Performance Evaluation of Vertical Gardens

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1 International Journal of Architecture, Engineering and Construction Vol 5, No 1, March 2016, Performance Evaluation of Vertical Gardens Ratih Widiastuti 1,, Eddy Prianto 2 and Wahyu Setia Budi 3 1,2 Architecture Department, Faculty of Engineering, Diponegoro University Tembalang-Semarang, 50275, Indonesia 3 Physics Department, Faculty of Mathematics and Sciences, Diponegoro University Tembalang-Semarang, 50275, Indonesia Abstract: This paper presents a study about vertical garden as one of the most popular greenery systems in the modern era. The aims of this research are to study the thermal performance of the vertical garden in the office building and the influence of weather parameter toward the thermal performance of vertical garden. The object study was the application of vertical garden in Pertamina branch office building, Semarang, Indonesia. The vertical garden model has been verified with a set of measurement tools that measured weather parameter and thermal performance for both bare and vegetated façades. The measurement demonstrated that the plant layer on the façades can effectively reduce the interior surface temperature on the façades. The average difference was 2.1 C. When the outdoor air temperature increased, surface temperature of vegetated façades also increased. The effective thermal resistance of a plant layer gradually decreases when the air temperature rises. It can be concluded that the performance of vertical garden is influenced by the weather around the building. Keywords: Interior surface temperature, thermal reduction, weather condition, vertical garden DOI: /IJAEC INTRODUCTION Recently, greenery aspect has spread widely as an architectural element to design building façades and roofs. It becomes more popular along with rapid modernization that changed the existing ecosystems and replacing with hard materials such as asphalt, paving and concrete which resulted temperature increase in every day. Though not a new concept, greenery aspects in the building has increased the percentage of greenery in urban built-up area and bring back the vanishing urban green space (Wong et al. 2003). One of the most popular greenery systems is vertical garden. On the market, many kinds of vertical gardens are available and it is possible to distinguish them according to their constructive technology and to the type of green cover which can be grass or plants. The possibility of reducing heat transfer through the building envelope became a plus point of vertical garden (Holm 1989). In Indonesia, research related to greenery aspects on the building as a passive cooling system for energy saving was so rare. Mostly the research discussed thermal comfort based on the trees quantity in the outdoor space such as streets, pedestrian or parks. This research studies about the thermal performance of the vertical garden in the office building and the influence of weather parameter toward the thermal performance of vertical garden. 2 LITERATURE REVIEW 2.1 What is Vertical Garden Green wall or vertical garden is the term used to refer to all forms of vegetated wall surfaces (Sharp et al. 2008). Vertical garden is not only for building aesthetic, but also provides a sustainable, energy saving, comfortable and healthy environment for building occupant (Rashid et al. 2010). It is rooted into the ground, on the wall or in modular panels attached to the façades. It is also called a system to attach plants to civil engineering structures and walls of buildings or vertical greened façades are walls that are either partially or completely covered with vegetation, and they have exuberant green looks (Yeh 2010). *Corresponding author. shine_frontier@yahoo.com 13

2 Some plants are able to grow on walls by taking root in the substance of the wall itself. Typical of these are mosses, lichens, grasses and vines. For these to grow successfully on walls and buildings, some kinds of support structure is usually essential (Johnston and Newton 2004). According to growing method, vertical garden can be classified as green façades and living wall system (Dunnett and Kingsbury 2004; Köhler 2008). Green façades are made up of climbing plants either growing directly on a wall or in specially designed supporting structures. The system of plant shoot grows up the side of the building while being rooted to the ground. Green façades use climbing plant attached directly to the building surface or supported by cables or trellis, as seen in Figure 1. Figure 2. Living wall system illustration: (a)planter box system, (b)foam system, (c)mineral wool system Figure 1. Illustration of green façade On the other hand, living wall systems are constructed from modular panels which contain soil or other artificial growing mediums, for example planter box, foam, felt, geotextile, perlite and mineral wool, as seen in Figure 2, the panels require hydroponic cultures using balanced nutrient solutions to provide all or part of the plant s food and water requirements (Sharp 2007; Dunnett and Kingsbury 2004). This system usually employs evergreen plants as small shrubs which do not naturally grow vertically. 2.2 Thermal Benefits-Temperature Reduction Plants, especially vertical greening systems can protect the building envelope against the sunshine and freezing weather, which is beneficial for the thermal behaviour of the building indoor as well as outdoor. Vertical greening systems improve thermal insulation capacity through external temperature regulation. The extent of the savings depends on various factors such as climate, distance from the sides of buildings, building envelope type and density of plant coverage (Wong et al. 2010; Akbari et al. 1997). Therefore, applying vertical garden can influence both the cooling and heating (Akbari et al. 1997). Vegetation can play an important role in the topoclimate of towns and the micro-climate of buildings (Wong et al. 2010). Despite that, vegetation can dramatically reduce the maximum temperatures of a building by shading walls from the sun, with daily temperature fluctuation being reduced by as much as 50% (Dunnett and Kingsbury 2004). The shading and the corresponding reduction of the temperature, are the reason that climbers commonly used in Mediterranean areas against walls or as a canopy over terraces (Hermy et al., 2005). Plant canopies that shade buildings move the active heat from the building envelope to leave (McPherson et al. 1988). 14

