ISSN: 2617-2070 (Print) ; 2617-2070 (Online) o Advanced...

Journal of Advanced Sciences and Engineering Technologies (2019) Vol 2 No1, 13-28

13

ISSN:2617-2070(Print);2617-2070(Online)

JournalofAdvancedSciencesandEngineeringTechnologies

availableonlineat:http://www.jaset.isnra.org

*FayadhM.Abed1MakiH.Zaidan,1AbdullahK.Jasim

1Department of MechanicalEngineering, College of Engineering,TikritUniversity,Iraq*[email protected],

Keywords:Coolingbuildings

Undergroundpiping

Heatexchanger

Geothermal

A R T I C L E I N F O

Articlehistory:Received01jan2019Accepted15-Jan-2019Availableonline02febuary2019DOI:http://dx.doi.org/10.32441/jaset.02.01.02

Copyright©2018byauthor(s)andThisworkislicensedundertheCreativeCommonsAttributionInternationalLicense(CCBY4.0).

http://creativecommons.org/licenses/by/4.0/

JournalofAdvancedSciencesandEngineeringTechnologiesJournalofAdvancedSciencesandEngineeringTechnologies

InvestCooling Buildings Using A Geothermal andunderwaterpipingsystemstechniques(HotandDryweathers)A B S T R A C T

The conventional cooling systems in hot and dry climateregionsare insufficientandcouldnotmeet therequirementsof the summer season severe conditions. The low coolingefficiencyofsuchsystemscanbepromotedbycombiningthesystemswithanearthandwaterheatexchangersystems.Thepresent study aims to achieve a proper environment forcooling the livingbuildings.This target couldbeachievedbyusing a geothermal system. The environment conditions aretested. The tests are applied on carefully, for a single room,whichiswell-isolatedusingwood.Thisroomisconnectedtotwo pipes, which is pass underground and underwater heatexchanger pipes. Solar intensity, ambient temperature,humidity,andtemperaturesinundergroundpipe,underwaterpipe and the test chamber, all are recorded. All tests arecarried out in April, may, June and July, respectively. Theobtainedresultsindicatedthattheairtemperatureinsidethetestroomhasbeendecreasedby40%comparedwiththecaseof unused of a heat exchanger. A comparison between thetheoreticalandexperimentalresultsisdone. Inaddition,theresultsshowedthattheair-coolingtemperatureinthecaseofusinganundergroundpipeislesswith30Cdegreescomparedwith that of the underwater pipe. The reduction in the air-coolingtemperaturecomparedwiththeambienttemperatureis(12-18)degrees©201xJASET,InternationalScholarsandResearchersAssociation

OpenAccess

Fayadh M. Abed. et al. / Journal of Advanced Sciences and Engineering Technologies

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Introduction

The Islamic civilization buildings have manydifferent design characteristics, which take intoconsideration utilizing the natural change of thewind flow inside the buildings that helps increating a comfortable condition. Developmentthrough history and the discovery of the naturalenergy resources (oil and gas) in addition toinventing the electrical instruments. All of thatleadtoreplacementofthenaturalcoolingsystemswiththemodernonethatcauseanincreaseintheenvironmental pollution, costs, and exhaustingenergy.Developmentofthe

industrial creates a global warmingphenomenon, increasing the fuel costs and apolitical crisis. Using the electrical machines anddevices is a heavy consumer of energy whichconsidered an environmental pollutant. Theconsumption of energy can be limited by usingcolored glasses, painted walls and ceiling [1].Energyconsumptioncouldbeminimizedbyusingacoloredglass,paintedwallsandceilings in lightcolors[2]Misguidedceilings[3].Greenroofs[4,5].Buildings are responsible for emitting of about70%ofthesulfuroxides[6].

Intherecentyearsmostofthebuildingsarebuilt of cement which can store heat. Themechanical systems of air conditioner consumehigh energy in order to maintain a comfortableenvironment in the closed place whereas thepassive design of buildings is defined technicallyin which the air cooling is occurred withoutenergyconsumptionbypumpsandfans[7].Inthebuilding,doors,windows,floors,wallsandceilingsplay an important role in determining theeffectiveness and efficiency of its designconsideringheatreceptioninwinterandrejectedheat in summer. This can be achieved by usingshading and isolation tominimize heat exchangebetweentheinsideandoutsidethedoor.Sincetheclimate conditions in Iraq is considered too hotbecause of the increase of the sun intensity andthe vast change and variation of the airtemperature. For this reason, the passivetechniques are used to decrease the effect of theclimate impacts on buildings. These passivetechniques use an insulating materials and aircontrolsystem.Andthishelpinsavingenergyanddecreasing the demanded for cooling [8]. Ninetypercentage of energy could be saved with usingthe passive buildings compared with thetraditional one [9]. Therefore, using isolation

ceiling,greenceilingorisolationwithceramicandpolishing is very important. Splashing water onthe mineral roofs during partially cloudy, hot,humid dayweather could also reduce the indoortemperatures[10].

