Façade Assessment of Thermal Fluctuation Attributable to the Productive Facade: Shading Coefficient and Spectral Properties Analysis

Productive facades can be a promising green infrastructure for dealing with urban heat islands and food insecurity. Although producing productive facades has proved satisfactory, the cooling effect of small green spaces is still being debated. The incident solar radiation on the leaves is reflected, absorbed, or transmitted, potentially regulating the surrounding air temperature. Therefore, this study aims to discuss how the spectral properties of productive facades are related to the surrounding air temperature. A field experimental building model was carried out to investigate the fluctuation of temperature-affected radiation. Pumpkin (Cucubita pepo) and Sweet Potatoes (Ipomoea batatas L) were applied for the productive façade, which was placed in east and west orientations. The research method analyses air temperature’s daily behaviour and spectral properties of the productive facades. The results revealed that the cooling effect of productive facades fluctuates. Among the spectral properties, absorptance and reflectance have a strong correlation with air temperature, with r=0.56 (east side) and r = 0.68 (west side) for Pumpkin, while r=0.68 (east side) and r=0.72 (west side) for Sweet Potatoes. Existing microclimatic factors, namely humidity and solar radiation, contribute to the degree of this correlation. The findings of this study will provide implications for the design of environmentally sound technology aiming to obtain a better cooling effect and contribute to the food provision for urban communities.


Introduction
Urbanization has altered the microclimate in cities and increased the air temperature, causing cities to be warmer than surrounding rural areas.This is referred to as an urban heat island (UHI).The UHI phenomenon is primarily driven by urban development, which uses materials that effectively store shortwave radiation [1] [2].Natural land covers, such as forests, grass, and water bodies, formed cool spots, whereas artificial land covers formed hot spots, causing an increase in air temperature [3].
The predicted increase in demand for housing, facilities, and infrastructure for the urban population is the reason for the high density of buildings in urban areas.The world's population in the city is expected to rise to nearly 70% by 2050 [4].In the case of Indonesia, 68% of its population will likely be housed in cities by 2050.By this time, the population density of inner city areas will have increased dramatically, while peripheral areas will expand at a rate comparable to China [5].As a result, urbanization affects cities' urban microclimate and food security.
Vertical greening has long been recognized as a strategy for presenting a natural impression in urban areas, mainly where land availability is limited and pollution or degradation is present.Productive Façade (PF) is a type of vertical farming that can be combined with urban vertical greening to create productive green spaces.As a result, it can help provide food for urban communities.Vertical cultivation is ideal for developing on limited land because the plants are grown on development media and are not affected by soil quality [6].Several studies have shown that the ability to produce vertically cultivated food is comparable to, if not superior to, conventional (horizontal) agriculture [6][7] [8].On the other hand, the cooling effect of small (horizontal) green spaces is still being debated.According to [9] and [10], small green spaces do not play a role in cooling urban spaces.Plants produce a cooling effect by intercepting incident solar radiation; plants partially reflect and use solar radiation for biological activities such as evapotranspiration, photosynthesis, and lymphatic storage [11].
Green Facade (GF) is a vertical greening system that makes use of vines [12,13] or hanging plants [13].This article will discuss PF using the GF system, as GF is considered cheap, straightforward to obtain, and simple to maintain [14].Thus, it improves social acceptance in its application.Moreover, evapotranspiration and sun shading are the main contributions of a GF to achieving energy savings in buildings during warm periods [15].However, green foliage absorbs the most significant amount of shortwave (solar) radiation, significantly impacting evapotranspiration as a form of latent heat [11].[16] studied the cooling effect of a solar-exposed green facade on the west side.The maximum cooling effect of the green facade on a hot summer day was discovered to be caused by plant transpiration at 21.6% and shading at 79.4% [15].
The net solar radiation absorbed by the GF includes the GF's spectral properties, such as reflectivity (rgl), transmissivity (tgl), and absorptivity (agl), as well as the external wall surface solar reflectivity (rew) [11].10.7%of studies on temperature reduction GF discuss the role of Leaf Area Index (LAI), followed by topics on percentage coverage (8.3%) as well as species (8.3%), plant height (3.6%) and foliage thickness (2.7%), according to our review of the literature.Although plant spectral properties are a tool that can provide various information on the physiological status of plants, where physiological processes can influence the amount of radiation absorbed by leaves and its dissipation, ultimately regulating leaf temperature [17], few studies have discussed the spectral properties of GF concerning the air temperature around.Therefore, this article will discuss PF's ability to produce a cooling effect and how the PF shading determines the air temperature pattern around this environmentally sound technology.

