Article Thermal Assessment of a Novel Combine Evaporative Cooling Wind Catcher

Azam Noroozi * and Yannis S. Veneris

School of Architecture, National Technical University of Athens, Section III, 42 Patission Av., 10682 Athens, Greece; [email protected] * Correspondence: [email protected]; Tel.: +30-210-772-3885 (ext. 3567)

Received: 5 January 2018; Accepted: 13 February 2018; Published: 15 February 2018

Abstract: Wind catchers are one of the oldest cooling systems that are employed to provide sufficient natural ventilation in buildings. In this study, a laboratory scale wind catcher was equipped with a combined evaporative system. The designed assembly was comprised of a one-sided opening with an adjustable wetted pad unit and a wetted blades section. Theoretical analysis of the wind catcher was carried out and a set of experiments were organized to validate the results of the obtained models. The effect of wind speed, wind catcher height, and mode of the opening unit (open or closed) was investigated on temperature drop and velocity of the moving air through the wind catcher as well as provided sensible cooling load. The results showed that under windy conditions, inside air velocity was slightly higher when the pad was open. Vice versa, when the wind speed was zero, the closed pad resulted in an enhancement in air velocity inside the wind catcher. At wind catcher heights of 2.5 and 3.5 m and wind speeds of lower than 3 m/s, cooling loads have been approximately doubled by applying the closed-pad mode.

Keywords: wind catcher; cooling system; experimental validation; thermal modeling

1. Introduction Wind catchers are small with heights between 5 and 33 m raised from the roof of the buildings. They serve as a cooling system to provide favorable ventilation and pleasant interior environment with low technologies. Wind catchers are commonly constructed in the majority of hot and dry or humid regions [1,2]. A wind catcher usually consists of a , stalk, catgut, chain, and shelf [3]. It works under the influence of two driving forces: buoyant force, which is due to the temperature difference, and external winds [4]. In hot-arid climate, the ambient air is usually hot, dry, and there is often dust and sand in it. This makes the unprocessed air insufferable [5]. In traditional wind catchers, the air passing over the water surfaces, like porous pots, pond, etc., was used for improving natural cooling and . Such systems retain a balance between the two important parameters of evaporative cooling and ventilation. The concept works based on the absorption of the relatively large amount of energy needed for evaporation of water from the air at the vicinity of the wetted surface. This leads to a reduction in temperature and an increase in density of the air that subsequently results in the downward movement of the fresh air through the wind catcher [6]. Lack of control over the water evaporation process was the major drawback of the system. Several researchers have analyzed various designs of wind catchers. Montazeri et al. [7] demonstrated that the maximum performance obtained at the air incident angle of 90◦. Awbi et al. [8] showed that the efficiency of four-sided wind catchers were much higher than that of the circular ones at the same wind speed. Dehnavi et al. [9] found the most efficient form of the squared wind catchers for decreasing the indoor air temperature were those equipped with the plus blades. Ghadiri et al. [10]

Energies 2018, 11, 442; doi:10.3390/en11020442 www.mdpi.com/journal/energies Energies 2018, 11, 442 2 of 15 concluded that the height of wind catcher influenced the ventilation rate and volumetric flow rate at the different opening ratios of the wind catcher. Engelmann et al. [11] tried to simulate a typical office building to investigate the potential of different ventilations and cooling strategies. Some other researches have studied wind catchers equipped with evaporative cooling systems. Bahadori [12] introduced two new designs of the wind catchers including wind catchers with wetted columns and those with wetted surfaces. Goudarzi et al. [13] studied a new design of wind catcher constructed from a four-quadrant-peak wind-catcher rooftop, nozzles, and turbines. Kalantar [14] experimentally and numerically studied the cooling performance of a wind catcher with water sprayers on top in a hot and dry region. Haghighi et al. [15] evaluated the performance of a wind catcher coupled with shower cooling system. Saffari et al. [16] carried out a numerical study on the wind catcher consisting of wetted curtains hung in the column. Elzaidabi [17] constructed an indirect system by combining a modified wind catcher and a diamond-shaped psychometric energy core (PEC) unit. Pearlmutter et al. [18] developed a multi-stage down-draft evaporative cool (DECT). A survey of the literature reveals the acceptable level of indoor comfort and savings in energy using the wind catcher integrated evaporative cooling system (WCIECS). However, optimal operation of some of these wind catchers have been limited to only when the wind speed was low or very high [12]. Furthermore, from the architectural point of view, some of them have had less of a resemblance to those of traditional buildings. For this reason, the present research proposed a novel traditional wind catcher equipped with wetted blades and an adjustable opening pad. Governing expressions of the designed wind catcher were developed using the thermodynamic laws and a set of experiments were conducted to verify the obtained models.

