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ARTICLE IN PRESSG Model

Energyand Buildings xx (2012) xxxxxx

Contents lists available at SciVerse ScienceDirect

Energy and Buildings

j ournal homepage: www.elsevier .com/ locate /enbui ld

Highlights

Energy and Buildingsxx (2012)xxxxxxEmpirical study of a wind-induced natural ventilation tower under hot

andhumid climatic conditions

Lim Chin Haw, Omidreza Saadatian,M.Y. Sulaiman, SohifMat, Kamaruzzaman Sopian

Empirical study conducted on wind-induced ventilation tower in hot and humid climate. Air flow rates, air change rates and air speed

were analyzed. At external wind speed of0.1m/s, the wind tower extraction flow rates is 10,000m3/h. Average ACH for wind-induced

ventilation tower is 57 ACH and is above ASHRAE 62 standard requirement.
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Please cite this article in press as: L.C. Haw, et al., Empirical study of a wind-induced natural ventilation tower under hot and humid

climatic conditions, Energy Buildings (2012), http://dx.doi.org/10.1016/j.enbuild.2012.05.016

ARTICLE IN PRESSG ModelENB3745111

Energy and Buildings xxx (2012) xxxxxx

Contents lists available at SciVerse ScienceDirect

Energy and Buildings

journal homepage: www.elsevier .com/ locate /enbui ld

Empirical study ofa wind-induced natural ventilation tower under hot

and humid climatic conditions2

Lim Chin Haw, Omidreza Saadatian, M.Y. Sulaiman, SohifMat, Kamaruzzaman SopianQ13

SolarEnergyResearch Institute, Universiti KebangsaanMalaysia, Selangor,Malaysia4

5

a r t i c l e i n f o6

7

Article history:8

Received 12 January 20129

Received in revised form 22 March 20120

Accepted 18 May 2012

2

Keywords:3

Wind-induced natural ventilation tower4

Hot and humid climate5

Air changes per hour (ACH)6

Airflow rates7

a b s t r a c t

Stack ventilation and wind-induced ventilation are the two main methods for inducing natural venti-

lation. Stack ventilation by itselfcannot create enough air flow to achieve good indoor air quality forbuilding occupants under hot and humid climatic conditions. The low performance ofstack ventilation

in hot and humid climate isdue to the low temperature differences between indoor and outdoor temper-

ature ofa building. On the other hand, the wind-induced ventilation method performance is independent

oflow temperature difference. Therefore, it has potential use to improve the indoor air quality for build-

ings in the hot and humid climate. This paper examines the wind-induced natural ventilation tower

performs under hot and humid climate. The study reveals that the wind-induced ventilation tower has

higher extraction airflow rate comparing to other wind ventilators in the market. Analysis shows the

wind-induced natural ventilation tower can produce high air changes per hour (ACH) for indoor build-

ing environment in the hot and humid climate. Study results also show the wind-induced ventilation

towers extraction flow rate is 10,000m3/h at external wind velocity of 0.1 m/s. With the same exter-

nal wind velocity, it produces average of 57 ACH. The results of this study will be useful for designing

wind-induced natural ventilation tower in hot and humid climate.

2012 Elsevier B.V. All rights reserved.

1. Introduction8

Mechanical cooling systems in buildings are the main produc-9

ers of carbon dioxide emissions, which have negative impacts on0

environment and amplify global warming, particularly in hot cli-

mate [1]. Natural ventilation is an effective passive strategy to2

improve indoor air quality [2]. Natural ventilation method provides3

fresh air to a space and dilutes the indoor pollution concentra-4

tion [3]. The minimum standard for ventilation rate requirement5

is to dilute the odours and concentration of CO2 to an accept-6

able level. Building occupants will get enough supply of oxygen7

when the CO2 concentration is at an acceptable level [4]. Fig. 18

shows the dilution of pollutant concentration with ventilation9

rate. The higher the ventilation rate, the lower is the pollutant0concentration in the indoor environment. However, as the need

for ventilation rate increases, the energy load and demand also2

increase. Therefore, natural ventilation method is a better tool3

to reduce the energy cost in comparison to mechanical systems.4

Allard [4] suggested that natural ventilation is more cost-effective5

compared with the capital, maintenance and operational costs of6

Corresponding author. Tel.: +60 122018451; fax: +60 3 89214593.

E-mail address: [email protected](L.C. Haw).

mechanical systems. In addition, it also does not need any plant

room space [5].

