Effect of VertEffect of vertical greenery on mean radiant temperature in the tropical urban...
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Landscape and Urban Planning 127 (2014) 52–64 Contents lists available at ScienceDirect Landscape and Urban Planning j o ur na l ho me pag e: www.elsevier.com/locate/landurbplan Research Paper Effects of vertical greenery on mean radiant temperature in the tropical urban environment Tan Chun Liang a,∗ , Wong Nyuk Hien a,1 , Steve Kardinal Jusuf b,2 a Department of Building, National University of Singapore, 4 Architecture Drive, Singapore 117566, Singapore b NUS Environmental Research Institute, National University of Singapore, 4 Architecture Drive, Singapore 117566, Singapore h i g h l i g h t s • Mean radiant temperature (t mrt ) in front of 2 green walls was measured, showing reduction of t mrt for up to 1 m. • One green wall is removed midway during measurement, resulting in time lag and increase in t mrt of up to 12.8 ◦ C. • GIS software used to generate t mrt map shows the extent of t mrt reduction due to green wall varies at different times of the day. a r t i c l e i n f o Article history: Received 26 April 2013 Received in revised form 12 March 2014 Accepted 5 April 2014 Available online 4 May 2014 Keywords: Outdoor thermal comfort Mean radiant temperature Vertical greenery Geographical information systems Urban vegetation a b s t r a c t Studies on vertical greenery generally focus on the measurement of air temperature, surface temperature and cooling load. There is a lack of information on how vertical greenery can influence outdoor thermal comfort. The objective of this study is to quantify the effects of mean radiant temperature (t mrt ), as the first step towards determining the thermal quality of outdoor space due to installation of vertical greenery. The t mrt of two green walls (Green Wall A and Green Wall B) was measured up to 2 m away at intervals of 0.5 m. Two datasets were obtained, one consisting of t mrt , surface and air temperature collected from the two green walls and the second for just green wall A and the exposed concrete wall after Green Wall B was removed. t mrt was measured using customised globe thermometers calibrated for local use. Data was analysed using a GIS, thus enabling convenient visual comparison between t mrt profiles at different times. The diurnal t mrt profile was altered significantly due to the installation of vertical greenery. When both green walls were present the peak t mrt occurred at 15:00 h, but with more concrete exposed when one wall was removed, the peak occurred at 17:00 h and was 10.9–12.9 ◦ higher at 0.5 m away from the wall. Vertical greenery thus helped to reduce t mrt both during the day and at night, to varying extents. The proposed methodology enables systematic quantification of the effects of vertical greenery on t mrt . © 2014 Elsevier B.V. All rights reserved. 1. Introduction Vegetation can play an important role in the climate of cities as well as the microclimate of buildings. Besides providing a conducive environment for social activity (Gobster, 1998; Maas et al., 2009; Troy & Grove, 2008), promotion of mental health (Grahn & Stigsdotter, 2010; Korpela & Hartig, 1996; Takano, Nakamura & Watanabe, 2002), the introduction of greenery is a useful mitigation strategy in rising temperature due to climate ∗ Corresponding author. Tel.: +65 6516 4691. E-mail addresses: [email protected], terrencefi[email protected] (C.L. Tan), [email protected] (N.H. Wong), [email protected] (S.K. Jusuf). 1 Tel.: +65 6516 3423. 2 Tel.: +65 6516 4691. change. For high-density urban environments, greenery can help to cool the air and provide shade. It can also lower a building’s energy consumption by providing better outdoor boundary conditions. Urban greenery can bring about benefits to the microclimate through several physical processes (Wilmers, 1991; Dimoudi & Nikolopoulou, 2003): – Plant and tree shade can lower the solar heat gain on the building envelope; – Shading reduces terrestrial radiation due to lower surface tem- perature; and – Latent heat of cooling in the atmosphere is increased due to added moisture in the air via plant evapotranspiration. Numerous studies have validated the cooling effect of urban greenery (Sad de Assis & Barros Frota, 1999; Ca, Asaeda, & Abu, http://dx.doi.org/10.1016/j.landurbplan.2014.04.005 0169-2046/© 2014 Elsevier B.V. All rights reserved.