2. Wind Catcher Description The designed device is a unidirectional wind system that was equipped with two evaporative cooling parts. A prototype of the assembly was shown Figure1. The construction has a foursquare cross section and its dimensions have been determined according to the previous works [12,19]. It is comprised of a head, which is the upper part of the structure and includes two parts of an opening and hinged evaporative cooling unit. The hinged pad works like a filter and is soaked by water sprayers placed on its top. Moreover, it can manually be opened or closed in a swinging motion based on the wind speed. The roof of the wind catcher is flat [19]. The column, the middle part of the wind catcher, consists of number of vertical cloth curtains as the wetted blades section. Blades have been suspended from the bottom of the head and is extended to the air distribution window. Water spraying pipes have been applied to sprinkle water on some of the blades. The excess water is collected in a pool located at the bottom for re-pumping to the system. A window, which is deployed at the bottom part of the column, distributes the fresh and cold air (comes from the wind catcher) into the building. Different types of wind catcher functions based on the natural forces of wind pressure and stacks work to direct the air through buildings. When wind speed is suitable, air pressure on the opening face to the wind is positive while the leeward opening meets a negative pressure. Air enters the wind catcher through the opening with positive pressure and forced out through the opening with negative pressure. Therefore, wind catcher acts as a ventilator in which the fresh air is taken into the building and the hot and polluted air is discharged [4]. The proposed system is a one-sided wind catcher that is orientated to capture favorable winds. Consequently, wind speed is the most dominant driving force for moving the air through the conduit. When wind speed is almost zero, wind catchers need a driving force, caused by buoyancy effect, to operate. The pad unit and blades section are wetted by the water nozzles installed on their top. When warm air passes near the wetted pad and blades, due to the temperature difference between water and air flow, the convective mechanism becomes active. Simultaneously, the water evaporation process reduces air temperature close to the Energies 2018, 11, 442 3 of 15 wet-bulb temperature. Therefore, the density of the air increases leading to a pressure difference from Energies 2018, 11, x FOR PEER REVIEW 3 of 15 the top to the bottom of the column. This makes an efficient flow due to the buoyancy effect.

Closed Pad Open Pad

Wetted Pad Wetted Pad

Wetted Blades Wetted Blades

Figure 1. The schematic view of the designed wind catcher with open and closed pad. Figure 1. The schematic view of the designed wind catcher with open and closed pad. 3. Analytical Modelling 3. AnalyticalThe Modelling objective of the study is to assess the temperature and variations of the air flow rate through the constructed wind catcher. When the pad is closed, the air passes through the wetted Thestraw objective and the of water the study evaporation is to assess results the in temperature a reduction in and temperature humidity and variations an increase of the in airrelative flow rate throughhumidity the constructed (RH) of the wind flowing catcher. air. WhenOn the theother pad side, is closed,when the the pad air is passes open, throughthe entering the air wetted flows straw and theparallel water to evaporation the pad. So, resultsthe pad inacts a like reduction a screen. in temperature and an increase in relative humidity (RH) of theTemperature flowing air. drop On theof the other air when side, passing when thethrough pad the is open, wetted the straw entering is obtained air flowsby the parallelfollowing to the pad. So,expression the pad acts[20] like a screen. Temperature drop of the air when passing= through( the wetted) straw is obtained by the following(1) expression [20] where is the efficiency of the straws, 𝑇𝑇𝑡𝑡 and𝑇𝑇𝑎𝑎 − 𝜂𝜂 𝑇𝑇are𝑎𝑎 − respectively𝑇𝑇𝑤𝑤𝑤𝑤 dry and wet bulb temperatures of ambient air (°C), and defines theTt air= Ttemperaturea − η(Ta − afterTwb )the pads (°C). The efficiency of the pad (1) 𝜂𝜂 𝑇𝑇𝑎𝑎 𝑇𝑇𝑤𝑤𝑤𝑤 depends on the thickness of the straw (dp) in centimeter and air speed through the pad ( ) in meters where η is the efficiency of the𝑇𝑇𝑡𝑡 straws, Ta and Twb are respectively dry and wet bulb temperatures per second◦ as the equation ◦ 𝑖𝑖 of ambient air ( C), and Tt defines the air temperature after the pads ( C). The efficiency𝑣𝑣 of the pad 0.02325 + 0.899 < 1m/s depends on the thickness( ) = of the straw (dp) in centimeter and air speed through the pad (vi) in(2 meters) 0.0452 𝑖𝑖 + 0.26 0.635 + 0.57774 + 0.714 𝑖𝑖 > 1m/s per second as the equation𝑖𝑖 − 𝑉𝑉4 3 2 𝑣𝑣 𝑓𝑓 𝑣𝑣 � 𝑖𝑖 𝑖𝑖 𝑖𝑖 𝑖𝑖 𝑖𝑖 − 𝑉𝑉 = 𝑉𝑉0.04631− 𝑉𝑉1.444 × 10 𝑉𝑉 ln 𝑣𝑣 (3) ( 2.5 −0.02325Vi + 0.899 −3 𝑑𝑑𝑝𝑝 vi < 1 m/s ( ) = 𝑝𝑝 𝑝𝑝 Sincef vi the evaporative cooling4𝐿𝐿�𝑑𝑑 � by the� 3 pad is− assumed2 to be𝑑𝑑 an� isenthalpic process, the RH of the (2) −0.0452Vi + 0.26Vi − 0.635Vi + 0.57774Vi + 0.714 vi > 1 m/s air after the pad given by the expression

