Article Windcatcher to Improve Ventilation Efficiency

Young Kwon Yang 1 , Min Young Kim 1 , Yong Woo Song 2 , Sung Ho Choi 2 and Jin Chul Park 1,*

1 School of Architecture and , Chung-Ang University, Seoul 06974, Korea; [email protected] (Y.K.Y.); [email protected] (M.Y.K.) 2 Graduate School, Chung-Ang University, Seoul 06974, Korea; [email protected] (Y.W.S.); [email protected] (S.H.C.) * Correspondence: [email protected]; Tel.: +82-2-820-5261

 Received: 13 July 2020; Accepted: 21 August 2020; Published: 28 August 2020 

Abstract: Windcatcher louvers are designed to capture air flowing outside a building in order to increase its natural ventilation. There are no studies that have designed the shape of the to increase the natural ventilation efficiency of the building. This study aimed to conduct a computational fluid dynamics simulation and mock-up test of a Clark Y airfoil-type windcatcher louver designed to increase the natural ventilation in a building. The following test results were obtained. The optimal angle of attack of the airfoil was calculated via a numerical analysis, which demonstrated that the wind speed was at its highest when the angle of attack was 8◦; further, flow separation occurred at angles exceeding 8◦, at which point the wind speed began to decrease. The results of the mock-up test demonstrated that the time required to reduce the concentration of fine particles in the indoor air was 120 s shorter when the windcatcher was installed than when it was not, which indicating that the time to reduce particles represents a 37.5%reduction. These results can be seen as reducing the consumption of ventilation in the building because the natural ventilation efficiency is increased.

Keywords: windcatcher louver; building ventilation efficiency; indoor ; computational

1. Introduction An increasing number of people in the modern world spend as much as 80% of their time indoors; therefore, the quality of the air they breathe should be high [1]. According to the World Health Organization, approximately 40% of the occupants in buildings worldwide experience health problems caused by contaminated indoor air [2] and the National Institute for Occupational Safety and Health in the United States has announced that ‘lack of ventilation’ is responsible for 52% of the contamination found in indoor air [3]. An effective method for improving the air quality in a building is to increase the performance of its ventilation system, which helps dilute the contaminants in indoor air, such as fine particles and bioaerosols, with an inflow of fresh air. Because natural ventilation in a building is based on the indoor–outdoor pressure differential, wind pressure, and gravity, a high ventilation efficiency is difficult to achieve if there is a neutral zone in which no inflow or outflow of air occurs. However, if a building receives wind from outside or if the difference in the temperature inside and outside the building is large, a high ventilation efficiency can be achieved. In addition, if the windows are not designed to support cross ventilation, the possibility of wind-based ventilation is eliminated, which further decreases the ventilation efficiency [4]. However, the natural ventilation rate (5.14 ACH; ) is approximately 40% higher than the ventilation rate of an system (3.02 ACH) when the outdoor environment is excellent (pressure differential, wind pressure). Further, when natural ventilation is utilized,

Energies 2020, 13, 4459; doi:10.3390/en13174459 www.mdpi.com/journal/energies Energies 2020, 13, x FOR PEER REVIEW 2 of 21

EnergiesHowever,2020, 13, 4459 the natural ventilation rate (5.14 ACH; air changes per hour) is approximately2 40% of 19 higher than the ventilation rate of an air conditioning system (3.02 ACH) when the outdoor environmentbuilding energy is excellent can be e ff(pressureectively saveddifferential, [5]. In wind other pressure). words, applying Further, natural when ventilationnatural ventilation efficiency is utilized, building energy can be effectively saved [5]. In other words, applying natural ventilation enhancement technology to buildings without an external environment is a manner in which building efficiency enhancement technology to buildings without an external environment is a manner in energy can be saved. which building energy can be saved. Furthermore, poorly designed natural ventilation systems installed in buildings may negatively Furthermore, poorly designed natural ventilation systems installed in buildings may negatively affect the health of the occupants, due to the accumulation of harmful substances caused by the reduced affect the health of the occupants, due to the accumulation of harmful substances caused by the ventilation efficiency [6]. Therefore, the efficiency of natural ventilation systems should be improved reduced ventilation efficiency [6]. Therefore, the efficiency of natural ventilation systems should be to minimize the potential for health problems. improved to minimize the potential for health problems. However, natural ventilation exhibits a limitation of lower efficiency than mechanical ventilation. However, natural ventilation exhibits a limitation of lower efficiency than mechanical To compensate for the low efficiency of natural ventilation, mechanical ventilation should be ventilation. To compensate for the low efficiency of natural ventilation, mechanical ventilation should considerably increased, which increases building energy consumption. If the natural ventilation be considerably increased, which increases building energy consumption. If the natural ventilation efficiency can be increased to produce an effect similar to that of mechanical ventilation, building efficiency can be increased to produce an effect similar to that of mechanical ventilation, building energy consumption can be reduced by approximately 30% [7]. energy consumption can be reduced by approximately 30% [7]. An airfoil is a two-dimensional airplane wing-shaped section [8]. While several studies have An airfoil is a two-dimensional airplane wing-shaped section [8]. While several studies have applied airfoil shapes to automobiles or systems, such architecture is rarely found in real applied airfoil shapes to automobiles or wind power systems, such architecture is rarely found in real life [9–13]. Examples include a study conducted by Liu et al. who installed a general windcatcher life [9–13]. Examples include a study conducted by Liu et al. who installed a general windcatcher louver on the roof of a building to analyze the corresponding pressure distribution and air currents [14]. louver on the roof of a building to analyze the corresponding pressure distribution and air currents Kang and Lee conducted a wind tunnel test and computational fluid dynamics (CFD) analysis of a [14]. Kang and Lee conducted a wind tunnel test and computational fluid dynamics (CFD) analysis louver-type vent installed on the roof of a factory building [7]. Chiang et al. conducted a mock-up test of a louver-type vent installed on the roof of a factory building [7]. Chiang et al. conducted a mock- and experimented with changing the ventilation flowing into a room by varying the width and length up test and experimented with changing the ventilation flowing into a room by varying the width of a horizontal louver mounted in a window [15]. However, thus far, to the best of our knowledge, and length of a horizontal louver mounted in a window [15]. However, thus far, to the best of our no study has employed an airfoil louver as a windcatcher. knowledge, no study has employed an airfoil louver as a windcatcher. The effect of applying a simple right-angled louver on natural ventilation and airflow has been The effect of applying a simple right-angled louver on natural ventilation and airflow has been studied; however, the effect of an airfoil-shaped louver on the natural ventilation efficiency has not studied; however, the effect of an airfoil-shaped louver on the natural ventilation efficiency has not been studied thus far. In other words, this study is the first to utilize an airfoil-shaped louver for been studied thus far. In other words, this study is the first to utilize an airfoil-shaped louver for improving airflow speed [14,16]. improving airflow speed [14,16]. In the current study, the performance of an airfoil-type windcatcher louver designed to increase In the current study, the performance of an airfoil-type windcatcher louver designed to increase the efficiency and performance of a natural ventilation system was evaluated. First, the optimal angle the efficiency and performance of a natural ventilation system was evaluated. First, the optimal angle of the airfoil was determined via a CFD simulation. Then, a mock-up test was conducted to evaluate of the airfoil was determined via a CFD simulation. Then, a mock-up test was conducted to evaluate the ventilation performance of the louver. A flowchart of the structure of the remainder of the paper is the ventilation performance of the louver. A flowchart of the structure of the remainder of the paper shown in Figure1. is shown in Figure 1.

