fgb, Adadam

Solar coolingWeather variables

alys-effely wTheriab

nitude (V), the wind direction (h) and the relative humidity (RH). First order correlation functions are

nergyd it wichinesgy is u[2] pr

in a similar way as in a conventional electricity-driven compres-sion machine. The vapor produced in the evaporator incorporatesto the solution in the absorber, releasing the absorption and dilu-tion heats to ambient. If only one generator is used, the system isnamed single-effect. This is the most common technology utilizedfor solar cooling, allowing the use of conventional at plate collec-tors [4,5].

needed for the determination of the wind heat transfer coefcient,namely the on-surface wind velocity of each solar collector and thesupercial temperature of the glass cover. Only an on-site weatherstation is currently available and in some cases even not; only thehourly or day averaged weather data is available from a neighborpublic station.

Many researchers in the last years have studied the effect ofwind over the thermal losses of single solar collectors, obtainingdifferent heat transfer correlations, e.g. [79], but with varying re-sults, because of the different operating conditions. More recently,

Corresponding author. Tel.: +34 91 624 8465; fax: +34 91 624 9430.

Applied Energy 88 (2011) 14471454

Contents lists availab

lseE-mail address: mvenegas@ing.uc3m.es (M. Venegas).based on a checklist for the correct integration of a solar coolingsystem in buildings. The checklist is based on the feedback of Euro-pean solar cooling experiences in the framework of the IEA Task 25.IEA Task 38 is still improving the dissemination of the state of theart, evaluation procedures and overview of this sector [3].

The most common working uids used in absorption machinesare H2OLiBr and NH3H2O pairs, the former being better and risk-less for air-conditioning applications. In these machines, refriger-ant vapor is separated in the generator thanks to the heattransferred by the external driving uid, which is supplied by thesolar plant. The vapor enters into the condenser and evaporator

operating data summarized in manageable gures of merit arerequired.

The global performance of the solar cooling facility depends onthe way the solar energy is managed in the daytime. The variabilityof weather conditions and solar radiation also contribute to the dif-culty in obtaining conclusions from real facilities monitoringcampaigns, especially on the dependence from the meteorologicalparameters such as solar radiation, temperature, humidity andwind. In particular, wind effect on operating solar facilities hasnot been satisfactorily documented. The instrumentation currentlyavailable in commercial solar cooling facilities is not what isStatistical analysisAbsorptionFlat plate collectors

1. Introduction

Increasing the use of renewable esocietys main targets nowadays annear future. Absorption-cooling maworldwide when solar thermal enerpurposes [1]. Mugnier and Quinette0306-2619/$ - see front matter 2010 Elsevier Ltd. Adoi:10.1016/j.apenergy.2010.10.011given. The analysis of the data allows concluding that the most inuential variables on the daily coolingenergy produced and the daily averaged solar COP are H, V and h. The period length of cold-water produc-tion is determined mainly by H and T .

2010 Elsevier Ltd. All rights reserved.

resources is one of thell be in the foreseeableare employed broadlysed for air-conditioningesented a methodology

Nowadays small-scale systems receive increasing attention fortheir potential application to single-family housing or to smallbuildings. For example, Desideri et al. [6] describe different techni-cal installations for solar cooling, their way of operation, advanta-ges and limits, analyzing their technical and economic feasibility.The dissemination of the solar cooling systems depends much onthe economy, real energy saving and emission reduction. Thus, realKeywords:along the day (H) and the average values, along the operating period of the solar cooling facility (fromsunrise to the end of the cold-water production), of the ambient temperature (T), the wind velocity mag-Experimental diagnosis of the inuence operformance of a solar absorption coolin

M. Venegas a,, M.C. Rodrguez-Hidalgo a, R. SalgadoaDpto. Ingeniera Trmica y de Fluidos, Universidad Carlos III de Madrid, Avda. UniversibDpto. Ingeniera Mecnica, Universidad Interamericana de Puerto Rico, Recinto de Bay

a r t i c l e i n f o

Article history:Received 28 July 2010Received in revised form 6 October 2010Accepted 6 October 2010Available online 30 October 2010

a b s t r a c t

This paper presents the anusing a commercial singletions. The facility works onCarlos III de Madrid, Spain.of ve daily operational va

