Shading performance of tropical climbing plant: Anemopaegma chamberlaynii on green façade M.K.A.M.Sulaiman¹ ²*, M.Jamil¹, M.F.M.Zain¹, W.Kuttler², and M.F.Shahidan³ ¹Department of Architecture, Universiti Kebangsaan Malaysia, Malaysia. m.khairulazhar@yahoo.com ²Institute of Applied Climatology and Landscape Ecology, University of Duisburg-Essen, Germany. ³Department of Landscape Architecture, Universiti Putra Malaysia, Malaysia. Abstract An appropriate selection of climbing plant for Green Façade (GF) is a crucial step to achieve optimum performances for a better living sustainable environment. The main target is to avoid frustration towards expectation on effectiveness of this passive cooling technique. Climbing plants on GF provide shades and intercept amounts of solar radiation hence lessen heat flux transfer through wall behind the GF. Consequently, it reduces immediate ambient air temperature and surface temperature of the behind wall. Different physical characteristic of each climbing plant offers different quality of shades. An experiment for evaluation on shading performance of tropical species of climbers used on GF has been conducted using Anemopaegma chamberlaynii (AC). A control experiment with small scale size of freestanding wall [1.5m (h) x 1.0m (w) x 0.15m (t)] attached with GF (modular trellis) and planter box at ground was built for this study. The aim of the experiment was to establish shading coefficient of climbing plant. Photo pixel recognition and measurements of solar radiation transmitted behind GF were carried out in formation of climbing plant shading coefficient. Efficient shading performance of AC was observed with increasing area of total leaf coverage especially with higher number of leaf layer which contributed to plant canopy density. Keywords: Green Façade, Tropical Climbers, Shading Performance, Shading Coefficient. 1. Introduction An intervention in bringing vegetation into manmade environment has been attested to stimulate a better living sustainable environment. Innovations on implementing vegetation on horizontal and vertical exterior façade of building such as green roof, green wall and green façade have been identified in encouraging potentials to ameliorate not only on external and internal building environment but also current and future urban climate conditions [1]. These innovations are also promoting energy efficiency on cooling load usage. A key factor to successful outcomes depends on vegetation used in the system [2-5]. Thus, a careful decision on plant selection to be used is a crucial step to be taken in optimizing the performance of the system. Furthermore, it is essential to avoid frustration on the expectation of effectiveness of these systems as passive cooling technique. In this study, green façade (GF), which is one of vertical greenery systems applied in building construction industry is discussed. GF is a vertical manner planting system rooted in the ground or planter pot, using supporting structure such as modular trellis, wire mesh or cable for climbing plants in screening exterior surface of building façade. The main advantage of climber is to provide shades onto vertical structure, i.e. wall at the rear of GF, promoting thermal benefit of GF system. According to Perez et al. [2], surface temperature of a wall attached with GF significantly decreased by 15.18 C, and intermediate air temperature of the layer between GF and wall was reduced by almost 1.4 C in summer. Also, in the presence of GF in front of wall, the amount of heat flux being transferred into the interior space of building has been reduced. GF intercepted almost 80% of heat flux before it was reflected and transmitted to behind wall [6]. Thus, according to Sunakorn and Yimprayoon [7], GF helped to reduce the indoor air temperature by 0.9 C on average, therefore promoting a favourable indoor thermal environment for occupant. Climbers as outermost layer absorb direct and diffuse radiation, thus intercepting the amount of heat to be transmitted to the rear of GF. Incoming energy from radiation has been converted for climber biophysiology such as photosynthesis and transpiration. Canopy of climbers cast shadow onto building facade, therefore decrease the amount of heat to be transferred and consequently regulate local ambient air temperature and thermal environment. 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. Leaves distribution and arrangement in canopy in form of leaf layer contributes to thickness of foliage. According to Holm [8], increasing number of leaf layer in plant canopy tends to diminish total incident energy transmitted. Energy transmitted through two layers of leaf reduces radiation by about 5%
comparing to single leaf layer of Hedera helix. Therefore, this study aimed to establish fundamental database knowledge of shading coefficient for tropical climber to apply on GF for optimum performance of this innovation. Investigation of shading performance was conducted for species of tropical climber, namely Anemopaegma chamberlaynii. 2. Shading Performance of Vertical Plant Canopy Generally, Leaf Area Index (LAI) is widely used to measure shading performance on growth of plant canopy. LAI is defined as fraction of total onesided of leaf surface for plant canopy over ground surface. Proportion of solar radiation transmission underneath of horizontal plant canopy and outside of canopy is used to establish LAI. It was found that plant with larger LAI reduces heat flux transmitted, and modifies immediate ambient and indoor air temperature [4, 9-11]. This assessment methodology is commonly used for horizontal plant canopy instead for vertical canopy plant, which most measurements were taken underneath plant canopy. Thus, measurement of shading coefficient is otherwise applied to investigate shading performance of vertical plant canopy. Shading coefficient is one of the assessment methodologies that is usually used to evaluate shading performance especially for conventional shading device in the field of thermal design for building. Ip, et al. [12], has introduced a noble measurement technique to establish dynamic shading coefficient of vertical canopy plant in