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Studies on vertical greenery generally focus on the measurement of air temperature, surface temperature and cooling load. There is a lack of information on how vertical greenery can influence outdoor thermalcomfort. The objective of this study is to quantify the effects of mean radiant temperature (tmrt), as the first step towards determining the thermal quality of outdoor space due to installation of vertical greenery.The tmrt of two green walls (Green Wall A and Green Wall B) was measured up to 2 m away at intervals of 0.5 m. Two datasets were obtained, one consisting of tmrt, surface and air temperature collected from the two green walls and the second for just green wall A and the exposed concrete wall after Green Wall B was removed. tmrt was measured using customised globe thermometers calibrated for local use. Data was analysed using a GIS, thus enabling convenient visual comparison between tmrt profiles at differenttimes. The diurnal tmrt profile was altered significantly due to the installation of vertical greenery. When both green walls were present the peak tmrt occurred at 15:00 h, but with more concrete exposed whenone wall was removed, the peak occurred at 17:00 h and was 10.9–12.9◦ higher at 0.5 m away from the wall. Vertical greenery thus helped to reduce tmrt both during the day and at night, to varying extents.The proposed methodology enables systematic quantification of the effects of vertical greenery on tmrt.
Transcript of Effect of VertEffect of vertical greenery on mean radiant temperature in the tropical urban...
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Landscape and Urban Planning 127 (2014) 52–64
Contents lists available at ScienceDirect
Landscape and Urban Planning
j o ur na l ho me pag e: www.elsev ier .com/ locate / landurbplan
esearch Paper
ffects of vertical greenery on mean radiant temperature in theropical urban environment
an Chun Lianga,∗, Wong Nyuk Hiena,1, Steve Kardinal Jusufb,2
Department of Building, National University of Singapore, 4 Architecture Drive, Singapore 117566, SingaporeNUS Environmental Research Institute, National University of Singapore, 4 Architecture Drive, Singapore 117566, Singapore
i g h l i g h t s
Mean radiant temperature (tmrt) in front of 2 green walls was measured, showing reduction of tmrt for up to 1 m.One green wall is removed midway during measurement, resulting in time lag and increase in tmrt of up to 12.8 ◦C.GIS software used to generate tmrt map shows the extent of tmrt reduction due to green wall varies at different times of the day.
r t i c l e i n f o
rticle history:eceived 26 April 2013eceived in revised form 12 March 2014ccepted 5 April 2014vailable online 4 May 2014
eywords:utdoor thermal comfortean radiant temperature
ertical greenery
a b s t r a c t
Studies on vertical greenery generally focus on the measurement of air temperature, surface temperatureand cooling load. There is a lack of information on how vertical greenery can influence outdoor thermalcomfort. The objective of this study is to quantify the effects of mean radiant temperature (tmrt), as the firststep towards determining the thermal quality of outdoor space due to installation of vertical greenery.
The tmrt of two green walls (Green Wall A and Green Wall B) was measured up to 2 m away at intervalsof 0.5 m. Two datasets were obtained, one consisting of tmrt, surface and air temperature collected fromthe two green walls and the second for just green wall A and the exposed concrete wall after Green WallB was removed. tmrt was measured using customised globe thermometers calibrated for local use. Datawas analysed using a GIS, thus enabling convenient visual comparison between tmrt profiles at different
eographical information systemsrban vegetation
times. The diurnal tmrt profile was altered significantly due to the installation of vertical greenery. Whenboth green walls were present the peak tmrt occurred at 15:00 h, but with more concrete exposed whenone wall was removed, the peak occurred at 17:00 h and was 10.9–12.9◦ higher at 0.5 m away from thewall. Vertical greenery thus helped to reduce tmrt both during the day and at night, to varying extents.The proposed methodology enables systematic quantification of the effects of vertical greenery on tmrt.
© 2014 Elsevier B.V. All rights reserved.
. Introduction
Vegetation can play an important role in the climate of citiess well as the microclimate of buildings. Besides providing aonducive environment for social activity (Gobster, 1998; Maast al., 2009; Troy & Grove, 2008), promotion of mental health
Grahn & Stigsdotter, 2010; Korpela & Hartig, 1996; Takano,akamura & Watanabe, 2002), the introduction of greenery is aseful mitigation strategy in rising temperature due to climate∗ Corresponding author. Tel.: +65 6516 4691.E-mail addresses: [email protected], [email protected] (C.L. Tan),
[email protected] (N.H. Wong), [email protected] (S.K. Jusuf).1 Tel.: +65 6516 3423.2 Tel.: +65 6516 4691.
ttp://dx.doi.org/10.1016/j.landurbplan.2014.04.005169-2046/© 2014 Elsevier B.V. All rights reserved.
change. For high-density urban environments, greenery can help tocool the air and provide shade. It can also lower a building’s energyconsumption by providing better outdoor boundary conditions.