Applied

journal homepage: www.ell rights reserved.operational variables on thesystem

. Lecuona a, P. Rodrguez a, G. Gutirrez a

30, 28911 Legans, Madrid, Spainn, 500 Carretera Dr. John Will Harris Bayamn, PR 00957-6257, United States

is of the performance of a solar cooling facility along one summer seasonct waterlithium bromide absorption chiller aiming at domestic applica-ith solar energy using at plate collectors and it is located at Universidadstatistical analysis performed with the gathered data shows the inuenceles on the system performance. These variables are solar energy received

le at ScienceDirect

Energy

vier .com/locate /apenergy

Nomenclature

C specic heat of external uids (kJ/kg K)CE daily cooling energy produced (kW h)H daily solar irradiation on the horizontal surface (kW h)Htilted daily solar irradiation on the tilted surface (kW h)Itilted solar irradiance on the tilted surface (kW/m2)_m mass ow rate (kg/s)_Q thermal power (kW)RH daily averaged relative humidity along the operating

period of the solar cooling facility (%)SCOP daily efciency of conversion of solar radiation into

coolingt time (h)tcooling daily period along which cold water is produced in the

evaporator (h)

V daily averaged wind velocity magnitude along the oper-ating period of the solar cooling facility (m/s)

Greek symbolsh daily averaged wind direction along the operating peri-

od of the solar cooling facility, measured from the frontside and in respect to the front-rear vertical symmetryplane of the collector ()

g collector efciency

Subscriptsa ambientbeg beginninge evaporatorend end

1448 M. Venegas et al. / Applied Energy 88 (2011) 14471454Medinelli Sanino and Rojas Reischel [10] have analyzed the inu-ence of wind velocity magnitude and relative humidity over a solarenergy water heating system incorporating a storage tank. More-over, the inuence of wind direction has not been studied in detail,limiting the experimental correlations obtained to wind incidenceangles measured in intervals of 45 [8], or global studies withoutobtaining correlations and just for particular types of collectors[11].

Up to the knowledge of the authors, there is not information onthe effects of wind velocity magnitude and direction on real work-ing solar cooling facilities. Researches on the magnitude of theinuence of these and others ambient variables on small-scale res-idential solar cooling system performance seem to be importantand, as far as the authors knowledge, not available. Natural ambi-ence variability and the different possible layouts difcult the der-ivation of general rules, but some trends and sensibilities ofdemonstration facilities could guide the designer, planneror researcher.

The phenomenological interpretation of the physical process issimplied when solar cooling facilities are adequately instru-

T temperature (C)T daily averaged ambient temperature along the operat-

ing period of the solar cooling facility (C)mented to allow for a statistical analysis of the experimental data.Statistical tools, along with phenomenological interpretation,should shed light on solar cooling performance evaluation andthe effect of weather conditions, so that manageable results couldbe offered to researchers, designers and other technology agents.

Fig. 1. Conguration of theThis analysis will be performed in the present paper. The facilityunder study is based on a commercial single-effect lithiumbromide absorption chiller located at the Universidad Carlos IIIde Madrid downtown Legans, south of Madrid, Spain. The regionhas a Mediterranean-continental climate, with hot dry summers,where solar cooling is applicable. This region is representative ofwide zones in which solar cooling can contribute to energy sustain-ability and electricity-demand peak shaving in summer. Usingstandard industry practice, the absorption chiller is integrated intoa solar thermal plant congured to generate hot water, which insummer is used for air-conditioning purposes.

2. Experimental facility

The facility can be divided into four loops as shown in Fig. 1. Therst loop consists of insulated piping and 20 at plate solar collec-tors arranged in four parallel straight lines: VITOSOL 100 w2.5model, by Viessmann Werke GmbH and Co KG, each one having2.5 m2 aperture area. Rodrguez-Hidalgo et al. [12] showed thatthis total aperture area is representative of what is appropriate

i inleto outletfor attending a signicant fraction of a single-family housing cool-ing demand in Madrid. The manufacturers normalization curve ofthe collectors is:

solar cooling facility.