Location and Time
This research was conducted in Kendari City, Southeast Sulawesi Province, Indonesia.Geographically, Kendari City is located in the southern part of the equator, between 3 o 54'40" -

Experimental Model
To determine the thermal performance of VGS, an actual climate test was carried out by creating a green facade on a building model measuring 1m x 1 m.The distance between building models is 2 m.The model uses the same materials generally used in buildings in Kendari, namely red brick plastered.The roof of the building model uses a gable roof with a corrugated iron roof covering without paint in the finishing.The floor around the model is covered with cement plaster with a distance of 50 cm.The green facade frame is made of wood and placed 20 cm from the surface of the building model facade.Green facades are placed on the East and West sides of the building.The plants used for PF are Pumpkin (Curcubita pepo), which is called PFP, and sweet potatoes (Ipomoea batatas), which are hereafter called PFSP.The results of the green facade measurements are then compared with measurements on the bare wall surface to determine the cooling effect.

Material and Method
The shading effect is influenced by outdoor environmental conditions, especially solar radiation and canopy characteristics.Solar radiation incident on leaves is reflected, absorbed, or transmitted.Plant shading ability can be described as extinction or shading coefficient (k) [18].k represents how strongly a canopy absorbs light at a given wavelength [19].k depends on its canopy architecture, namely LAI and its optical properties [20], in which the Lambert beer formula is determined by the proportion between the incident radiation on the leaves and that transmitted under the canopy.Transmittance (Ʈ) is the amount of light transmitted as a fraction of the amount of light striking an object [21].Moreover, k calculated from Beer's law may provide accurate estimates of radiation interception by a sole crop or by the dominant crop of a mixture [20].The efficiency with which plants intercept solar radiation depends on the incident radiation, leaf area distribution, the optical properties of the canopy (reflection, transmission, absorption), and leaf angle [22].However, leaf angle measurements in microclimate field measurements are only sometimes possible.Therefore, measuring the amount of radiation that plants intercept as a component in calculating k can provide an idea of the leaf angle of the plant.The more vertical leaf, the closer the k value to 0, and the more horizontal leaf, the closer the k value to 1 can be described as 0 < k < 1 [23] Furthermore, when exposed to hot conditions, plants can reduce the amount of accepted radiation through reflection and movement.They can dissipate excessive heat via radiation emission, heat convection, and transpiration [24].Reflectance is the fraction of light reflected from the leaf surface [25].According to Kirchhoff's law, the sum of reflectance (ρ), transmittance (Ʈ), and absorptance(α) equals 1. Taking into account that theoretical introduction, some of the assumptions used in this article are as follows: 1.The term "sun radiation" used in this paper indicates electromagnetic radiation regardless of its type.
2. The amount of solar radiation intercepted is calculated based on Beer's Law, namely [20]: ( Where: the proportion of solar radiation transmitted by the plant canopy extinction coefficient base number logarithm (2,7183) Leaf Area Index the radiant flux densities above the canopy (W.m -2 ). the radiant flux densities below the canopy (W.m -2 ).
5. This article adopts the Yin & Struik (2015) [27] assumption that 50% of the total solar shortwave radiation is Photosynthetically Active Radiation (PAR) and that the absorptance of incoming PAR by photosynthetic pigments in entirely healthy leaves is 90%.