Urban greenery can bring about benefits to the microclimatethrough several physical processes (Wilmers, 1991; Dimoudi &Nikolopoulou, 2003):
– Plant and tree shade can lower the solar heat gain on the buildingenvelope;
– Shading reduces terrestrial radiation due to lower surface tem-perature; and
– Latent heat of cooling in the atmosphere is increased due to added
moisture in the air via plant evapotranspiration.Numerous studies have validated the cooling effect of urbangreenery (Sad de Assis & Barros Frota, 1999; Ca, Asaeda, & Abu,
C.L. Tan et al. / Landscape and Urban
Fig. 1. Surface temperature
Fig. 2. Measurement setup. Globe thermometers were attached to poles
Planning 127 (2014) 52–64 53
measurement spots.
with white PVC pipes housing surface and air temperature loggers.
54 C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64
and ta measurement points.
1DGG122&iagGeti(cfPb(
Table 1Properties of green walls.
Green Wall A Green Wall B
System Suntory Midorie System Shimizu Parabienta System
Dimensions (H × W) 2.27 m × 1.90 m 3.18 m × 2.40 m
Types of plants used Piper sarmentosum Hemigraphis alternataPhilodendron Portulaca grandifloraCordyline terminalis Nephrolepis acutifoliaSchefflera
TM
Fig. 3. Position of tmrt
998; Chen, Ooka, Huang, & Tsuchiya, 2009; Chudnovsky, Ben-or, & Saaroni, 2004; Emmanuel, Rosenlund, & Johansson, 2007;ao, 1993; Gill, Handley, Ennos, & Pauleit, 2007; Giridharan, Lau,anesan, & Giovoni, 2008; Honjo & Takakura, 1991; Jauregui,991; Jonsson, 2004; Lin, Li, Zhu, & Qin, 2008; Nichol & Wong,005; Saito, Ishihara, & Katayama, 1991; Shashua-Bar & Hoffman,000; Shashua-Bar & Hoffman, 2004; Weng & Yang, 2004; Wong
Chen, 2005; Wong & Chen, 2006). Recognising the positivempacts of greenery, many governments have initiated policiesiming to improve the condition of the city through the addition ofreenery (Beatley, 2000; City of Sydney, 2011; GLA, 2011; HKSARovernment, 2010; NYC, 2011; Ra, 2006; Zhao, 2011). Urban green-ry can be categorised in a variety of ways. Some examples includehe Green Plot Ratio (GPR), a concept that is developed by combin-ng the concepts of Leaf Area Index (LAI) and Building Plot RatioBPR) (Ong, 2003). The Urban Neighbourhood Green Index (UNGI)an be used by planners to quantify the proximity to greenery
or each neighbourhood (Gupta, Kumar, Pathan, & Sharma, 2012).ark provision ratio and per capita green cover are urban planningenchmarks that have been used in countries such as SingaporeTan, Wang, & Sia, 2013).able 2easurement period.
Period Measurementduration
No. of days measured No. of
A27th September2011 to 3rdJanuary 2012
99 5
B4th January 2012 to13th March 2012
70 9
LAI 3.8 3.5
The primary metric for greenery is land cover. This metric issometimes further delineated into lawns and shrubs-and-trees. Thecooling effect exhibited by plants is a result of its metabolic pro-cesses, such as photosynthesis, evapotranspiration, respiration and
uptake of minerals from the air and ground. The extent to whichplants engage in these processes is directly related to the amountof green matter, usually found in the leaves of the plant (Jones,1992). Urban Green Spaces (UGS) also acts as urban lungs, helpingdays used for analysis Dates used foranalysis
Purpose
06/10/2011Measurement forGreen Wall A andGreen Wall B
13/10/201116/10/201117/10/201125/11/2011
15/01/2012
Measurement forGreen Wall A.Green Wall B isremoved
16/01/201217/01/201221/01/201201/02/201208/02/201210/02/201211/02/201207/03/2012
C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64 55
ing se
ta&
fadc1i
Fig. 4. CCTV footage of site show
o absorb pollutants and releasing oxygen, provide clean air, waternd soil, and balances the city’s environment (Hough, 1989; Levent
Nijkamp, 2004).For high-density cities that do not have adequate land to provide
or UGS, roof gardens and vertical greenery are often employed aslternative forms of green cover. Urban areas with high populationensity such as Hong Kong and Singapore are characterised by their
ompact city form and land scarcity (Ganesan & Lau, 2000;Neville,993). Singapore, for instance, has paid particular attention to max-mising the available high-rise environment to create a ‘Vertical
lf-shading and overshadowing.