Temperature of the external uids at the inlet and outlet of the

Energ 0:83 3:36 Ti TaItilted

0:013 Ti Ta

2

Itilted

!1

Collectors are oriented to south with a surface azimuth angle of11 east, and are tilted 40, corresponding to the local latitude, on aat horizontal roof of a prismatic four-story building. Their topsprotrude over the 1 m high of the perimeter protection wall shownin Fig. 2. This building belongs to the Campus complex which islocated at 40200 north and 3450 west. It is surrounded by a smallcity downtown environment made of high-rise buildings.

The second loop comprises a commercial-grade thermal storagetank of 2000 l capacity, heat exchanger and the correspondinginsulated piping. Water is pumped from the collector eld to theplate heat exchangers in a closed loop. The function of the heatexchangers is to prevent mixing between the antifreeze uid usedin the collectors and the pure water circulating through the storagetank, which is located in the building cellar.

The third loop consists of the absorption chiller and its corre-sponding piping. Hot water from the storage tank is pumped at aconstant rate to the absorption chiller generator as the energyinput. Temperature is not controlled at the inlet of the generator,

Fig. 2. View of the at plate collector eld, perimeter protection wall and urbansurrounding.

M. Venegas et al. / Appliedso it varies according to the temperature in the storage tank. Thereis no backup boiler operative for this test campaign.

Finally, water from the fourth circuit is chilled in the machineevaporator. All the cooling energy produced is delivered to thelaboratory using fan-coils. The daily cold water produced repre-sents the real daily cooling energy (CE) of the absorption chiller.It is a widely implemented pump-less Yazaki WFC 10 of 35 kWnominal cooling capacity. This machine size was of the smallestcapacity available in the market when the project started. Anexternal open wet cooling tower jointly cools the absorber andthe condenser.

Flow rates produced by constant velocity pumps are smallerthan the nominal values. These ow rates were kept constant (gen-erator: 0.46 l/s, condenserabsorber: 0.88 l/s, evaporator: 0.30 l/s),since the beginning of the experimental campaign, to maintaingeneration, condensationabsorption and evaporation tempera-tures at the favorable level.

The facility includes an independent weather station located6.5 m above the collector eld, with no obstructions in the sur-rounding. It gathers instantaneous data of the following variables[13]:

Solar irradiance on the horizontal plane, using a class 1 pyra-nometer, model CM3 manufactured by Kipp & Zonen B.V..generator, evaporator and condenserabsorber. Measurementswere taken using type T thermocouples with an uncertainty of0.5 C.

Volumetric ow rates of the external uids. Magnetic owmeters delivered this information with an uncertainty of 0.5%of the ow rate after calibration.

3. Data reduction

Fig. 3 shows a scheme of the experimental facility in which tem-perature and ow rates readouts are presented for July 22 of 2005,at 16:20 h local standard time. This time is ofcially 2 h in advanceto meridian time in summer.

The instantaneous cooling power produced by the absorptionchiller _Qe, is calculated using:

_Qe _meCeTe;i Te;o 2The daily cold produced (CE) is calculated summing up all the

energy obtained throughout each day. In Eq. (3) the summationis performed for the 144 data points saved throughout each day:

CE DtX144i1

_Qe 3

The daily overall efciency of the solar cooling facility SCOP iscalculated as the ratio between CE and the solar irradiation onthe tilted surface along the day Htilted.

SCOP CEHtilted

4

The cooling time tcooling is the period elapsed between the begin-ning and the end of cold-water production in the evaporator:

tcooling tend tbeg 5

4. Results and discussion

Legans is close to Madrid, both located near the center ofSpain, having about 2800 sunny hours per year [14]. Incident totalsolar irradiation in an average day of the 2005 summer season, on ahorizontal surface and on a 40 tilted surface located in the collec-tors eld, reached 7.2 and 6.5 kW h/m2 respectively.