Theory and Case Study of Airfoil Windcatcher Airfoil ⇩ CFD Modeling & Simulation Review the Distribution of Airflow and Pressure ⇩ Design and Built of Airfoil-type Windcatcher Louver & Mock-up Test Confirm Natural Ventilation Performance of Building ⇩ Results and Discussion ⇩ Conclusions

Figure 1. FlowFlow chart chart of of the the structure structure of the remainder of the paper.

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2. Literature Review 2. Literature Review 2.1. Windcatcher 2.1. Windcatcher Windcatchers are architectural elements that were used in ancient Egypt to naturally ventilate indoorWindcatchers air. These elements are architectural are still used elements in Middle that wereEastern used regions, in ancient including Egypt the to small naturally Arab ventilate states of indoorthe Persian air. These Gulf, such elements as Dubai, are still Pakistan, used in and Middle Afgh Easternanistan. regions,Windcatchers including can be the categorized small Arab as states one- ofdirectional, the Persian two-directional, Gulf, such as Dubai,and multidirectional, Pakistan, and Afghanistan.depending on Windcatchersthe direction used can beto catch categorized the wind. as one-directional,They can be further two-directional, categorized and based multidirectional, on their design, depending i.e., whether on the they direction utilize used descending to catch the or wind.ascending They air can currents. be further Windcatchers categorized designed based on theirto use design, descending i.e., whether air currents they utilizecompress descending the air and or ascendinglower the room air currents. temperature. Windcatchers The top part designed of theto use descendingis installed in air a currentshigh place, compress such as thea , air and lowerand is the blocked .on all sides but The one, top partwhich of thehas toweran open is installed structure in to a highdraw place, in the such wind. as aThe chimney, wind andcoming is blocked through on the all sidesopen butside one, creates which a descending has an open air structure current to that draw falls in toward the wind. the The room wind center coming and throughcools the the room. open A sidefew advantages creates a descending of this approach air current are that that a falls separate toward process the room is not center required and to cools cool thethe room.incoming A few air advantagesand the cooling of this efficiency approach incr areeases that with a separate the speed process of the is not descending required toair cool current the incoming[13,17]. air and the cooling efficiency increases with the speed of the descending air current [13,17].

2.2.2.2. AirfoilAirfoil AsAs shownshown inin FigureFigure2 2[ [18],18], anan airfoilairfoil resemblesresembles aa two-dimensionaltwo-dimensional sectionsection shapedshaped asas anan airplaneairplane wingwing andand has a a streamlined streamlined shape shape that that includes includes a round a round leading-edge leading-edge and and a sharp a sharp trailing-edge. trailing-edge. The Themost most commonly commonly used used airfoils airfoils in inthe the United United States States are are those those utilized utilized by by the NationalNational AdvisoryAdvisory CommitteeCommittee forfor AeronauticsAeronautics (NACA)(NACA) andand ClarkClark YY [[19–21];19–21]; however,however, otherother airfoilsairfoils areare alsoalso utilized,utilized, suchsuch asas thethe low-speedlow-speed ultralightultralight AircraftAircraft (ULM)(ULM) wing,wing, airliner,airliner, propellerpropeller blade,blade, andand supersonicsupersonic interceptorinterceptor shapes,shapes, whichwhich areare depicteddepicted in in Figure Figure3 [322 [22–29].–29].

Energies 2020, 13, x FOR PEER REVIEW FigureFigure 2.2. BasicBasic conceptconcept ofof anan airfoilairfoil [[13].13]. 4 of 21

Low-speed ULM (1 m) Airliner (8 m)

Propeller blade (15 cm) Supersonic interceptor (2 m)

Figure 3. Cont.

Blackbird (6 cm) Turbofan blade (80 cm)

Dolphin flipper fin (10 cm) Turbine blade (8 cm)

Figure 3. Various airfoil shapes [22–29].

Most existing airfoils help increase the sub-atmospheric pressure by changing the air flow of the leading edge via a slat. In such airfoils, air is blown from the leading edge at high pressure toward the tailing edge along the upper surface until it is drawn into the vent at the corner of the tailing edge. The addition of an air current on the upper surface of the airfoil can increase the sub-atmospheric pressure on the top surface even at low pressures. In contrast, the Co-Flow Jet (CFJ) Airfoil proposed by Lefebvre et al. [30] changed the aerodynamic characteristics of an airfoil without using a slat. This configuration is depicted in Figure 4.

Figure 4. Operating principles of the CFJ Airfoil [30].

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Low-speedLow-speed ULM ULM (1 (1 m) m) Airliner Airliner (8 (8 m) m)

Energies 2020, 13, 4459 4 of 19 PropellerPropeller blade blade (15 (15 cm) cm) Supersonic Supersonic interceptor interceptor (2 (2 m) m)

BlackbirdBlackbird (6 (6 cm) cm) Turbofan Turbofan blade blade (80 (80 cm) cm)

DolphinDolphin flipper flipper fin fin (10 (10 cm) cm) Turbine Turbine blade blade (8 (8 cm) cm)

