Shading Performance of Plant and Perforated Metal in The Thermal, Light, and Building-occupant Perception

Visual and thermal comfort are essential aspects influencing the activity of building occupant. For buildings with glass facades, the integration of shading devices becomes essential to enhance user comfort. This study aims to compare the effects of artificial (perforated metal) and biotic shading (Vernonia elliptica plant) on the thermal and visual parameters as well as perception of respondents regarding both devices. The study was carried out using a 1m x 1m x 1m box model. Perforated metal had a diameter of 3 cm and a spacing of 2 cm with a 29% openness factor, while the Vernonia elliptica had 2 levels of density, namely LAI 1 and LAI 2. The results showed that there was no significant difference in the average air temperature and RH produced by shading of vegetation LAI 1, LAI 2, and perforated metal. However, the use of vegetation reduced the illuminance significantly compared to the other device. The average DF of perforated metal ranged from 15.4 to 25%, while a range of 1.9-4.1% was obtained for LAI 1 and LAI 2. These results were inconsistent with building occupant’s perception that the vegetation had a better effect on the thermal aspect than the visual aspect.


Introduction
Indonesia is located near the equator and contains several islands surrounded by the ocean, leading to the presence of a warm-humid tropical climate.This climate is characterized by distinct dry and wet seasons and is typically marked by high humidity, high rainfall, and air temperatures ranging from 18-38 degrees Celsius [1].In the context of weather conditions, the facades of high-rise buildings play an essential role in mitigating the impact of external factors, such as high air temperatures, intense solar radiation, and the potential for glare from daylight reflections [2,3].However, the majority of these buildings use glass curtain-wall facades, which can lead to discomfort for occupants due to heat and glare.To address this issue, shading devices are essential to reduce glare, specifically from a low sun angle and direct solar radiation penetration [4,5].
Over the years, various types of shading devices have been developed with unique characteristics, with this current report focusing on two, namely perforated metal and vertical greenery system (VGS).These two types were selected due to the presence of a common principle in filtering the sun penetration through their porosity.Perforated metal is artificial and often produced from various materials, while VGS is natural/biotic.The evaluation of light and thermal aspect as well as the occupant's perception is expected to provide insights to architects and building owners when making 1301 (2024) 012013 IOP Publishing doi:10.1088/1755-1315/1301/1/012013 2 decisions for future applications.The effectiveness of perforated metal in regulating lighting is influenced by the size of the hole diameter and spacing, which is closely related to the sun's position [6].Based on the results, a comparison was carried out between two types of the device with the same openness factor but different dimensions and spacing.The first sample with a smaller hole and spacing reduced lighting by 39% to 15%, while the second sample with the double dimension had a lower transmission coefficient reduction result of 40% to 32%.[6] Artificial shading devices can be substituted with biotic variants using plant as a natural solar tracker.VGS can be used to prevent radiation naturally and serve as a biotic sun tracker aesthetically [7,8,9].Furthermore, the VGS planting system is often classified into various categories, including a hanging system, creeping/climbing, planter boxing, modular, and movable.Some variables that must be considered during its application to improve visual comfort include the selection of suitable plant species for tropical climates.This is because the type of plant affects light variable, which depends on the area of leaf.Another variable is placement which considers the integration of facade elements, the orientation of penetration of the sun and daylight, and the occupant's visibility to improve the quality of light in the room [10,11,12].Some of the disadvantages of applying VGS as facade elements comprise its maintenance and uncontrolled life cycle in response to climatic conditions due to its biotic nature [13,14].Climatic conditions affect this device due to their effects on specific aspects of plant, such as the species to be used, leaf thickness, growth rate, evaporation, and life cycle [10,11,12].Therefore, this study aims to compare the effects of artificial and biotic shading on the thermal (temperature & humidity) and visual (illuminance) parameters as well as perception of respondents regarding both devices.

