Solar Radiation Transmission of Green Façade in the Tropics

Abstract

Green façade (GF) is attached on external building wall to intercept an amount of excessive global solar radiation towards vertical building envelope. An improvement on habitable thermal environment is led by reduction of incident solar radiation on the external façade of wall. The main objective of this study is to investigate the amount of solar radiation transmitted through green façade attached on building opaque wall. The investigation was carried out via comparison experiment using two identical thermal labs; one was attached with GF at eastern and western orientations, and one was for control. The experiment was conducted on clear sunny day in Universiti Putra Malaysia, Serdang, Malaysia. The results showed that the reduction of incident solar radiation on external wall with GF was enhanced indoor thermal environment. It can be noticed through reduction on external and internal surface temperature of behind walls attached with GF.

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Kongres Penyelidikan & Inovasi UKM2013
Kongres Penyelidikan
& Inovasi UKM2013
http://www.ukm.my/
Solar Radiation Transmission of Green Façade in the Tropics
Mohd Khairul Azhar Mat Sulaiman, Maslina Jamil & Muhammad Fauzi Mohd Zain
Jabatan Seni Bina, Fakulti Kejuruteraan dan Alam Bina,Universiti Kebangsaan Malaysia, 43600 UKM Bangi Malaysia
Abstract
Green façade (GF) is attached on external building wall to intercept an amount of excessive global solar radiation towards
vertical building envelope. An improvement on habitable thermal environment is led by reduction of incident solar radiation on
the external façade of wall. The main objective of this study is to investigate the amount of solar radiation transmitted through
green façade attached on building opaque wall. The investigation was carried out via comparison experiment using two identical
thermal labs; one was attached with GF at eastern and western orientations, and one was for control. The experiment was
conducted on clear sunny day in Universiti Putra Malaysia, Serdang, Malaysia. The results showed that the reduction of incident
solar radiation on external wall with GF was enhanced indoor thermal environment. It can be noticed through reduction on
external and internal surface temperature of behind walls attached with GF.
Keywords: Green Façade, Solar Radiation Transmission, Thermal Performance, Passive Cooling
1. Introduction
Being a tropical climate region, Malaysia located near to equator, naturally receives abundant of sunshine and
thus solar radiation throughout a year. According to Azhari et al. (2008), Malaysia receives on average annually of
4.96kWh/m² per day of global solar radiation. An excessive radiation causes many problems especially on habitable
thermal environment and cooling energy consumption when building envelope gains unnecessary heat from global
solar radiation.
An introduction of green façade (GF) into built environment, is one of passive cooling solution to prevent
building envelope from receiving undesirable amount of solar radiation. GF is a vertical greenery system with
intervention of vertical vegetation; i.e. climbing plant on supporting system such as trellis, wire mesh or cable,
which mounted on exterior building façade as external shading layer. By intercepting the amount of solar radiation
towards external façade of wall, it leads to lessen heat gain and promoting a better sustainable living environment
and energy efficiency (Wong et al, 2010). Climbing plant such as vines on trellis of GF becoming outermost layer
intercept great amounts of radiation for biophysiological purposes and at the same time, provide shades on opaque
wall behind GF. Shade created by climbing plant canopy which consists of leaves, branches and twigs is affected by
biological-horticultural characteristics of the plant species and the environmental growth conditions (Koyama, et al.
2103). Leaves distribution and arrangement in canopy in form of leaf layer contributes to thickness and density of
plant canopy (Holm, 1989). Higher ratio of overlapping area of leaf layer has rapidly diminishes fractional area of
sunflecks of solar radiation after entering vertical plant canopy (Mõttus, M., 2004). Thus, the remaining portion of
solar radiation which able to transmit through the plant canopy is one of heat gain sources for behind wall of GF and
can be noticed on fluctuation of external and internal surface temperature.