The 2005 summer season was not exceptional. It included 57operating days between June 25 and August 31, the useful daysrepresent 84% (days in which the chiller worked). During thenon-useful days either solar irradiation was not sufcient forstarting the absorption machine (3 days) or data were not recordeddue to technical reasons (8 days). Air temperature, using a Linear Thermistor Network of themodel 50U-44212, manufactured by Vaisala.

Relative humidity, using also the sensor of the model50U-44212.

Wind velocity magnitude and direction, using an anemometerof the model 05103 manufactured by R.M. Young Company.

The facility is monitored by a data acquisition system that iscontrolled by a computer program. Data gathered by the weatherstation and information from the solar plant and the absorptionmachine (temperatures and ow rates) are recorded on the com-puter in intervals of Dt = 10 min. Data from the absorption chillerinclude:

gy 88 (2011) 14471454 1449In Fig. 3 the only two components directly inuenced by theweather variables H, T , V, h and RH are enclosed by a dash line.These components are the collector eld and the cooling tower.

85 C 92 C

86 C

74 C

25 C

20 C

l/s

0.9 l/s

0.46 l/s

0.53 l/s 0.3 l/s 2.3 bar

lity

1450 M. Venegas et al. / Applied Energy 88 (2011) 144714540.3

Fig. 3. Experimental data of the solar cooling faciThe rest of components: storage tank, heat exchanger, absorptionchiller and fan-coils are thermally isolated in an adequate way.They are located inside non-air-conditioned rooms (cellar and lab-oratory), as usual, thus being only indirectly inuenced by theweather conditions.

The hot water in the storage tank was under well-mixed oper-ating conditions, i.e., the temperature of the thermal uid insidethe tank was approximately homogeneous. Location of the inlet

0

5

10

15

20

25

30

35

40

45

50

6:00 8:00 10:00 12:00 14:Local standar

Pow

er (k

W)

Solar radiant powerPower supplied to the storage tCooling power

Fig. 4. Daily behaviour on a representative summer sunny day (Ju75 C

68 C

13 C

9 C

(July 22nd of 2005 at 16:20 local standard time).and outlet ports in the tank (see Fig. 3) guarantees this perfor-mance. In previous experimental studies [15,16], it was shown thatthis conguration allows higher cooling production than in strati-ed operating conditions (higher temperature at the top of thetank and lower at the bottom). In addition, the well-mixed operat-ing regime extends the period to supply the heating power to theabsorption machine throughout the day, increasing this way theheat power supply in the evening, when the condensationabsorp-

00 16:00 18:00 20:00 22:00d time (hh:mm)

Collectors powerank Power supplied to the chiller

ly 1st of 2005) of thermal powers in the solar cooling facility.

tion temperature is decreasing. At the same time, cold demand isimportant in the evening for housing applications [12]. Thus, a bet-ter match between the cooling energy supply and the demand isobtained.

When the hot water temperature from the storage tank de-creased, typically late in the evening (about 20:00 local standardtime), and it was not hot enough for transferring heat to the solu-tion in the generator, the machine continued producing cold waterfor a period of about 30 min, being driven by thermal inertia and/orinternally stored refrigerant, indicating a noticeable transienteffect related to the chiller. For a typical day, this hot water tem-perature in the storage tank corresponded to 64 C. The followingmorning (8:00 local standard time), water in the storage tankwas stratied, reaching about 60 C in the top and 50 C in thebottom. The beginning of operation reintroduces the well-mixedregime in a short time.

Fig. 4 offers a comparison between the solar radiant power, thepower transferred to the thermal uid inside the collectors, thepowers supplied to the storage tank and to the chiller and the cool-ing power produced by the absorption machine for a representa-tive summer sunny day. Data correspond to July 1st of 2005. Thetransient effects during the morning and the evening can be ob-served. Oscillations in the morning and the evening are related tothe stop of the pump located in the second loop (Fig. 1), with theobjective of avoiding that the storage tank water be cooled bythe thermal uid circulating through the collectors. The extension

of the operating period of the absorption chiller throughout theday, due to use of a well-mixed conguration for the storage tank,is experimented at the evening.