There are mainly two fundamental principles of natural ven-

tilation; namely stack effect and wind driven ventilation [6]. The

stackeffects are caused by temperature differences between indoor

and outdoor of buildings, and it happens when the inside building

temperature is higher than the outside temperature. As the warm

indoor air rises and exits the building openings, it is replaced by

the cooler and denser air from below. Naghman et al. [6], observed

the stackeffect reduces when the temperature differencesbetween

the indoor and outdoor of buildings are small. In hot and humid

conditions, the temperature difference between the indoor and

outdoor temperature is low. Due to the low-temperature differ-

ence, thestackventilation methodis unableto createhigher airflow

to achieve good airchanges for the building occupants. Hughes and

Cheuk-Ming [7], discovered that wind driven ventilation provides

76% more internal ventilation than buoyancy effects. According

to Elmualim [8], natural ventilation using wind towers should

be exploited whenever possible particularly in the hot summer

months.

Wind-induced natural ventilation is based on pressure differ-

ences created by the wind. Walls and roof of a building have

influence over the airflow pattern around that building. The walls

which are facing the windward direction are compressed and thus

creating a positive pressure. On the contrary, the leeward wind

direction walls face a negative pressure or lower pressure caused

0378-7788/$ seefrontmatter 2012 Elsevier B.V. All rights reserved.

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2 L.C. Haw et al. / Energy and Buildings xxx (2012) xxxxxx

Fig. 1. Dilution of pollutant concentration with ventilation rate [5].

by higher air velocity. This pressure difference between the twoopposite points on the building geometry is the driven force of the

wind-induced natural ventilation strategy.

Wind towers or wind catchers are not common architectural

features in hot and humid regions. Most modern building designs

in hot and humid regions are not equipped with passive archi-

tectural features for improving natural ventilation except through

windowand door openings. The integration of wind-induced natu-

ralventilation towerdesign intobuildingdesign has the potentialto

induce air changes for the indoor building environment and thus

improve the indoor air quality for building occupants. Givoni [9]

states the wind-induced natural ventilation method could achieve

desirable air velocity in the indoor building environment. It will

help to improve the air changes and cooling effect for the building

occupants, especially in the hot and humid climate.

Beside wind towers, there are other architectural features,

which have been integrated into building designs that have signif-

icant influence on improving the indoor air quality. Some of these

architectural features that have proven to improve the indoor air

quality includes atriums [10], courtyards [11], wing walls [12] and

dome roofs [13].

One of the major architectural features that influence the per-

formance of the wind tower is the roof geometrys design of the

wind-induced natural ventilation tower itself. By and large, roof

is one of the most exposed parts of the building features to the

oncoming wind. The roof geometry or shape has great influence in

creating the behaviour of the airflow around buildings. The airflow

behaviourcreated bythe roof geometrycan beused to enhance nat-

uralventilation [1]. Thephenomenonat work aroundthe roof of the

wind-induced natural ventilation tower is known as the Bernoulli

Effect. The principle of Bernoulli Effect explains that when there

is an increase in the velocity of a fluid, it decreases its static pres-

sure. Due to this phenomenon, there is negative pressure at the

contraction of a Venturi Tube [14].

A cross-section of an airplane wing or airfoil has a half Venturi-

shape. If the airplane wing profile is inverted, it will create a

negative pressure atthe bottomof theroofprofilelevel.Fig.2 shows

a profile of a Venturi-shaped roof with positive pressure above and

negative or low pressure below the roof. Because of the negative

pressure and low-pressure at the bottom of the roof surface, air

will be sucked out of any opening at the top of the tower. Using

this idea, Venturi shaped roof geometry is designed for the wind-

induced natural ventilation towerin our study. Blocken et al.[2] and

Van Hooff etal. [15] in thetheir research projects imparted that the

Venturi shaped roof is effective in providing significant negative

pressure to induce air movement. Fig. 2 shows the experimen-

tal house with Venturi shaped roof geometry for its wind-induced

natural ventilation tower.

The following objective is the three main objectives of the

research:

(i) To analyze the ability of a wind-induced natural ventilation

tower forincreasing airmovement, airchanges perhour (ACH)

and air flow rate under hot and humid climatic conditions.

(ii) To evaluate the effectiveness of a wind-induced natural

ventilation tower against ASHRAE Standard 62 ventilation

requirement.

(iii) To explore the viability of the application of a wind-induced

natural ventilation tower on building under thehot andhumid

climatic conditions.