Existing Microclimate
The PF thermal performance measurements for air temperature (Ta), relative humidity (RH), and solar radiation (I) are presented in Table 1 and Table 2.The average value from the three measurement days shows that the second day had the highest humidity value, 83% on the East and 81% on the West.The lowest average humidity value occurred on the third day, namely 71% on the East and 69% on the West.This is related to solar radiation, whose value is the opposite of humidity.In this case, the highest average radiation occurred on the third day, namely 448,96 W.m-2 on the East side and 439,75 W.m-2 on the West side.In contrast, the lowest average radiation value happened on the second day.

PF Cooling Effect
The thermal performance described the thermal difference between bare walls and PF.The cooling effect occurs when the air temperature in front of the bare wall is higher than that of the PF.The opposite is the warming effect due to PF.Meanwhile, without a temperature difference between the two conditions, there is no thermal effect due to PF, which mostly happens in the morning and late afternoon.The data presented in this article are from the day that showed the best cooling effect, namely on the first day, except for the PFP on the west side, where the cooling effect occurred on the third day.The cooling effect on the east side of the PFP occurs for 10 hours in the daytime, with the highest value of 5,4 o C, as shown by Figure 3 (c-E).The best cooling effect on the PFSP was found on the east side, occurring for 8 hours with the highest value of 8.2 o C, as shown by Figure 5 (c-E).

Spectral Properties
The graph shows the k value, which fluctuates according to the radiation received on the leaf surface and transmitted below the leaf surface.Generally, the highest k value of PFP on the east side occurs at 11:00 a.m.-01:00 p.m., ranging from 0.76-0.89,as shown by Figure 3(a-E).The highest k value of PFP on the west side occurs at 12:00 a.m.-04:00 p.m., which runs from 0.83-0.96,as shown by Figure 4(a-W).This hottest time shows that the k value is influenced by the angle of solar radiation towards this vertical green area.The cooling effect behavior on the PFP on the east and west sides is quite different.The cooling effect of the east side PFP occurs when the value of k=0.2-0.4,α=0.20-0.35,ρ = 0.25-0.38,Ʈ= 0.44-0.55,as shown by Figure 3(a-E), which is generally when the east side PFP reaches the lowest k, α, and ρ values.In this case, more solar radiation is transmitted below the leaf surface.Meanwhile, the cooling effect of the west side PFP occurs when the values of k = 0.95-1, α = 0.42-0.43,ρ = 0.52, and Ʈ = 0.04-0.06as shown by Figure 4(a-W), in general, when the west side PFP reaches the highest k, α, and ρ values.In this case, more solar radiation is absorbed and reflected into the environment.Moreover, the highest k value of PFSP on the east side occurred at 11:00 a.m.-01:00 p.m., which ranged from 0.75-0.80,as shown by Figure 5 (a-E), except on the third day, where the highest k value (0.76-0.99) occurred at 02:00 p.m.-06:00 p.m.The cooling effect generally occurs when k = 0.4-0.5, α = 0.27-0.38,ρ = 0.36-0.45,and Ʈ = 0.16-0.41.In this case, PFSP reflects more solar radiation into the environment, especially on the first and third days.With high air humidity, PFSP transmits more light below the leaf surface, reaching a value of Ʈ = 0.41.The highest k value for PFSP on the west side occurs at 10:00 a.m.-03.00 p.m., as shown by Figure 6 (a-W), which ranges from 0.75-0.93.The cooling effect of PFSP on the west side generally occurs when k = 0.75-0.8,α = 0.41, ρ=49, and Ʈ = 0.08-0.1,which happens right before or after the k value reaches the maximum.The cooling effect on the west side occurs when more solar radiation is absorbed and reflected into the environment.

