The Influence of Surrounding Tall Buildings on Increasing Energy Use in BRI II Tower Jakarta

Jakarta has many tall buildings with office functions. This high-rise office building has been built since the 1970s and is still used today. This long-used building will experience a decrease in performance so that the high use of energy in the building, especially air conditioning and have an impact on increasing temperature on the environment. Retrofit is one way to improve building performance and reduce environmental impact. This study aims to take into account the influence of the environment on energy use as input for retrofitting. With retrofits carried out on a large number of high-rise office buildings, it is expected to reduce the impact of heat on the environment so as to support the Sustainable Development Goals on affordable and clean energy and climate action. With the simulation method using energy plus software, environmental influences will be simulated on the addition of heat that occurs in buildings.


Introduction
Jakarta is one of the cities with the highest number of tall buildings ranked thirteenth in the world with 414 tall buildings above 100 meters (The Council on Tall Buildings and Urban Habitat, 2022).Construction of modern high-rise buildings in Jakarta began in 1950 on Jalan M.H Thamrin which then expanded to Jalan H.R. Rasuna Said and Jalan Jendral Gatot Subroto.Then this area developed into a business district called the Golden Triangle of Jakarta.In the picture below there is a map of Jakarta's land use until the 2030 planning, it can be seen that the purple area is an office area.According to research from Research Colliers International Indonesia, Jakarta's business center currently reaches 5.4 million m 2 with a very dense land condition, so buildings that are old enough need to be renovated or will be demolished to be replaced with new ones.
The grouping of offices in business centers results in mobility and density of activities at certain hours.The number of tall buildings with glass facades, the lack of green land and dense buildings resulted in the central business area experiencing an increase in microclimate temperatures.Based on observations and measurements in 2000 conducted by the Indonesian IOP Publishing doi:10.1088/1755-1315/1324/1/012092 2 Meteorology and Geophysics Agency, it was stated that 47.34% of Jakarta's urban land experienced Urban Heat Island (1).This figure has been much reduced compared to UHI which occurred in 1999 which was 60.26%.

Figure 1. Urban Heat Island in Jakarta
The increase in temperature in the central business area has an impact on increasing the cooling load of air conditioning so that energy use in the building increases.The large amount of energy use for air conditioning is also caused by the many designs of building envelopes with glass that reflects solar radiation (2).Based on the function of the building, office high-rise buildings are the third most wasteful building function after shopping centers and hotels (3).Therefore high-rise office buildings have an urgency to retrofit.
The BRI II building is a state-owned rental office built in the 90s with a glass façade of more than 70%.This building has a floor plan with a centralized form which is the typology of most office buildings in Jakarta.This building uses a central AC system which is then modified by replacing it with a VRF AC system.This modification of the ME system aims to improve user comfort and energy efficiency by using air conditioners that can regulate existing cooling loads.However, based on preliminary analysis, it was found that this building can still be carried out energy efficiency through retrofitting the building envelope.
For microclimate control, BRI II Building has utilized the surrounding environment very well through several efforts that have been made such as making ponds, planting shade trees, planting grass and minimizing the use of materials that have high albedo values.The BRI II building has managed to avoid increasing the microclimate temperature with the site's cooling efforts, but the heat control caused by the surrounding building facades has not been controlled.In the picture below, you can see efforts to reduce the ambient temperature by making greenery and ponds in the BRI II Building area.

Figure 2. BRI II Tower's Surrounding Area
This BRI 2 building has a large enough land so that it has a green area around it.This is very different from other buildings that have very limited land so they do not have green areas.The situation around the BRI 2 Building can be seen in the picture below, where in the North there are still many people's houses with a height of 2 to 3 floors that are converted into shops, canteens and other facilities, in the West there is the GKBI Building in the form of a rental office with a height of 131 meters and a total of 40 floors, in the South there is the Atmajaya Campus and several other high-rise buildings with rental office functions such as Plaza Central, Sampoerna Strategic, in the east there is BRI Building 1 which serves as the office of the BRI Board of Directors and Benhil Superblock Building which is being built as high as 340 meters or 75 floors.The position of the BRI II Building against the surrounding buildings has the potential to provide shadowing on the building in accordance with the movement of the sun. Figure 6 below is a picture of the movement of sunlight in March 2020 during the building's operating hours.This shading can potentially reduce the cooling load in the building, but on the other hand can reduce the entry of natural light into the building which will increase energy use for artificial lighting.Surrounding tall buildings that might potentially affect the amount of energy used, especially air conditioning due to shadowing or radiation from the casing material used.The following is a picture of the cut site of the BRI II Building where on the left side there is the GKBI Building and the right side of the BRI I Building.