 h + ( ) + ( −3 ) i dp (4) L dp = 0.04631 − 1.444 × 10 dp ln (3) 𝑝𝑝 𝑡𝑡 𝑔𝑔 𝑡𝑡 𝑝𝑝 𝑎𝑎 𝑔𝑔 𝑎𝑎 2.5 where is the specific heat of the air𝐶𝐶 (J/𝑇𝑇 (kg K𝜔𝜔)ℎ), T 𝐶𝐶is the𝑇𝑇 dry𝜔𝜔 ℎair temperature, is the humidity ratio Sinceof the the air evaporative (kg/kg), and cooling is by the of pad the issaturated assumed vapor tobe at anthe isenthalpicair temperature. process, and the which RH of the 𝐶𝐶𝜌𝜌 𝜔𝜔 air afterrefer the to pad thegiven interior by and the exterior expression airflows, respectively. ℎ𝑔𝑔 𝑡𝑡 𝑎𝑎 In the second part, the entering air passes through the conduits. To determine temperature and RH variations of the air inside the conduit,+ its height +is divided to smaller parts (with a length of CpTt ωhg tCpTa ωhg a (4) 0.5 m) in which the wall and ambient temperatures, solar radiation, and wind speed were assumed where Cρ is the specific heat of the air (J/(kg K)), T is the dry air temperature, ω is the humidity ratio of the air (kg/kg), and hg is enthalpy of the saturated vapor at the air temperature. t and a which refer to the interior and exterior airflows, respectively. Energies 2018, 11, 442 4 of 15

In the second part, the entering air passes through the conduits. To determine temperature and RH variations of the air inside the conduit, its height is divided to smaller parts (with a length of 0.5 m) in which the wall and ambient temperatures, solar radiation, and wind speed were assumed to be constant. When the pad is open, it works like the screens inside the conduit, a similar calculation has been considered for the open pad. So it assumed as the first part of the conduit unit. The energy balance equation for each part of the column can be written as [21,22]

Isαbs + hobs(Ta − Ts) + Ieαbe + hobe(Ta − Te) + ho(bw + bn)(Ta − Tn) . . (5) +maCp(Tin − Tout) = mw Lv where b is the area of the walls (m2), I is solar beam on the walls (W/m2), α is the wall absorptivity . (decimal), ma is the mass flow rate of the wind entering the wind catcher (kg/s), Cp is the specific heat 2 of the humid air (J/(kg K)), ho is heat transfer coefficient of ambient air (W/(m K)). Lv is the of the evaporation (J/g) and the subscripts s, e, w, and n refer to the south, east, west, and north walls of the wind catcher, respectively. The rate of the water vaporization is calculated by [23]

. mv = hD Am(wc − wa) (6)

2 2 where hD is the mass transfer coefficient (g/(m s)), Am is wetted surface of the column (m ), wc is the humidity ratio of the saturated air at the desired temperature. wa is the humidity ratio of the inner air flow. Mass transfer coefficient can be expressed as

hi hD = (7) Cρ

2 where hi is the inner convection heat transfer coefficient of the air (W/(m K)) which was given by Equation (8). hi = 2.8 + 3vi (8) Finally, the cooling load calculated the various parts of the column as

. Q = maCp(∆T) (9)

To obtain the air velocity inside the wind catcher, we use the expression [12,20,24]

2   L Vi 1 2 gZρ 1 1 f + ∆Pp = CpwρVw + − (10) D 2g 2 R To Ta where f, L, D, Cpw, Z, vw, To, and R respectively show the friction coefficient of the conduit (dimensionless), length of the conduit (m), hydraulic diameter of the conduit (m), the pressure coefficient of wind (dimensionless), height of the wind catcher (m), wind velocity (m/s), outlet ◦ temperature of the wind catcher ( C), and the gas constant for air (J/(kg K)). ∆Pp stands for pressure drop in the opening pad which has been calculated using the empirical expression

( 0.755 1.029vidp vi < 1 m/s ∆Pp = 4 3 2  0.755 (11) 4.9 0.1885vi − vi + 2.091vi − 1.42vi + 0.4056 dp vi > 1 m/s

4. Experimental Procedure In order to evaluate the performance of the system under real operating conditions, and to validate the obtained analytical expressions a set of experiments were carried out during May 2017 at the campus of Bozrgmehr University, Qaen (33◦4303600 N and 59◦1100400 E) . According to Köppen and EnergiesEnergies2018 2018, 11,, 44211, x FOR PEER REVIEW 5 of 15 5 of 15