Geometry and Shading mechanism by plant
The geometry of plant as an individual organ consisted of stems, leaf, and flowers.Amongst these organs, leaf had essential functions as radiation receivers, photosynthesizing, and growing-developing organs [15].Furthermore, the phytometric features depended on leaf area density (usually in terms of leaf area index/ LAI), angle, and dispersion [16].LAI was the amount of one-sided leaf area that grew above a square meter of ground area.Several studies had shown that LAI often increased during the early stages of growth, reached a peak, and then decreased due to withering [16].Leaf area density represented the spatial distribution of the organ's area in a volume around the x,y,z points and had a statistical distribution showing the average appearance of the elements.Leaf angle was also known as leaf orientation, as reported by previous studies.Leaf dispersion described the spatial relationship between the organ's overlap or location patterns relative to surrounding foliage.This parameter was different from the spatial distribution of the area.A high u(x,y,z) showed the presence of a large leaf area in a location but did not show the shade spread by leaf elements.Leaf dispersion was related to the relative efficiency of light interception for a certain area density and distribution [17].
Shading mechanism to light depended on the layer of leaf to transmittance and reflectance of light.The reflectance and transmission characteristics of leaf could be attributed to their good distribution over the entire range of wavelengths, absorbent materials at certain wavelengths, and rough surfaces [18].In terms of the thermal aspect, there was a relationship between foliage thickness and temperature decrease through evapotranspiration.The latent heat used in evapotranspiration could reduce the amount of longwave radiation emitted at night [19], but at low air movement and high RH, the higher LAI could cause a temperature increase [20].

Geometry and Shading mechanism by perforated metal
The geometry of perforated metal consisted of the holes and the spacing between each of them.This metal could be produced from various materials, such as iron, steel, or aluminum.As shading mechanism, the radiation could affect optical properties related to the direct component of the transmitted radiation.Furthermore, two components that were classified as screen transmittance algorithms were the screen beam and the scattering transmittance.The screen beam transmittance was a parameter that blocked sunlight and sun radiation with a screen material by assessing the emission of solar radiation through the opening.The scattering transmittance was the additional cause of the radiant flux of the solar radiation through the diffuse (scattered) reflectance of the screen material.The aspect ratio of the screen material was expressed by ɣ= D/S (D=diameter; S=spacing) [21,22].

Vernonia elliptica and Perforated Metal Data
Vernonia elliptica was a vine and creeper plant, with ornamental leaf, which required full sun, and a little water.[www.nparks.gov.sg]

Methodology
This was a quantitative study, which compared artificial (abiotic) and biotic devices.Building occupant perception was collected using a questionnaire to obtain opinions about these two kinds of shading.The study procedures were carried out from April 15-22 nd , 2022 with shadings facing to the West.The equipment used included two identical boxes of 1m x 1m x 1m and a glass opening of 1m x 1m.The inner part of both boxes was finished in black to ensure that the box was only influenced by the opening.The biotic shading used here was Vernonia elliptica with LAI 1 and LAI 2, and the artificial (abiotic) shading used was perforated metal with a diameter of 3 cm and a spacing of 2 cm (openness factor = 29%).To obtain valid data, the measurement was carried out by measuring the condition with vegetation and perforated metal at the same time and on consecutive days when the climatic conditions tended to be the same.In this study, the outdoor point of measurement was placed between the two boxes, and the indoor point was inside the box, at its center.The measuring instruments were a hobo data logger U12-012 for indoor temperature, relative humidity (RH %), and 4 illuminance, as well as hobo pendant for outdoor temperature and illuminance.