representing shading performance over annual growing and wilting cycle. Basically, the concept of shading coefficient of building s shading device calculation has been adopted to calculate shading coefficient of vertical plant canopy. Shading coefficient (SC) is defined as the proportion of solar radiation gain behind the canopy and in front of canopy. It is expressed as: SC = solar gain behind GF at direct normal solar incidence solar radiation in front of GF at direct normal solar incidence (1) As the vertical plant canopy is a compacted of numbers of different leaf layers (k) which have corresponding area, A k in the plane of canopy, shading coefficient (SC) can be expressed as: n k=1 A k T k A f + A 0 + n k=1 A k SC = A 0T 0 + (2) where A 0 is the area of open gaps in the canopy (m²), T 0 solar radiation transmitted of open gaps (=1), T k solar transmitted for 1 to k leaf layer (0-1), k number of leaf layers, A k area of canopy with kth leaf layers (m²), A f area of climbing frame (m²). 3. Experimental Methodology 3.1 Plant Selection Due to weather tolerance, tropical climber was used as this study was conducted in tropical region. A native plant to surrounding climatic condition promotes better growth development and performance. The selection of the plant species is based on criteria formulated in Table 1. It is also worth to mention that the selection climbing plant depends on the availability in the nursery. Thus, Anemopaegma chamberlaynii (AC) was selected as the climber in this investigation (Fig 1). Criteria of AC are shown in Table 2. Fig 1. Specimen of Anemopaegma chamberlaynii. Table 1: Selection criteria for climbing plant. Factor Selection Criteria Remarks Growth rate Vigorous and fast Limitation of research time for plant to grow Coverage Spreading Able to maximise coverage on supporting structure within time frame given Weather tolerance Full sun Full sun to act as shading device and able to withstand extreme weather conditions Maintenance Low Low on fertilizing, pesticides monitoring and watering. Climbing pattern Twinning and clinging System selected with trellis supporting structure; not suitable for adhesive type Leaf size Large Larger leaf provides large shading effect Availability in nursery High supply of preferable climber Limited supply in market for climber
Table 2: Criteria for selected tropical climbing plant. Growth rate Coverage Criteria Weather tolerance Leaf size Climbing pattern Maintenance Vigorous Spreading Anemopaegma chamberlaynii Full sun and hardy Small 5cm Twinning with hooked tendrils Low Most of the vegetation being native to tropical region is evergreen all through the year. Located near to an equatorial, vegetation receives abundant solar radiation throughout the year. Thus, the results of measurement were assumed can be predicted for an annual performance. 3.2 Control experiment A control experiment is not a new concept for thermal performance investigation of green façade. Researchers [13-16] have already developed a mock-up model in their studies resembling an actual size of GF and building wall. A small scale of GF with wire mesh trellis attached at freestanding wall was built for this study. The size of freestanding wall was 1.5m(h) x 1.0m(w) x 0.15m(t) and 1.5m(h) x 1.0m(w) for trellis, with planter box at the bottom. Fig. 2 shows the details measurement of mock-up of GF. The planter box was painted with white colour for heat absorption reduction and it was planted with three numbers of climbers. Each of climbers was ensured at almost similar height before being transferred into the planter box. Climbers were left for a month for establishment of canopy before any measurements were taken. Modules were arranged at west facing orientation. The experiment was conducted for the time period of 30 days (10 th September-9 th October 2012) at Faculty of Design and Architecture, Universiti Putra Malaysia (2.99 N, 101.71 E). It was conducted to establish shading coefficient of climber. Measurement techniques developed by Ip. et al. [12] were implemented in this study, however slightly modification has been made due to parameter and limitation of this study. Fig 2. Details measurement of single set of mock-up of GF 3.3 Leaf Coverage A pixel segmentation of digital image was used to investigate the establishment of leaf coverage [11, 16]. Similar method was employed by Ip et al.[12] to identify the number of leaf layers in vertical plant canopy. A pixel recognition technique relies on the principle that a particular leaf layer in the canopy is related to a particular range in colour on the digital image. It was used to calculate leaf coverage at transparent glazing material for an opening or a wall. Digital image was captured at the backside of GF, which was viewed from inside of the room through transparent glazing opening. The opening was attached with GF at the front. However, slight changes had been made to tailor parameters set for this study; an investigation on opaque façade instead of glazing façade had been realised. To capture a digital image from the backside of GF is certainly impossible for an opaque wall. Thus, to overcome this problem, photo session was done at night time; with black and dark background conditions, when only light source came from floodlights. Fig 3. Placement of floodlights at top and bottom of module and measurement of solar radiation at front and behind of GF. Light sources from two units of 50-Watt cool white LED waterproof floodlight placed at the top and bottom of the module in between the freestanding wall and GF. The arrangement was able to create effect of colour shades that represented different leaf layers. Placement of floodlights in between of module is shown in Fig. 3. Photos were captured by Nikon D3100 digital camera at front of GF at regular distance. Fig. 4 shows an example of photo taken at night time producing different shades of green colour. Digital images were analysed by a pixel segmentation and recognition function in the graphic software Adobe Photoshop CS3. A pixel recognition procedure distinguished the different green shades of climber canopy and thereby extracts their relative areas over an opaque wall.