Displacement of the maximum of the solar radiant power from12:00 to the right of the scale is due to the following reason. Thatday in Legans, the difference between the local standard time andthe meridian standard time (local time zone for the standardmeridian, in this case the Greenwich meridian) is 2 h. If the locallongitude and the correction for the time equation are also takeninto account, a difference of 2 h and 18 min is obtained betweenthe local standard time and the solar time.

Table 1 gives the minimum, maximum and average valuesalong the season of the operational variables considered in thisstudy: H, T , V, h and RH. Table 2 gives the goodness of the t param-

Table 1Ranges of operational and dependent variables.

Variable Minimum Maximum Averagea

H (kW h) 253 410 360T (C) 19.7 31.8 27.5V (m/s) 1.4 3.9 2.3h () 12 175 90RH (%) 12.9 46.9 28.3SCOP (%) 0.7 11.0 6.7CE (kW h) 1.8 38.1 22.3

M. Venegas et al. / Applied Energy 88 (2011) 14471454 1451tcooling (h) 3.3 10.7 7.8

a It is the average along the whole season considering the operating period of thesolar facility: from sunrise to the end of cold-water production.

Table 2Parameter R2 evaluating the lineal relationship between operational variables.

Variable H T V h RH

H 0.00 0.01 0.02 0.05T 0.12 0.07 0.34V 0.02 0.02h 0.00RH

0

200

400

600

1 6 11 16 21 26

H (k

Wh)Da

Fig. 5. Solar irradiation on the horizontal surface H and average ambient teter R2 of the correlation between the individual operational vari-ables, showing a general high degree of independence betweenthem.

Figs. 57 show the evolution of these variables along the wholeseason. Solar irradiation is decreasing along the testing campaign,as indicated in Fig. 5, while average ambient temperature oscillateswith random appearance. Average wind velocity magnitude anddirection, shown in Fig. 6, and average relative humidity, shownin Fig. 7, neither have a clear tendency along the season, also show-ing a random appearance.

Table 1 gives also the minimum, maximum and average valuesalong the season of the dependent variables used to evaluate thesolar cooling facility performance: SCOP, CE and tcooling. Figs. 8and 9 show the evolution of these variables along the same period.In this case, SCOP and CE show a similar tendency throughout theseason, but the evolution of tcooling is different.

Using STATISTICA software, the relationship between theaforementioned operational variables and the dependent oneswas evaluated through a multiple regression model. First orderleast squares ts, valid for data between the limits given in Table1, appear in Eqs. (6)(8). The simplicity of these models seeks facil-itating the evaluation of operative solar cooling facilities.

SCOP 3:8 104 H 1:6 103 T 8:9 103 V 1:4 104 h 4:8 104 RH 9:2 102

0:013; R2 71% 6

CE 0:15 H 0:33 T 3:16 V 0:04 h 0:18 RH 32:69 4:24; R2 75% 7

tcooling 3:7 102 H 2:9 101 T 7:4 103 V 6:3 103 h 1:5 102 RH 14:6 0:86; R2 78%

8

31 36 41 46 51 5615

25

35

45

T (

C)

H Ty

emperature T. Day 1 corresponds to June 25 and day 57 to August 31.

045

90

135

180

1 6 11 16 21 26 31 36 41 46 51 56

Day

(d

egre

es)

1

2

3

4

5

V (m

/s)

Theta V

Fig. 6. Average values of wind velocity magnitude V and direction h. Day 1 corresponds to June 25 and day 57 to August 31.

10

20

30

40

50

1 6 11 16 21 26 31 36 41 46 51 56

Day

RH

(%)

Fig. 7. Average relative humidity RH. Day 1 corresponds to June 25 and day 57 to August 31.