Figure 5. BRI Tower Section Area
The sheath material used in the GKBI and BRI I Buildings is important to know to conduct further analysis of the influence of tall buildings around the Sudi case.The following is the sheath material used by GKBI Building and BRI I Building.

GKBI Tower Material
Material Specifications Source Glass Program and the World Green Building Council.Energy plus is a software that has BLAST (Building Loads, Analysis and Thermodynamics) and DOE-2 programs developed since the 19, 8, As a tool for energy and load simulation.This program is closely connected to the HVAC system in the building so that it can optimize building performance.Therefore, the Department of Energy of America developed this program to solve the problem of saving energy.
Energy plus works to calculate the heating and cooling load in the building so that it can simulate the air conditioning system used in the building.Energy plus works by connecting several software at once so that it can perform analysis related to energy in buildings at once in one software.Stage of literature study.This stage is carried out to find data and previous research on heat transmission, energy use in multi-storey office buildings, air conditioning in tall buildings, green buildings, energy calculations in buildings and methods of saving as well as regulations and standards regarding how to measure, take data, calculate energy and local regulations regarding renovations related to modifications to be carried out.This study was conducted to find out in detail in designing the next stage of research and the limitations and variants related to this study.
x Data collection stage 1.The first data collection is to record multi-storey office buildings that have the potential to make changes to the envelope.Multi-storey office buildings in Jakarta are recorded and studied about the shape, year of establishment and the formation of the envelope.Within the time limit, the multi-storey office building included in the data collection is the first office building built in Jakarta until 2010.The determination of this period is based on research from Bayu Utomo, a President Director of PT Taspen Properti stated that multi-storey buildings are used for a minimum of 50 years and 100 years for monumental buildings.So the determination of the year of establishment of buildings that have the potential to make modifications by pulling back 50 years from the year of the establishment of green building buildings in 2030 and net zero energy in 2050.
x Data collection stage 2 Data collection stage 2 is the collection of data directly related to the object of study that has been selected.Data needed as existing data related to energy use, especially air conditioning, such as: existing IKE data, the number of building users and equipment used.This data is useful as data on the causes of heat caused from inside the building and as an analysis of initial or existing energy use.Building work drawing data in the form of floor plans, views, cuts and façade details, which will be used for analysis of heat entering through the casing and existing construction data that is used as a limitation in modification.Surrounding environmental data, in the form of material data used on the site and surrounding buildings.The last is to collect BMKG data from nearby stations for the last 3 years according to the ASHRAE Handbook to determine the average temperature to be conditioned.
x Field survey stage At the stage of field survey, measurements of temperature, humidity, wind speed and radiation temperature were carried out inside and outside the building, conducting thermal shooting to determine the radiation that occurred in the casing for 7 days.Observe environmental conditions that cause differences in microclimate. x

Model Creation
In this stage, models are made according to field conditions.The model created consists of the study case building and surrounding tall buildings.This model is also depicted in detail casing according to conditions in the field with appropriate materials, openings and building shapes.Then this model is placed at coordinates that match the field to get a simulation model that matches the field. x

Model Calibration Stage
This stage calibrates the model with the aim of ensuring that the model that has been made is really in accordance with field conditions.Calibration is carried out by analyzing models that have been created with Energyplus software accessed through parametric programs, then the temperature results formed in the microclimate and interior are compared with the measurement results.
x Simulation This first simulation stage was carried out to determine the influence of the surrounding environment, especially tall buildings around it, on energy use in the case study object.Simulations were carried out with Energypus and Open Studio software incorporated in Grashopper's parametric-based modeling.With this software will be depicted heat maps that occur in the environment and fluctuations in energy use in buildings.The energy simulation in this study case was conducted twice, first as a building that ignores surrounding buildings and the second involving adjacent surrounding tall buildings.This simulation aims to determine how much influence the environment has on energy use, especially in tall buildings located in areas with many tall buildings around it.

Results and Discussion
The simulation carried out is the calculation of energy use in the BRI II building by making the surrounding tall buildings as an influencing factor.So in conducting an analysis in Energy plus, a modelof the surrounding buildings is included, namely the GKBI and BRI I Buildings and includes sheath material to test the relationship of surrounding tall buildings to energy use.In this test, the tread material is ignored with the intention that the heat that occurs outside the building comes from the reflection of heat from the surrounding building or the shadowing will be more visible.The assessment focuses more on energy use in air conditioning, so lighting and everything else needs to be done in more depth.
The next analysis to trace the cause of the large cooling load of the air conditioner.In table below explains that the consumption of cooling load is divided into external load and internal load.Internal loads consisting of the use of electronic equipment, artificial lighting and human numbers provide a load of 55% of the total cooling load, while the external load which is heat entering through the casing is 45% of the total cooling load.Of the total external loads of the building, the heat that enters through radiation is the greatest heat that enters the building.