3 Another statement by (Akbari et al. 1997), said that cooling energy potential of shade trees by reduction of the local ambient temperature. Irradiance reductions due to plants can reduce energy for space cooling. Vertical garden improves thermal insulation capacity through external temperature regulation (Stec et al. 2005). Since 1996, an observation has been conducted on the surface temperature of vertical garden in different settings at the University of Toronto (Bass et al. 2003). The results have consistently demonstrated that among the materials found in urban areas such as lightcoloured brick, wall and black surface, vertical garden has cooler surface temperature. After that, a new round of testing was conducted comparing a vertical garden with a light-coloured metal surface, which is typically found on roofs to shelter equipment. The purpose was not only to compare the temperature of the two surfaces (metal and leaf) but to also assess the shading potential of a vertical garden. The shading effect of vertical greenery systems reduces the energy used for cooling by approximately 23% and 20% the energy used by fans, resulting in an 8% reduction in annual energy consumption (Bass et al. 2003). Because in the fact, more thermal energy flows into the non-shaded walls due to direct exposure to the sun and resulted in higher surface wall temperature (Papadakis et al. 2001). Thermal behavior and effectiveness of vegetation covers with different average absorption of solar radiation and diffusive properties (Takakura et al. 2000). Nevertheless, toward interior thermal comfort, vertical garden gives an effect of increasing air humidity, which is create discomfort for building occupants, especially in the evening (Widiastuti 2014). 3 MATERIALS AND RESEARCH METHODOLOGY 3.1 Description of Vertical Garden Model In this section the vertical garden will be described in detail, including planting system, irrigation and plant species. The kind of vertical garden used is geotextile system that consists of an aluminum structure, a PVC panel installed on it, and felt layers. The plants are growing in the plant pockets which are always irrigated. They cannot grow indefinitely because of the limited pocket space, this is why it is not appropriate to apply plants with large thick roots. A continuous watering system that functioning automatically is needed. At the top and side of the vertical garden is a flexible pipe for the irrigation. The water flow through the nozzle and the distance between each nozzle is 15 cm. Frequency of water flow depends on the season, weather conditions and local climatology conditions and orientation of the façades. The vertical garden is installed on an external not insulated wall. The material of the wall is the bricks and the thickness is 15 cm included internal and external plaster. The plants used in the vertical garden model are combination of various types of plants. They are Phalaenopsis sp., Dracaena warneckii and some of local climber plants. Detail of the vertical garden model can be seen in Figure Experiment Desription The measurement on the experiment of the performance of vegetation-covered walls was conducted to validate the vertical garden model. The experiment consisted of measuring the interior façade thermal performance of a building non-covered and covered with Figure 3. Detail of vertical garden models 15

4 plants in the Pertamina office building in Semarang city, Central Java, Indonesia, as seen in Figure 4. One interior area of the façade oriented east, approximately 4 m above the ground, was selected for the measurements of vertical garden performance and other interior area, approximately 10 m above the ground, in the same oriented façade was selected for measurement of bare wall (non covered vegetation), as seen in Figure 5. The interior spaces are non air-conditioned office space. The experiment was conducted during one day in October 6, 2013; from early morning (06:00 am) until evening (06:00 pm). The measurements were collected at the 1 hour time intervals. The weather conditions during the experiment are summarized in Table 1. The following parameters were measured as individual points (variables) during the experiment: 1. Outdoor air temperature; 2. Surface temperature of the interior wall behind the bare façade; 3. Surface temperature of the interior wall behind the vegetated façade; 4. Relative humidity; 5. Wind speed near the façade. The indoor-outdoor air temperature, relative humidity and wind speed near the façade were measured 30 cm from the façade using 4 in 1 Environment Tester LM Wind speed measurements were made at a single Figure 4. Location of experiment site, Pertamina branch office building, Semarang Figure 5. Exterior side of field measurement 16