Fig. 2. Venturi shaped roof geometry and experimental house with wind-induced natural ventilation tower.
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L.C. Haw et al. / Energy and Buildings xxx (2012) xxxxxx 3

2. Researchmethodology2

There are numerous research methods in studying the wind-3

induced natural ventilation system. Those include: Reduced-scale4

atmospheric boundary layer wind tunnel experiments:5

(i) Numerical simulation with computational fluid dynamics6

(CFD).7

(ii) Reduced-scale water tank experiments.8(iii) Analytical.9

(iv) Semi empirical formulae and full-scale empirical methods.0

Full-scale empirical method is rare due to its time consuming

and high cost of measuringequipmentfor the full-scaleexperimen-2

talbuilding.AccordingtoVanHoof[15], the full-scalemeasurement3

method is very valuable in giving insight to the wind-induced4

natural ventilation study. This research undertook to build a full-5

scaleexperimental building with a wind-induced ventilation tower6

for onsite measurement and analysis. A full-scale model of wind-7

induced ventilation tower was built at the Green Technology8

Innovation Park at National University of Malaysia,Bangi, Selangor,9

Malaysia (Latitude North 2.93537 and East Longitude 101.78183)0

as shown in Fig. 2. A data acquisition system was installed at theexperimental building. All data from the sensors were logged into2

thedatalogger every 10min intervalsfor 24h perday from October3

2010 to January 2011. The measurement parameters, details of4

the equipment and sensors of the data acquisition system will5

be described in the following section of this paper. Subsequently,6

the empirical data is analyzed and the results are used to validate7

against FloVent simulation results. FloVent is a ComputationalFluid8

Dynamics (CFD) simulation software used in the simulation of the9

experimental house with wind-induced natural ventilation tower0

and without the wind-induced natural ventilation tower.

3. The experimental housewithwind-induced natural2

ventilation tower3

The experimental house is a two-storey detached building with4

a flat concrete roof. The total volume space of the experimental5

house is 232.76m3. The ground floor is an open area concept with6

a concrete staircase that leads to the first floor. The first floor is7

raised at 3.2m on 4 pillars above the ground level. This open area8

concept allows a free flowing of air movement in the interior of the9

building.0

Fig. 3 shows the ground and first floor dimension with 11.25 m

lengthby 5.55 m width and3.2 m height. Thewind-induced natural2

ventilation tower is built on the top of the experimentalhouse.The3

experimental house is orientated along the North-South axis. The4

front facadeof the experimentalhouse is facing southern direction.5

The total height of the wind-induced natural ventilation tower is6

2.81m with a Venturi-shaped roof geometry of 5.56m width by7

5.20m length as shown in Fig. 4.8

3.1. Data acquisition and monitoring system9

The schematic diagram of the data acquisition and monitoring0

system for onsite measurement and analysis is shown in Fig. 5.

The diagrammatic shows6 different locations of monitoringpoints.2

The parameters identified for the data acquisition and monitoring3

are the air velocity (m/s), pressure (Pa), relative humidity (%) and4

ambient temperature (C).5

The data logger installed is of Graphtec GL800 with 20 chan-6

nels. The pressure sensor is of Piezo-resistive sensitive element7

type with measuring range of500 Pa to +500Pa and a resolution8

of 1 Pa. The air velocity sensors are of hotwire type with measuring9

Fig. 3. Ground, first and roof plans of the experimental house.

range of 020 m/s with a resolution of 0.01m/s. The temperature

sensors are PT100 Class A element with measuring range from

0 Ct o5 0 C with a resolution of 0.1 C. Fig. 5 illustrates the sensors

connection to the data logger using RS232 system. All the sensors

were calibrated by Kimo Instruments in France before installa-

tion andcommissioning. The calibration certificates for the sensors

were also delivered together with the sensors. The Graphtec GL800

was equipped with USB memory slot. All the data were logged and

stored in a USB memory drive. All the data were logged automat-ically every 10min intervals and 24h per day. The data was than

retrieve every 2 to 3 weeks for analysis. The data collection dura-

tion was from October 2010 to January 2011. There are total of 13

sensors installed though out the experimental house as showed in

Fig. 5. All the measurements were taken with both the windows

opened at the front of the experimental house and top windows of

thewind-induced natural ventilation tower.This will enablethe air

movement to flow freely from the front of the experimental house

and upwards the wind-induced ventilation tower. Fig. 5 shows a

weather station is installed on the concrete flat roof of the exper-

imental house. The weather station is to record the wind velocity

(m/s) and wind directions within the vicinity of the experimental

house.The total heightof theweather station from theground level

to the top of the anemometer is 11.4m.


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Fig. 4. Locations of the monitoring and sensors points.