The result from the measurement and analysis of the lighting aspect 4.1.1 Vegetation LAI 2 vs perforated metal with a hole diameter of 3 cm and spacing of 2cm.
The results showed that LAI 2 had an illuminance range of 20-850 lux at 6 am until 3.30 pm.A value of 200 lux was obtained at 8 am but reduced to 20 lux in the evening around 3 -3.30pm, with a high of 3654.1 lux during the day.Furthermore, the average DF obtained in this study was 1.9 -3.72% range.For perforated metal, an illuminance range of 140-5900 lux was recorded at the same time, with a peak of 10290 lux and an average DF of 16.3-25%.Therefore, the daily illuminance variations were less pronounced with LAI 2 vegetation compared to perforated metal.Compared to perforated metal with a hole diameter of 3 cm and 2 cm spacing between holes, LAI 2 vegetation could reduce illuminance by 87.41% more.The ability of vegetation LAI 2 to reduce illuminance was less effective under cloudy sky conditions, particularly in the evening when illuminance levels were around 10,000 lux.However, during clear sky conditions in the afternoon, where illuminance could reach up to 30,000 lux, it proved to be effective in mitigating glare.

Vegetation LAI 1 vs perforated metal with a hole diameter of 3 cm and spacing of 2 cm
The vegetation LAI 1 had an illuminance range of 30-1260 lux between 6 am and 3.30 pm.A value of 340 lux was obtained around 8 am but reduced to 30 lux between 3 and 3.30 pm.Furthermore, the average DF obtained in this study ranged from 2.85-4.1%.The results showed that perforated metal had an illuminance range of 220-5900 lux at the same time, with an average DF of 15.4 -20.4%.The average measurement result of air temperature and air humidity, on vegetation usage compared to perforated metal with a hole diameter of 3cm as shading opening, is presented below: In the vegetation LAI2 compared to perforated metal with 3 cm diameter holes: • The temperature and relative humidity measured from the 15th until the 18th of April 2022 had similar characteristics.The air temperature in the morning was equally low with the lowest value of approximately 30˚ Celsius.In the afternoon, perforated metal had approximately 40 degrees Celsius, which was higher compared to the use of vegetation.In the evening, the temperature dropped back to approximately 30˚Celsius.• The average relative humidity in the afternoon for vegetation LAI 2 and perforated metal was 40%.
In the morning and evening when the air temperature reduced, the highest relative humidity was 80%.

Vegetation LAI 1 vs Perforated Metal with a Hole Diameter of 3 cm and a Spacing between
Holes of 2cm.Data on the usage of vegetation LAI 1, with 3cm diameter holes perforated metal having a similar tendency with the usage of vegetation LAI 2; • The air temperature on the 19th of April 2022 measured approximately 30˚ to 40˚ Celcius and could be considered a hot temperature.Around 2 p.m., it reduced to 25˚Celsius.Furthermore, the air temperature on the 20th, 21st, and 22nd of April in the morning was approximately 25 ˚Celsius and reached 40˚Celcius in the afternoon.Perforated metal air temperature was slightly above 40˚Celcius and in the evening, both perforated metal and the vegetation LAI 1 reduced back to 25˚Celsius.• On the 19th of April 2022 in the morning around 7 am until the evening around 4 pm, the relative humidity reached 50% in both the usage of vegetation LAI 1 and perforated metal with 3 cm diameter holes.After 4 p.m., the average of relative humidity observed was 80%.
The average relative humidity on the 20th, 21st, and 22nd of April in the night until morning around 8 am, both in the usage of vegetation LAI 1 and perforated metal with a hole diameter of 3cm, was 80%.Furthermore, in the afternoon until evening at 5-6 pm, the average value obtained was 50 %, which gradually reached 80% in the night.

User perception
Apart from quantitative data collection, building occupant perception was also taken from a total of 51 respondents, consisting of students and office workers who worked using laptops or other electronic devices for drawing, reading, and writing.The data collected from the respondents are presented in Table 2.