Garden City’, via the introduction of rooftop gardens, vertical green-ery and sky terraces (Tan, 2012).
Most of the many studies on the use of vertical greenery focuson temperature reduction ecosystem services (Chen, Li, & Liu,2013; Cheng, Cheung, & Chu, 2010; Perini, Ottelé, Fraaij, Haas,& Raiteri, 2011; Wong, Chen, Ong, & Sia, 2003; Wong, KwangTan, Chen, et al., 2010). Vegetation can reduce the impact of the
Urban Heat Island (UHI) effect by shading heat-absorbing surfacesand cooling the air through evapotranspiration (McPherson, 1994).Vegetation can also reduce diurnal temperature fluctuation due
56 C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64
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Period A
Peri od B
profile
tTol2cMTPWat(T
gdh
Fig. 5. Surface temperature
o exposure to direct solar radiation (Dunnett & Kingsbury, 2004).he surface temperatures of vertical greenery systems have beenbserved to be cooler than common building materials such asight-coloured bricks, walls and black surfaces (Bass & Baskaran,003). This reduction of surface temperature can lead to a lowerooling load for the building interior (Alexandri & Jones, 2008;azzali, Peron, Romagnoni, Pulselli, & Bastianoni, 2013; Papadakis,
samis, & Kyritsis, 2001; Peck, Callaghan, Bass, & Kuhn, 1999;érez, Rincón, Vila, González, & Luisa, 2011; Wong, Tan, Tan, &ong, 2009). Vertical greenery can also help insulate buildings
gainst noise. Various studies have shown that the sound adsorp-ion coefficient of walls increases with greater greenery coverageVan Renterghem, Hornikx, Forssen, & Botteldooren, 2013; Wong,an, Tan, Chiang, & Wong, 2010).
Although much has been written about the benefits of verticalreenery for surface temperature reduction and lowering energyemand for cooling building interiors, little has been written aboutow vertical greenery affects outdoor mean radiant temperatures
s for Period A and Period B.
(Alexandri & Jones, 2008; Bass & Baskaran, 2003; Chen et al.,2013; Cheng et al., 2010; Dunnett & Kingsbury, 2004; McPherson,1994; Papadakis et al., 2001; Peck et al., 1999; Perini et al., 2011;Wong et al., 2003; Wong, Kwang Tan, Chen, et al., 2010). Muchless is known about how the implementation of vertical greenerywill affect outdoor mean radiant temperature. The evaluation ofthermal environments is done via comfort or heat stress indices(d’Ambrosio Alfano, Palella, & Riccio, 2011; Epstein & Moran, 2006;Fanger, 1972; Gagge, 1971; Höppe & Mayer, 1987; Parsons, 2003)and often requires the measurement of air temperature, meanradiant temperature, air velocity and relative humidity. The meanradiant temperature (tmrt) can be considered as one of the mainfactors contributing to both indoor and outdoor thermal comfort,as indicated in previous studies validating the relation between
thermal comfort, shortwave and long wave radiation fluxes fromthe surroundings (Mayer & Höppe, 1987; Mayer, 1993). The objec-tive of this study is to quantify the effects on tmrt due to exposureto vertical greenery. This is done by measuring the tmrt in front of
C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64 57
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Time (Hrs)
Point 1 Poin t 2 Poin t 3 Poin t 4 Poin t 5 Point 6 Poin t 7
Point 8 Poin t 9 Poin t 10 Point 11 Poin t 12 Point 13 Poin t 14
Point 15 Poin t 16 Poin t 17 Point 18 Poin t 19 Point 20 Poin t 21
Point 22 Poin t 23 Poin t 24 Point 25 Poin t 26 Point 27 Poin t 28
∆T= 1.5 °C
Period A
Period B
ofiles
tst
2
tWct
-
Fig. 6. Air temperature pr
wo green walls over a period of time. One of the green walls isubsequently removed to understand the impact on its removal onmrt.
. Methodology
Two sets of data were derived. The first set of data consisted ofmrt collected from the two green walls (Green Wall A and Green
all B). Green Wall B was then removed and the second set of dataonsists of data of only green wall A and the exposed concrete wall
hat was Green Wall B.Measurements are made for the following:
Air temperature (ta) in front of the green walls;
for Period A and Period B.
- Surface temperature (ts) of concrete wall behind green walls; and- Estimation of mean radiant temperature (tmrt) in front of the
green walls.