Discussion
The k values for both PFP and PFSP on both sides show the same trend, namely fluctuating and tending to increase in midday.This is in line with research by [28], who found that the highest value is usually recorded at noon, and relatively high values are also recorded immediately after sunrise and before sunset due to a high proportion of diffuse light.The average k value of PFP for east orientation = 0.47-0.51,while that of PFP for west orientation = 0.51-0.62.In the case of PFSP, the average k value for east orientation= 0.45-0.56 and for west orientation = 0.42-0.55.This is by research conducted by [28], that k = 0.3-0.5 for herbaceous plants with upright leaves and 0.7-1.0 for plants with horizontal leaves.Thus, it can be assumed that the leaf angle of the east-oriented PFP is distributed more upward than that of the west-oriented PFP.As the percentage of incident radiation penetrating the canopy changes markedly with the sun's angle [28], it can also be said that the angle between the light beam and the vertical green layer is smaller on the east side than on the west side.This can be seen from the highest k value on the east side, which occurs at noon, when the higher light is almost parallel to the PF, while on the west side, it occurs in late afternoon when the sun moves away from the vertical line (imaginary line of noon) when the higher light tends to perpendicular to the plane.Vertical.This aligns with research by [29], which argued that radiation interception would be higher when leaves are steep to light.However, not all radiation intercepted by plants will be absorbed.
Furthermore, the average spectral properties of the eastern orientation PFP are α=0.29-0.32,ρ=0.36-0.39,and Ʈ = 0.16-0.20,while the western PFPs have an average of α = 0.29-0.34,ρ = 0.36-0.42,and Ʈ = 0.10-0.12.In the case of PFSP, the average spectral properties for east orientation are α= 0.1-0.3,ρ=0.2-0.4,Ʈ=0.16-0.5, while those of western orientation are α= 0.26 -0.32, ρ=0.32-0.39,Ʈ=0.15-0.17.The spectral properties of both types of PF on both the east and west sides show similar behavior, namely that the incident radiation received by plants is reflected chiefly into the air and absorbed.A leaf with a higher absorption value indicates that a significant amount of radiant thermal energy is absorbed by the leaf, possibly leading to a higher temperature [30].The k values of both types of PF, which are less than 0.7, are considered to have low light extinction coefficients, by which they are more effective in the transfer of radiation into the canopy and thus result in better utilization of radiation by the canopy, where the leaves then absorb it.However, the optimum solar radiation plants need for photosynthesis is 209.3W.m -2 -558.2W.m -2 [31].Proteins would be irreversibly denatured if the plants absorb this energy with the same efficiency as they do in the visible spectrum [26].Therefore, the Light Harvesting Complexes stress-related (LHCSR) of the leaf flips the switch, and some of the energy is lost as heat if proton build-up indicates that too much sunlight is being harvested [32] Moreover, Pearson correlation points out that a relationship between air temperature and the spectral characteristics of PFP in east orientation is rα =0.40-0.56,rρ =0.40-0.56,rƮ= -0.18 -1.2 and in west orientation are rα = 0.49-0.68,rρ =0.49-0.68,rT=-0.18-0.05.While the Pearson correlation of PFSP in east orientation is rα = 0.01-0.67,rρ = 0.01-0.67,and rƮ = -0.12-0.39, and in west orientation are rα= 0.39-0.73,rρ=0.39-0.73 and rƮ=-0.35-0.15.Among the spectral properties, absorptance and reflectance are strongly related to air temperature.Shortwave (solar) radiation absorption makes up the most considerable portion of the sensible heat vegetation can hold, which significantly impacts evapotranspiration, a form of latent heat [11].The amount of radiation energy a plant canopy can absorb will determine how quickly plants transpire [33].
According to [34], transpiration is the process by which water from a leaf evaporates into the atmosphere around it.Heat avoidance through transpiration involves maintaining leaf temperatures several degrees below the air temperature and minimizing the damage associated with above-optimum temperatures [15].However, it will work well when sufficient water is available [24].Leaf temperature increased with decreasing transpiration rates under low soil water availability [17].Unfortunately, it was observed that there was a tendency for Pumpkin and Sweet Potatoes to fold their leaves in at noon, which may indicate the high radiation accepted and the shortage of water availability in the container.Therefore, the warming effect mostly happened during those times.In addition, moisture stress has the effect of increasing leaf temperature.Stomata remain open when humidity is high, even though radiation is high.Rice panicles maintained 6.8°C lower temperatures than air because of soft moistness and more noteworthy transpirational cooling [35], like first-day estimation.Interestingly, the panicle temperature expanded by 4°C above the surroundings under damp circumstances because of restricted transpirational cooling [36], which may be the same condition on day 2, when the RH average achieved 85%.
Besides playing a part in heat evasion, happening will likewise affect the water content in leaf cells, in which leaves will mirror the light when their water content declines [17].The reflectance of a dried leaf is generally more noteworthy than that of a new leaf at all wavelengths [21].The reflectance of a fully turgid leaf increases as more water is lost.Still, the patterns of this increase vary depending on the leaf type [19], considering that water or leaf pigments absorb energy [25].In addition, reflectance may also be contributed by leaf angle.Reflectance PFP and PFSP on west orientation is higher than on East orientation, as k of PF west is higher than that of k of PF on east orientation.This aligns with that identified by [21] as its incidence angle rises from 0° to 70°.Recently, [37] found that as the leaf's inclination angle is raised, so does the leaf's reflectance, which also decreases with the angle.It was similar to that found in this research that PF east has lower reflectance than of the West, as the radiation rises with the increase in inclination angle on east PFP, and it increases in the afternoon.