Figure 3. Various airfoil shapes [22–29]. FigureFigure 3. 3. Various Various airfoil airfoil shapes shapes [22–29]. [22–29]. Most existing airfoils help increase the sub-atmospheric pressure by changing the air flow of the MostMost existing existing airfoils airfoils help help incr increaseease the the sub-atmospheric sub-atmospheric pressure pressure by by changing changing the the air air flow flow of of the the leading edge via a slat. In such airfoils, air is blown from the leading edge at high pressure toward the leadingleading edge edge via via a a slat. slat. In In such such airfoils, airfoils, air air is is blown blown from from the the leading leading edge edge at at high high pressure pressure toward toward tailing edge along the upper surface until it is drawn into the vent at the corner of the tailing edge. thethe tailing tailing edge edge along along the the upper upper surface surface until until it it is is draw drawnn into into the the vent vent at at the the corner corner of of the the tailing tailing edge. edge. The addition of an air current on the upper surface of the airfoil can increase the sub-atmospheric TheThe addition addition of of an an air air current current on on the the upper upper surfac surfacee of of the the airfoil airfoil can can increase increase the the sub-atmospheric sub-atmospheric pressure on the top surface even at low pressures. In contrast, the Co-Flow Jet (CFJ) Airfoil proposed pressurepressure on on the the top top surface surface even even at at low low pressures. pressures. In In contrast, contrast, the the Co-Flow Co-Flow Jet Jet (CFJ) (CFJ) Airfoil Airfoil proposed proposed by Lefebvre et al. [30] changed the aerodynamic characteristics of an airfoil without using a slat. byby Lefebvre Lefebvre et et al. al. [30] [30] changed changed the the aerodynamic aerodynamic characteristics characteristics of of an an airfoil airfoil without without using using a a slat. slat. This This This configuration is depicted in Figure4. configurationconfiguration is is depicted depicted in in Figure Figure 4. 4.

Figure 4. Operating principles of the CFJ Airfoil [30].

2.3. Clark Y Airfoil

The Clark Y airfoil was designed by Virginius E. Clark in 1922 and is now widely used in the design of general-purpose aircraft as it has a simple design with a flat floor. A Clark Y airfoil has a FigureFigure 4. 4. Operating Operating principles principles of of the the CFJ CFJ Airfoil Airfoil [30]. [30]. maximum thickness of 11.7% and a camber of 3.4% at 28% and 42% of the chord length, respectively.

The cross section, lift, and drag coefficients of a Clark Y airfoil are shown in Figure5, and the X and Y coordinates of various points on a Clark Y airfoil are listed in Table1. Ideally, the blade size, tip speed ratio, etc. of an airfoil should be based on the Reynolds number; however, this is typically neglected and a value of NRe = 100,000 is employed instead. The lift of a blade depends on the angle of attack, which is based on the relative direction of the wind, current length of the blade, and line angle. A Clark Y airfoil achieves its maximum output when the angle of attack is set to 8◦, and although the specifics of the various types vary, no significant errors arise if the lift coefficient is set to CL = 1 and the angle of attack is set in the range 4–6◦ [12]. If the angle of attack exceeds 8◦, flow separation may occur along with a rear vortex, which will disrupt the flow of the air current.

Energies 20202020,, 1133,, x 4459 FOR PEER REVIEW 55 of of 20 19 Height Height [ratio]

Length [ratio]

(a) (b)

Figure 5 5.. CrossCross-section,-section, lift, lift, and and drag drag coefficients coefficients of ofa Clark a Clark Y airfoil Y airfoil (a) Cross (a) Cross section section of Clark of Clark-Y,-Y, (b) (b) Clark-Y lift and drag coefficientClark [12-Y]. lift and drag coefficient [12].

TableTable 1. DataData describing describing a Clark Y airfoil [12]. [12].

Y [%] Y [%] X [%] X [%] UpUpperper Bottom Bottom 0.00 0.003.50 3.50 3.50 3.50 1.25 1.255.45 5.45 1.93 1.93 2.50 2.506.50 6.50 1.47 1.47 5.00 5.007.90 7.90 0.93 0.93 7.50 7.508.85 8.85 0.63 0.63 10.00 10.009.60 9.60 0.42 0.42 15.00 15.0010.68 10.68 0.15 0.15 20.00 20.0011.36 11.36 0.00 0.00 30.00 11.70 0.00 30.00 11.70 0.00 40.00 11.40 0.00 40.00 11.40 0.00 50.00 10.52 0.00 50.00 60.0010.52 9.15 0.00 0.00 60.00 70.009.15 7.35 0.00 0.00 70.00 80.007.35 5.22 0.00 0.00 80.00 90.005.22 2.80 0.00 0.00 90.00 95.002.80 1.49 0.00 0.00 95.00 100.001.49 0.12 0.00 0.00 100.00 0.12 0.00 The airfoil-type windcatcher evaluated in this study was a Clark Y airfoil designed to be suitable for The airfoil-type windcatcher evaluated in this study was a Clark Y airfoil designed to be suitable openings, such as those in windows. The designed airfoil helped increase the size of the sub-atmospheric for openings, such as those in windows. The designed airfoil helped increase the size of the sub- pressure region by allowing air to be ejected from its top, which then flows along its surface. atmospheric pressure region by allowing air to be ejected from its top, which then flows along its surface.3. Simulation

3.3.1. Simulation CFD Analysis Conditions A CFD analysis using the Star-CCM+ (ver.13.03) software suite developed by CD-Adapco (Melville, 3.1. CFD Analysis Conditions NY, USA) was employed to assess the natural ventilation performance of the designed airfoil when usedA as CFD a windcatcher analysis louver. using the A K-epsilon Star-CCM+ model (ver.13.03) served as software a turbulence suite model developed as it exhibits by CD a low-Adapco error (rateMelville, even NY for USA relatively) was employed large models to assess due tothe its natural support ventilation for tetra gridsperformance in indoor–outdoor of the designed air current airfoil when used as a windcatcher louver. A K-epsilon model served as a turbulence model as it exhibits a low error rate even for relatively large models due to its support for tetra grids in indoor–outdoor air current analyses [7,14]. The following three-dimensional steady-state incompressible flow equations [15] were used in the analysis:

Energies 2020, 13, 4459 6 of 19 analyses [7,14]. The following three-dimensional steady-state incompressible flow equations [15] were used in the analysis: ∂u i = 0 (1) ∂xi ! ∂   ∂ ∂k ρkuj = αkµe f f + Gk + Gb ρ (2) ∂xi ∂xj ∂xj − where x: direction of flow, u: velocity (m/s), ρ: density (kg/m3), k: turbulent flow energy (m2/s2), µ: viscosity coefficient (Pa s), µ : the value of effective permeability, Gk: variable by mean velocity, · eff Gb: variable by buoyancy, ε: turbulent kinetic energy dissipation rate (m2/s2) and i, j: vector of flow. The parameters used in the CFD analysis to determine the changes in the pressure and wind speed around the airfoil are listed in Table2. The base size of the mesh was set to 0.01 m and the target size was set to 50%, which translates to a minimum step size of 0.005 m and is sufficiently small to accommodate the target model used in the simulation. The grid was configured as a polyhedral mesh to facilitate three-dimensional analyses, and the inlet value was set to 3.6 m/s, which is the average wind speed measured at Seoul in 2017. The ‘K-epsilon Turbulence’ model was used to simulate the vertical louver to analyze the variation in airflow corresponding to the installation angle. The ‘K-omega Turbulence’ model was used to simulate the horizontal louver to analyze the variation in airflow corresponding to the variation in the angle of the Clark Y airfoil louver.