4. Onsitewind data analysis and windprofile

Based on the wind data collection and analysis of the wind rose

diagram (Fig. 6) from November to January 2011, the prevailing

wind is seen as blowing from the North direction. Fig. 6 shows the

wind speed classification. It shows that 64.3% are classified as calm

days and34.3%of the days have wind velocity ranging from 0.5m/s

to 2.1m/s.Meanwhile, 1.3% of thedays have wind velocity between 2

2.1 and 3.6 m/s and 0.1% of the days have wind velocity between 2

3.6m/s and 5.7m/s. The wind data analysis revealed that the site 2

has low outdoor wind velocity. 2

Fig. 6 shows the orientation of the experimental house. The 2

front facade of the experimental house is facing the south direc- 2

tion whereas the prevailing wind is blowing from the north 2

Fig. 5. Dataacquisition system and weather station.


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Fig. 6. Wind rose from November2010 to January 2011 andorientation of experimentalhouseand classification of wind velocity for thesite.

direction towards the rear of the experimental house. The6

anemometer height at the weather station is 11.4m. The mean7

wind velocity recorded by the anemometer at the height of 11.4m8

is0.85m/s.The wind data collectedfromtheweatherstationis used9

forthe generation of thesite Wind Profile. TheLog LawModel equa-0

tion is used to compute the mean wind velocity at 10m reference

height (Vref). Subsequently, the mean wind velocity (V10) at 10 m2

reference height is used to generate the wind profile for the site3

using FloVent Boundary Layer Generator software. FloVent Bound-4

ary Layer Generator software is available free at Mentor Graphics5

Inc., website. The Log LawModel equation that is used to determine6

the mean wind velocity (Vz) is as follows:7

VZ = Vref

log(Z/Zo)

log(Zref/Zo)

(1)8

where Vz, mean wind velocity at height Z (Gradient wind), Vref,9

0.85 m/s (mean wind velocity at reference heightZref), Zref, 11.4m0

(reference heightof anemometer at site),Z,370 m [height forwhich

the wind velocityVz is computed (gradient height)],Zo, 0.5 (rough-2

ness length of log layer constant).3

For the purpose of the computation, the Class type of the site4

neededto be identifiedfrom various types which is listedin Table 15

[16].6

Our site falls under Class 6. Class 6: Terrain type of Parkland,

bushes; numerous obstacles,x/h10is used forthe computation.

Therefore,

V114 = 0.85

log(370/0.5)

log(114/0.5)

(2)

V114 = 0.85

8.53

3.52

(3)

V114 = 2.06 m/s (4)

Inorderto determinethe mean wind velocityat referenceheight

(Vref) of 10 m from Eq. (1), Vref can be calculated as follows:

Vref =Vz

[log(Z/Zo)/ log(Zref/Zo)](5)

V10 =2.06

[log(370/0.5)/ log(10/0.5)](6)

V10 =2.06

[8.53/3.32](7)

V10 = 0.80 m/s (8)

In order to generate thewind gradient of thesite,the mean wind

velocity (Vref) of0.80 m/s at reference heightof 10m is inserted into


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Fig. 7. Wind profile generated by FloVent BoundaryLayer Generatorsoftwarefor thesite of theexperimental house.

Fig. 8. Model of the experimental house with wind-induced natural ventilation

tower in FloVent CFDcode.

FloVent atmospheric boundary layer (ABL) Generator software for

generation of the Boundary Layer. Subsequently, the atmospheric

boundary layer in PDML format which is produced by FloVent ABL

Generator is imported into FloVent CFD software for final simula-

tion.

Fig. 7 shows the wind gradient graph of the site of the exper-

imental house. This information is important for designing a

wind-induced ventilation tower. The Wind Profile changes from

urban to open country due to the terrain roughness. The wind

Fig. 9. CFD simulation of the air flow around and inside the experimental house

with wind-induced natural ventilation tower.

profile at the Urban Centre is much steeper compare to the wind 2

profile for Rough wooded country and Open country or sea. 2

5. Validation of FloVent CFD codeagainst empirical results 2

A model of the experimental house with wind-induced natu- 2

ral ventilation tower is built and used in the FloVent CFD code for 2

simulation. Fig. 8 shows the model of the experimental house with 2

wind-induced natural ventilation tower. The simulation results are 2

used to validate against the empirical measurement results. 2

Table 1

Atmospheric boundary layer (ABL) characteristic for different terrain roughness [16].