Vegetation’s (trees and plants) aroundbuildings give a positive result which decreaseemissionanddrop-downtemperature inadditionto offering a decorative site and approve thebuildingssight[11].

Saving energy could reach 24% of heatduringJuneprovidedthattreesareplantedonthesouthern and western side of the model house[12].Inspiteofthepositiveresultsofthepreviousresearch regarding energy-saving refrigerationtechniques, the economic aspects had not beenstudied.Forcoolingtechnology,usingawoodwallin theworstcases likeveryhighheat, the lackofrain and total mechanical irrigation, where thecostofplantingand sustaining trees,diseaseandpest control, irrigation and purchasing ofmaterials has been studied [13]. The economicstudy isconsideredasoneof the importantmainthings for most projects to save money, andenergy,anddecreaseemission.

An analysis study of the energy and costsusingaphotovoltaicsystemwithaTrumbwall inthe climate using different types of photoelectricglasses. The results show that decreasing of thecoolingloadandCO2emissionswhenusingTrumbwallwithdoubleglassfilledwithArgongas.[14].

Most researchers have directed theirattention to the use of heat exchanger and solarcollectors which are placed in the front of thebuilding southward, in order to get a high solarintensity. This is due to the solar collectorsintensity is the main feature of using the solarcollectors. [15]. an empirical study has beencarriedoutinIraqusingtwomodels:thefirstoneis designed in a traditional method, and thesecondmodel is designed in amethodof passivehome type. The results indicated that thepossibilityofreducingtheroomtemperaturetobe31oCbyusingapassivehouseinsteadof42oCinthe case of the traditional house. And the energyconsumption could be reduced to be 80% [16].Engineers meet many problems in the design ofthe passive cooling systems merged in thebuildings because ofmany difficulties due to thechange in the built-in design and using thesesystemsinanunsuitablecircumstance.


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The objective of this work is to overcomethedifficultiesofusingthetraditionalmethodsforconditioning the house, these methods are airconditioning and water-cooling system. This isduetotheextremeweatherofIraqespeciallywiththe very high temperature during the summerseason. And utilizing the solar energy in aneconomicalway.Itissuggestedtouseoneofthesetwo alternatives. Supplying air to the house bypipes.Thesepipespassthrougheither;

- Asumpofacirculatedwater- The earth soil where the pipe lays three

metersunderneaththegroundsurfaceInbothcases,exchangingheatwouldhappen. Inthefirstbetweenthepipeandthewater,whichiscalled Water Heat Exchanger and in the second,heat exchange would happen between the pipeand the soil which is then called Ground HeatExchanger.

Blowing air through thepipes andventilating airbytheindoorpartofthecoolingsystem,bothareachievedbyutilizingthesolarenergy.

Nomenclature Subscripts

ReReynoldsNumberµDynamicviscosity(Ns/m)VVelocity(m/s)NuNusseltnumberPrPrandtlnumberhHeattransfercoefficient(w/m2k)kThermalconductivity(w/mk)DDiameter(m)Ttemperature(oC)m•massflowrate(kg/s)𝑄Airflowrateinthetube(m3/hr)𝐿𝑡Thermalentrylength(m)𝐿LengthofthePipe(m)AnArea(m2)EffCoolingeffectiveness(%)HEHeatexchangerUGUndergroundUWUnderwaterRHRelativehumidity(%)iinletoutoutletssurfacewwatergground

Methodology

MaterialsandEquipment’s

The purpose of the present research is to designan improveda cooling systembasedon selectingtwo heat exchanger pipes. The two pipesspecifications and the operating conditions areexplained in the following sections. The coolingsystemconsiststestroom,fan,twoheatexchangerpipes, pumping, water sump, and trench ditch.Undergroundpipewhichismadefromaluminumof 0.074m (3 inches) diameter and15m length,and theunderwaterpipe ismadeofaluminumof0.074m(3inches)diameterand9mlength.