0%

3%

6%

9%

12%

1 6 11 16 21 26 31 36 41 46 51 56

Day

SCO

P (%

)

0

10

20

30

40

50

60

CE

(kW

h)

SCOP CE

Fig. 8. Solar coefcient of performance SCOP and cooling energy produced by the solar facility CE. Day 1 corresponds to June 25 and day 57 to August 31.

3

5

7

9

11

1 6 11 16 21 26 31 36 41 46 51 56

Day

t coo

ling (

h)

Fig. 9. Cooling time tcooling along the test campaign. Day 1 corresponds to June 25 and day 57 to August 31.

1452 M. Venegas et al. / Applied Energy 88 (2011) 14471454

evaporation temperature varies also, as the cooled room was not

EnerIn spite of the moderate values of R2, they can be acceptable ow-ing to the high variability of the natural processes involved alongthe season. STATISTICA software also gives information aboutthe relative importance of each operational variable in the depen-dent ones. The height of the bars in Fig. 10 represents the weight ofeach weather variable in the prediction of the dependent one, i.e.,how much a dependent variable is sensitive to an operational one,in a numerically homogeneous way. The results presented inFig. 10 correspond to the data of the 57 days used for perform

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

SCOP CE tcooling

RH Theta V T H

Fig. 10. Weight of the operational variables in the prediction of the dependentones.

M. Venegas et al. / Appliedthe linear regression.As observed, the major effect on SCOP, CE and tcooling is due to

the solar irradiation, as could be expected. Solar irradiation di-rectly contributes to improve the performance of the solar facility,increasing the temperature in the storage tank and, as a result,the generation temperature of the absorption chiller. Thus, highersolar irradiation becomes into higher values of SCOP, CE andtcooling.

Fig. 10 allows also concluding that the solar irradiation H, windvelocity magnitude V and direction h mainly determined SCOP andCE. The time along which cold water is produced, tcooling, is highlysensitive to the solar irradiation H and the average ambient tem-perature T.

Ambient temperature is a variable having a noticeable inuenceon solar cooling facilities, modifying their performance in two dif-ferent known ways:

Higher ambient temperature contributes to improve the perfor-mance of the solar collectors, reducing the heat losses to theambient (see Eq. (1)). Consequently, the thermal uid reachesa higher temperature through the solar collectors, leading theabsorption chiller to a better performance because the drivinggeneration temperature is higher.

Ambient temperature also modies the condensationabsorp-tion temperature of the absorption machine, but indirectly.Higher ambient temperature increases the cooling tower tem-perature and leads to a decrease in the absorption machine per-formance, because temperature lift increases, meaning this thetemperature difference between recooling (condensation andabsorption circuits) and chilled water temperature.temperature controlled. This is a result of the solar cold beingnot able to fully match the load. Moreover, in Madrid region, lowair humidity generally accompanies high ambient temperatureevents, limiting the temperature of the water coming from thewet cooling tower in hot days, as the wet bulb temperature doesnot increase at the same rate than the dry bulb temperature.

Another interesting result found is the notable inuence ofwind velocity magnitude on SCOP and CE. A quantication of itsinuence can be performed using the rst order correlations ob-tained. Predicted values for SCOP and CE, using Eqs. (6) and (7),are calculated in two cases:

Using real values of wind velocity magnitude. Wind velocity is reduced to the minimum value used to obtainthe correlations, V = 1.4 m/s.

Gains obtained in SCOP and CE, due to the reduction of windvelocity magnitude from real values to this minimum value, corre-sponds to 11% and 12% respectively for the whole test campaign.As observed, the increase of the wind velocity magnitude spoilsthe collectors performance, increasing the top glass cover convec-tion heat losses. This result is in accordance with previous theoret-ical studies evaluating the inuence of wind over solar thermalplants [20].

Wind direction has also a signicant importance on system per-formance, according to Fig. 10. In the present study, wind directionis measured taking as reference the front side of the collectors (0).It is measured symmetrically respect to the front-rear plane of thecollectors layout, taking a value of 90when wind is parallel to col-lector surface. From Eqs. (6)(8), wind direction effect is worstwhen incidence angle approaches the front side of the collectors,i.e. front impinging wind. This result is similar to that reportedby Fleck et al. [11] evaluating a solar plant not for air-conditioningpurposes.