Class Terrain description Zo (m) Iu (%) Exp. Zg (m)

1 Open sea, fetch at least 5 km 0.0002 0.1 9.2 D 215

2 Mud flats, snow, no vegetation, no obstacles 0.005 0.13 13.2 D 215

3 Open flat terrain; grass, few isolated obstacles 0.03 0.15 17.2 C 275

4 Low crops; occasional large obstacles,x/h> 20 0.1 0.18 27.1 C 275

5 High crops; scattered obstacles, residential suburban, 15


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7V5V4V2V1V

EmpiricalMeanAirVelocity(m/s) 13.054.072.090.003.0

FloVentSimulaon 23.024.042.090.082.0

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

AIRVEL

OCITY(m/s)

SENSORSLOCATION

Validation between Empirical Mean Air Velocity

(19th Nov 2010 -6 Feb. 2011) & FloVent Simulation

Fig. 10. Comparison between the empirical mean air velocity and FloVent CFD code simulation.

The atmospheric boundary layer conditions which is generated8

by FloVent ABL generator is also used in the simulations. Fig. 99

shows the simulation of wind flow around and inside the exper-0

imental house with wind-induced natural ventilation tower.

The FloVent CFD code uses a Cartesian-type grid for simula-2

tion. The system grid is defined in the x, y and z directions. The3

total number of cells used for the modelling is 239,904 cells with4

the maximum grid cell aspect ratio of 1.89. The turbulence model5

used forthe simulation isk turbulence model with global system6

setting of datum pressure at 1 atm. The ambient and external tem-7

perature was set at33 C. The overall solution control was set using8

an outer iteration of 1000, and the fan relaxation was set at 1.0.The9

simulation was run until it reached convergence. Fig. 10 shows the0

comparison between the empirical mean air velocity and FloVent

CFD code results.2

Fig. 11 shows the output of the FloVent CFD code simulation3

results. The root mean square deviation (RMSD) between empirical4

data and CFD simulation results shows 6.7%. The tabulation of the5

RMSD is shown in Table 2.6

The RMSD reveals that FloVent CFD code simulation has a7

good agreement with the empirical results. Following the satisfac-8

tory validation of FloVent CFD code simulation result, we proceed9

to simulate the experimental house without the wind-induced0

Fig. 11. FloVent CFDcode simulation result of the experimental house with wind-

induced natural ventilation tower.

Fig. 12. FloVent CFDcode simulation resultof theexperimental house without the

wind-induced natural ventilation tower.

ventilation tower. Fig. 12 shows FloVent CFD code simulation

output of the experimental house without the wind-induced ven-

tilation tower. The model of the experimental house has the rear

windows open to allow only cross ventilation through the house

during the simulation. The simulation was carried out with similar

atmospheric boundary layer conditions and other ambient condi-tions settings.

Table 2

The root mean square deviation between empirical data andCFD code.

Location Empirical mean

velocity

CFD % of absolute

deviation (X)

X2 (%)

V1 0.30 0.28 6.7 44.4

V2 0.09 0.09 1.1 1.2

V4 0.27 0.24 11.1 123.5

V5 0.45 0.42 6.7 44.4

V7 0.31 0.32 3.2 10.4

Root mean square deviation (RMSD) 6.7


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0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

12am

to1am

1am

to2am

2am

to3am

3am

to4am

4am

to5am

5am

to6am

6am

to7am

7am

to8am

8am

to9am

9am

to10am

10am

to11am

11am

to12pm

12pm

to1pm

1pm

to2pm

2pm

to3pm

3pm

to4pm

4pm

to5pm

5pm

to6pm

6pm

to7pm

7pm

to8pm

8pm

to9pm

9pm

to10pm

10pm

to11pm

11pm

to12am

AverageIndoorAirVelocity(m/s)

Average Indoor Air Velocity (m/s)

23-Oct-10 22-Oct-10 21-Oct-10 02-Nov-10 03-Nov-10Fig. 13. Average indoor air velocity.

6. Results and discussion

6.1. Empirical data analysis

Fig. 13 shows theindoor average airvelocitytaken from thefield

measurement. The indoor air velocity fluctuates between 0.05m/s

and 0.45m/s. Fig. 13 reveals that the indoor average air velocity

is low between midnight and early morning and increases grad-

ually after 10am and culminates between 3 pm and 5 p m with a

maximum average air velocity of 0.45 m/s.

Fig. 14 indicates that approximately 2022% of the indoor air

velocity is 0.2m/s and above. It mostly occurs in the afternoon.

The high air velocity is caused by lighter air density due to higher

air temperature in the afternoon. Since the air temperature is high,

it causes thehumidityto decrease. This phenomenon allows theair

to flow much easier in the afternoon in comparison to the morning

period because it has lighter density.

The airvelocity data taken from theexperimentalhouseare cat-

egorized into four categories. The four categories of air velocity are

as follows:

(i) 0.05 m/s and below,

(ii) 0.050.1 m/s,

(iii) 0.10.2m/s,

(iv) 0.2m/s and above.