Datacollections

All the system data such as, design and workparameters are recorded using three sensors:solar meter, temperature and humidity sensors.All thematerials,whichareusedinthisresearch,are available in the local market, simple,lightweightandeasytoinstall.Toachievetheaimof this research, many tests are carried out todetermine the optimum variables of design andwork conditions. All the tests are carried out inTikrit City (34.6158o N, 43.678o E), where theclimateishotanddry.ThetestsarecarriedoutinApril,May,JuneandJuly,wheretheclimateishotanddryduringthesemonths.

SiteofTestClimate of Tikrit city is hot and dry with annualaverage ambient temperature of 32 °C. Theclimate of Tikrit city (34. 35°N, 43.37°E) isdiverse,hotanddryinspringandsummer(April-July)withamaximumairtemperatureupto440C.The other metrological data (Sunshine period,solar intensity, maximum and minimumtemperature) are measured and presented inTable1.Table1:MetrologicaldatathatmeasuredforTikrit

Meantemp.(Min)0C

Meantemp.(Max)0C

Meansolarintensity(w/m2)

Meansunshineperiod(hours)

Month

18286808.3April24347009.5May2841755 11.2June3044.77010.9July29427209.5August


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ExperimentalsetupTheexperimentalsetupforthesystemconsistsanUndergroundandunderwater air heat exchangerpipes that connected to the east side of the testroom.Thetestroomdimensionsare(2.1m×1.0m × 1.1 m) (length × width × height) of twowindows of (0.3 m × 0.3 m) on the south andnorthfacingwallandadoorof(1.0m×0.8m)onthewest-sidewalls. Toprevent the ambient heatlosses, a thermo cool insulation is placed on theintersticesaroundthedooraswellasontheglasspanes of windows. The experimental setup, asshown in Figs. 1 and 2, comprises two pipes,horizontalgalvanizedAluminumpipeof(0.074m(3inches)diameter,15mlength)buriedonaflatland, dry soil at a depth of 3.0m. and Aluminumpipe (0.074 m (3 inches) diameter, 9 m length)that immersed inwater.At the inlet,openendofthese pipes is connected to 180 W single phasemotor of 2750 RPM, 0.055 m3/s blowers. At itsrated speed, the blower runs at 250 V andprovidesmaximumflowvelocityof12m/sinsideeach pipe. The outlet pipes are connected to thetest room as shown in Fig. 2. Air flow velocitythroughthepipescouldbevariedbychangingtheblowerspeedwiththehelpofanautotransformer(single phase, 0–220V, 0.7A maximum current,with a least count of 1V). Five thermocouplessensorswereinsertedatafixedintervalalongthe3 m depth (starting from the ground surface) ofpipe.Theseintervalsare0m,0.25m,0.5m,1.0m,and3.0m,respectively.OtherThreetemperaturesensorsarefixedattheinlet,outletandinsidethetestroom.Testmethodologyexperimentsandsimulation

Underground and underwater heat exchangerspipes are simulated to show the effect ofvariationsoftheflowratechanges,pipediameter,pipelength,thetemperatureandhumidity.Atthetime of experimentation, these scenarios werefollowedfordifferenttestconditionsasdescribedbelow:

(1)Test-I(Operatedon7,15and21May):Inthistest, only thermal conditions (ceiling cover andgreentreesasshowninFigure.3a,bandc)oftheroomandambientweremonitored.(2)Test-II (Operated on 7, 15, and, 21 June): Inthis test the (conditioned air) from theunderground heat exchanger pipe is directlysuppliedtotheroom.AsshowninFigure.3dande

(3)Test-III (Operated on 7, 15, and, 21 July): Inthis test, the (conditioned air) from theunderwater heat exchanger pipe is directlysuppliedtotheroom.asshowninFigure.3f. The system testwas conducted along the period,ApriltoJuly2018for8-hourdurationdailyfrom8a.m.to4p.m. Theairflowvelocitiesthroughbothtubeswere maintainedtobe2.5m/s,3.5m/sand5 m/For each case, the observed temperaturesvaluesofall thesensors(ambient,outletpipesofheat exchanger and test room), solar intensity,ambient relative humidity and test room relativehumiditywererecordedhourly.

Fig.1: Underground heat exchanger pipe withthermocoupleandhumiditysensor.