5. Conclusions

This paper evaluates the performance of a commercial absorp-tion air-conditioning facility in Madrid, working when drivenexclusively by solar thermal energy. The following main conclu-sions have been obtained from the present study:

The statistical analysis developed using daily data allowedrevealing the inuences of the weather variables, whichFig. 10 summarizes; offering real working data to the researchcommunity and facility planners.

The most important variable inuencing the daily averagedSCOP, CE and tcooling is the daily solar energy received H. SCOPThe response of the absorption machine to a rise in both tem-peratures (generation and condensationabsorption) determinesthe global performance of the system. The effect of an increase inthe ambient temperature over the global performance of a realworking solar absorption cooling facility is novel information.

From Eqs. (6)(8) it can be concluded that the average ambienttemperature T has a positive inuence on SCOP, CE and tcooling. Theresults obtained indicate that the inuence of the higher genera-tion temperature is stronger than the effect of the higher conden-sationabsorption temperature, which tends to decrease theperformance of the absorption chiller. This is supported by theoret-ical and experimental studies on the operation of absorption chill-ers, such as [1719], among others. It must be remarked that the

gy 88 (2011) 14471454 1453and CE are mainly inuenced by H, the wind velocity magnitudeV and direction h. The time along which cold water is produced,tcooling, is highly sensitive to H and T .

Average ambient temperature during solar facility operationwas found to have a positive inuence on SCOP, CE and tcooling.The positive inuence of the resulting higher generation tem-perature was identied to be greater than the negative onecoming from the higher cooling tower water temperature,which tends to decrease the performance of the absorptionmachine. This effect is benecial to the solar cooling technologyperformances, as it indicates that a higher cooling load can bematched on hot clear sky days.

Wind effect has been found to be important in reducing ef-ciency. Its effect is worst when incidence angle approachesthe front side of the collectors, i.e. front impinging wind. Asthe wind velocity magnitude increases, the performance ofthe solar cooling facility decreases, mainly reducing SCOP andCE. Gains obtained in SCOP and CE, due to the reduction of windvelocity magnitude from real values to the minimum residualvalue found experimentally (1.4 m/s), corresponds to 11% and12% respectively for the whole test campaign. This indicatesthe convenience of including the effect of wind in studies andprojects. It also indicates that installing non-shadowing windprotection devices in future facilities, especially in windy loca-tions, can improve cold production.

of parameters critical for the performance of the solar cooling

This work has been partially funded by the research grants

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[3] http://www.iea-shc.org/task38/index.html; July 27, 2010.[4] Balaras CA, Grossman G, Henning HM, Infante Ferreira CA, Podesser E, Wang L,

et al. Solar air conditioning in Europe an overview. Renew Sust Energy Rev2007;11:299314.

[5] Henning HM. Solar assisted air-conditioning of buildings an overview. ApplTherm Eng 2007;27:173449.

[6] Desideri U, Proietti S, Sdringola P. Solar-powered cooling systems: technicaland economic analysis on industrial refrigeration and air-conditioningapplications. Appl Energy 2009;86:137686.

[7] Sartori E. Convection coefcient equations for forced air ow over at surfaces.Sol Energy 2006;80:106371.

[8] Sharples S, Charlesworth PS. Full-scale measurements of wind-inducedconvective heat transfer from a roof-mounted at plate solar collector. SolEnergy 1998;62:6977.

[9] Kumar S, Sharma VB, Kandpal TC, Mullick SC. Wind induced heat losses fromouter cover of solar collectors. Renew Energy 1997;10:6136.

[10] Medinelli Sanino LA, Rojas Reischel RA. Modeling and identication of solarenergy water heating system incorporating nonlinearities. Sol Energy2007;81:57080.

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Experimental diagnosis of the influence of operational variables on the performance of a solar absorption cooling systemIntroductionExperimental facilityData reductionResults and discussionConclusionsAcknowledgementsReferences