Fig. 14 shows thatapproximately5560% of theindoor airveloc-

ity is in the category of 0.05m/s and below. The air velocity in

Fig. 14. Indoor air speed categories.

the category of 0.05m/s andbelow can be slightly uncomfortable3

butthis is compensated by the lower temperature during midnight 3

and early hours of the morning. The field measurement analysis 3

by Azni et al., [17] suggests the mean air velocity for conventional 3

Malaysian homes only ranges from 0.03m/s to 0.08m/s only (see 3

Table 3). This problem of low air movement can be enhanced with 3

the application of wind-induced natural ventilation tower. The 3

wind-induced natural ventilation tower method without any aid 3

of the mechanical system has the potential to increase the mean 3

indoor air velocity ranging from 0.08m/s to 0.12 m/s [17]. 3

Figs. 15 and 16 expose that there is a correlation between the 3

external wind velocity and the extraction air flow rate. The higher 3

theexternalwind velocity,the higherwill be theextraction airflow 3

rate. Fig. 15 shows the empirical data analysis covering dates from 3

21st and 23rd of October 2010, 2nd and 3rd November 2010 and 3

30 December 2010.Each of the days indicateda similar pattern and 3

trend between external wind velocity and extraction air flow rate. 3

Fig. 16 shows the average extraction air flow rate. 3

6.2. Comparisons of various design technologies 3

Based on the CFD simulation, without the wind-induced nat- 3

ural ventilation tower, the experimental house only managed to 3

generate 7 ACH as compare with the wind-induced ventilation 3

tower which is 57 ACH. This reveals that the wind-induced natural 3

ventilation tower method is more effective than cross ventilation 3

method in improving ACH. 3

Lai [18] conducted a field experiment and measurement on a 3

wind catchermodel ABS500 MonodraughtTM with 450mm diame- 3

ter. The research discovered that at outdoor wind velocity of 2 m/s, 3

the wind catcher can achieve an extraction flow rate of 30l/s or 3

108m3/h. Comparing the wind catcher with the wind-induced 3

natural ventilation tower at the same external wind velocity of 3

2 m/s, the wind-induced natural ventilation tower is able to gen- 3

erate higher extraction flow rate of 47,634.6m3/h (see Fig. 16). 3

The extraction flow rate of Venturi shaped roof wind-induced 3

Table 3

Mean indoorair speedfor residential types [17].

House type Mean indoor air speed (m/s)

Semi-detached 0.08

Bungalow 0.03

Terrace 0.08


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y=7323.5x3 -22484x2 +36380x+6429.2

R = 0.9809

y=7944.2x2 +4474.1x+10351

R = 0.9826

y=660.56x3 +7517.2x2+664.42x +13310

R = 0.9907

y=16881x3 -49410x2+50596x+3029.3

R = 0.9839

y=36430x2 +8655x+7782R = 0.9451

0

100000

200000

300000

400000

500000

600000

4.543.532.521.510.50

ExtractionFlowRateofWindInducedVentilation

Tower

(m3/hr)

External Wind Speed (m/s)

02-Nov-10 03-Nov-10 23-Oct-10 21-Oct-1030-Dec-10 Poly. (02-Nov-10) Poly. (03-Nov-10) Poly. (23-Oct-10)

Poly. (21-Oct-10) Poly. (30-Dec-10)

Fig. 15. Daily extraction airflow rate (m3/h) for wind-induced natural ventilation tower.

natural ventilation tower is equivalent to 441 units of ABS 5006

MonodraughtTM model wind catcher. In addition, at external wind7

velocity of 0.1m/s, the wind-induced natural ventilation tower8

is capable to generate ventilation rate of 10,000m3/h (Fig. 16).9

This ventilation rate of 10,000m3/h surpasses the ASHRAE Stan-0

dard 62:2001 ventilation rate requirement of 1260 m3/h. Another

ventilation system called Wing Jetter [19] designed by HASEC Cor-2

poration in Japan has a similar concept design with the roof natural3

ventilation tower for its roof geometry. Based on a laboratory test,4

it can generate 110 l/s or 396 m3/h at external wind velocity of5

6 m/s. The Wing Jetter stands at approximately 1.5 m high by 1.5 m6

wide and weighs up to 50kg. However, Naghman et al. [6] argues7

that it has yet to obtain comprehensive field data to judge on the8

performance of Wing Jetter.9

The ventilation rate in buildings can be expressedin terms of air

changes perhour (ACH). ACH is the numberof times in an hour that

a volumeof air equal tothevolumeof a roomor buildingis renewed

with fresh outdoor air. The ACH is important in order to achieve

desirable indoor air quality for building occupants. The volume of

experimental house with wind-induced natural ventilation tower

is 232.76m3.