Fig. 2.(a) Underground heat exchanger,(b)Undergroundchannel(3meterdepth)


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Fig.3 (a) Test room without isolation (b) Roofinsulation with white ceramic glass (c) Usinggreen Trees (d) Temperature sensors atdifferent depths, (e) Under Ground plasticpipe,(f)UnderWateraluminumpipe

DesignoftheUndergroundHeat

ExchangerPipe

The heat exchanger consists of 0.074m (3inches) diameter and 15 m length aluminumtubes.Thegroundheatexchangerisburiedat3m depth underground. Each pipe is connectedto a fan at 1 m above the ground surface tomaintain the air flow inside the tube, and thesecondendof thetube isconnectedtothetestroomwhich ismade of wood frame of (210 x100 x 110) cm dimensions. This system isillustratedinFigs1.and2.

DesignoftheUnderwaterHeatExchangerPipe

The heat exchanger, which consists ofaluminum tubes of 0.074 m (3 inches)diameterand9mlength.Theheatexchangerplaced in a water sump (4x1.5x1.7) mdimensions,whichisfilledwithwater.Oneofthe pipe ends is connected to the room andthe other one is connected to a variablespeed blower and the pipe is immersedinside the water sump as shown in Fig.4.Temperature and humidity are recorded

insideandoutsideoftheroomatJune2018.

Fig. 4Underwater heat exchanger pipewiththermocoupleandhumiditysensor One of the most important part of planning anycooling or heating system for buildings is thedetermination of the size of the system. Thefollowing conditions are taken into account:weather conditions (temperature and wind);desired inside temperature; what is the buildingmadeof(woodframe,adobe,brick,etc.),andhowwell it is made; areas of wall, ceiling, floors,windows, and doors; volume of each room; theplacementofexteriorwindowsanddoors;volumeofeachroom; theplacementofexteriorwindowsand doors, and heating system specifications.Thisinformationformsthebasisofwhatiscalleda heat balance which will help us to find theheatingsystemsizeofvirtualbuilding.

3.1ModelingandAnalysis

ANSYS andMATLAB software have been used tomodel the system check and compare with thetestsresultsusingwaterheatexchangerpipe[17-20].Thefollowingisasampleofcalculation:

Re = ! ! !!

(1)

For turbulent flow the thermal entry length andNusseltnumbercorrelationsarewrittenas:

Lt = 10×D(2)

Nu = 0.023 Re!.! Pr!(3)

n = 0.4 for heating

ℎ = 𝑁𝑢𝑘𝐷

(4)


18

𝐴𝑠 = 𝜋𝐷𝐿 (5)

m = ρ×A𝑐×V

𝐴𝑐 = 3.14× !!

!(6)

𝑇!"# = 𝑇! − 𝑇! − 𝑇!" 𝑒𝑥𝑝ℎ𝐴𝑠𝑚𝐶!

(7)

( )( )

100in out

in w

T Tx

T Tη

−=

−(8)

Tables2and3showinputandoutputdatarespectively.

Table2:inputdata

Table3:Outputdata

Flowrate 𝑸=32m3/hr 𝑸=64m3/hr 𝑸=96m3/hrParameters

Lt(m)

As(m2

)

Nu hw/m.k

Eff%

ToutoC hw/m.k

Eff%

ToutoC

hw/m.k

Eff%

ToutoC

UGP 0.75 3.53 56.4 19.9 97 25.54 19.4 96 25.4 27.8 95.9 25.7UWP 0.75 2.11 56.4 19.9 87.7 28.12 19.4 87 28.17 27.8 85.7 28.3

Table4:SimulationdatarequiredforANSYS

Ta=TioC D(m) L(m) T(oC)

UGP 37.6 0.075 15 25.17UWP 37.6 0.075 9 26.8

BoundaryCondition meshDesignmodelerPipe:WallOutlet: PressureoutletwithzerostaticpressureInlet:VelocityinletInput data: L , D , V ,Tin,Tg,Tw

Nodes:27584

Elements:81942

Smoothing:Fine

Transition:Slow


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Resultsanddiscussions

tests are conducted underweather conditions inTikrit city (34.6158o N, 43.678o E). Tests wereconducted during April, May, June, and July. Theeffect of the heat exchanger type as a coolingsystem either cooled by water or located in thesoil at 3-meter depth, both are explained. Inaddition to that, the type of the isolation such asplanting or covered by ceramic are also studied.Theresultsarepresentedasfollow:RoomtemperatureprofilewithoutHEMeasurementofthesolarintensityvaluesandtheair temperatures distribution inside and outsidethe test room are conducted. These data arerecorded without adding any techniques asmentioned previously. It is carried out for thecondition of 2.5 m/sec air speed. Results arepresentedinFig.5.Itshowsthatthevariationsofthe temperature profile inside and outside isnearlythesameandthisisconsideredasanormalcondition because there is no any enhancement.And this is an indication that the coolingenhancementisrequired.

