Study of Shading Types in Heat Transfer Calculation in High-Rise Building

Tall buildings require a lot of energy in their use. The energy needed is mainly for thermal comfort in the buildings. The heat gained by the building comes from solar radiation. Nowadays many tall buildings use translucent materials. This definitely increases the heat gain that enters the building. Shading is used to reduce the heat that hits the translucent facade. Calculations are needed to see the effectiveness of shading. the purpose of this study is to analyze the effectiveness of using shading in OTTV calculations. The method used is a quantitative approach. A quantitative approach is used. The result is that horizontal shading only reduces heat gain by 20 percent. Vertical shading is able to reduce heat gain by 25 percent on the north and south sides. Vertical shading is more effective because it can handle lower angle sunlight. a combination of both shading is needed to be able to get a smaller multiplier number so that the calculation results meet the standards.


Introduction
Facade materials indirectly affect energy use in high-rise buildings [1].In the 1990s, high-rise buildings still predominantly used massive elements as building skins.In the 2000s, glass became the trend for building skin materials [2].This will certainly affect energy use in buildings.In terms of heat transfer, massive materials will be better for blocking heat from sunlight because heat only moves by conduction [3].For glass materials, heat transfer occurs by conduction and radiation so that the loss due to heat entering the building is greater than the massive field.
Heat transfer is also affected by the U-value or heat transfer coefficient of the material.This coefficient is the property of the façade material.The higher the U-value, the easier it is to transfer heat through the material.For example, to compare the coefficient values of brick and glass materials, brick is 2 W/m 2 /K and clear glass is 4.8 W/m 2 /K.A higher number indicates a material that transfers heat more easily.
Tall buildings are dominated by the use of transparent materials such as glass.Because of its nature to transmit sunlight, this part should be shaded so that not all sunlight enters and heats the inside of the building.Glass when made already has a value called "Shading Coefficient".But this value is not enough to provide protection against sunlight so the added value of extra shading is required.
Shading is a very important element of a facade [4].Therefore, the shading must work effectively.Some of the factors that affect this are location, altitude and orientation [5].Furthermore, regarding location, each region on the earth's surface has a different position or what can be called latitude and longitude.The values of latitude and longitude determine the trajectory of the sun, which in turn affects the performance of the shade.
Overall Thermal Transfer Value (OTTV), is a number that indicates the amount of thermal energy entering the building per square meter [6].In calculating OTTV, it is assumed that the building is closed with no openings [7].Therefore, it is necessary to use air conditioning in the room.The higher the OTTV calculation result, the higher the cooling load and vice versa.Based on the Building Conservation Design Standard issued by the Ministry of PUPR, the OTTV value in Indonesia should not exceed 45 W/m 2 .Other countries have different standards based on local climatic conditions.
The purpose of this research is to analyze the effectiveness of using shading in OTTV calculations in relation to energy, façade materials, shading, and OTTV values.

The methodology
This study employs a quantitative approach as its research method.Quantitative research, according to Sugiyono [8], investigates populations or samples using specific instruments to test hypotheses.In the initial research stage, the high-rise building model to be analyzed is identified, including aspects such as shape, size, orientation, facade material, and arrangement.First, identify the type of shade to be utilized, specifying its dimensions, location relative to the glass surface, and distance between shades.Next, conduct OTTV simulations to calculate the optical thermal transmittance value.Finally, evaluate the results and draw appropriate conclusions.

Result and Discussion
The high-rise office building will be examined, including its shape, size, orientation, facade material, and arrangement.The study employed a model of a tall building.Figure 1 illustrates this structure with 19 floors, standing 76 meters tall, and measuring 60 meters long and 24 meters wide [9].The floor-to-floor height is 4 meters, which consists of a massive facade with precast concrete material as high as 1.2 meters and a transparent facade with glass as high as 2.8 meters.The high-rise office building will undergo thorough analysis of its shape, size, orientation, facade materials, and arrangement.Determine the type of shade to be used, including dimensions, location on the glass plane, and spacing between shades.Horizontal and vertical shades are used.The horizontal shade has a length of one meter.It is placed directly above the window.The vertical shade has a depth of one meter from the window.The distance between the shades is one meter.The effectiveness of the static facade in mitigating solar radiation is calculated using OTTV simulation.This simulation involve conduction and radiation calculation in determine overall value.
Opaque material only has conduction process and transparent material has conduction and radiation process.This condition makes one calculation for one orientation.There will be three calculation which are conduction in wall, conduction in glass and radiation in glass.In final, value from each orientation is sum and divided by four to get average value.For convenience, the calculation results are presented in a table.According to Table 2, two types of heat transfer methods are conduction and radiation.Conduction occurs inside opaque materials.It takes time or a delay for the heat from the sunlight to penetrate the material and heat the room.Heat transfer rate is further affected by temperature difference between the room's interior and exterior.It affects the heat transfer rate of the wall, as more massive areas will take longer for the heat to penetrate the wall, and more glass areas will increase the heat transfer rate.The ratio between opaque and transparent areas is a critical factor to consider in designing a building facade.Therefore, it is crucial to maintain a balanced ratio between these two areas to ensure optimal thermal performance.
For heat transfer in both opaque and transparent fields, the conductance value in the OTTV formula is only affected by the conductance of the material, the difference between the outside and inside temperature, and the reflectance of the surface.These three things affect the heat transfer value.In contrast, the radiation transfer in glass material is different.The radiation that occurs is a factor of the shading coefficient and the solar factor (SF).The shading coefficient itself is the ratio between the width and height of the shade to the glass plane, the closer to 0, the smaller the heat transfer value, and vice versa.The SF is then affected by the orientation of the building.Every orientation has its own factor.It can be seen that the west side has the highest SF.Therefore, the west side of the building should not be too wide.The SF for the south side is the smallest because it is not directly exposed to sunlight.When designing green buildings, the factors of building orientation, opening area, materials will be important to refer to the heat transfer formula.
Horizontal shading serves as a coefficient in heat transfer calculations, reducing the radiation value.It consistently applies a coefficient of 0.8 for all orientations, resulting in a 20% reduction of heat received by the façade.

Conclusion
The OTTV calculation results for horizontal and vertical shading are still above the standard of 45 W/m 2 .The contributing factors are the opaque to transparent plane ratio, the building orientation, and the type of shading.Based on the OTTV value, vertical shading has a lower OTTV value.Compared to the conduction that occurs on walls and glass, heat radiation on glass material contributes the most heat.This shows the importance of placing shading on the glass plane and choosing the right orientation.Vertical shading is more effective because it can handle lower angle sunlight.Horizontal shading is less appropriate when placed in the south and north directions.A combination of horizontal and vertical shading should be considered as a way to obtain a lower multiplying factor so that the calculations reach standard values.

Figure 1
Figure 1 Building Dimension for OTTV CalculationsOrientation of building model set wide side facing sun path which is east and west.Facade material used in this orientation is full opaque to reduce overheat.In south and north facing facade, there will be opaque and transparent facade.In office, outside view is important so, transparent material needed

Figure 2
Figure 2 Building Orientation

Figure 3
Figure 3 Types of Shading

Table 1 .
Data required for OTTV Calculation

Table 2 .
OTTV with Horizontal Shading each Orientation

Table 3 .
OTTV Value with Horizontal Shading

Table 4 .
OTTV with Vertical Shading each Orientation

Table 5 .
OTTV Value with Vertical ShadingVertical shading in Table4has different coefficient values because of shape of shading.The north and south sides have a ESM of 0.75.