Table 2. Simulation design.

Item Settings Space Three Dimensional Mesh Polyhedral Mesh Base size 0.01 m Mesh Size Target size 50% (0.005 m) Time Analysis of windcatcher louver by angle Steady Fluid state Air Flow Segregated Flow Viscosity Turbulent Horizontal louver: K-epsilon Turbulence Reynolds-turbulent flow Vertical louver: K-omega Turbulence

3.2. CFD Modeling

3.2.1. Installation Angle of the Vertical Louver The variation in airflow corresponding to the installation angle of the vertical louver was analyzed. For the angle of the louver, an additional 45◦ was considered along with the generally installed 90◦. Three analyses, including the base model, were conducted. The base model is a general window without louvers. The building model considered for the analyses is shown in Figure6, and the wind speed was set at 3.6 m/s, the average wind speed in 2018 in Seoul, South Korea. The modeling of the installation angle of the louver is shown in Figure7. Energies 2020, 13, 4459 7 of 19 Energies 2020, 13, x FOR PEER REVIEW 7 of 21 Energies 2020, 13, x FOR PEER REVIEW 7 of 21

Figure 6. Window modeling for simulation analysis. Figure 6. WindowWindow modeling for simulation analysis.

(a) Base model

(b) Louver installed at 90°

(c) Louver installed at 45°

Figure 7. ModelingModeling of of the the installation angl anglee setting applied to simulation. 3.2.2. Clark Y Airfoil Shaped Horizontal Louver 3.2.2. Clark Y Airfoil Shaped Horizontal Louver As the CFD analysis was based on the wind speed recorded in Seoul in 2017, the louver was As the CFD analysis was based on the wind speed recorded in Seoul in 2017, the louver was installed with the leading edge facing toward the west, which was the main direction of the wind in installed with the leading edge facing toward the west, which was the main direction of the wind in 2017, and the length of the cord was set to 220 mm. Even though the characteristics of a Clark Y airfoil 2017, and the length of the cord was set to 220 mm. Even though the characteristics of a Clark Y airfoil vary depending on the shape, performance that is almost optimal can be achieved without a large vary depending on the shape, performance that is almost optimal can be achieved without a large error if the lift coefficient is CL = 1 and the angle of attack is in the range 4–6 [13]. In the simulation, error if the lift coefficient is CL = 1 and the angle of attack is in the range 4–6°◦ [13]. In the simulation, the angle of attack was set to 0, 1, 2, 4, and 8 for comparison purposes (Figure8). the angle of attack was set to 0, 1, 2, 4, and 8°◦ for comparison purposes (Figure 8). A total of 327,841 cells were generated in the meshing phase during modeling. Each cell comprised tetrahedral cells (12), hexahedral cells (5480), wedge cells (210), pyramid cells (8), and polyhedral cells (322,131). Interior faces were generated into 1,878,532 cells, which exhibited triangular (93,022), quadrilateral (567,154), and polygonal (1,218,356) shapes. As shown in Table 3, through the validation function in the Star-CCM+, it was confirmed that more than 99.9% of faces are valid.

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(a) (b) (c)

(d) (e)

FigureFigure 8. Diagrams 8. Diagrams showing showing the the angles angles used used in thein the simulation. simulation. (a )(a 0)◦ ,(0°,b ()b 1)◦ 1°,,(c )(c 2)◦ 2°,,(d ()d 4) ◦4°,,(e ()e 8) ◦8°..

A total of 327,841 cells were generatedTable 3. Mesh in the validation meshing diagnostic phase during result. modeling. Each cell comprised tetrahedral cells (12), hexahedral cells (5480), wedge cells (210), pyramid cells (8), and polyhedral Face Validity cells (322,131). Interior faces were generated into 1,878,532 cells, which exhibited triangular (93,022), quadrilateral (567,154), and polygonal0.80 (1,218,356) <= , < 0.90 shapes. As 0.03% shown in Table3, through the validation function in the Star-CCM+, it was confirmed0.90 <= , < 0.95 that more than 0.021% 99.9% of faces are valid. 0.95 <= , < 1.00 0.036% Table 3. Mesh validation diagnostic result. 1.00 99.913% Face Validity 4. Mock-Up Test 0.80 <=, < 0.90 0.03% 0.90 <=, < 0.95 0.021% 4.1. Design and Built of the Windcatcher0.95 Louver<=, < 1.00 0.036% The Clark Y airfoil in this study was1.00 a maximum 99.913%of 1200 mm long, 220 mm wide, and 30 mm high, which allowed it to fit into the window used in the mock-up test. The schematic of the external 4. Mock-Upstructure of Test the windcatcher louver is shown in Figure 9, while the interior and the direction of the flow channel are shown in Figure 10. The high-pressure air ejected from the vent of the windcatcher 4.1. Design and Built of the Windcatcher Louver louver flows toward the tailing edge along the upper surface, thereby increasing the area of the sub- atmosphericThe Clark Y pressure airfoil in formation this study region. was a maximum of 1200 mm long, 220 mm wide, and 30 mm high, which allowed it to fit into the window used in the mock-up test. The schematic of the external structure of the windcatcher louver is shown in Figure9, while the interior and the direction of the flow channel are shown in Figure 10. The high-pressure air ejected from the vent of the windcatcher louver flows toward the tailing edge along the upper surface, thereby increasing the area of the sub-atmospheric pressure formation region.

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(a) (a)

(b) (b)

(c) (c) Figure 9. Clark Y airfoil windcatcher: (a) cross section, (b) overall shape of the windcatcher, and (c) FigurepressureFigure 9.9. distribution. ClarkClark Y Yairfoil airfoil windcatcher: windcatcher: (a) cross (a) cross section, section, (b) overall (b) overall shape shapeof the ofwindcatcher, the windcatcher, and (c) andpressure (c) pressure distribution. distribution.