Mohd Khairul Azhar Mat Sulaiman, Maslina Jamil & Muhammad Fauzi Mohd Zain
The main objective of this study is to investigate solar radiation transmission of GF attached on external
building wall at eastern and western orientations. The evaluation of transmitted solar radiation is based on external
and internal surface temperature of opaque walls.
2. Experimental Methodology
A comparison study on stationary experiment was conducted for one month duration, 1st-30th April 2013 on
two identical thermal labs at Faculty of Design and Architecture, Universiti Putra Malaysia, Serdang (2.99°N,
101.71°E). Both of two thermal labs have similar properties in terms of design, size, materials, openings, orientation
and surrounding environment. Size of thermal lab is 3.05m (l) x 3.0m (w) x 3.6m (h). These thermal labs are using
cement and sand brick with plastering on both sides which is common wall widely used in construction industry in
Malaysia. Orientation of building followed cardinal compass orientation and bare opaque walls are facing towards
east and west orientation. Double roofs system had been retrofitted for both thermal labs with naturally ventilated air
gap of 0.25m in between to prevent overheating from direct solar radiation (Lee et al. 2009; Susanti, Homma, and
Matsumoto 2011). All fenestrations on north and south wall were sealed with white A0 size drawing papers to
eliminate thermal infiltration. Proper calibrations had been carried out before any measurements taken for both
thermal labs and all instruments involved in this experiment.
Figure 1: Thermal lab attached with GF (left), control thermal lab (right) and Onset Hobo weather station set up
nearby thermal labs (arrow).
One of the thermal labs had been attached with GF in front of opaque walls at distance of 0.15m on east and
west orientation. Climbing plant was used for this experiment is Thunbergia gradiflora. For each GF, a total of 9
nos. of climbers in individual white polystyrene boxes were used to maximize the percentage of trellis coverage.
Range of coverage percentage for both GFs is 85 to 95%. Meanwhile, east and west orientation walls at another
thermal lab were left plain without any GF attached, for control thermal lab. Figure 1 shows both of thermal labs
which were used in this study. For indoor condition, both thermal labs were empty and no activity occurred along
experiment is conducted.
Figure 2 shows the instruments used in the experiment. Control thermal lab was installed with Onset Hobo S-
LIB-M003 solarimeters in front of east and west orientation of opaque wall to measure incident solar radiation,
whereas solarimeters were installed at behind of GF for test thermal lab to measure incident solar radiation been
transmitted. All solarimeters were installed in vertical direction at middle of the walls and height of 1.5m from
ground level. All measurements were recorded using U30-NRC Onset Hobo data logger at interval of 10 minutes.
For each east and west wall, at external and internal surface, 8 sets of single channel Onset Hobo U12 type K
thermocouple data loggers were used for the measurement of surface temperature. Measurements were recorded at
interval of every 10 minutes.

Prosiding Kongres Pengajaran & Pembelajaran UKM2013 (2013): 000- 000
An Onset Hobo weather station was set up nearby to collect meteorological parameters which include ambient
air temperature, relative humidity, global solar radiation, wind speed, wind direction and rainfall as shown in Figure
1. It is worth to mention, for the purposes of this study, measurement of surface and air temperature are the only
relevant parameters to be used for thermal evaluation. Other measurements were carried out for underway
interrelated research. All results obtained in this study are on clear sunny day in the month, 16th April 2013.
Figure 2: Positions of instrument for both thermal labs.
3. Findings
On clear sunny day of 16th April 2013, average ambient air temperature is 32.7°C. Average global solar
radiation measured horizontally at weather station set up nearby is 460.9 W/m². Higher amounts of global solar
radiation were recorded at noon time, from 1200h until 1400h, with maximum global solar radiation, 866.8 W/m² at
1200h as shown in Figure 3. At this duration of time, horizontal surface such as roof receives highest amount of
solar radiation (Jayasinghe, Attalage, and Jayawardena 2003).
Figure 3: Comparison of mean global solar radiation, measured horizontally at weather station (Station), measured
vertically in front of wall of control thermal lab (Control) and in between GF and wall at GF attached thermal lab
(Green) and at eastern and western orientations on clear sunny day, 16th April 2013.