Since the wind speed was mostly changing during the test period, a blower (Pars200, Parskhazar Geiger,co.,this , climate Iran) haswith been an adjustable classified rotary ascold speed desert of the climaterotor was (BWk). utilized Theto provide average a constant temperature air in the warmestvelocity month inside of the the win yeard catcher is 27.6’s conduit.◦C. The tests were conducted at three levels of wind velocity through the conduit (1, 1.5, 2.5 m/s) and the wetted pad remained close during the tests. × TheFive prototype temperature had asensors height (SMT160 of 2.5 m,, Tika cross-section co., Tehran, ofIran 0.20) were 0.20used m,to measure and the temperat air openingures length of 0.40 m.of the Other inlet, dimensions outlet, and outer of the surfaces wind of catcher the walls are of depicted the wind incatcher Figure as 2well. The as wallsambient. were The constructed sensors from polycarbonatewere connected with to the a personal thickness computer of 6 mm by means whose of outer a temperature surfaces transmitter were covered (TM 1323, by a Tika shiny co., aluminum sheetTehran, to minimize Iran). A solar solar radiationpower meter absorption. (TES 1333, TES The co, blade Taipei, section Taiwan) with was a utilized ‘plus shape’ to measure configuration solar were maderadiation up of four intensity gunny on south screens and with east walls. width Relative of 0.10 humidity m and length(RH) of ofambient 1.80 m.air, Thethe inlet pad, and was the installed in outlet of the wind catcher were determined using RH sensors (SUN-25H, SUNWARD co., Tehran, the air opening. A 1 cm thick straw layer was used in the construction of the pad. Drip tubing was Iran). Each test was conducted from 9 a.m. to 3 p.m., and the useful data were recorded at 30 min employedtime intervals to sprinkle of during water theon day. the pad and the blades.

Front View Side View

Wetted Pad

(a)

(b)

Figure 2. (a) The photograph of the designed wind catcher, (b) The dimensions of the wind catcher. Figure 2. (a) The photograph of the designed wind catcher, (b) The dimensions of the wind catcher.

Since the wind speed was mostly changing during the test period, a blower (Pars200, Parskhazar Co., Tehran, Iran) with an adjustable rotary speed of the rotor was utilized to provide a constant air velocity inside the wind catcher’s conduit. The tests were conducted at three levels of wind velocity through the conduit (1, 1.5, 2.5 m/s) and the wetted pad remained close during the tests. Five temperature sensors (SMT160, Tika Co., Tehran, Iran) were used to measure temperatures of the inlet, outlet, and outer surfaces of the walls of the wind catcher as well as ambient. The sensors were connected to a personal computer by means of a temperature transmitter (TM 1323, Tika Co., Energies 2018, 11, 442 6 of 15

Tehran, Iran). A solar power meter (TES 1333, TES Co., Taipei, Taiwan) was utilized to measure solar radiation intensity on south and east walls. Relative humidity (RH) of ambient air, the inlet, and the outlet of the wind catcher were determined using RH sensors (SUN-25H, SUNWARD Co., Tehran, Iran). Each test was conducted from 9 a.m. to 3 p.m., and the useful data were recorded at 30 min time intervals of during the day.

5. Experimental Validation To verify the obtained expressions, the results of the models were compared with those of experiments using the Pearson correlation coefficient (r), the root mean square deviation (e) and the mean absolute error (MAE) criteria which were determined as [25,26]

N ∑ X Y − (∑ X )(∑ Y ) r = i i i i (12) r q 2 2 2 2 N ∑ Xi − (∑ Xi) N ∑ Yi − (∑ Yi)

s 2 ∑ (e ) e = i (13) N and 1 MAE = e (14) N ∑ i h − i where e = Xi Yi , X and Y are respectively the ith theoretical and empirical data; and N is the i Xi i i number of observations.

6. Result and Discussion

6.1. Model Verification To verify the obtained models, the predicted data of outlet temperature and relative humidity were compared with those observed by the experiments. After that, the effect of some design parameters and operating conditions on the performance of the designed wind catcher was investigated using the validated models. Figure3 shows variations of solar radiation intensity, ambient temperature, and comparison between experimental and calculated outlet temperature of the wind catcher at the three inside air velocities of (a) 1, (b) 1.5, and (c) 2.5 m/s. The measurements indicate that the temperature drop inside the designed wind catcher has been between 9.29 and 14.63 ◦C. The temperature decrease in a modular wind catcher with wetted surfaces found to be in range of 9.2–13.6 ◦C[27]. The root mean square deviation (e) ranges from 0.04925 to 0.10728 while the observed correlation coefficient is between 0.9312 and 0.9438. The maximum deviations between the analytical and the experimental temperatures are 1.21, 1.60, and 2.04 ◦C at the air velocities of 1, 1.5, and 2.5 m/s, respectively. Also, the result indicates that min absolute error associated with the theoretical expressions has been lower than 10%. A study that had been conducted to simulate indoor temperature of a green house in Iraq based on thermo-physical properties of the green house components, showed that the predicted data had an absolute error of lower than 10% [28]. The results of similar research achieved an mean absolute deviation of lower than 20% between the predicted and the experimental temperatures of a greenhouse equipped with a heat-pump [29]. Based on the observation, it can be said that there is a suitable agreement between the experimental and theoretical data. Energies 2018, 11, 442 7 of 15 Energies 2018, 11, x FOR PEER REVIEW 7 of 15

calculated temp. experimental temp. 36 1000 ambient temp. solar radiation intensity ) 32 900 2 W/m 28 800 C) ° 24 700 r = 0.98383 Max.dev=2.0428 e = = 0.10728 MAE = 0.1065 20 600