Conclusion
This research is an initial stage in better understanding how the vertical greenery system modifies the existing microclimate around it.The shading coefficient and spectral property PF were essential in regulating its surrounding air temperature.The findings give implications on designing PF, namely morphological leaf selection, LAI, leaf angle arrangement, plant watering and fertilization, and appropriate crop cultivation calendar for two-sided planted façade possibility.In the context of urban green infrastructure, these findings will give implications on what direction PF should be placed regarding the radiation and cooling mechanism.In the broader scope, it can even provide clues to the urban community, such as the suitable hours and location for outdoor space activities.
The abundant radiation available over the tropics and subtopics presents consequences regarding air temperature and outdoor thermal comfort.However, through years of sun radiation, the tropics and subtopics give a broader opportunity for crop cultivation, contributing to food provision and microclimate modifiers for urban community habitation.

Figure 1 .
05" South Latitude and 122 o 26'33'' -122 o 39'14'' East Longitude.The climate in Kendari is tropical, with significant rainfall.In the Koppen and Geiger classification, the climate in Kendari is classified as an Equatorial Climate (Af).Kendari City's daily air temperature fluctuates.Actual climate tests were conducted in February and March of 2023.The data used were those from February 10, February 25, and March 16, 2023.Under clear sky conditions, data collection took place from 05:00 a.m.(in the early morning) to 08:00 p.m. (in the late afternoon).At a distance of 50 cm from the green facade, solar radiation, air temperature, humidity, and wind speed are measured every hour.Sun-powered radiation estimations are likewise done on the PF's rear to determine how much sun-based radiation is communicated.The estimating equipment is set in the veneer's focal point to limit the microclimate's impact outside the PF.Clear Sky Condition: (a) 05:00 a.m., (b) 07:00 a.m., (c) 02:00 p.m., (d) 08:00 p.m.

Figure 2 .
The Process of Productive Façade Development: (a) Building Model Preparation; (b) Productive Façade Sweet Potatoe; (c) Productive Façade Pumpkin 2.3.Equipment A digital thermohyrometer, Intell Smart type AS817, measured air temperature and humidity.The graduating point was 0.1 o C and 0.1% RH, with temperatures ranging from -10 o C to 50 o C and a 5-98% humidity range.Solar radiation was measured with a solarimeter manufactured by Lutron, type SPM-1116SD.Before being used, all equipment was calibrated by the Calibration Laboratory of the Meteorology, Climatology, and Geophysics Center for Region IV Indonesia.IOP Publishing doi:10.1088/1755-1315/1307/1/0120084

Figure 3 .Figure 4 .
Figure 3. Microclimate Parameters of PFP East Orientation on the First Day

Table 1 .
The Average Value of the Microclimate Parameter for East Orientation

Table 2 .
The Average Value of the Microclimate Parameter for West Orientation