Mohd Khairul Azhar Mat Sulaiman, Maslina Jamil & Muhammad Fauzi Mohd Zain
As this study is to investigate incident solar radiation on vertical wall, it can be noticed similar trend pattern of
solar radiation measured at east and west orientation for both thermal labs shown in Figure 3. The measurements
were taken at vertical direction. Due to orientation of the wall, eastern wall orientation received higher amount of
radiation in the morning (0700-1300h) meanwhile for western wall orientation at the afternoon (1300-1900h). The
amount of solar radiation transmitted behind GF dramatically low compared to amount of incident solar radiation in
front of opaque wall of control thermal lab. A total reduction of solar radiation behind GF was 70.9% compared to
control thermal lab at eastern orientation. Meanwhile, at western orientation GF, total reduction of solar radiation
was 57.1% compared to control thermal lab. The results were verified the presence of GF in front of opaque wall as
shading element which is significantly able to reduce incident solar radiation from penetrate through opaque wall.
Figure 4 shows solar radiation differences between control and test thermal lab for both orientations. At east
orientation, maximum difference of incident solar radiation was demonstrated by 459.6 W/m² at 0900h. On the other
hand, difference of incident solar radiation been recorded was 486.9 W/m² at 1600h for west orientation.
Figure 4: Solar radiation difference, Control vs. Green on clear sunny day, 16th April 2013.
To evaluate thermal performance of solar radiation transmission provided by application of GF, an external
and internal surface temperature is discussed. Average temperatures of external and internal wall surface for GF
attached thermal lab and control thermal lab were depictured and shown in Figure 5. The average temperature of GF
thermal lab for internal and external surface was lower compared to control thermal lab. In addition, temperature
fluctuations for thermal lab attached with GF for inside and outside of surface temperatures at both orientations were
more stable than the control thermal lab walls. Interesting finding can be observed on almost similar temperature
profile for indoor surface temperature of both wall orientations at GF attached thermal lab, confirming a stable
indoor ambient air temperature due to reduction of heat gain and heat transfer from outer surface.
The maximum difference of temperature was observed on external wall surface at eastern and western
orientation, reaching 15.0°C and 21.0°C, respectively (Figure 6). Smaller differences of temperature at internal wall
surface compared to external surface temperature differences. However, temperature reductions at external and
internal surface were attested on reduction of incidence solar radiation of GF. The results also proved that heat gain
and transfer through behind wall attached with GF was declined compared to opaque wall without GF. Smaller
amounts of solar radiation transmitted at opaque wall behind GF provide a better internal and external surface
temperature of wall and consequently enhanced indoor air temperature.

Prosiding Kongres Pengajaran & Pembelajaran UKM2013 (2013): 000- 000
Figure 5: Comparison of mean surface temperature, °C measured at weather station (outdoor station), external and
internal wall surface of eastern and western orientations at GF attached thermal lab (Green) and control thermal lab
(Control) on clear sunny day, 16th April 2013.
Figure 6: Internal and external surface temperature difference, Control vs. Green on clear sunny day,
16th April 2013.

Mohd Khairul Azhar Mat Sulaiman, Maslina Jamil & Muhammad Fauzi Mohd Zain
4. Conclusion
The presence of GF in front of opaque wall has given a significant contribution towards thermal environment
enhancement. It can be notified through reduction amount of incidence solar radiation on opaque wall in term of
solar radiation transmission. In this study, the amount of solar radiation transmitted behind GF dramatically low
compared to amount of incidence solar radiation in front of opaque wall. Total reductions of solar radiation behind
GF are 70.9% and 57.1% compared to control walls of thermal lab at eastern and western orientation, respectively.
Maximum difference of incidence solar radiation is 459.6 W/m² at east orientation and 486.9 W/m² at west
orientation. Smaller amount of solar radiation transmission is generating smaller surface temperature of wall behind
GF. A stable indoor ambient air temperature is formed due to reduction of heat gain and heat transfer from outer
surface which can be noticed from the lesser internal and external surface temperature.
Acknowledgement
The authors are grateful for the financial support from the Research Grant from the Universiti Kebangsaan
Malaysia; UKM-AP-PI-12-2010, and Ministry of Education; LRGS/TD/2011/UMS/PG/03.
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