Properties of the two green walls are shown in Table 1. Bothgreen walls are categorised as plant carrier systems. The SuntoryMidorie system consists of a lightweight sponge material which issupplemented with nutrients. This system uses a dripping system,where an irrigation pipe is installed on the top most and waterslowly drips to the lower part of the wall, such that excess water
flows back to the water tank. The light-weight Shimizu ParabientaSystem is a panel-type wall greening system which uses a drippingsystem where pipes are connected directly onto each panel of theplanting media, and any excess water flows to the drain.
58 C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64
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Period A
Peri od B
or Poi
wmwtewX
uid
Fig. 7. Comparison of tmrt profile f
The surface temperature of the concrete wall behind the greenalls was measured using thermocouples (Fig. 1). There was a ther-ocouple wire attached to the concrete wall behind each greenall (Points X1 and Z1), as well as one between the green walls
hat is directly exposed to the sun (Point Y1). For every point in thexterior, there was a corresponding point on the other side of theall to measure the temperature on the building interior (Points2, Y2 and Z2). There was a total of six measurement points.
The tmrt and ta in front of the green walls were estimated
p to 2 m away in intervals of 0.5 m. The sensors were approx-mately 1.7 m above ground. The two green walls have similarimensions and plant carrier system but consist of different plant
nts 1–7 for Period A and Period B.
types. The measurement of tmrt is done via the use of a globe ther-mometer (Kuehn, Stubbs, & Weaver, 1970; Nikolopoulou, Baker, &Steemers, 1999; Vernon, 1932). The globe thermometer was firstdeveloped for indoor measurements, but has later been appliedoutdoors (Nikolopoulou & Lykoudis, 2006). The Vernon globe is a150 mm diameter copper sphere painted black with a thermome-ter positioned in the middle of the sphere. For convenience, smallerglobes were developed. The 38 mm globe thermometer is a com-mon option as the globe used is a table tennis ball, which can be
readily purchased and conveniently replaced (Humphreys, 1977).The accuracy of the 38 mm globe thermometer can be adjusted tocater to outdoor conditions by recalibrating the mean convection
C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64 59
ints 2
cLotWbiim
i1(gaglt
tafih(m2wa(Soitmmhtamg
B. The removal of Green Wall B has resulted in an increase in surfacetemperature of 6.7 ◦C. The maximum difference in diurnal surfacetemperature for the building interior (Point Z2) for Period A was0.3 ◦C, but significantly larger for Period B (up to 3.8 ◦C). With the
Table 3Instruments used for measurement.
Variable Instrument
Air temperature, ta HOBO Weatherstation, H21-001Globe temperature, tg HOBO Thermocouple Data Logger, U12-014Wind speed, Va HOBO Weatherstation, H21-001Surface temperature, ts HOBO Thermocouple Data Logger, U12-014Shading characteristics Close-circuit televisionLeaf Area Index, LAI Canon All-In-One Printer, MP276
Table 4Time range used for analysis.
Time range Period Condition of wall
1 00:00–07:00 h Night to sunrise
Fig. 8. Po
oefficient. This method has been tested in Sweden (Thorsson,indberg, Eliasson, & Holmer, 2007) and shown to be effective inutdoor conditions. For this study, tmrt is estimated using cus-omised globe thermometers calibrated for localised usage (Tan,
ong, & Jusuf, 2013). The LAI of both green walls were calculatedy removing a 10 cm by 10 cm segment of the green wall, measur-
ng the total leaf area size with a flatbed scanner and extrapolatingt to the size of the green walls. Close-circuit television was used to
onitor the effects of shading on estimated tmrt.Measurements were conducted on the roof top of Block SDE2
n the National University of Singapore, Singapore (1◦17′44′′ N03◦46′36′′ E). Also known as the Greenery Technology LaboratoryGTL), the site measures approximately 9 m by 9 m (Fig. 2). Tworeen systems were installed on an existing wall. The environmentround the green walls is open space, and the room behind thereen walls is a smoke-stop lobby that is not mechanically venti-ated. There was no machinery or heat generation equipment nearhe green walls.
