wind induced tower
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Energyand Buildings xx (2012) xxxxxx
Contents lists available at SciVerse ScienceDirect
Energy and Buildings
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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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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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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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6am
to7am
7am
to8am
8am
to9am
9am
to10am
10am
to11am
11am
to12pm
12pm
to1pm
1pm
to2pm
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to3pm
3pm
to4pm
4pm
to5pm
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7pm
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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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L.C. Haw et al. / Energy and Buildings xxx (2012) xxxxxx 9
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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10 L.C. Haw et al. / Energy and Buildings xxx (2012) xxxxxx
0
50
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150
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250
12.0
0am-1.0
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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
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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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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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[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.
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[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.
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[19] HASEC Inc., Wing Jetter System: An Epoch-making Ventilator Achieved byApplication of Wing Theory, HASEC Inc., Tokyo,Japan, 2007.
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