5 Table 1. Weather conditions during the experiment Values of weather condition Outdoor air temperature ( C) Relative humidity (%) Wind speed (m/s) Highest values Average values Lowest values point near vegetated façade. The surface temperatures were measured using an infrared-surface thermometer. Instruments are visible in Figure 6. 4 DISCUSSION SURFACE TEMPERATURE AND RESPOND TO WEATHER 4.1 Respond to Relative Humidity Figure 6. Measurement instruments: (a) infrared surface thermometer, (b) 4 in 1 environment tester LM-8000 Data collecting was done by two assistants at the same time in every 1 hour. 3.3 Experimental Results and Analysis The experimental day was in sunny condition. Table 2, show the average, maximum and minimum values of the measured thermal properties. Bare and vegetated façade temperature measured can be seen in Figure 7. The average interior surface temperature of the bare façade was 32.7 C, while of the vegetated façade was 30.6 C. The interior surface temperature of the vegetated façade was always lower than bare façade (mean difference is 2.1 C). The peak interior surface temperature of vegetated façade occurred around (at 3:00 pm), (32.15 C), while the bare façade occurred around (at 2:00 pm) (34.8 C). This can be explained as thermal lag of the façade, which appears approximately during one hour. Although the thermal lag was short and it was not a focus of this study, it should be noted that the effect of this thermal lag beneficial to reduce cooling loads during peak hours. When the relative humidity of air is low, plants significantly decreased the rate of evaporation and made temperature increased. Upon the relative humidity is high (at ), the rate of evaporation from plants greatly increases. Its use heat from the air to evaporate water. Automatically, its will reduce surface temperature (at ). It can be said that, decrease of interior surface temperature equal to relative humidity. The area of façade covered with vertical garden cools better at higher humidity levels than bare façade, can be seen in the Figure Respond to Outdoor Air Temperature The interior façade surface temperatures generally increased in response to increasing air temperatures, Figure 9. Even though surface temperature of the bare façade was higher and closely matched with outdoor air temperature, but at higher air temperatures, the façade plant layer was also less effective in cooling the interior façade surface temperature. It can be seen that when outdoor air temperature increase, surface temperature of vegetated façade increase too. Therefore, it can be concluded that the effective thermal resistance of a plant layer gradually decreases when the air temperature rises. 4.3 Respond to Wind Speed Wind can improve the micro-climate and has a specific effect in the building planning. Increasing wind speed aspect made the interior façade surface temperature decreased. It was happened because of heat flux through convection. The faster air movement then the greater heat released (Frick and Suskiyatno 2007). Though, wind speed was low (average 0.5 m/s), but Table 2. Measured thermal properties of the bare and vegetated façade Measured façade properties Maximum Average Minimum Bare wall interior surface temperature ( C) Vegetated wall interior surface temperature ( C) Difference in interior surface temperatures ( C) (bare vs vegetated wall) Temperature difference between outside air temperature and interior surface bare façade ( C) Temperature difference between outside air temperature and interior surface vegetated façade ( C)

6 Figure 7. Temperature measurement of bare and vegetated façade Figure 8. Temperature measurement of bare and vegetated façade respond to relative humidity Figure 9. Temperature measurement of bare and vegetated façade respond to outdoor air temperature 18

7 Figure 10. Temperature measurement of bare and vegetated façade respond to wind speed when the wind speed increased (from 0.4 m/s to 0.8 m/s and from 0.8 m/s to 1.0 m/s), the reduction in interior façade surface temperature between bare and vegetated façade also increased, can be seen in Figure 10. Since wind speed was low, vertical garden layer will act as a buffer that keeps wind from moving along on the building surface. Stagnant air made insulating effect and significantly reduced the amount of heat transfer in the building. As a consequence, these effects made thermal inside the building material reduced and made it cooler. 5 CONCLUSION In this research, a field measurement performed the purpose of studies about performance of thermal reduction of surface temperature in the interior building façade by applying vertical garden. The first analysis was done with the result of measurement the interior façade thermal performance of vegetated façade and bare façade in the Pertamina branch office building in Semarang city. The measurement demonstrated that the plant layer on the façade can effectively reduced interior surface temperature on the façade. It can be seen from the interior surface temperature of the vegetated façade was always lower than bare façade. Thermal lag of vegetated façade was also slower than bare façade, which means beneficial to reduce cooling loads during peak hours. The second analysis was done with the result of respond thermal performance to weather parameter. The measurement of the ambient temperature and humidity confirm that the area of façade covered with vertical garden cools better at higher humidity levels than bare façade. When the outdoor air temperature increased, surface temperature of vegetated façade also increased. The effective thermal resistance of a plant layer gradually decreased when the air temperature rose. In other hand, when the wind speed increased, the reduction in interior façade surface temperature between bare and vegetated façade also increased. These effects made thermal inside the building material reduced and made it cooler. It can be concluded that performance of vertical garden influenced by the weather around the building. 6 ACKNOWLEDGEMENT We gratefully thank PT Pertamina Indonesia, branch office Semarang for giving the licence to conduct this research using vertical garden application in its building. REFERENCES Akbari, H., Kurn, D. M., Bretz, S. E., and Hanford, J. W. (1997). Peak power and cooling energy savings of shade trees. Energy and Buildings, 25(2), Bass, B., Liu, K., and Baskaran, B. (2003). Evaluating rooftop and vertical gardens as an adaptation strategy for urban areas. NRCC A020, Institute for Research and Construction, National Research Council, Ottawa, Canada. Dunnett, N. and Kingsbury, N. (2004). Planting Green Roofs and Living Walls. Timber Press, Portland, Oregon, USA. Frick, H. and Suskiyatno, B. (2007). Dasar-Dasar Arsitektur Ekologis. Kanisius, Yogyakarta, Indonesia. Holm, D. (1989). Thermal improvement by means of 19

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