(a) (b) (c) (a) (b) (c) FigureFigure 10. 10.Internal Internal shape shape of the of airfoilthe airfoil and and the correspondingthe corresponding air flow air flow patterns. patterns. (a) Overview (a) Overview of airflow, of Figure 10. Internal shape of the airfoil and the corresponding air flow patterns. (a) Overview of (b) Airflow insideairflow, the louver, (b) Airflow (c) Airflow inside on the the louver, louver (c surface.) Airflow on the louver surface. airflow, (b) Airflow inside the louver, (c) Airflow on the louver surface. 4.2.4.2. Mock-Up TestTest 4.2. Mock-Up Test TwoTwo mock-up mock-up test test rooms rooms were were constructed constructed in Seoul, in SouthSeoul, Korea,South toKorea, analyze to the analyze natural the ventilation natural performanceventilationTwo mock-up performance of the windcatchertest roomsof the were louver.windcatcher constructed The roomslouv iner. were Seoul,The identical,rooms South wereKorea, and identical, each to analyze had dimensionsand the each natural had of 2500dimensionsventilation mm 2500ofperformance 2500 mm mm2500 × 2500of mm.the mm windcatcher The × 2500 roof mm. and louv wallsThe er.roof of The theand setup roomswalls were ofwere the constructed setupidentical, were of andconstructed sandwiched each had of × × panelssandwicheddimensions 100 mm ofpanels 2500 thick, mm100 and ×mm a2500 window thick, mm and× with2500 a dimensionswindmm. owThe withroof of and 2000dimensions walls mm of 2000 ofthe 2000 setup mm mm waswere × installed 2000constructed mm in was the of × south-facinginstalledsandwiched in the wallpanels south-facing of each100 mm room. wallthick, The of specificationsandeach a room. wind owThe of withthespecifications rooms dimensions are summarizedof theof 2000rooms mm in are Table × summarized 20004. mm was in Tableinstalled 4. in the south-facing wall of each room. The specifications of the rooms are summarized in Table 4.

Energies 2020, 13, 4459 10 of 19

Table 4. Specifications of the mock-up rooms.

Parameter Contents Height 2.5 m Number of Floors 1st floor Building Direction facing south Floor Height 2.4 m Room 1 6.25 m2 Floor Area (12.5 m2) Room 2 6.25 m2 Room 1 no airfoil present Envelope of Roof Room 2 airfoil present

Windcatcher louvers were only installed in Room 2 at a location 50 mm away from the top and bottom of the window to facilitate an efficient flow of outside air and to compare the ventilation performance without (Room 1) and with (Room 2) louvers. During the tests, the concentration of fine particles and the air current, temperature, and were measured. The outside wind direction was set as either from the west (incidence angle of 0◦) or south (incidence angle of 90◦), depending on the test conducted. These wind directions correspond to the prevailing wind directions in Seoul, South Korea, and the building orientation was such that the south wind with an incidence angle of 90◦ flowed in a direction perpendicular to the wall and directly into the window. The measurement methods and a summary of the results are provided in Tables4 and5; Figure 11 shows the plan and perspective view of the mock-up rooms. Table6 lists the measurement instruments used in the tests.

Table 5. Experimental method and location of the windcatcher.

Wind Flow Experiment Number Room Number Windcatcher Louver Wind Direction 3.5 m/s 1 0◦ 1 not present 3.5 m/s 2 90◦ 3.5 m/s 3 0◦ 2 present 3.5 m/s 4 90◦

The purpose of the tests was to measure the time required to reduce the concentration of contaminants in the air with and without the windcatcher. After the concentration of fine particles in the air in the mock-up room was set to approximately 1000 µg/m3, the window was opened in each room and the time required to reach a concentration of 30 µg/m3 was measured. The test was conducted as four separate experiments to compare the results of different configurations; the wind speed was set to 3.6 m/s for all tests. The direction of the wind was from the west (0◦) in Experiments 1 and 3, and from the south (90◦) in Experiments 2 and 4. The windcatcher was not used in Experiments 1 and 3 but was present in Experiments 2 and 4 (Figure 12). Energies 2020, 13, x FOR PEER REVIEW 10 of 21

Windcatcher louvers were only installed in Room 2 at a location 50 mm away from the top and bottom of the window to facilitate an efficient flow of outside air and to compare the ventilation performance without (Room 1) and with (Room 2) louvers. During the tests, the concentration of fine particles and the air current, temperature, and humidity were measured. The outside wind direction was set as either from the west (incidence angle of 0°) or south (incidence angle of 90°), depending on the test conducted. These wind directions correspond to the prevailing wind directions in Seoul, South Korea, and the building orientation was such that the south wind with an incidence angle of 90° flowed in a direction perpendicular to the wall and directly into the window. The measurement methods and a summary of the results are provided in Tables 4 and 5; Figure 11 shows the plan and perspective view of the mock-up rooms. Table 6 lists the measurement instruments used in the tests. The purpose of the tests was to measure the time required to reduce the concentration of contaminants in the air with and without the windcatcher. After the concentration of fine particles in the air in the mock-up room was set to approximately 1000 μg/m3, the window was opened in each room and the time required to reach a concentration of 30 μg/m3 was measured. The test was conducted as four separate experiments to compare the results of different configurations; the wind speed was set to 3.6 m/s for all tests. The direction of the wind was from the west (0°) in Experiments 1 and 3, and from the south (90°) in Experiments 2 and 4. The windcatcher was not used in Experiments 1 and 3 but was present in Experiments 2 and 4 (Figure 12.).

Table 4. Specifications of the mock-up rooms.

Parameter Contents Height 2.5 m Number of Floors 1st floor Building Direction facing south Floor Height 2.4 m Room 1 6.25 m2 Floor Area (12.5 m2) Room 2 6.25 m2 Room 1 no airfoil present Envelope of Roof Room 2 airfoil present Energies 2020, 13, 4459 11 of 19 Energies 2020, 13, x FOR PEER REVIEW 11 of 21

Wind Flow Experiment Number Room Number Windcatcher Louver Wind Direction 3.5 m/s 1 0° 1 not present 3.5 m/s 2 90° 3.5 m/s 3 0° 2 present 3.5 m/s 4 90°

Table 6. Specifications of the measurement equipment used in the tests.