Temperature ( 16 500 Solar radiation intensity ( intensity radiation Solar

12 400

Time (h)

(a)

calculated temp. experimental temp. 36 1000 ambient temp. solar radiation intensity ) 32 900 2 C)

° 28 800

24 700 r = 0.931225 Max.dev= 1.602245 20 e = 0.055781 MAE = 0.0217 600 Temperature (

16 500 Solar radiation intensity(W/m 12 400

Time (h) (b)

Figure 3. Cont.

Energies 2018, 11, 442 8 of 15 Energies 2018, 11, x FOR PEER REVIEW 8 of 15 Energies 2018, 11, x FOR PEER REVIEW 8 of 15

calculated temp. experimental temp. calculated temp. experimental temp. 36 ambient temp. solar radiation intensity 1000 36 ambient temp. solar radiation intensity 1000 ) ) 2 2 32 900 32 900 C) ° 28C) 800 ° 28 800 r = 0.942535 Max. dev= 1.21063 24 r = 0.942535 Max. dev= 1.21063 700 24 e = 0.049258 MAE = 0.0288 700 e = 0.049258 MAE = 0.0288 20 600 20 600 Temperature ( Temperature ( 16 500 16 500 Solar radiation intensity(W/m

12 400 Solar radiation intensity(W/m 12 400

Time (h) Time (h) (c) (c) Figure 3. Hourly variations of experimental and calculated outlet air temperature under the FigureFigure 3.3. HourlyHourly variations ofof experimental experimental and and calculated calculated outlet outlet air temperature air temperature under theunder conditions the conditions of Qaen city during 3–5 May 2017, at the air speeds of (a) 1, (b) 1.5, and (c) 2.5 m/s. conditionsof Qaen cityof Qaen during city 3–5 during May 3 2017,–5 May at the 2017, air at speeds the air of speeds (a) 1, ( bof) 1.5,(a) 1, and (b)( 1.5,c) 2.5 and m/s. (c) 2.5 m/s.

Variations of experimental and calculated RH of the outlet air during three days of the Variations of experimental and calculated RH of the outlet air during three days of the experimentVariations were depicted of experimental in Figure and 4. calculatedIt can be seen RH offrom the the outlet figure air duringthat the three designed days of wind the experimentcatcher experiment were depicted in Figure 4. It can be seen from the figure that the designed wind catcher haswere been depictedelevated RH in Figure of the 4moving. It can air be by seen 39.55 from to 64%. the figure The range that theof RH designed increase wind in the catcher wind catcher has been has been elevated RH of the moving air by 39.55 to 64%. The range of RH increase in the wind catcher designedelevated by RH Khani of the et movingal. [27] airwas by from 39.55 23 to– 64%.53%. TheThe rangeroot mean of RH square increase deviations in the wind are catcher lower designed than designed by Khani et al. [27] was from 23–53%. The root mean square deviations are lower than 0.04586,by Khani the values et al. [ 27of] Pearson was from correlation 23–53%. Thecoefficient root mean are higher square than deviations 0.9188 are and lower the difference than 0.04586, 0.04586, the values of Pearson correlation coefficient are higher than 0.9188 and the difference betweenthe values the experimental of Pearson correlation and analytical coefficient RH areis lower higher than than 5%. 0.9188 This and means the difference that the betweenobtained the between the experimental and analytical RH is lower than 5%. This means that the obtained expressionsexperimental could and satisfactorily analytical predict RH is lower the RH than of the 5%. outlet This air. means that the obtained expressions could expressionssatisfactorily could predict satisfactorily the RH of predict the outlet the air.RH of the outlet air.

84 calculated RH experimental RH ambient RH 30 84 calculated RH experimental RH ambient RH 30 28 80 28 80 26 26 76 24 76 24 22 72 22 72 20 20 68 18 68 r = 0.918964 MAE = 0.0409 18 r = 0.918964 MAE = 0.0409 16 64 e = 0.042951 Max. dev=1 16 64 e = 0.042951 Max. dev=1 14 14 60 12 60 12 10 56 10 56 8 8 52 6 52 6 AmbientRerative Humidity (%) Inside RelativeHumidity (%) 4 AmbientRerative Humidity (%) 48Inside RelativeHumidity (%) 4 48 2 2 44 0 44 0

Time (h) Time (h) (a) (a)

Figure 4. Cont.