Singapore has a tropical rainforest climate with no distinc-ive seasons, uniform temperature and pressure, high humidity,nd abundant rainfall. Near-surface air temperatures usually rangerom 23 ◦C to 32 ◦C. The relative humidity averages around 79%n the morning and 73% in the afternoon. April and May are theottest months, and the monsoon season from November to MarchNational Environment Agency, 2011). For this study, measure-
ents were conducted from 27th September 2011 to 13th March012. The measurement period was divided into Period A and B,here Period A denoted the measurement of both green walls,
nd Period B denoted measurement with Green Wall B removedTable 2). Only data for clear, sunny days were used for analysis.election of the days was based on solar irradiance data measuredn-site with a pyranometer. Measurements were made at 1 minntervals and averaged to hourly intervals for analysis (Table 3). Aotal of 28 points were set up for tmrt and ta measurement. Each
easurement point, which consists of a customised globe ther-ometer fixed at 1.7 m above ground and an air temperature sensor
oused in a PVC pipe, was secured with a concrete footing. For
he purpose of discussion, the measurement points are alignednd named as shown in Fig. 3. Air temperature was measured ateasurement spots 1 to 28 as well as the weather station. As thereen walls were exposed to self-shading and overshadowing at
, 4 and 6.
different periods of the day, daily data were grouped into fiveperiods corresponding to changes in exposure to solar radiation(Fig. 4, Table 4).
3. Results and discussion
3.1. Surface temperature (ts)
The surface temperatures of the two green walls was comparedto a portion of the wall directly exposed to the sun. The aim of thiscomparison is to determine the surface temperature reduction dueto the green walls. Data for five days were used for the analysis ofPeriod A and for nine days were used for the analysis of Period B.The daily data were averaged to produce a single profile for everymeasurement point.
An increase in surface temperature is observed for Point Z afterthe removal of Green Wall B. Point Z1 has a flat profile for Period A,but increased steadily to reach a peak of 34.3 ◦C at 17:00 h for Period
2 07:00–14:00 h Self-shaded3 14:00–17:00 h Exposed to direct sunlight4 17:00–19:00 h Overshadowing from trees5 19:00–00:00 h Sunset to night
60 C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64
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(Wm
-2)
Mea
n Ra
dian
t Tem
pera
ture
(°C)
Time (Hrs)
Poin t 2 Poin t 4 Poin t 6 Solar Ir radi ance
-10.0
90.0
190.0
290.0
390.0
490.0
590.0
690.0
790.0
24.0
29.0
34.0
39.0
44.0
49.0
54.0
59.0
0:00
1:00
2:00
3:00
4:00
5:00
6:00
7:00
8:00
9:00
10:0
011
:00
12:0
013
:00
14:0
015
:00
16:0
017
:00
18:0
019
:00
20:0
021
:00
22:0
023
:00
0:00
Sola
r Irr
adia
nce
(Wm
-2)
Mea
n Ra
dian
t Tem
pera
ture
(°C)
Time (Hrs)Poin t 2 Poin t 4 Poin t 6 Solar Ir radi ance
Period A
Time Range 4
Time Range 1 Time Range 2 Time Range 3 Time Rang e 5
Time Range 4
Time Range 1 Time Range 2 Time Range 3 Time Range 5
Period B
t solar
eg
sPhitpnoo
Fig. 9. Plot of Points 2, 4 and 6 agains
xception of Green Wall A, diurnal temperature fluctuations haveenerally increased.
The exposed concrete surface (Point Y1) exhibited the highesturface temperature for both periods (Fig. 5). The highest value foreriod A was 35.7 ◦C at 15:00 h. The maximum value was muchigher for Period B (44.6 ◦C at 17:00 h) and occurred 2 h later. The
ncrease in temperature was 8.9 ◦C. The interior surface tempera-ure (Point Y2) also increased after the removal of Green Wall B. The
rofile of Point Y2 was relatively flat for Period A, but increased sig-ificantly and peaking at 34.6 ◦C at 19:00 h for Period B. The removalf Green Wall B has significantly increased the surface temperaturef the exposed concrete wall. The temperature of Y1 is generallyirradiance for Period A and Period B.
much higher than Point Z1. This may be due to the fact that PointY1 was located closer to a structural concrete column, and thusexposed to a higher thermal mass.
The surface temperature of Point X2 was similar to Point X1for Period A but was consistently higher in Period B. No significantfluctuations were observed. The removal of Green Wall B had nosignificant effect on Green Wall A.
3.2. Air temperature (ta)
Air temperatures at all 28 measurement points in front ofthe green walls were analysed. Fig. 6 shows that the range of
C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64 61
interv
ar1Kr1
3
sn(it
mdFopi2
pcMt
Fig. 10. Comparison of tmrt profiles at 0.5 m
ir temperature did not fluctuate greatly. The maximum rangeecorded was about 1.1 ◦C for Period A, and increased slightly to.5 ◦C for Period B. This is similar to a study conducted by Wong,wang Tan, Chen, et al. (2010), where the ambient temperatureange recorded 0.6 m from green walls and a concrete wall was.25 ◦C.