Particulate Meter Airflow Measurement Measurement Item (a) Thermo-hygrometer (b) Measurement Instrument Instrument NameFigureFigure of the 11. 11. Equipment PlanPlan and and perspective perspective TSI DUSTTRAK view view of of 8530the the mock-up mock-up SATOrooms. rooms. SK-L200T (a ()a )mock-up mock-up plan plan KIMO view, view, AMI310, (b (b) )louver louver SOM900 Concentration 0.001– Temperature Temperature applicationapplication location. location. −15–65 20–80 (mg/m3) 400 (°C) (°C) TableTable 6. Specifications 5. Experimental of themethod measurement and location equipment of the windcatcher. used in theHumidity tests. Range 0–100% RH Humidity (%RH) Particulate Meter Airflow Measurement Measurement Item Particle Size (μm) 0.1–10 Thermo-Hygrometer10–99.9 Measurement Instrument (%RH) Wind SpeedInstrument 0.00–5.00 Name of the Equipment TSI DUSTTRAK 8530 SATO SK-L200T KIMO(m/s) AMI310, SOM900 Concentration Temperature Temperature ±3% of the Measuring 3 0.001–400 0.115–65 °C at −9.9 Temperature 20–80 (mg/m ) (◦C) − (◦C) leading value instrument Temperature to 65.0 °C, 1 Humidity(°C) Range 0–100%±0.25°C RH specification (%RH) Particle Size Humidity(°C) °C at −10 °C or 0.1–10 10–99.9 Humidity (µm) (%RH) Wind Speed ±0.5% of factory set point less 0.00–5.00±1.8%RH (%RH)(m/s) Measuring Accuracy internal flow controlled instrument 0.1% RH at 3% of the (Flow Accuracy) Temperature ± specification leading value 0.115.0◦C at to9.9 99.0% to (◦C) ±3% of the TemperatureHumidity − Wind Speed 0.25◦C 65.0 C, 1 C at ± 0.5% of factory set point ( C) RH,◦ 1%◦ RH at leading value ± ◦ (%RH) Humidity(m/s) Accuracy internal flow controlled 10 ◦C or less 1.8%RH − less than (%RH) ±±0.05 m/s (Flow Accuracy) 0.1% RH15.0% at 15.0 to 3% of the Humidity Wind Speed ± 99.0% RH, 1% RH leading value (%RH) (m/s) at less than 15.0% 0.05 m/s ±

(a) (b)

Figure 12. Setup of the mock-up experiment. ( (aa)) measuring measuring device, device, ( (b)) louver louver application.

5. Results and Discussion

Energies 2020, 13, 4459 12 of 19

5. Results and Discussion

5.1. CFD Simulation Results

5.1.1. Installation Angle of the Vertical Louver The variation in airflow according to the installation angle of the vertical wind-up louver was analyzed. The analysis results helped verify that when a collection louver was installed, eddy currents were generated and adversely affected the airflow into the room. As the airflow collides with the louver and returns, a back-pressure gradient is generated, resulting in vortex and wake. Eventually, the flow separation occurred, and the velocity of the airflow entering the room further decreased. The same result was obtained even when the airflow speed decreased to 1/10th the existing speed. The simulation results for the base model are shown in Figure 13, those obtained after lowering the airflow velocity are shown in Figure 14. These results demonstrate that the installation of additional louvers other than the Clark Y airfoil-shaped window frame has an adverse effect on improving airflow speed. Energies 2020, 13, x FOR PEER REVIEW 13 of 21

(a) Base model

(b) Louver installed at 90°

(c) Louver installed at 45°

Figure 13. Result of the installation angle setting simulation. (a) Base model, (b) Louver installed at Figure 13. Result of the installation angle setting simulation. (a) Base model, (b) Louver installed at 90°, (c) Louver installed at 45°. 90◦,(c) Louver installed at 45◦.

Energies 2020, 13, 4459 13 of 19 Energies 2020, 13, x FOR PEER REVIEW 14 of 21

(a) 3.6m/s west wind (b) 0.3m/s west wind

Figure 14. Wind speed change result. ( a) 3.6m/s 3.6m/s west wind ( b) 0.3m0.3m/s/s west wind.

5.1.2. Clark Y Airfoil Shaped Horizontal Louver The pressure distribution and variation in the air current caused by the Clark Y airfoil-typeairfoil-type windcatcher louver were analyzed to determine the optimaloptimal angle of attack for the louver. In this test, test, the angle of attack was set to 0, 1, 2, 4, 4, and and 8°, 8◦, and and the the area area of of the the sub-atmospheric sub-atmospheric pressure pressure formation and the wind speed were found to increase for largelarge anglesangles ofof attack.attack. However, at angles exceeding 88°,◦, flow flow separation separation occurred occurred and and a arear rear vortex vortex appeared. appeared. When When the the angle angle of attack of attack was was 0° and 0◦ and 8°, the 8◦, themaximum maximum wind wind speeds speeds were were approximately approximately 4.8 m/s 4.8 mand/s and5.7 m/s, 5.7 m respectively./s, respectively. In other In other words, words, the thearea area covered covered by the by thesub-atmospheric sub-atmospheric pressure pressure formation formation expanded expanded and and the thewind wind speed speed increased increased for forlarger larger angles. angles. As the angle of the louver increases, the negative pressure forming area (circle with a red dotted line) on the louver surface increases proportionally. In addition, as the negative-pressure-forming area increases, the wind speed increases (red square), whereas the positive-pressure-forming area increases at the lower end (Figure 15). Based on the results of this CFD study, the angle of attack to be applied to the mock-up louver was selected.

5.2. Mock-Up Test Results In the mock-up test, the concentration of fine particles in the air in the rooms was increased to approximately 1000 µg/m3. Then, the time required to reduce the concentration to 30 µg/m3 for various louver configurations and wind incidence angles was measured to determine the natural ventilation performance of the louver. The results of the test were as follows. In Experiment 1 (no windcatcher; wind incidence angle of 0◦), the time required to reduce the concentration of fine particles from 1001 to 29.9 µg/m3 was 6 min (360 s) (Figure 16). In Experiment 2 (no windcatcher; wind incidence angle 3 of 90◦), the time required to reduce the concentration of fine particles from 1007.3 to 30 µg/m was 5 min 20 s (320 s) (Figure 17). In Experiment 3 (windcatcher present; wind incidence angle of 0◦), the time required to reduce the concentration of fine particles from 999.9 to 30.5 µg/m3 was 5 min (300 s) (Figure 18). In Experiment 4 (windcatcher present; wind incidence angle of 90◦), the time required to reduce the concentration of fine particles from 1003 to 29.5 µg/m3 was 3 min 20 s (200 s) (Figure 19).

