, Jodhpur, New Delhiand Bangalore. Fintikakis et al. (2011) studied theurban micro-climatic conditions in the historic centreof Tirana in order to integrate the information in therehabilitation of specific open space. A newnumerical model of earth-to-air heat exchanger isdiscretized into n sections perpendicular to theexchanger pipe by Tittelein et al (2009).

In this paper, authors extend these studies by

conducting an exergetic heating performance analysisof the system, using thermal data collected at the site.The objectives of this work are to assess the entiresystem and its essential components for performanceevaluations and comparisons, as well as possibleefficiency improvements.

The passive heating system was tested only inexperimental studies often without windows, andwere actually applied in occupied a agriculturalbuilding. The tests were without any internal heat

source. Still, the paper demonstrates the potential ofthe system under the climatic conditions prevailingduring the experiments, but without any of the effectsof interior heat generation and with solar energy

t ti th h i d

utilizes an underground galvanized pipe incombination with a blower to keep the greenhousetemperature at the set condition. A positive

displacement type of airblower (twin lobecompressor ) of 736 Watt capacity and volumetricflow rate of 5300 m3/h was fitted with the suctionhead positioned in the southwest corner of thegreenhouse (Ozgener and Ozgener, 2010a-d; Ozgeneret al, 2011; Yildiz et al, 2011, 2012; Ozgener andOzgener, 2013a,b ).

ANALYSIS

Exergy analysis, as described in this paper and inmore detail in a series of recent studies by Ozgenerand Ozgener (2009), (2010a-d), (2013a,b), Ozgener(2011), (2012), Ozgener et al (2011), has beenapplied to evaluate the performance of the system.The balance equations (mass, energy and exergyflows in the system and its components) are writtenfor steady-state steady-flow control volume systems,and the appropriate energy and exergy equations are

derived for this system and its components (Ozgenerand Ozgener, 2009;Ozgener and Ozgener, 2010a-d;Ozgener, 2013a,b;Ozgener, 2011; 2012;Ozgener etal., 2011; Ozgener and Ozgener 2011). All theformulas used represent the experimental data andconditions of the study and are intended for generalprediction of the performance of the tested passiveEAHE heating system.

Performing exergy analysis of the system studied

Physical exergy is the majority of the process.Therefore, chemical exergy, potential exergy, nuclearexergy, magnetic exergy, and kinetic exergy (kineticenergy) were neglected in this study.

h l b l b d i

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000

00,,00,,

/ln6078.16078.11/6078.11ln

/ln/ln

ava

vavpapvpapa

RRRT

PPRRTTCCTTTCC

(3)

where the specific humidity ratio is

mmw / (4)

and, T0, P0 are reference temperature and atmosphericpressure.Specific exergy of ideal gas (air)

(5)

Multiplying flow or specific exergy given in Eqs.(3)-(5) by the mass flow rate of the fluid gives theexergy rate

(6)

The exergy content of the solar radiation absorbed bythe solar collecting area of PV is

(7)

It is usually more convenient to estimate entropy

generation genS first, and then to evaluate the exergy

destroyed or the irreversibility I directly from thefollowing equation:

(8)

E d i f h EAHE PV d

overall system inefficiency. In this context, differentways of formulating the exergetic (or exergy)efficiency (second law efficiency, effectiveness, orrational efficiency) proposed in the literature havebeen given in detail elsewhere (Kotas, 1985, Szargut,1998). Taking Eqs. (2) and (6) the general exergyefficiency of the system can be written as follows:

(12)

The exergy efficiency of earth to air heat exchangermay be written as follow:

(13)

The exergy efficiency of the PV is calculated asfollows

(14)

The exergy efficiency of the blower (fan) can be

defined as follows

(15)

Xsol ar

Xd estPV

E

E

1

AST

TE T

sun

Xsola r .).1(0

b

XinXoutb

W

EE

inaina

k

koutainaa

Xin

EAHEXde st

Xin

Xou tEAHE

mT

TQm

E

E

E

E

,,

0,,

,

1

1

1

Xin

Xdestsys

E

E

1

0

0

0

00,, ln..)ln( P

PTRT

TTTTC aapaCp

aaX mE .