.3. Profile of tmrt across measurement Points 1–7
The tmrt profiles for Period A for measurement Points 1–7 arehown in Fig. 7. It can be observed that a portion of the readingsear the bottom does not deviate significantly across the 7 points19:00 h to 07:00 h). As the sun rised to its zenith, the average tmrt
ncreased steadily, and the difference between the 7 points begino exhibit increasing amounts of deviation.
A distinct pattern is observed from 15:00 h to 17:00 h, whereost readings peak at Point 4. This pattern exhibits itself most evi-
ently at the highest recorded tmrt at 15:00 h. A comparison withig. 3 shows that Point 4 was the spot that was closest to the partf the wall that was exposed to direct sunlight, whereas the otheroints are covered with Green Walls A and B. This pattern dimin-
shed significantly until the fluctuations cease from approximately1:10 h onwards.
The same patterns were observed for Period B. However, higher
eak readings were recorded. This is expected, as there was moreoncrete surface that was exposed to direct sunlight for Period B.easurements of Points 5–7 are also higher than in Period A duringime range 3. The difference in tmrt value is clearly only significant
als from the wall for time range 3, Period B.
during time range 3 (14:00–17:00 h). Outside of this time range,the difference in tmrt between Points 1–7 is minimal.
3.4. Profile of tmrt for Points 2, 4 and 6
The diurnal tmrt profile is compared with the corresponding solarirradiance profile. To simplify the analysis, only 3 points were plot-ted. The points are show in Fig. 8.
Fig. 9 shows the diurnal tmrt plots across Points 2, 4 and 6for Period A and Period B. Time ranges 1 and 5 show no relationbetween the tmrt profile and solar irradiance (due to the absence ofsunlight). Time range 2 shows an increase in tmrt with solar irra-diance. Similarly, time range 4 shows a similar trend, with tmrt
decreasing with solar irradiance correspondingly. It can be seenthat the tmrt values correspond to fluctuations of direct and intensesolar irradiance (time range 3). More importantly, the largest dif-ferences in tmrt for the different points occur during periods of peaksolar irradiance. In other words, tmrt in front of the Green Walls arereduced during periods of peak solar irradiance.
Similar to Period A, time range 1 and the later part of time range5 show no relation between the tmrt profile and solar irradiance(due to the absence of sunlight). Time range 2 shows an increase intmrt with solar irradiance. Similarly, time range 4 shows a similartrend, with tmrt decreasing with solar irradiance correspondingly.It can be seen from time range 3 that the tmrt values reached their
peak at approximately 17:00 h, and it does not correspond to thesolar irradiance peak to the likes of Period A. It would seem thatthe exposure to increased concrete surface area has resulted in adelay of the diurnal tmrt peak. Increased longwave radiation may
62 C.L. Tan et al. / Landscape and Urban Planning 127 (2014) 52–64
51.0
62.2
53.0
58.6
63.7
65.0
58.8
60.5
50.0
52.0
54.0
56.0
58.0
60.0
62.0
64.0
66.0
Point 2 Point 9 Point 16 Poin t 23
Mea
n Ra
dian
t Tem
pera
ture
(°C)
53.0
55.9
58.9
61.5
65.9
62.3
63.863.6
50.0
52.0
54.0
56.0
58.0
60.0
62.0
64.0
66.0
Poin t 4 Poin t 11 Poin t 18 Poin t 25
Mea
n Ra
dian
t Tem
pera
ture
(°C)
53.1
55.7
59.959.5
64.0
59.1
63.363.1
50.0
52.0
54.0
56.0
58.0
60.0
62.0
64.0
66.0
Point 6 Point 13 Point 20 Point 27
Mea
n Ra
dian
t Tem
pera
ture
(°C)
Period A Period B
eriod
hs
0Grig
Fig. 11. Comparison of points for P
ave been stored and subsequently emitted by the exposed wallurface, resulting in the time lag.
This time lag is further scrutinised by comparing tmrt profiles at.5 m intervals away from the wall (Fig. 10). It can be seen from
raph A that the tmrt rises rapidly from 14:00 h to 15:00 h andeaches its peak at 17:00 h, when the solar irradiance has passedts peak. As the distance from the wall increases, this phenomenonradually decreases until the effect cannot be observed on Graph D
s A and B at peak solar irradiance.
(2 m away). A comparison shows that the time lag is approximately2 h.