Energies 2018 11 Energies 2018, 11,, x ,FOR 442 PEER REVIEW 9 of9 of15 15

calculated RH experimental RH ambient RH 30 84 28 80 26 24 76 22 72 20 18 68 r = 0.945909 Max.dev=2.84 e= 0.023884 MAE = 0.0508 16 64 14 60 12 10 56 8 52 6 AmbientRerative Humidity (%) Inside RelativeHumidity (%) 4 48 2 44 0

Time (h) (b)

84 calculated RH experimental RH ambient RH 30 28 80 26 76 24 22 72 20 68 18 r= 0.918817 Max. dev= 2.63 16 64 e= 0.030973 MAE =0.0466 14 60 12 10 56 8 52 6 AmbientRerative Humidity (%) Inside RelativeHumidity (%) 4 48 2 44 0

Time (h)

(c)

Figure 4. Hourly variations of experimental and calculated outlet air relative humidity under the Figure 4. Hourly variations of experimental and calculated outlet air relative humidity under the conditions of Qaen city during 3–5 May 2017, at the air speeds of (a) 1, (b) 1.5, and 2.5 m/s. conditions of Qaen city during 3–5 May 2017, at the air speeds of (a) 1, (b) 1.5, and 2.5 m/s. 6.2. Effect of Wind Speed and Wind Catcher Height 6.2. Effect of Wind Speed and Wind Catcher Height The effect of wind speed and wind catcher height were analytically investigated on the air The effect of wind speed and wind catcher height were analytically investigated on the air velocity velocity inside the conduit, temperature and cooling load. Since the position of the inlet pad could inside the conduit, temperature and cooling load. Since the position of the inlet pad could influence the influence the operating parameters of the wind catcher, the tests were carried out with both open and operating parameters of the wind catcher, the tests were carried out with both open and closed pads. closed pads. The effect of wind velocity and height of the wind catcher on air velocity inside the conduit at The effect of wind velocity and height of the wind catcher on air velocity inside the conduit at the two modes of the pad (open and closed) has been illustrated in Figure5. Clearly, increasing the the two modes of the pad (open and closed) has been illustrated in Figure 5. Clearly, increasing the wind speed increase the air velocity in the column. In addition, the rate of changes is higher at the wind speed increase the air velocity in the column. In addition, the rate of changes is higher at the lower heights of the wind catcher. This is due to the fact that increasing the length of the wind catcher lower heights of the wind catcher. This is due to the fact that increasing the length of the wind catcher increases the pressure drop which results in a slower growth of air velocity in the column. Figure5 increases the pressure drop which results in a slower growth of air velocity in the column. Figure 5 also indicates that at the conditions of wind existence, inside air velocity is slightly higher when the also indicates that at the conditions of wind existence, inside air velocity is slightly higher when the pad was open. This is because of the air pressure drop occurred with passing through the pad. Vice pad was open. This is because of the air pressure drop occurred with passing through the pad. Vice versa, when the wind speed is zero, the closed pad results in a relatively higher air velocity inside

Energies 2018, 11, 442 10 of 15 versa,Energies when 2018 the, 11 wind, x FORspeed PEER REVIEW is zero, the closed pad results in a relatively higher air velocity10 of inside 15 the wind catcher. The air flow inside the wind catcher at the condition of no external wind is under the wind catcher. The air flow inside the wind catcher at the condition of no external wind is under the influence of the buoyancy effect (depends on the air temperature) and the pressure drop (because the influence of the buoyancy effect (depends on the air temperature) and the pressure drop (because of the length of the ). So, since the temperature drops at the closed-pad mode are higher, the air of the length of the duct). So, since the temperature drops at the closed-pad mode are higher, the air velocitiesvelocities were were higher higher compared compared with with the open-pad.the open-pad. However, However it, seems it seems that that the the effect effect of of pressure pressure drop is considerabledrop is considerable at the taller at windthe taller catchers wind catchers which finally which havefinally been have resulted been resulted in a decrease in a decrease in air in velocity air at thevelocity height ofat the 5 m. height of 5 m.

closed pad 4 Height 2.5m Height 3.5m Height 5m 3.6

3.2 ) 𝑠𝑠 ⁄ 2.8 𝑚𝑚 2.4

2

AirSpeed ( 1.6

1.2

0.8

0.4

0 0 1 2 3 4 5 Wind Speed ( ⁄ )

𝑚𝑚 𝑠𝑠 (a)

open pad 4 Height 2.5m Height 3.5m Height 5m 3.6

3.2 ) 𝑠𝑠 ⁄

𝑚𝑚 2.8

2.4

2 AirSpeed ( 1.6

1.2

0.8

0.4

0 0 1 2 3 4 5 Wind Speed ( ⁄ )