genXde st STEI

0

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series universal data loggers are new generationmicrocontroller based instruments compatible withIEC (International Electrotechnical Commission) 668

standards. E-680 series indicate measurements from32 different points on instrument display anddetermine the alarm conditions by comparison of twoset points for each channel. The instruments can beconnected to an RS-485 communication line and thedata can be collected and stored in a centrally locatedPC. It has a resolution of 0.1 C, 1 W/m2 fortemperature and its accuracy of 0.5% (Ozgener andOzgener, 2011). TESTO 6621 temperature and

relative humidity (RH) transmitters have 0.5

o

C, and2.5 % RH, respectively. Air flow velocities weremeasured by Lutron AM-4206M anemometer and itsaccuracy and resolutions are 2% 0.2 m/s, 0.01 m/s,respectively.

RESULTS AND DISCUSSION

The results of long-term observations in the Bornova

area of Izmir on exergetic efficiency fluctuations ofthe system are presented in the form of tables, barcharts and graphs. The experimental system wascommissioned in June 2009 and experimental datacollection has been conducted since then. The data,consisting of hourly thermodynamics records a yearlyheating periods for 2009-2012, were measured atthe Solar Energy Institute of the Bornova Campus atEge University. At the present time, the databasecontains more than 30000 records of measurements.The thermodynamic properties of the air used in thepresent study are based on the actual data taken fromthe system measured and recorded average valuesfor 2009, 2010, 2011, and partly 2012 heating

temperature difference between the inlet and outletwas approximately 6.2C . In addition, the mass flowrate of air was measured to be 0.56 kg/s. During the

heating period, the rate of extracted heat from air tothe ground was found to be 10.74 kW on average.Using the the database, which contains more than30000 records of measurements taken duringexperimental study, the mean exergy efficiency of theEAHE, as given in Table 1-3, was determined to be54 %, the mean exergy efficiency of fan was 72%and overall exergy efficiency was 69% for 2009-2012 heating period. Table 1-3 also shows that 46%

of the total exergy flow entering the EAHE is lost,while remaining 54% is utilized. The highest exergyloss is found to be 96% from the PV component byusing Eqs. (5)-(7). Exergetic efficiencies of PV arrayswere found to be 4%, respectively. This result wasconsistent with the exergy destruction associated withthe air blower and amounts to some 0.20 kW. About9% of the required electric energy was obtained fromsolar photovoltaic cells with the remaining 91%coming from conventional resources. As expected

that maximum supplement provided by the solarphotovoltaic cells was measured to be greater than55% between the hours 13:30 and 13:40.

In the present study, the results obtained from theexperiments were evaluated to determine the overallperformance of the system. During periods of nosunlight the north-facing wall was insulated to reducethe potentially large heat losses through that wall.

The design of passive greenhouse systemsrequires the strategic placement of windows, storage

masses, occupied spaces. Results of the study can beused in conjunction with fundamental principles ofsolar radiation geometry and tilt factors, as describedby Kreith and Kreider (1978), and Kreith andG i (2007) t hi i d d i Th

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pipe lengths in meters per kW of heatingcapacity were found to be 4.7.

Seasonal fluctuations of exergetic efficiencyhave been obtained for the soil depths up to 3m by measurements over the period of 2009-2012. Results are reported as average

monthly monitored values of s of the system

for the 2009 - 2012 heating seasons.

Experimental results also show that meanheating exergetic efficiency value wasobtained to be 69% for successive 3 yearsheating seasons. The maximum yearly meanexergetic efficiency was 71% in 2009 heatingseason.

The highest irreversibility on a system basisoccurs in the PV unit, followed by the fan, andEAHE, respectively. In addton, theremaining system components have arelatively low influence on the overallefficiency of the system.

ACKNOWLEDGEMENTS

The support for this work provided by Ege Universityand TUBITAK (The Scientific and TechnologicalReaearch Council of Turkey). Authors are gratefulfor the financial support provided for the projectunder project grant no. of 09GEE003 and 10GEE007by Ege University Research Fund, last but not least,authors are thankful to TUBITAK Dr. L. Ozgenerand Dr. O. Ozgener are awarded a grant by

TUBITAK as fellow at Cornell University, Ithaca,NY, USA.