Fig.5solarintensityandtemperatureprofileRoom temperature profile with roof

isolationandwithoutHE

The second test is conductedwith theuseof anisolate ceiling of the test room with ceramic.Results of tests indicated that the temperatureinside is less than the outside temperature with3.5 0C. As shown in Fig 6. This temperaturereduction is a result of using isolation ceilingwhichleadstoreducetheheatgainthroughit.

Fig. 6 the Effect of ceiling isolation ontemperatureprofile

Room temperature profile with green treesandwithoutHE

Thethirdtestwasconductedusingthesameapproach that used in the second test withusingagreentree.Thegreentreesmadethetestroomundershadowwithoutanychangein the other parameters. The test resultsshowed that the temperature values insidethetestroomdecreaseswith40CasshowninFig.7.

Fig.7 The Effect of the green trees on

temperatureprofile.

The effect of the relative Humidity withdifferentconditions

Thehumiditydatavaluesare recordedduring the

period (sunrise to sunset).Humidity profiles areplotted in Fig. 8. The maximum and minimumvalues of relative humidity are determined. Allprofiles have the same trends as isolationsceramic or green trees are utilized. However, as


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greentreeisused,boththeexternalandinternalconditionareinfluenced.

Fig. 8Relativehumidity profiles in the

testroomat theconditionsofusing isolation,andgreentrees

EffectofburialdepthofthepipeThe experimental data are recorded in threedifferent days, as shown in Table 5. They revealtemperature change (soil temperature at4 mdepth under the ground surface level). It wasobservedthatthediurnalvariationintheambienttemperature and solar radiation does not affectthe temperatures. The ground surfacetemperature was less than the ambienttemperature and it decreases as the depthincreases and finally converges to a constantvalue. The observed temperature at this burialdepthisusedtovalidatetemperatureobtainedbyFluentsimulationby15.0.7asshowninFig.9.Thetests were carried out over solar radiationintensity ranged from 100 to 760 W/m2. Theresults showed that theminimumtemperature isrecorded for 3.0 m underground depth. Themaximum recorded difference between the soilandtheambienttemperatureat3.0depthswas16oC. This test is conducted in order to determinethe best and useful depth for the heat exchangerpipe.Table5:Temperatureatdifferentdepth(May2018)

Location oftemperaturesensor

Measured Temperature at12p.m.(0C)7May15May 21May

4mdepth 23.3 23.4 23.33mdepth 23.3 23.3 23.41mdepth 25.4 25.5 25.50.5 mdepth

27.5 27.4 27.4

0.25 m 29.4 29.3 29.2

depthat groundsurface

35.4 34.5 36.0

Fig.9 The effect of pipe depth on the airtemperaturesinsidethetestroom

The effect of the airflow rate on itstemperatureinsidethetestroombyusingtheundergroundheatexchangepipe

The airflow influences temperatures of theunderground heat exchanger pipe and the airtemperatureinsidethetestroom,botheffectsarepresented in Fig. 10. Solar intensity and ambientair temperature are plotted with the heatexchangertemperatureandthetestroom.Resultsshow that the maximum reduction in the airtemperature inside the test room occurs at theflowrateof32m3/hr.andthisreductionisnotanoptimum value, but it is related to the designparameters such as pipe length, diameter,material, and work conditions like flow rate. Inaddition, the cooling process which is conductedby the airflow inside the pipe depends on thethermalresistancebetweentheairflowinsidethepipe and its walls. This process is necessary todeterminetheoptimumconditionsinsidethetestroom.

Fig.10EffectoftheairFlowrateontheoutletundergroundtemperatureprofile.


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ComparisonbetweendifferentairflowratesFig. 10 shows the temperature profiles of theexperiments results for the airflow rates (32, 64,and96)m3/hrrespectively.Thetestswerecarriedout at constant pipe temperature of theunderground heat exchanger and solar radiationintensity range (350 - 750W/m2). Both, themodeled one and the experiment results show asimilar temperaturepatternsof theundergroundand the underwater heat exchanger pipes at awiderangeoftheenvironmentalconditions.Table5showsasampleoftestsoftemperaturesprofilesatdifferentconditions.

