Application of Green Façade as Passive Cooling Technique for Energy Efficiency Mohd Khairul Azhar bin Mat Sulaiman Architecture Department, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia. Institute Applied Climatology & Landscape Ecology, Faculty of Biology, University of Duisburg-Essen, Essen, Germany. m.khairulazhar@yahoo.com  

Contents Introduction Objectives Methodology Results & Discussion Conclusion

Introduction Building Energy Efficiency can be improved by implementing Active Energy Efficient strategies Passive Energy Efficient strategies Heating, Ventilation & Air-conditioning (HVAC) systems, electrical lighting Building envelope – insulation, material, shading devices, green roof, green facade Energy savings of 31.4% and peak load savings of 36.8% were recorded for high-rise apartments in hot and humid climate of Hong Kong by implementing passive energy efficient strategies (Cheung, C.K. et al., 2005). In Greece, application of external shading (e.g. awning) and light-coloured roof and external wall reduced the space cooling load by 30% (Balaras C.A. et al, 2000)

For green façade, Wong et al, 2009, conducted a simulation study on energy saving for 10 floors building attached with 100% coverage of greenery on green façade at external wall. Reduction of 17.93% on energy cooling load compared to building with no-greenery at exterior facade. Issue Government of Malaysia has announced, which ordered government offices to set an air-conditioning temperature no lower than 24° Celsius for optimum indoor thermal comfort and energy saving step. According to Ministry of Energy, Green Technology and Water, by lowering one degree (23° C) on air-conditioning thermostat, overall expenditure will increase from 4 to 7 per cent annually – BERNAMA, Malaysia National News Agency, reported on 11 August 2011 Thus, this study is investigating on application of green façade as passive cooling technique for energy saving step on cooling period of office building.

Green façade (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. As passive cooling technique in providing conducive indoor thermal environment and energy efficiency, GF acts as external shield offer shades to the building facade avoiding undesirable excessive radiation and reducing heat flux transfer through exterior surface (Chen, Li, and Liu 2013, Jim and He 2011). transmitted radiation cooling load cooling load solar radiation solar radiation indoor outdoor indoor outdoor control unit green unit

However, a key factor to successful outcomes is depending on vegetation used in the system (Wong N.H. et al, 2003; Perez et al, 2009; Hodo-Abalo, S. et al, 2012, Fang C.F., 2008). Thus, a carefully decision on plant selection to be used is a crucial step to be taken for optimization on performance of the system. Furthermore, this step need to be engaged is to avoid frustration on the expectation of effectiveness of these systems as passive cooling technique. This study aimed to investigate performance of selected tropical climbing plants used on GF for energy efficiency on cooling load for office building. Selected tropical climbers used for this study are Thunbergia grandiflora and Argyreia nervosa. Research Objective To investigate on energy saving of space cooling load for building attached with Green Façade (GF) at eastern and western orientation walls using selected tropical climbers; Thunbergia grandiflora and Argyreia nervosa.

Research Methodology

Results & Discussion 1st experiment was conducted on 08th June 2013, one unit of thermal lab attached with GFs on east and west wall, using Thunbergia grandiflora. Meanwhile, the other one was left plain. On east orientation, leaf area index (LAI) for Thunbergia grandiflora is 4.14, and west is 4.08. Leaf size-15cm, dense plant canopy. The experiment was conducted on sunny day, from 0800 to 1700hr. Average outdoor ambient temperature and solar radiation is 31.7 °C and 324.9W/m², respectively. Energy savings: 17.2% per day Peak load savings: 25.0% Energy rate savings: RM0.24/day

Results & Discussion 2nd experiment was conducted on 04th August 2013, one unit of thermal lab attached with GFs on east and west wall, using Argyreia nervosa. Meanwhile, the other one was left plain. On east orientation, leaf area index (LAI) for Argyreia nervosa is 3.72, and west is 3.84. Leaf size-27cm (large), medium dense plant canopy. The experiment was conducted on sunny day, from 0800 to 1700hr. Average outdoor ambient temperature and solar radiation is 33.1 °C and 527.0W/m², respectively. Energy savings: 15.2% per day Peak load savings: 34.2% Energy rate savings: RM0.22/day

Results & Discussion Temperatures of the interior wall surface and indoor air are important parameters to evaluate the indoor thermal environment. Indoor surface temperature on east and west orientation walls of test cell with GF has a smaller temperature fluctuation comparing to control cell walls. Similar results were demonstrated on indoor air temperature fluctuation. It can be seen that the GF has a promising effect on stabilizing the indoor environment when the air conditioner is on. Consequently, it helps in reducing energy consumption for cooling loads. Thunbergia grandiflora Argyreia nervosa

Results & Discussion

Results & Discussion

Results & Discussion Previous results are indicated GF was performed significantly for building energy efficiency. Both of climbers on GF were demonstrated able to promote energy savings on cooling periods. Next experiment was conducted to identify which climbers on GF is performed effectively in reducing energy consumption for cooling load. The 3rd experiment was conducted to compare performance between Thunbergia grandiflora (TG) and Argyreia nervosa (AN) on GF on 28th August 2013. One unit of thermal lab attached with GFs on east and west wall, using Thunbergia grandiflora. Meanwhile, the other one was attached with GFs on east and west wall, using Argyreia nervosa. The experiment was conducted on sunny day, from 0800 to 1700hr. Average outdoor ambient temperature and solar radiation is 30.1 °C and 328.0W/m², respectively.

Results & Discussion Results are indicated GF was performed almost similar for building energy efficiency despite of having different LAI (TG; average LAI of 4.11 and AN; average LAI of 3.78). This is due to leaf size of AN (average of 27cm) which can provides large of leaf coverage (Ip et al., 2010). However, TG was identified as most suitable climber for energy efficiency compared to AN. Energy savings of TH vs AN: 5.2% per day Peak load savings of TH vs AN : 15.4% Energy rate savings TH vs AN : RM0.03/day

Results & Discussion Interior surface temperature of walls for both climbers were illustrated having a similar inclined pattern. However, interior surface temperature of AN at east orientation was identified having highest increment due to lower LAI; i.e. 3.72. Nevertheless, at west orientation, AN was performed efficiently even with lower LAI compared to TG. It was assumed that AN with large leaf size has provided large of shaded area on behind opaque wall.

Conclusion GF has a promising effect on building energy efficiency as passive technique for cooling effect through shading on building envelope. GF is stabilizing the indoor environment when the air conditioner is on. Consequently, it helps in reducing energy consumption for cooling loads. Effectiveness of GF may perform significantly with suitable selection of climber on GF. Thunbergia grandiflora was identified as best climber to be applied on GF for energy savings of cooling loads.

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