NOMENCLATURE

V Unit of electrical potentialdifference (volt)

W

Work rate (kW)

Greek Letters Exergy (Second law) efficiency (-)

Specific exergy (kJ/kg)

specific humidity (kgwater vapor/kgair)

Subscripts

Superscripts

(.) a dot per unit time

Abbreviations

EAHE Earth-to-Air Heat ExchangerMAAT Monthly Average Ambient TemperaturePV Solar Photovoltaic Cell Systems

0 restricted reference state

a airb blower

dest destroyed

electrical electrical conversion

gen generated

in inlet

m electrical values at maximum

out outlet

sys systemw water vapor

v vapor

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Renewable Energy CRC Press Taylor&FrancisGroup, New York, USA, 2007.

Kotas, T.J. (1985), The exergy method of thermal

plant analysis Anchor Brendon Ltd, Tiptree,Essex. Great Britain, 1985.

Misra, R., Bansal, V., Agarwal, G. D. , Mathura, J.and Aseri, T. (2012), Thermal performanceinvestigation of hybrid earth air tunnel heatexchangerEnergy and Buildings49, 531-535.

Nayak, S., Tiwari, G.N. (2010), Energy metrics ofphotovoltaic/thermal and earth air heat exchangerintegrated greenhouse for different climatic

conditions of IndiaApplied Energy, 87, 2984-2993.Ozgener, L. (2011), A review on the experimental

and analytical analysis of earth to air heatexchanger (EAHE) systems in Turkey Renewableand Sustainable Energy Reviews 15(9), 4483-4490.

Ozgener, L. (2012), Coefficient of Performance(COP) Analysis of Geothermal District HeatingSystems (GDHSs): Salihli GDHS case study.Renewable and Sustainable Energy Reviews

16(2):1329-1333.Ozgener, L., Ozgener, O. (2009), Exergy analysis of

drying process:An experimental study in solargreenhouse. Drying Technology Journal 27(4),580-586.

Ozgener, O., Ozgener, L. (2010a) Exergoeconomicanalysis of an underground air tunnel system forgreenhouse cooling systemInternational Journalof Refrigeration33(5),995-1005.

Ozgener, O., Ozgener, L. (2010b) Exergetic

assessment of EAHEs for building heating inTurkey: A greenhouse case study Energy Policy 38(9), 5141-5150.

Ozgener, L., Ozgener, O. (2010c) Experimentalt d f th ti f f

cooling system International Communications inHeat and Mass Transfer38 (6), 711-716.

Szargut, J., Morris, D.R. and Stewart, F.R. (1998),

Exergy analysis of thermal, chemical, andmetallurgical processes Edwards Brothers Inc.USA, 1998.

Tittelein, P., Achard, G. and Wurtz, E. (2009),Modelling earth-to-air heat exchanger behaviourwith the convolutive response factors methodApplied Energy86(9), 1683-1691.

Trzski, A., Zawada, B. (2011),The influence ofenvironmental and geometrical factors on air-

ground tube heat exchanger energy efficiencyBuilding and Environment46, 1436-1444.Vaza, J., Sattlerb, M. A. (2011), Experimental and

numerical analysis of an earthair heat exchanger,E. D. dos Santosa, L. A. Isoldia Energy andBuildings43, 2476-2482.

W.J. Wepfer, R.A. Gaggioli, E.F. Obert, (1979),Proper evaluation of available energy forHVACASHRAE Transactions85(1), 214-230.

Yildiz, A., Ozgener, O. and Ozgener, L. (2011),

Exergetic performance assessment of solarphotovoltaic cell (PV) assisted earth to air heatexchanger (EAHE) system for solar greenhousecoolingEnergy & Buildings 43 (11), 3154-3160.