Effect of pipe diameter and length for theundergroundheatexchangeronthetestroomairtemperature

Fig.11showsthetestroomtemperaturevariationalong thedayhours, fordifferentpipediameters.From this figure, it can be seen that roomtemperature varies proportionally at morninghours, while almost constant during afternoonhours. In addition, a peak value is noticed ateleveno’clockAM.Also, it couldbe seen that thepipe diameter effect on the temperaturedifference between the room and ambienttemperatureareatthefollowingdecreasingorder(3, 4, 6 and 8 inch). i.e., using a small diameterpipegavethebestefficiencyofthermalexchange.Fig.12showsthetestroomtemperaturevariationduring the day hours for different pipe lengths.ThisFigureshowsthesametemperaturevariationcurves behaviors of Fig.12. Curves. Moreover,fromthisfigureitisobviousthatthe longestpipehastheoptimumperformanceamongallsizes.

1. Fig.11Testroomtemperaturevariationoveraday.(Undergroundsimulationresults)

Fig. 12. Test room temperature variationalong thedayhours(Undergroundsimulationresults)

4.9 The effect of using the underwater heatexchangepipe.

Thethirdpartofthestudywasconducted,intwopipesof thesame lengthanddiameters.Botharemade from a galvanized aluminum. These pipesare immersed inawatersumpof9m3size.Eachpipewas tested separately. Both ends of the twopipesareopenabovethewatersurfacelevel.Theambient airflow enters through one end of thepipe and exit through the other, which isconnected, to the test room. The process of air-cooling happens through the airflow inside thepipe. The reduction in the ambient airtemperaturedependsonthelength,anddiameter,of thepipe that immersed inside thewater sumptemperature and the air temperature. Therecorded data for water, test room air, and theambient temperatureallarepresented inFig.13.These results showed that the maximumreduction in the ambient temperature of the testroom is 40% for air flow rate 32 m3/hr all arepresentedinFig.14.

Fig. 15 illustrates the variation of the room andambient temperatureduringthedayhoursat thefollowing pipe diameter (4, 6 and 8 inch). It isclearthattheusingofasmallpipediametergavethe lowest temperature ranges because it isincreased the internal air velocity, then gave thebest effectiveof thermal exchange. Fig. 16 showsthevariationoftestroomtemperaturesduringtheday hours for different pipe lengths. From thisfigureitisclearthatthelongestpipehasthebestperformance among all lengths because it isincreasedthesurfaceareaofthermalexchange.


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Table 6: Temperature values of the underwaterandundergroundspipeandtestroomin14th,15th,and16thJune/2018atQ=32m3/hr

Where;TUWP:UnderwaterpipeTUGP:UndergroundpipeTa:ambienttemperature

Fig.13Testroomtemperaturevariationoveraday.

Fig. 14 Effect of the airflow rate ontemperature insidethetestroomusingunderwaterpipe(Underwatersimulationresults)

Fig. 15 Effect of the pipe diameter on the airtemperature inside the test room by usingunder water pipe (Underwater simulationresults).

Fig. 16 Effect of the pipe length on itstemperature inside the test room by usingunder water pipe (Underwater simulationresults)

of the underground and underwater heatexchangerontherelativehumidity

The test results of the outlet temperature of theUnderground, underwater heat exchanger pipesand the test room; all are plotted in Figs 17 and18. The results showed that the outlettemperatures of the under groundwater are lessthan that of theUndergroundpipe.These resultsshowed that the test room temperatures (usingunderwater pipe) is lower by 20% comparedwiththeuseof theundergroundpipe. itcouldbeconcludedthat, reaching thedesiredtemperaturefor the outlet air, this could be achieved byincreasing the length of the underwater pipelength. Also, it couldbenoticed that therelativehumidityvalueshavethefollowingvalues,33.8%,

Time(PM)

Ta(°C)

Solarintensity

W/m2

TUGP(°C)

TUWP(°C)

TestroomatTUGP(°C)

Testroom atTUWP(°C)

12 28.0 695 25.4 27.7 31.4 39.01 27.9 752 25.3 28.4 31.6 40.22 29.0 612 26.1 28.3 31.3 39.33 28.2 507 25.8 28.6 30.6 38.64 27.7 516 26 28.7 30.3 39.8