Energies 2020, 13, 4459 14 of 19

Energies 2020, 13, x FOR PEER REVIEW 15 of 21

(a) Pressure distribution at 0° angle of attack (b) Airflow and wind speed at 0° angle of attack

(c) Pressure distribution at 1° angle of attack (d) Airflow and wind speed at 1° angle of attack

(e) Pressure distribution at 2° angle of attack (f) Airflow and wind speed at 2° angle of attack

(g) Pressure distribution at 4° angle of attack (h) Airflow and wind speed at 4° angle of attack

Figure 15. Cont.

Energies 2020, 13, 4459 15 of 19

Energies 2020, 13, x FOR PEER REVIEW 16 of 21

(i) Airflow and wind speed at 4° angle of attack (j) Airflow and wind speed at 4° angle of attack

EnergiesEnergies 2020 2020, ,13 13, ,x x FOR FOR PEER PEERFigure REVIEW REVIEW 15. Analysis of the pressure distribution for different angles. 1717 of of 21 21

igure 15. Analysis of the pressure distribution for different angles.

As the angle of the louver increases, the negative pressure forming area (circle with a red dotted line) on the louver surface increases proportionally. In addition, as the negative-pressure-forming area increases, the wind speed increases (red square), whereas the positive-pressure-forming area increases at the lower end (Figure 15). Based on the results of this CFD study, the angle of attack to be applied to the mock-up louver was selected.

5.2. Mock-Up Test Results In the mock-up test, the concentration of fine particles in the air in the rooms was increased to approximately 1000 μg/m3. Then, the time required to reduce the concentration to 30 μg/m3 for various louver configurations and wind incidence angles was measured to determine the natural ventilation performance of the louver. The results of the test were as follows. In Experiment 1 (no windcatcher; wind incidence angle of 0°), the time required to reduce the concentration of fine Figure 16. Results of Experiment 1. particles from 1001 to 29.9 μg/mFigureFigure3 was 16. 16.6 min ResultsResults (360 of ofs) ExperimentExperiment (Figure 16). 1. 1. In Experiment 2 (no windcatcher; wind incidence angle of 90°), the time required to reduce the concentration of fine particles from 1007.3 to 30 μg/m3 was 5 min 20 s (320 s) (Figure 17). In Experiment 3 (windcatcher present; wind incidence angle of 0°), the time required to reduce the concentration of fine particles from 999.9 to 30.5 μg/m3 was 5 min (300 s) (Figure 18). In Experiment 4 (windcatcher present; wind incidence angle of 90°), the time required to reduce the concentration of fine particles from 1003 to 29.5 μg/m3 was 3 min 20 s (200 s) (Figure 19).

FigureFigure 17. 17. Results ResultsResults of of Experiment Experiment 2. 2.

FigureFigure 18. 18. Results Results of of Experiment Experiment 3. 3. Energies 2020, 13, x FOR PEER REVIEW 17 of 21

Figure 16. Results of Experiment 1.

Energies 2020, 13, 4459 16 of 19

Figure 17. Results of Experiment 2.

Figure 18. Results of Experiment 3. Energies 2020, 13, x FOR PEER REVIEW Figure 18. Results of Experiment 3. 18 of 21

FigureFigure 19. ResultsResults of of Experiment Experiment 4. 4.

TheThe times times required required to to reduce reduce the concentration concentration of fine fine particles in Experiments 1 and and 2 2 in in which which nono windcatcher windcatcher was was used used differed differed by 40 s, while th thoseose obtained obtained in in Experiments 3 3 and and 4 4 in in which which the the windcatcher was used differed differed by 1 min 40 s (100 s) (Table7 7).). InIn other other words, words, the the effect effect of the wind incidence angle was higher when the windcatcher was was installed.installed. When When the the results results of of Experiments Experiments 2 2 (no (no windcatcher) windcatcher) and and 4 4 (windcatcher) (windcatcher) were were compared, compared, thethe times times required required to to reduce reduce the the concentration concentration of of fine fine particles particles in inExperiments Experiments 2 and 2 and 4 were 4 were 5 min 5 min 20 s20 (320 s (320 s) and s) and 3 min 3 min and and 20 20 s s(200 (200 s), s), respectively, respectively, exhibiting exhibiting aa difference difference of of 120 120 s. These These results demonstratedemonstrate that that the the addition addition of of a a windcatcher windcatcher lo louveruver decreased decreased the the time time required required to to reduce reduce the the concentrationconcentration of of fine fine particles in indoor air by up to 37.5% (Tables 8 8 and and9 9as as well well as as Figure Figure 20 20).).

Table 7. Summary of the experimental results.

Wind Incidence Concentration of Particle Matter Windcatcher Time Angle PM10 Reduction Time 19:38:39 1001 μg/m3 Expt. 1 unapplied 0° 6 min (360 s) 19:44:39 29.9 μg/m3 23:20:16 1007.3 μg/m3 Expt. 2 unapplied 90° 5 min 20 s (320 s) 23:25:36 30 μg/m3 18:32:39 999.9 μg/m3 Expt. 3 applied 0° 5 min (300 s) 18:37:39 30.5 μg/m3 20:56:16 1003 μg/m3 Expt. 4 applied 90° 3 min 20 s (200 s) 20:59:36 29.5 μg/m3

Table 8. Effects of the incidence angle of the wind for different louver configurations.

Experiment Wind Incidence Particle Matter Time Difference to Reduce Windcatcher number Angle Reduction Time Particle Matter 1 0° 6 min (360 s) Unapplied 40 s 2 90° 5 min 20 s (320 s) 3 0° 5 min (300 s) Applied 100 s 4 90° 3 min 20 s (200 s) Energies 2020, 13, 4459 17 of 19

Table 7. Summary of the experimental results.

Wind Incidence Concentration Particle Matter Windcatcher Time Angle of PM10 Reduction Time 19:38:39 1001 µg/m3 Expt. 1 unapplied 0 6 min (360 s) ◦ 19:44:39 29.9 µg/m3 23:20:16 1007.3 µg/m3 Expt. 2 unapplied 90 5 min 20 s (320 s) ◦ 23:25:36 30 µg/m3 18:32:39 999.9 µg/m3 Expt. 3 applied 0 5 min (300 s) ◦ 18:37:39 30.5 µg/m3 20:56:16 1003 µg/m3 Expt. 4 applied 90 3 min 20 s (200 s) ◦ 20:59:36 29.5 µg/m3

Table 8. Effects of the incidence angle of the wind for different louver configurations.