Yildiz, A., Ozgener, O. and Ozgener, L. (2012),Energetic performance analysis of a photovoltaicassisted closed loop earth to air heat exchangerfor solar greenhouse cooling: an experimentalstudy for low energy architecture in AegeanRegionRenewable Energy16(8), 6438-6454.
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Table 1: Average monthly monitored values for 2009 heating season

Months2009

MAAT

destxE EAHE Q TExtracted

EnergyConsumed

Energy

First and second law performance

evaluation results

kW kW C kWh kWh

Blower EAHE System

I

(%)

II

(%)

I

(%)

II

(%)

COP

(-)

II

(%)

January - - - - - - - - - - - -

February - - - - - - - - - - - -

March - - - - - - - - - - - -

November 14.6 2.10 10.65 5..90 798.75 54.75 - 92.66 97.79 56.28 14.59 70.99

December 13.1 2.21 10.83 6.00 758.1 51.10 - 88.33 97.61 55.29 14.84 70.07

Average 13.9 2.15 10.74 5.95 778.3 52.93 59.36 90.49 97.7 55.79 14.72 70.53

Total

uncertainty(%)

1.5

5 4 0.5 5 5 4 6 3 5 4 5

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Months2010

MAAT

destxE EAHE

kQ T

Extracted

Energy

Consumed

Energy

First and second law performance evaluation results

kW kW C kWh kWh

Blower EAHE PV System

I

(%)

II

(%)

I

(%)

II

(%)

I

(%)

II

(%)

COP

(-)

II

(%)

January 10.6 2.22 14.4 8.01 1728 87.6 - 65.79 96.77 54.62 - - 19.78 69.54

February 12.6 2.22 10.83 6.00 758.1 51.1 - 77.64 97.56 54.91 - - 14.84 69.73

March 13.3 2.83 10.83 6.01 649.8 43.8 - 82.53 97.63 55.43 - - 14.83 70.20

November 18.1 - - - - - - - - - - - - -

December 13.3 2.31 3.61 2 234.7 47.5 - 82.53 99.00 53.21 4 4 4.94 67.99

Average 13.6 2.39 9.92 5.5 842.65 57.5 59.36 77.12 97.74 54.54 4 4 13.59 69.37

Totaluncertainty

(%)

1.55 4 0.5 5 5 4 6 3 5 5 5 4 5

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Months 2011MAAT

destxE EAHE

kQ T

Extracted

Energy

Consumed

Energy


kW kW C kWh kWh


I

(%)

II

(%)

I

(%)

II

(%)

I

(%)

II

(%)

COP

(-)

II

(%)

January 10.5 2.16 17.42 9.65 1620.06 67.89 - 65.29 96.38 55.85 - - 23.86 70.77

February 10.0 2.28 12.27 6.80 1374.24 81.76 - 62.87 97.00 53.34 - - 16.81 68.29

March 11.7 2.20 13.17 7..30 1119.45 62.05 - 71.91 97.10 55.14 - - 18.05 70.00

November 11.9 2.20 12.87 7.13 1119.69 63.51 - 76.21 97.17 55.19 - - 17.63 70.03

December 10.7 2.71 7.22 4.00 1600.20 70.50 - 66.31 98.00 52.79 - - 9.89 67.70

Average 10.9 2.31 10.59 6.98 1376.73 69.14 59.36 68.52 97.13 54.46 4 4 17.25 69.36

Totaluncertainty

(%)

1.55 4 0.5 5 5 4 6 3 5 5 5 4 5

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Tabe 4: Average monthly monitored values for 2012 heating season

Months 2012MAAT

destxE EAHE

kQ T

Extracted

EnergyConsumed

Energy


kW kW C kWh kWh


I

(%)

II

(%)

I

(%)

II

(%)

I

(%)

II

(%)

COP

(-)

II

(%)

January 6.9 2.38 12.64 7 1516.8 87.6 - 52.39 96.40 50.71 4 4 17.30 65.82

February 7.4 2.78 10.83 6 1028.8 69.4 - 53.50 96.80 51.02 4 4 14.84 66.10

March - - - - - - - - - - - - - -

November - - - - - - - - - - - - - -

December - - - - - - - - - - - - - -

Average 7.2 2.59 11.74 6.5 1272.8 78.5 59.36 52.95 96.6 50.87 4 4 16.07 65.96

Totaluncertainty(%)

1.55 4 0.5 5 5 4 6 3 5 5 5 4 5

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Fig.1:Basic simplified PV assisted EAHE system schema adopted from (Ozgener and Ozgener, 2010a-d; Yildiz et al., 2011)

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Fig. 2: A view of PV assisted EAHE system

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