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30.3%and17.4%,forusingtheundergroundheatexchangers, underwater heat exchanger and theambient rspectively. Fig.17 shows thetemperature variation over the day hours for,solar radiation, ambient, underground pipe andunderwaterpiperespectively.Itcouldbenoticedthat the temperature drops down by using thewater heat exchanger more than for using theearth heat exchanger. This is because waterthermal conductivity is higher than that of thesoil,especiallywithaluminumpipes,whichgivesalmost the same temperature for both, pipesurfaceandthewater.Hencetheairflowshowsanegligible effect on the water temperature.Wherea, for the groundheat exchanger since theairflowratehasalargevalue,thisrequirealargerpipe to offer enough time for heat exchange.Therefore,thetestroomtemperatureusingwaterheat exchanger is less than that for using anunderground heat exchanger as shown in Fig.18.Fig. 19 shows the relative humidity variationalong the day for, ambient, test room, using anunderground and an under-water pipes. Therecordedvaluesare for32m3/hrair flowrateofdifferentflowratevalues.

Fig.17Testroomtemperaturevariationoveraday.

Fig.18AComparisonbetweentheTestRoomTemperatures variation, for using theundergroundandtheunderwaterpipes.

Fig. 19 A Comparison between the relativehumidityvariationoftheambientandthetestroom, using the underwater and theundergroundheatexchangerpipes.

A Comparison between experimental andtheoreticalresults

Fig.20showtheexperimentalandthetheoreticalcooling effectiveness variation during the dayhours. This is for using an underground heatexchangerof0.074m(3 inch)pipediameterand32 m3/hr air. Are flow rate. It could be noticedthat a high variation (theoretical) in the coolingeffectiveness value, especially at the morninghours. This is related to the fast change of theambient air temperature during the morninghours. The highest registered value for theexperimentalcoolingeffectivenesswas96.1%at8a.m.. Also, the highest difference value betweenthe experimental and the theoretical coolingeffectiveness is 8.2%. Table 7 shows acomparisonbetweenexperimentalandtheoreticalresults at different flow rates. .


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Fig20.Coolingeffectivenessvariationsoveradayhours.(Flowrate32m3/hr,usingundergroundheatexchanger).


25

Table 7. A comparison between theexperimentalandthetheoreticalresultsat

differentflowratevalues.

Simulationresults

Figs. 21 and 22 show the temperaturevariation of the test room during the dayhours,forthecaseofusingtheunderwaterheat exchanger. These Figures arecorresponding to the previous Figures 15and 16. And give the same temperaturebehavior and trends of those Figureswithmorefluctuation.

Fig. 21 Simulation results oftemperature distribution along theundergroundpipewithlength9m,0.075mdiameter

Fig. 22 Simulation results oftemperature distribution along theundergroundpipewithlength9m,0.075mdiameter

Fig. 23 Simulation results ofTemperature distribution alongunderground pipe with flow rate 32m3/hr,length18mand0.075mdiameter

Air Velocity = 6 m/s , Q=96 m3/hr



Time

% different

Cal. Temp.

Exp. Temp.

% different

Cal. Temp.

Exp. Temp.

% different

Cal. Temp.

Exp. Temp.

3.08 25.9 26.7 1.9 25.8 26.3 3.8 26 25 8 1.49 26.7 27.1 0.74 26.8 26.6 2.28 26.3 25.7 9 1.08 27.6 27.9 2.58 27.1 26.4 3.7 26.8 25.8 10 1.43 27.8 27.4 3.32 27.1 26.2 0.75 26.4 26.2 11 1.79 27.9 28.4 2.56 27.3 26.6 4.15 26.5 25.4 12 3.58 27.9 28.9 2.19 27.3 26.7 4.52 26.5 25.3 13 2.49 28.1 28.8 3.28 27.4 26.5 2.24 26.7 26.1 14 3.9 28 29.1 0.36 27.2 27.1 3.7 26.8 25.8 15

4.69 27.7 29 1.46 27.3 26.9 2.98 26.8 26 16 1.9 27.5 28.1 1.31 27 26.58 2.14 26.5 25.7 Average


26

Fig. 24 Simulation results ofTemperature distribution alongunderwater pipe with flow rate 96 m3/hr,length9mand3mdiameter.

Uncertainties&ErrorAnalysis

Ingeneral,anuncertaintyanalysisisquite complicated process. Therefore,applying engineering judgment roles is theunique choice in some uncertaintycalculations. This section summarizes theinstrument calibrations and uncertaintycalculations for the measured parameterssuchastemperatureandsolarintensity.AllK-type thermocouples were calibratedagainst the standard temperature (i.e., thereferenceRTD)atatemperaturerangeof0-100ºC. These thermocouples assemblieswere immersed in a liquidbath thermostattogether with the RTD. For the referenceRTD,themaximumuncertaintywas±0.3ºC.The uncertainty values of the instrumentswere estimated as follows. The bias errorwas calculated according to Fig liola andBeasley. Independent parameters, such astemperature, solar radiation, the bias error(A) and precision limit (P) were found bythecollectroot–sum–squares(RSS)method [21].