Light green with one leaf layer Open gap Dark green with dense leaf layer Fig 4. Photo of plant canopy showing different green shades taken at night time. 3.4 Transmitted Solar Radiation through Leaf Layers Measurement of normal incidence and transmitted solar radiation was taken using SL100 E Instruments solarimeter fixed on customised hand holder for ease of operation. Measurement was taken vertically at front of GF and behind GF as shown in Fig. 4. A large number of repeated measurements were carried out and average values were taken to minimise the experimental errors. Measurements were taken at one-leaf to four-leaf layers. Reading for five and above leaf layers was assumed to be similar with four-leaf layers. This was due to a small total area of coverage of leaf beyond fourleaf layers in canopy, thus it was difficult to be measured. Before any measurement was taken, specimen was left for foliage establishment and maximum coverage on GF. Therefore, it can be clearly seen in Fig.6 that coverage areas and number of leaf layers of AC for throughout 30 days of experiment are relatively consistent. Distribution areas of leaf layers coverage of AC was continuously stabilized until the end of experiment. From total area of climbing frame (1.5m²), AC managed to provide a total of 1.297m² covered area of leaves or 86.5% of an average of total leaf coverage areas (Fig. 7). AC also produced more than half of three-leaf and four-leaf layers from the total leaf coverage areas. Thus, it indicated the good quality of shades produced by AC due to high density of plant canopy. Fig 6. Area distribution of leaf layers of Anemopaegma chamberlaynii for 30 days experiment. 4. Result and Discussion 4.1 Leaf Coverage Digital images of tropical climber Anemopaegma chamberlaynii (AC), were taken in regular intervals and analysed using the pixel recognition technique in order to establish the leaf layers and their corresponding areas on the canopy. Images of different leaf layers and percentage of coverage areas for AC for a single day are illustrated in Fig. 5. Fig 7. Average of distribution area in meter sq. of different leaf layers for Anemopaegma chamberlaynii. Fig 5. Leaf coverage areas in percentage and different leaf layers of Anemopaegma chamberlaynii on 18 th days of experiment, 27 th September 2012.
4.2 Solar Radiation Transmission Solar radiation was measured at behind the leaf layers and simultaneously at front of the plant canopy. A proportion of solar radiation received before and after moving through the GF represents solar radiation transmitted through leaf layer. It can be expressed as: T k = I k I 0 (3) where T k is solar radiation transmission coefficient for k leaf layers, I k ; solar radiation per unit area behind k leaf layer (Wm ²) and I 0 is ambient solar radiation per unit area perpendicular to the leaf (Wm ²). Calculated solar transmission coefficients for each leaf layers are shown in Fig. 8 for AC. An average transmission values were represented by the horizontal line for each leaf layer. Table 3 summarises average solar radiation transmission values for AC for each corresponding leaf layer. Table 3: Average solar radiation transmission value for Anemopaegma chamberlaynii. Number of leaf layer Average solar transmission values 1-leaf layer 0.64 2-leaf layers 0.44 3-leaf layers 0.35 4-leaf layers 0.24 In average, AC was capable to provide suitable performance of coefficient value for each leaf layer, despite of having a small leaf size (~5cm). It was found that, the reduction of solar radiation transmission was influenced by the total density of AC which gave more than 70% of total coverage area with dense layer; three-leaf and four-leaf layers. Fractional area of sunflecks after solar radiation entering the canopy was rapidly diminished with higher ratio of overlapping leaf area of AC. The compactness of AC foliage intercepted solar radiation and shade provided by the dense layers had stabilised the energy transmitted towards the wall. However, one-leaf layer was proven incompatible compared to other leaf layers because of sparse and loose arrangement of leaf coverage. Significant negative correlation between leaf coverage area and solar radiation transmission is shown in Fig. 9. It was demonstrated that climber with denser plant canopy was more pronounce to provide cooling effect from the GF than sparse plant canopy. 1 layer Fig 9. Relationship between leaf coverage area and solar radiation transmission for Anemopaegma chamberlaynii. Fig 8. Solar radiation transmission for different leaf layers of Anemopaegma chamberlaynii. 4.3 Shading Coefficient The results of leaf coverage area and transmitted solar radiation of each leaf layer were applied to Eq. (2) for shading coefficient establishment of AC. The shading coefficient of AC was 0.21. Thus, establishment of shading coefficient indicated Anemopaegma chamberlaynii (AC) is suitable climbers to be applied on GF for reduction of solar radiation transmission towards behind wall.