Fig. 17 reveals the ACH pattern from 12am until 12 midnight.

The ACH starts to increase from average 5070 ACH between 1 pm

to 5 pm and it slowly decreases in the evenings until early morning

when it starts to increase again (see Fig. 17). Fig. 18 shows that the

daily average ACH generated by the wind-induced natural ventila-

tion tower for the experimental house fluctuates from 45 ACH to

maximum of75 ACH.

Fig. 16. The external wind speed against average extraction air flow rate of wind-induced natural ventilation tower.


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0

50

100

150

200

250

12.0

0am-1.0

0am

1.0

1am-2.0

0am

2.0

1am-3.0

0am

3.0

1am-4.0

0am

4.0

1am-5.0

0am

5.0

1am-6.0

0am

6.0

1am-7.0

0am

7.0

1am-8.0

0am

8.0

1am-9.0

0am

9.0

1am-10.0

0am

10.0

1am-11.0

0am

11.0

1am-12.0

0pm

12.0

1pm-1.0

0pm

1.0

1pm-2.0

0pm

2.0

1pm-3.0

0pm

3.0

1pm-4.0

0pm

4.0

1pm-5.0

0pm

5.0

1pm-6.0

0pm

6.0

1pm-7.0

0pm

7.0

1pm-8.0

0pm

8.0

1pm-9.0

0pm

9.0

1pm-10.0

0pm

10.0

1pm-11.0

0pm

11.0

1pm-12.0

0am

AirChangesperhour(ACH)

Air changes per hour (ACH) of Wind Induced Ventilation Tower

House from Nov 2010 - Jan 2011

20-Nov-10 21-Nov-10 01-Dec-10 02-Dec-10 25-Dec-1030-Dec-10 31-Dec-10 01-Jan-10 06-Jan-11 11-Jan-11

Fig. 17. Daily ACH of the experimental house with wind-induced natural ventilation tower.

0

10

20

30

40

50

60

70

80

90

20NOV2010

21NOV2010

1DEC2010

2DEC2010

25DEC2010

30DEC2010

31DEC2010

1JAN2011

6JAN2011

11JAN2011

AIR

CHANGESPERHOUR(ACH)

AVERAGE DAILY AIR CHANGES PER HOUR (ACH)

FOR WIND INDUCED VENTILATION TOWER HOUSE

Fig. 18. Average daily ACH generated by the wind-induced natural ventilation tower.

Fig. 19. Comparison of ACH between ASHRAE Standard requirement, house with wind-induced natural ventilation tower and with wind-induced natural ventilation tower.


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l i hi i l i l i i l d f i d i d d l il i d h d h id