(b) 𝑚𝑚 𝑠𝑠

Figure 5. Effect of wind speed and wind catcher height on air speed under the conditions of Qaen city Figure 5. Effect of wind speed and wind catcher height on air speed under the conditions of Qaen city at 12:00 p.m. on 3 May 2017 and the modes of: (a) closed pad, (b) open pad. at 12:00 p.m. on 3 May 2017 and the modes of: (a) closed pad, (b) open pad. The effect of wind velocity and height of the wind catcher on the outlet temperature at the two Themodes effect of the of windopen and velocity closed and pad height are depicted of the in wind Figure catcher 6. Changes on the in outlet wind temperaturespeed and theat height the two modes of the open and closed pad are depicted in Figure6. Changes in wind speed and the height Energies 2018, 11, 442 11 of 15 Energies 2018, 11, x FOR PEER REVIEW 11 of 15 hashas notnot a significant significant effect effect on on the the outlet outlet temperature temperature at at low low wind wind speeds speeds (lower (lower than than 2 m/s) 2 m/s) when when the thepad pad is closed. is closed. It seems It seems that that the the slow slow passing passing of of the the air air through through the the wetted wetted pad makes it almostalmost saturatedsaturated andand bringsbrings itit toto thethe lowestlowest possiblepossible temperature.temperature. ThisThis meansmeans thatthat thethe columnscolumns afterafter thethe padpad hashas nono effecteffect onon temperaturetemperature andand RHRH ofof thethe movingmoving air.air. However,However, atat higherhigher windwind speeds,speeds, whenwhen thethe airair velocityvelocity inside the wind wind catcher catcher is is significantly significantly high, high, only only a afraction fraction of ofevaporative evaporative cooling cooling can can be beaccomplished accomplished by bythe the pad pad while while the the process process is supplemented is supplemented by bythe thewetted wetted columns. columns. Therefore Therefore,, the theheight height of the of thecolumns columns is a iskey a key factor factor on the on theamount amount of cooling of cooling load load and and the thetemperature temperature drop drop of the of themoving moving air. air.When When the thepad pad is open, is open, the the outlet outlet temperature temperature increased increased with with wind wind velocity velocity which which is ismainly mainly due due to to the the increase increase in in moving moving velocity velocity of of the the air air through the wetted blades.blades. Furthermore,Furthermore, sincesince increasingincreasing thethe heightheight ofof thethe windwind catchercatcher hashas ledled toto aa decreasedecrease inin airair velocityvelocity andand alsoalso providedprovided aa higherhigher effectiveeffective surfacesurface for for the the wetted wetted screens screens (evaporation (evaporation area), area), the the outlet outlet temperature temperature is cooleris cooler at theat the higher higher wind wind catchers. catchers. On theOn openthe open pad mode,pad mode, the air the temperature air tempera inture the windin the catchers wind catchers with higher with heighthigher areheight reduced are reduced more, which more, is which in accordance is in accordance with the with results the ofresults the wetted of the columnswetted columns wind catcher wind proposedcatcher proposed by Bahadori by Bahadori et al. [12 ].et al. [12]. CoolingCooling loadload isis directlydirectly relatedrelated toto thethe airair velocityvelocity and the temperature drop in the column. FigureFigure7 a7a shows shows cooling cooling load load variations variations at the at differentthe different conditions conditions of the of wind the speed wind andspeed wind and catcher wind heightcatcher applying height applying the closed-pad the closed mode.-pad Clearly, mode. increasingClearly, increasing the wind the speed wind up tospeed 3 m/s up improvesto 3 m/s theimproves amount the of amount sensible of cooling sensible load. cooling While load. raising While the raising wind the speed wind more speed than more that than point, that leads point, to aleads decreasing to a decreasing trend in cooling trend in load. cooling This load. is mainly This due is mainly to the abruptlydue to the increase abruptly in the increase outlet temperaturein the outlet attemperature the higher at wind the speedshigher wind without speeds any considerablewithout any considerable increase in the increase air velocity. in the Onair velocity. the other On hand, the theother amount hand, ofthe cooling amount load of cooling has been load continuously has been continuously increased with increased the wind with speed the when wind thespeed pad when was openthe pad (see was Figure open7b). (see Comparing Figure 7b). the Comparing two modes the of wind two catchermodes of (Figure wind7 a,b)catcher indicates (Figure that 7a,b) at the indicates wind catcherthat at heightsthe wind of catcher 2.5 and heights 3.5 m and of the2.5 windand 3.5 speeds m and of lowerthe wind than speeds 3 m/s, of cooling lower loads than approximately3 m/s, cooling doubleloads approximately when applying double closed-pad when mode. applying While, closed at the-pad height mode. of 5 m,While, there at is the not height a significant of 5 m, difference there is betweennot a significant the two modes.difference However, between at thethe conditiontwo modes. of noHowever, wind flow, at the a maximum condition sensible of no wind cooling flow, load a ofmaximum 0.48 kW issensible achievable cooling if the load wind of 0.48 catcher kW heightis achieva wasble 5 m.if the wind catcher height was 5 m.

closed pad Height 2.5m Height 3.5m Height 5m =30°C 30

𝑻𝑻𝒂𝒂 28

26 C)

° 24

22

20

Temperature ( 18

16 0 1 2 3 4 5 Wind Speed ( ⁄ )

(a) 𝑚𝑚 𝑠𝑠

Figure 6. Cont.