5. Conclusion Selection of plant to be applied on GF is an important procedure as plant plays a key role in determining the overall effectiveness of the passive cooling technique. By establishing the fundamental knowledge on shading coefficient of the potential climber, it could increase the efficiency of this shading system. The shading coefficient of Anemopaegma chamberlaynii (AC) is 0.21. It was noted that AC is suitable climber to be applied on GF for optimum benefit in providing better living sustainable environment. As this study has experimented on white opaque wall attached with GF, it has been found that suitable climber to be applied on trellis should has higher total area of leaf coverage which consists of higher number of leaf layer. This will create higher volume of plant canopy density. Thus, it provides the best shading performance for the behind wall. A GF with only single leaf layer plant may not perform as efficiently as intended since heat from behind opaque wall can override the benefit of such greenery. 6. Acknowledgements Authors would like to thank Prof. Dr. Sharifah Mastura Syed Abdullah, Head of LRGS niche Global Warming, UKM, SUCOMBS Research Group, Faculty of Engineering and Built Environment, UKM and to Ministry of Education (MOE) for sponsoring my study. Thank you to Architecture Department, Faculty of Design and Architecture, UPM for allowing me to rent both of thermal labs. Special thanks to Zuhairi Yusoff, Ikmal Hisham Ismail, Muhammad Bukhari Kammarsuddin and Abd Fattah Abu Hadin from Department of Architecture, UKM, Rozaimi Abu Samah from Universiti Malaysia Pahang (UMP) and to Kak Ton (Mujia Tun) and Kres Tina from FSRB, UPM for their kind assistance and support. energy efficiency1995, New York: John Wiley & Sons, Inc. 7. Sunakorn, P. and C. Yimprayoon, Thermal performance of biofacade with natural ventilation in the tropical climate. Procedia Engineering, 2011. 21(0): p. 34-41. 8. Holm, D., Thermal improvement by means of leaf cover on external walls A simulation model. Energy and Buildings, 1989. 14(1): p. 19-30. 9. Barrio, E.P.D., Analysis of the green roofs cooling potential in buildings. Energy and Buildings, 1998. 27(2): p. 179-193. 10. Takakura, T., S. Kitade, and E. Goto, Cooling effect of greenery cover over a building. Energy and Buildings, 2000. 31(1): p. 1-6. 11. Shahidan, M.F., et al., A comparison of Mesua ferrea L. and Hura crepitans L. for shade creation and radiation modification in improving thermal comfort. Landscape and Urban Planning, 2010. 97(3): p. 168-181. 12. Ip, K., M. Lam, and A. Miller, Shading performance of a vertical deciduous climbing plant canopy. Building and Environment, 2010. 45(1): p. 81-88. 13. Jim, C.Y. and H. He, Estimating heat flux transmission of vertical greenery ecosystem. Ecological Engineering, 2011. 37(8): p. 1112-1122. 14. Laopanitchakul, V., P. Sunakorn, and A. Srisutapan, Climbing-plant on solid wall for reducing energy in tropical climate, in Sustainable Building Conference2008: Seoul, Korea. 15. Wong, N.H., et al., Thermal evaluation of vertical greenery systems for building walls. Building and Environment, 2010. 45(3): p. 663-672. 16. Koyama, T., et al., Identification of key plant traits contributing to the cooling effects of green façades using freestanding walls. Building and Environment, 2013. 66(0): p. 96-103. 7. References 1. Kuttler, W., Climate change on the urban scale - effects and counter-measures in Central Europe, in Human and social dimensions change, N. Chhentri, Editor 2012, In Tech: Croatia. p. 105-142. 2. Wong, N.H., et al., Investigation of thermal benefits of rooftop garden in the tropical environment. Building and Environment, 2003. 38(2): p. 261-270. 3. Pérez, G., et al., Behaviour of green facades in Mediterranean Continental climate. Energy Conversion and Management, 2011. 52(4): p. 1861-1867. 4. Hodo-Abalo, S., M. Banna, and B. Zeghmati, Performance analysis of a planted roof as a passive cooling technique in hot-humid tropics. Renewable Energy, 2012. 39(1): p. 140-148. 5. Fang, C.-F., Evaluating the thermal reduction effect of plant layers on rooftops. Energy and Buildings, 2008. 40(6): p. 1048-1052. 6.Brown, R.D. and T.J. Gillespie, Microclimatic landscape design creating thermal comfort and