Fig. 19 shows the average ACH for wind-induced natural venti-4

lation tower which is 57 ACH that amount is above the standard5

requirement set by ASHRAE Standard 62 ventilation for general6

spaces, offices, restaurants and shopping centres.7

Other studies conducted by Bansal et al. [20] and Bahadori [21]8

observed that thewind tower alone canprovide 20 ACHat an ambi-9

ent windvelocityof 1 m/s and itcan bereached to60 ACH using the0

combination of solar chimney and wind tower. The analysis result

ofour studyhas shown similarity with theresultsof studyby Bansal2

et al. and Bahadori. This shows that the Venturi shaped roof wind-3

induced natural ventilation tower can generate equivalent ACH in4

the hot and humid climate like the conventional wind tower in hot5

and arid of the Persian Gulf regions.6

7. Conclusions7

This research revealed that the Venturi shaped roof wind-8

induced natural ventilation tower has a great potential application9

in buildings under hot and humid climate. It can produce suffi-0

cient airflow rate and ACH for naturally ventilated buildings. The

study also showed that the aerodynamic performance of the Ven-2

turi shaped roof of the wind-induced natural ventilation tower can3

produce sufficient low pressure required to induce fresh air from4

outdoor into indoor spaces of building. Although 60% of external5

wind velocity in the hot and humid climate is under the category6

of below 0.5m/s, the wind-induced natural ventilation tower has7

shown its abilities to produce sufficient airflow rate and ACH for8

the building. Based on empirical data analysis, the Venturi shaped9

roof wind-induced ventilation tower is able to generate extraction0

air flow rate of 10,000m3/h and 57 ACH at external wind velocity

of 0.1m/s. If the experimental houses is without the wind-induced2

natural ventilation tower and only rely on cross ventilation, the air3

change is only 7 ACH. The wind-induced natural ventilation tower4

can be utilized to elevate the indoor air velocity to 1260m3/h in5

accordance to the ASHRAE Standard 62 requirement. In conclu-6

sion, the research also reveals that the performance of the Venturi7

shaped roof wind-induced natural ventilation tower is comparable8

to the performance of the conventional wind towers in hot arid of9

the Persian Gulf regions.0

Acknowledgement

The authors are grateful to Universiti Kebangsaan Malaysia2

and the Ministry of Higher Education Malaysia for the financial3

assistance under the Fundamental Research Grant (FRGS) for this4

research project. Without which this research would nothave been5

possible.

References

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[2] B. B locken , T. Van Ho of f, L. Aane n, B . Br on se ma, Computation al an aly-sis of the performance of a venturi-shaped roof for natural ventilation:venturi-effect versus wind-blocking effect, Computers and Fluids 48 (2011)202213.

[3] M.Liddament, Ventilation andbuildingsicknessa briefreview, AirInfiltrationReviewJournal 11 (3)(1990) 46.

[4] F. Allard, Natural Ventilation in Buildings, James & James (Science Publisher)Ltd., William Road, London NW1 3ER, UK, 1998, pp. 3537.

[5] M. Liddament, A Guide to Energy Efficient Ventilation, International EnergyAgency (IEA), Energy Conservation in Buildings and Community Systems Pro-gramme, Annex V Air Infiltration and Ventilation Centre, Coventry, England,1996.

[6] K. Naghman, S. Yuehong, S.B. Riffat, A review on wind driven ventilation tech-niques, Journal of Energyand Buildings 40 (2008)5681604.

[7] B.R. Hughes, M. Cheuk-Ming, A study of wind and buoyancy drivenflows through commercial wind towers, Energy and Buildings (2011),http://dx.doi.org/10.1016/j.enbuild.2011.1003.1022.

[8] A.A.Elmualim,Verificationof design calculationsof a windcatcher/towernatu-ralventilationsystemwith performancetestingin a realbuilding, International

Journal of Ventilation 4 (4) (2006) 393404.[9] B. Givoni, Climate Considerations in Building and Urban Design, John Wiley &

Sons, Inc., 1998.[10] A. Aldawoud, R. Clark, Comparative analysis of energy performance between

c ourtyard and atrium in buildings, Energy and Buildings 40 (2008)

209214.[11] I. Rajapaksha, H. Nagai, M. Okumiya, A ventilated courtyard as a passivecooling strategy in the warm humid tropics, Renewable Energy 28 (2003)17551778.

[12] C.M. Mak, J.L. Niu, C.T. Lee, K.F. Chan, A numerical simulation of wing wallsusing computational fluid dynamics, Energy and Buildings 39 (9) (2007)9951002.

[13] M.B. Gadi, Design and simulation of a new energy conscious system (venti-lation and thermal performance simulation), Applied Energy 65 (14) (2000)355366.

[14] N. Lechner, Heating Cooling Lighting: Sustainable Design Methods for Archi-tects, third ed., John Wiley & Sons, Inc., 2009.

[15] T. Van Hooff, B. Blocken, L. Aanen, B. Bronsema, A venturi-shaped roof forwind-induced natural ventilation of buildings: wind tunnel and CFD evalua-tion of different design configurations, Building and Environment 46 (2011)17971807.

[16] American Society of Civil Engineers, Wind Tunnel Studies of Buildings andStructures, ASCE Manuals and Reports on Engineering Practice, No. 67, USA,1999.

[17] Z.A.Azni, A.R.Samirah, S. Shaheera, Natural cooling and ventilation of contem-porary residential homes in Malaysia: impact on indoor thermal comfort, in:The 2005 World Sustainable Building Conference (SBO5), Tokyo, Japan, 2005.

[18] C.-m. Lai, Experiments on the ventilation efficiency of turbine ventilators usedfor building and factory ventilation, Energy and Buildings 35 (2003) 927932.

[19] HASEC Inc., Wing Jetter System: An Epoch-making Ventilator Achieved byApplication of Wing Theory, HASEC Inc., Tokyo,Japan, 2007.

[20] N.K. Bansal, R. Mathur, M.S. Bhandari, A study of solar chimney assisted windtower systemsfor naturalventilationin buildings, Journalof Buildingand Envi-ronment 29 (4) (1994) 495500.

[21] M.N. Bahadori, Viability of wind towers in achieving summer comfort inthe hot and arid regions of the Middle East, Renewable Energy 5 (2) (1994)879892.
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