Energies 2018, 11, 442 12 of 15 Energies 2018, 11, x FOR PEER REVIEW 12 of 15 Energies 2018, 11, x FOR PEER REVIEW 12 of 15

open pad open pad 30 =30°C 30 Height 2.5m Height 3.5m Height 5m =30°C Height 2.5m Height 3.5m Height 5m 𝑻𝑻𝒂𝒂 28 𝑻𝑻𝒂𝒂 28 26 26 C) ° C) 24 ° 24

22 22

20 20 Temperature ( Temperature ( 18 18

16 16 0 1 2 3 4 5 0 1 2 3 4 5 Wind Speed ( ⁄ ) Wind Speed ( ⁄ )

(b) 𝑚𝑚 𝑠𝑠 (b) 𝑚𝑚 𝑠𝑠 Figure 6. Effect of wind speed and wind catcher height on outlet temperature under the conditions of FigureFigure 6. 6.Effect Effect ofof windwind speedspeed andand windwind catchercatcher heightheight on on outletoutlet temperature temperature under under the the conditions conditions of of Qaen city at 12:00 p.m. on 3 May 2017 and the modes of: (a) closed pad, (b) open pad. QaenQaen city city at at 12:00 12:00 p.m. p.m. on on 3 3 May May 2017 2017 and and the the modes modes of: of: ( a(a)) closed closed pad, pad, ( b(b)) open open pad. pad.

closedclosed padpad 1.2 1.2 Height 2.5m Height 3.5m Height 5m Height 2.5m Height 3.5m Height 5m 1.1 1.1 1 1 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.5 0.5 0.4 Cooling Cooling (kW) load 0.4 Cooling Cooling (kW) load 0.3 0.3 0.2 0.2 0.1 0.1 0 1 2 3 4 5 0 1 2 3 4 5 Wind Speed ( ⁄ ) Wind Speed ( ⁄ )

𝑚𝑚 𝑠𝑠 (a) 𝑚𝑚 𝑠𝑠 (a)

Figure 7. Cont.

Energies 2018, 11, 442 13 of 15 Energies 2018, 11, x FOR PEER REVIEW 13 of 15

1.2 open pad Height 2.5m Height 3.5m Height 5m 1.1 1 0.9 0.8 0.7 0.6 0.5

Cooling Cooling (kW) load 0.4 0.3 0.2 0.1 0 1 2 3 4 5 Wind Speed ( ⁄ )

𝑚𝑚 𝑠𝑠 (b)

Figure 7. Effect of wind speed and wind catcher height on provided cooling load under the conditions Figure 7. Effect of wind speed and wind catcher height on provided cooling load under the conditions of Qaen city at 12:00 p.m. on 3 May 2017 and the modes of: (a) closed pad, (b) open pad. of Qaen city at 12:00 p.m. on 3 May 2017 and the modes of: (a) closed pad, (b) open pad.

7. Conclusions 7. Conclusions Thermal performance of a laboratory scale unidirectional wind catcher equipped with a Thermal performance of a laboratory scale unidirectional wind catcher equipped with a combined combined evaporative cooling system (moist blades section and wetted pad unit) was studied in the evaporative cooling system (moist blades section and wetted pad unit) was studied in the present present paper. Theoretical assessment of the wind catcher was carried out and a set of experiments paper. Theoretical assessment of the wind catcher was carried out and a set of experiments were were organized to validate the results of the obtained models. The effect of wind speed and wind organized to validate the results of the obtained models. The effect of wind speed and wind catcher catcher height were considered at the two situations of the opening pad. The results revealed that: height were considered at the two situations of the opening pad. The results revealed that: - Increasing the wind speed increases the velocity and the outlet temperature of the air in the - Increasingcolumn. The the temperature wind speed rise increases was especially the velocity considerable and the at outlet wind temperature speeds more of than the 3 air m/s in when the column.using the The closed temperature-pad mode rise which was subsequently especially considerable led to a significant at wind decrease speeds morein sensible than 3cooling m/s whenload. using the closed-pad mode which subsequently led to a significant decrease in sensible - coolingWhen the load. wind speed was zero, the closed pad resulted in a relatively higher air velocity inside - Whenthe wind the speed compared was zero, with the the closed open- pad resultedmode. While, in a relatively at the conditions higher air of velocitywind existence, inside theinside wind air catcher velocity compared was slightly with higher the open-pad when the mode. pad was While, open. at the conditions of wind existence, - insideIncreasing air velocity the height was of slightly the wind higher catcher when led the to pada de wascrease open. in air velocity especially at the higher - Increasingwind speeds. the height of the wind catcher led to a decrease in air velocity especially at the higher - windCooling speeds. load continuously increased with the wind speed when the pad was open. Whereas - Coolingwhen the load pad continuously was closed, the increased maximum with value the windof cooling speed load when was the achieved pad was at open.a wind Whereas speed of when3 m/s. the pad was closed, the maximum value of cooling load was achieved at a wind speed of 3 m/s. Author Contributions: Azam Noroozi contributed to the article with regards to writing, experiments, model development, analysis. Yannis S. Veneris contributed to the article with corrections and recommendations to the Author Contributions: Azam Noroozi contributed to the article with regards to writing, experiments, model development,articles contents analysis. and relevance. Yannis S. Veneris contributed to the article with corrections and recommendations to the articlesConflicts contents of Interest: and relevance. The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest. References

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