𝐴 = ±[(!!𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛)! + ( 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦)! ]!/!

(9)

The average value of the scale or theaverageofthemeasuredvalueisexpressedas;

𝐵 = !!

𝐵𝑖!!!!

(10)

The standard deviations (σ) of the sampledistributionis;

σ𝑏 = [ !!!!

(𝐵𝑖!!!! − 𝐵)! ] !/!

(11)

Themeanstandarddeviations(𝜎𝑏 ) forthesample was deduced using the followingrelation:

σ𝑏 = !!!

(12)

To use t distribution at 95 % confidenceintervalwith the (N-1)degreesof freedom,can found it from Table 8. The overallprecisionerrorlimitscanbewrittenas;

Pb = t N − 1 , 95% ×σ𝑏(13)

Integration between the elemental errorswas conducted to obtain the 95%confidenceofuncertainty(Ub),

𝑈𝑏 = ±[𝐴! + 𝑃𝑏! ]!/!(14)

The relative uncertainty (in percentage) iscalculatedas:

!"!% = ±(!"

!)×100

(15)

InEqs.10 through15 𝐵 isan independentparameter such as temperature, and solarintensity. The accuracy and resolution ofApplent AT4808 Handheld MultiChannelTemperature Meter, and DAYSTAR DS-05SolarMeterare0.2%+1°C,0.1°C,and±3%(0 - 1200 W/m2), 1 W/m2 respectively.Basedonequations9through15theresultsofuncertaintyarepresentedinTable9.


27

𝑇𝑎𝑏𝑙𝑒 8 𝑇ℎ𝑒 𝑣𝑎𝑙𝑢𝑒 𝑜𝑓 t N − 1 , 95% [22].

Table 9: Sample of experimental testsuncertaintycalculations

Conclusions

Thefollowingconclusionsmaybededuced:In summary, this paper argued that theproposal design and the obtained resultsimprove the weather conditions at the dryandhot regions.Thepresentwok confirmsthatusingofbothapproaches;undergroundandunderwaterheatexchangerpipe,bothreduce the test room temperature by 40%lower than theambientair temperature. Inaddition, these works provide additionalinformation about the use of theunderground heat exchanger pipe in suchsystemsand itwas studies todecide if it isbeneficial or not compared with the waterheat exchanger pipe. This may beconsidered an alternative method of usingsuch techniques in the cooling systems intheareaofhotanddryweathersandundershortage. Future investigations arenecessary to validate the conclusions thisstudy.Thus,theuseofsuchsystemsofair-coolingduct isveryeffective forair-coolingin summer as it may reduce energyconsumptionandcarbonemissionofactivecooling systems in tropical climaticconditions. Installing theundergroundheatexchanger pipe is easier than theunderwaterpipe.Theobtainedefficiencyinboth, modelled and experimental results,areinanacceptablerange(13%to17%).

Degrees of freedom

t 95 % Degrees of freedom

t95 %

1 12.706 18 2.101 2 4.303 19 2.093 3 3.182 20 2.086 4 2.776 21 2.080 5 2.571 22 2.074 6 2.447 23 2.069 7 2.365 24 2.064 8 2.306 25 2.060 9 2.262 26 2.056

10 2.228 27 2.052 11 2.201 28 2.048 12 2.179 29 2.045 13 2.160 30 2.042 14 2.145 40 2.021 15 2.131 60 2.000 16 2.120 120 1.980 17 2.110 ∞ 1.960

SolarIntensityw/m2

TaoC

RH%

TestRoomoC

TUGP

oCTUWPoC

A ±0.5 ±0.05 ±0.07 ±0.05 ±0.05 ±0.05 𝐵 616.6 39.35 32.2 31.04 25.72 28.3 𝜎𝑏 108.12 0.64 0.83 0.559 0.35 0.339 𝜎 b 54.06 0.32 0.41 0.279 0.17 0.169 Pb 138.99 0.82 1.16 0.719 0.45 0.43 Ub 138.99 0.82 1.16 0.72 0.46 0.43

(Ub/𝐵)% ±22.54 ±2.10 ±3.61 ±2.32 ±1.79 ±1.55


28

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