Experiment Wind Incidence Particle Matter Time Difference to Windcatcher Number Angle Reduction Time Reduce Particle Matter 1 0 6 min (360 s) Unapplied ◦ 40 s 2 90◦ 5 min 20 s (320 s) 3 0 5 min (300 s) Applied ◦ 100 s 4 90◦ 3 min 20 s (200 s) Energies 2020, 13, x FOR PEER REVIEW 19 of 21 Table 9. Particulate matter reduction with or without a windcatcher louver. Table 9. Particulate matter reduction with or without a windcatcher louver.

Windcatcher Experiment Wind Incidence Particle Matter TimeTime Difference Difference to Windcatcher Experiment Wind Incidence Particle Matter Louver Number Angle Reduction Time toReduce Reduce Particle Matter Louver Number Angle Reduction Time Matter unapplied Expt. 2 90◦ 5 min 20 s (320 s) unapplied Expt. 2 90° 5 min 20 s (320 s) 2 min (120 s) applied Expt. 4 90◦ 3 min 20 s (200 s) 2 min (120 s) applied Expt. 4 90° 3 min 20 s (200 s)

Figure 20. Comparison of the ventilation performance for different configurations of windcatcher Figure 20. Comparison of the ventilation performance for different configurations of windcatcher louver. louver. 6. Conclusions 6. Conclusions In thisIn study this study a CFD a CFD simulation simulation and and mock-up mock-up te testst were were conducted conducted on a on Clark a Clark Y airfoil-type Y airfoil-type windcatcherwindcatcher louver louver that wasthat was designed designed to to improve improve thethe natural natural ventilation ventilation of buildings. of buildings. The results The of results of the studythe can study be can summarized be summarized as follows:as follows:

(a) In(a) the In the CFD CFD simulation, simulation, when when a separate a separate vertical louver vertical is installed louver outside is the installed window,outside eddy the currents were generated and adversely affected the airflow into the room. Therefore, the window, eddy currents were generated and adversely affected the airflow into the room. installation of additional vertical louvers other than the horizontal louvers of the Clark Y airfoil Therefore,has an the adverse installation effect on of im additionalproving the verticalairflow speed. louvers other than the horizontal louvers of the Clark(b) YIn airfoilthe CFD has simulation, an adverse the eareaffect covered on improving by the sub-atmospheric the airflow speed. formation on the top of the (b) In thelouver CFD simulation,and the maximum the areawind coveredspeed increased by the as sub-atmospheric the angle of attack increased formation from on 0, the 1, 2, top 4, of the louverand and 8°. the Maximum maximum wind wind speeds speed of 4.8 increasedm/s and 5.7 as m/s the were angle measured of attack at angles increased of 0° fromand 8°, 0, 1, 2, 4, respectively, which was identical to the results of a previous study [11] in which the maximum wind speed was achieved at an angle of 8°. (c) In the mock-up test, the natural ventilation performance was evaluated with and without a windcatcher louver for various wind incidence angles. The times required to reduce the concentration of fine particles for wind incidence angles of 0° and 90° and no louver differed by 40 s, while the times required for the same incidence angles when a windcatcher was present differed by 1 min 40 s. Based on these results, the effect of the incidence angle of the wind was found to be greater when a windcatcher was installed, which suggests that a windcatcher can improve the natural ventilation performance in a building. Improved natural ventilation efficiency in buildings can reduce electricity consumption [5]. Therefore, utilizing a windcatcher is considered to help save building energy. (d) The time required to reduce the concentration of fine particles without and with a windcatcher for a wind incidence angle of 90° were 5 min 20 s (320 s) and 3 min 20 s (200 s), respectively, exhibiting a difference of 120 s. In other words, the time required for the concentration of fine particles to be reduced was 37.5% shorter when the windcatcher was installed.

Energies 2020, 13, 4459 18 of 19

and 8◦. Maximum wind speeds of 4.8 m/s and 5.7 m/s were measured at angles of 0◦ and 8◦, respectively, which was identical to the results of a previous study [11] in which the maximum wind speed was achieved at an angle of 8◦. (c) In the mock-up test, the natural ventilation performance was evaluated with and without a windcatcher louver for various wind incidence angles. The times required to reduce the concentration of fine particles for wind incidence angles of 0◦ and 90◦ and no louver differed by 40 s, while the times required for the same incidence angles when a windcatcher was present differed by 1 min 40 s. Based on these results, the effect of the incidence angle of the wind was found to be greater when a windcatcher was installed, which suggests that a windcatcher can improve the natural ventilation performance in a building. Improved natural ventilation efficiency in buildings can reduce electricity consumption [5]. Therefore, utilizing a windcatcher is considered to help save building energy. (d) The time required to reduce the concentration of fine particles without and with a windcatcher for a wind incidence angle of 90◦ were 5 min 20 s (320 s) and 3 min 20 s (200 s), respectively, exhibiting a difference of 120 s. In other words, the time required for the concentration of fine particles to be reduced was 37.5% shorter when the windcatcher was installed.

The results of this study demonstrate that the Clark Y airfoil-type windcatcher louver is a practical solution for improving the performance of natural ventilation systems in buildings. This saves electrical energy consumption corresponding to mechanical ventilation utilized in buildings. According to a study conducted by Park et al. (2020), if the natural ventilation efficiency is increased, the consumption of building energy can be reduced by approximately 30%. Therefore, the present ventilation system is considered to not only improve , but also reduce the ventilation consumption energy of the building. However, this experiment was applied to mock-up to see a fragmentary aspect. Therefore, for a more accurate analysis, it is determined that an experiment that responds to changes in wind speed according to altitude by applying it to an actual building is necessary. In the future, the durability, long-term annual energy analysis, economic feasibility, and applicability of the proposed windcatcher will be investigated in detail and the concept will be extended to other types of buildings.

Author Contributions: All authors contributed equally. Conceptualization, Y.K.Y., M.Y.K., J.C.P.; Methodology, Y.K.Y., M.Y.K., Y.W.S., J.C.P.; Formal analysis, Y.K.Y., M.Y.K., Y.W.S., S.H.C., J.C.P.; Resources, Y.K.Y., Y.W.S., S.H.C., J.C.P.; Data curation, Y.K.Y., M.Y.K., Y.W.S., S.H.C., J.C.P.; Writing—original draft preparation, Y.K.Y., J.C.P.; Writing—review and editing, J.C.P.; Visualization, Y.K.Y., M.Y.K., S.H.C; Supervision, J.C.P.; Project administration, J.C.P.; Funding acquisition, J.C.P. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by Basic Science Research Program, through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2019R1A6A3A01095517), and by the Chung-Ang University Research Scholarship Grants in 2020. Conflicts of Interest: The authors declare no conflict of interest.

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