Visual Parameter
The illuminance sufficient = 6.29 out of 7 (likert scale) The requirement to view = 6.13 out of 7 (likert scale) The glare-free window = 6.33 out of 7 (likert scale)

Figure 13. Visual Parameter in likert scaling
The occupant perception regarding the visual parameter included illuminance sufficiency, the requirement to see the view outside and a glare-free working environment.To get a more reliable result, a 7-level Likert scale was used for the procedures.The results showed that the highest parameter was the glare-free window opening with 6.33 out of 7, followed by the illuminance sufficiency at 6.29 out of 7, and the requirement to view at 6.13 out of 7 (see Figure 13).Figure 14 represents the occupant opinion regarding VGS and perforated metal to ward off glare.A total of 51% of the respondents stated that plant was the best, with only 13.7% selecting perforated metal as the best option to prevent glare.The arrangement of plant leaf allows for efficient air exchange, resulting in cooler air, the absorption of sunlight, natural cooling, the production of fresh oxygen, and the capacity to absorb carbon dioxide leading to cooler ventilation.Several studies had shown that leaf was better equipped for the process of evaporation due to their water content.
Perforated metal had the ability to conduct heat, which could increase the room temperature, and its small holes helped to reduce the volume of continuous wind.

Conclusion
In conclusion, the measurement showed that using vegetation of LAI 1 could reduce illuminance by 80.77% compared to perforated metal.Meanwhile, vegetation LAI 2 reduced illuminance by 87,41% compared to perforated metal, representing an increase of approximately 7,4% compared to the condition of LAI 1.In the case of illuminance sufficiency, the value obtained for LAI 1 was significantly higher than LAI 2. Based on these results, it was more adequate for the needs of office visual activities, which required an adequate illuminance of 2-5% DF.In the evening with cloudy skies, the effect of a large reduction in illuminance could reduce lighting below the standard.However, vegetation was more useful compared to perforated metal with an extremely high DF of approximately 20%, causing discomfort when glaring.
The usage of vegetation LAI 1, vegetation LAI 2, and perforated metal with a hole diameter of 3 cm as shading had a similar impact on room air temperature and relative humidity.For the usage of LAI 2 and LAI 1 in the afternoon, the room temperature was slightly lower (not even a single degree Celsius) with the average relative humidity being slightly more humid compared to perforated metal.Therefore, it could be concluded that there was no significant difference in the average air temperature and relative humidity in using shading of LAI 1, LAI 2, and perforated metal with a hole diameter of 3cm.
Compared to perforated metal, vegetation had a higher influence on the illuminance than on the thermal aspect, with a temperature difference of not more than one degree Celsius.This result was inconsistent with building occupant's opinion that vegetation caused higher reductions in temperature compared to perforated metal.Human perception was more influenced by natural pattern, color, and texture interacting with light and shades compared to perforated metal.

Acknowledgement
This research was funded by Hibah from the Faculty of Civil Engineering and Planning Petra Christian University.The author wants to give high appreciation to Dr. Sri Nastiti N. Ekasiwi and Dr. Asri Dinapradipta as promoter of 1 st author doctoral study at Institut Teknologi Sepuluh Nopember Surabaya, for the advice and input during this research, especially for the research methodology.

Figure 8 .
Figure 8.The thermal aspect of LAI 2 VS Perforated Metal on April 18 th , 2022

Figure 14 .
Figure 14.The opinion of respondents about warding off glare

Figure 15 .
Figure 15.The opinion of respondents about the pattern that affects the room's thermal

Table 1 .
The characteristics of Vernonia elliptica and Perforated Metal Family Name: Asteraceae Common Name: Curtain creeper Lifespan: Perennial Average leaf dimension : 15 mm x 35mm Average leaf spacing: 20 mm Material: Aluminium Dimension: 1200 x 1200 x3mm Hole diameter: 30 mm Spacing: 20 mm Openness factor: 29 % The thermal aspect of LAI 2 vs Perforated metal on April 16 th , 2022 The thermal aspect of LAI 1 VS Perforated Metal on April, 20 th 2022 Figure 9.The thermal aspect of LAI 1 VS Perforated Metal on April 19 th , 2022 9 Figure 10.

Table 2 .
Data The thermal aspect of LAI 1 VS Perforated Metal on April, 22 nd 2022