Table 2. Total Energy
Of the total energy used, energy used for cooling or air conditioning remains the most energy-consuming, amounting to 80% of the total energy used.For other energies it can also be said to be the same as the previous analysis which does not involve the surrounding tall buildings.

Figure 6. Total Enery Use
When related to the distance between buildings, it is likely that this area has a good distance between buildings so that the shading and radiation due to the proximity and envelope of other tall buildings does not result in a significant increase in energy consumption.In the figure below there is a site analysis where the tread material is considered uniform using the same material to determine the effect of the casing on increasing temperature in the microclimate which has the potential to increase cooling load.The temperature formed between BRI II Building and BRI I Building is 37.7 0 C, as well as the temperature around the GKBI Building of 37.7 0 C.As other areas far from the high-rise buildings are 38.8 0 C, meaning there is a temperature difference ranging from 1-1.5 0 C is lower due to shading from the building on the site so that the increase in temperature becomes lower.For the increase in building cooling load in the analysis of the average cooling load each month by including climate data for the last 15 years in each area, it was found that the peak occurred in October.The comparison of energy consumption per month per area can be seen in the table below.Based on these results and compared with climate data from BMKG for the last 3 years from the nearest Kemayoran station, the increase in cooling load was caused by an increase in temperature and humidity in October.
Analysis further traced the cause of the large cooling load of the air conditioner.The table below describes the consumption of cooling loads divided into external loads and internal loads.Internal load consisting of the use of electronic equipment, artificial lighting and the number of humans provides a load of 55% of the total cooling load, while the external load which is heat entering through the casing is 45% of the total cooling load.The biggest cause of the large external load is radiation through the glass then caused by conduction through the wall on the sheath.In the picture below there is a pie diagram that shows the percentage comparison of the total AC cooling load.Based on energy simulations that have been carried out using Energy plus software between building energy calculations involving surrounding tall buildings and not involving the influence of surrounding buildings, the results are obtained as in the following table.In simulation 1 which did not involve surrounding tall buildings in the simulation, energy consumption for space cooling was greater than in simulation 2 which involved surrounding buildings in the energy simulation.Simulation 2 gets 10kWh less energy for cooling compared to simulation 1 so that it gets a smaller Energy Index of 0.2 kwh/m2/year.In simulation 1, conduction on the wall occurred greater than in simulation 2. One of the causes is the difference in tribes in the microclimate around the building.In Simulation 1 the microclimate temperature is 2 degrees higher than in Simulation 2, this is due to heat radiation from direct sunlight absorbed by the tread covering material and re-emitted heat to the environment.In Simulation 2, the temperature in the microclimate is lower due to the shading that surrounds the site by tall buildings around it so that less heat is emitted.It can be seen in the figure below in the microclimate temperature analysis between simulations 1 and 2.
Then a comparison was made on the cooling load each month between Simulation 1 and Simulation 2. In certain months, Simulation 2 experienced an increase in cooling load, namely June, April and received a smaller cooling load in January, December.This is influenced by the apparent motion of the sun which results in the fall of shadows from other buildings to the BRI II Building and surrounding sites so that the cooling load is reduced.

Conclusion
Environmental influences in simulating energy use, especially cooling in buildings, are less significant to be used as a basis for energy use analysis, because the difference in cooling load results is only small and the peak point of heat is also the same with a slight difference in results.Some of the things obtained based on the simulation are: 1.The cooling load of the single building will be greater so that the calculation of total energy use of the single building building can be greater by 10 kwh or 0.2 kwh / m2 / year.2. In the single building simulation, the largest value occurs in conduction through wall material, while in buildings and their environment has the highest value in radiation.But the difference in values obtained is not too large, namely 5% for the difference in conduction values and 22% for radiation.This is because the surrounding building uses a glass casing so that its reflection causes a considerable increase in radiation value.By modifying the casing on the entire building, it will reduce the addition of heat radiation values from surrounding buildings So in calculating energy use in buildings, surrounding buildings need to be included in the analysis so as to produce appropriate energy calculations.With this simulation, it is also known that there are differences in the way of heat transmission when involving the environment which will result in errors in making thermal control solutions, especially in retrofitting facades.

Figure 3 .
Figure 3. Tall Buildings Around BRI II

Figure 4 .
Figure 4. Shadow Movement at BRI II tower's area

Table 3 .
Total Cooling Load Figure 8.Heat Sources in Buildings

Table 4 .
Energy Index ComparisonBased on the comparative analysis of heat sources in buildings in Simulation 1 and Simulation 2, it was found that Simulation 1 got the greatest heat from conduction through the sheath wall while in Simulation 2 the largest heat came from radiation through glass.The following is a comparison table of heat sources in buildings between Simulation 1 and Simulation 2.

Table 5 .
Heat Source Comparison