3.5. Profile of tmrt plotted against distance from wall
To understand the effect of tmrt with increasing distance fromwall, measurements are taken at 0.5 m increments, up to a maxi-mum of 2 m. Fig. 11 shows three sets of measurement for Periods A
C.L. Tan et al. / Landscape and Urban
afevBp2pP
i1
3(
tcits4Ttt
4
o
tbbitflBttGo
Fig. 12. GIS visualisation of tmrt .
nd B. The measurements are positioned at 0.5 m intervals startingrom the centre of the green walls and concrete column. The high-st tmrt value recorded for Period A is at 13:20 h and the highest tmrt
alue recorded for Period B is at 16:20 h. The removal of Green Wall has caused a general increase to the tmrt profile, especially to theoints closest to the wall. There is an increase of 12.7 ◦C for Point, 12.9 ◦C for Point 4, and 10.9 ◦C for Point 6. The increase in tmrt foroints away from the wall (Points 9–16–23, Points 11–18–25 andoints 13–20–27) ranges from 1.9 ◦C to 6.4 ◦C.
The effect on tmrt due to the removal of the wall is most signif-cant within a region of 0.5 m. The highest recorded difference is2.8 ◦C for Point 4.
.6. Visualisation of tmrt using geographical information systemsGIS)
All 28 points are used for data interpolation using GIS. This facili-ates rapid analysis of the conditions of the surveyed area. Hot spotsan be identified easily with this method. Measurements for a typ-cal clear sunny day are used for visualisation via GIS. Fig. 12 showshe tmrt map of selected timings from 15:55 h to 00:35 h. It can beeen that the hot spot (dotted circle), which corresponds to Point, has a significantly high value compared to the rest of the points.his trend can be observed until approximately 00:00 h, althoughhe magnitude of the difference differs drastically across differentimings.
. Conclusion
The purpose of this study is to observe the effect of green wallsn the temperature of a surrounding environment.
Surface temperature measured behind the green walls showhat the green wall can reduce the surface temperature of theuilding envelope. This effect is not restricted to areas coveredy the installation of a green wall; areas that are in close prox-
mity to the green wall can also experience a reduction in surfaceemperature. The implementation of green wall helps to reduceuctuations of surface temperature. The removal of Green Wall
only resulted in a slight increase in air temperature. However,
here is significant difference in the tmrt, especially within 1 m ofhe green walls. The maximum increase in tmrt after the removal ofreen Wall B is 12.8 ◦C. When one green wall is removed, the effectf time lag can be observed. The peak readings in tmrt are delayedPlanning 127 (2014) 52–64 63
for approximately 2 h. Since the LAI of both green walls are similar,no significant correlation between LAI and temperature reductioncan be ascertained.
Results show that the implementation of vertical greenery canlower the tmrt of its surroundings. The effect of this attenuation isevident for up to 1 m away from the wall. However, this lowering iseffective only during periods of intense direct solar exposure. Theeffect is minimal during times when the green walls experienceself-shading or overshadowing. Consideration should be made tothe placement of vertical greenery to ensure maximum exposure todirect sunlight so as to take advantage of its tmrt reducing attributes.
This study revealed that the effects of shading provide the opti-mal form of tmrt reduction. When both green walls were presentthe peak tmrt occurred at 15:00 h, but with more concrete exposedwhen one wall was removed, the peak occurred at 17:00 h and was10.9 ◦C to 12.9 ◦C higher at 0.5 m away from the wall. Measurementpoints further away from the wall also recorded an increase in tmrt
ranging from 1.9 ◦C to 6.4 ◦C. Areas that do not have access to shademay consider the utilisation of green walls, strategically placed toprovide further reduction to tmrt. This can help architects and urbanplanners make informed decisions during design conceptualisationand to achieve better overall outdoor thermal comfort.
The physical dimensions of the green walls are not considered inthe analysis, and may become a variable in subsequent attempts atmeasurement. Similarly, the type of plants used will also be variedto explore the effects of different types of plants on the effects ontmrt.
The use of GIS for data visualisation enables convenient visualcomparison between tmrt profiles of different timings. The inter-polated values serve to provide a method to assess the tmrt of anygiven space that is easily comprehensible to architects and plan-ners. From the figures, it is evident that vertical greenery facilitatedthe reduction of tmrt both in the day and at night, to varying extents.
The proposed methodology enables systematic quantification ofthe effects of vertical greenery on mean radiant temperature, andcan be used for the measurement of other forms of vegetation inthe tropical urban context.
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