Study of thermal comfort in the Sentra Primer Barat CBD Area using envi-met simulation

By 2045, it is estimated that almost 70% of Indonesia’s population will live in urban areas. However, the growing population and density of the city of Jakarta has led to a significant increase in temperature, which has a negative impact on the comfort of living in the region. Sentra Primer Barat CBD is one of the strategic central business districts in Jakarta. The purpose of this study is to identify the condition of thermal comfort in the Sentra Primer Barat CBD Area in two conditions, the current conditions and the planned conditions. The planned conditions are adapted into instructions on urban design guideline for Sentra Primer Barat. The study uses ENVI-met software to analyse thermal comfort. Microclimate parameters that are used for the study are air temperature, wind speed, humidity, and Tmrt (Temperature Mean Radiant). The parameters will then be reviewed and utilised to see their implications for thermal comfort index. The results shows a significant difference between the current conditions and the planned conditions. Under planned conditions, there is an increase in average air temperature and Tmrt, while average wind speed and average humidity see a decrease. This indicates higher potential of thermal discomfort in the study area. The thermal comfort index (PET) also deteriorate under the planned conditions. This research highlights the importance of improving thermal comfort in the Sentra Primer Barat CBD Area and provides guidance for better urban planning in the future. It is expected that environmental improvement efforts in this region can improve the residents’ quality of life and promote sustainability of the urban environment.


Introduction
By 2045, it is estimated that almost 70% of Indonesia's population will live in urban areas [1].Jakarta is one of the main migration destinations in Indonesia.Jakarta is also one of the hottest cities in Indonesia [2].Data shows that Jakarta's average air temperature in 2021 reached 28.8°C with a maximum temperature of 35.2°C, exceeding the thermal comfort standard of Jakarta residents which should be around 26.4°C [3].Jakarta is also expected to experience a significant increase in surface temperature every year [4].
Growing population and density of Jakarta due to urbanization has an impact on quality of life of the city's residents.One impacted aspect is the comfort of living in urban areas [5].Central business districts 1313 (2024) 012035 IOP Publishing doi:10.1088/1755-1315/1313/1/012035 2 with high intensity of human activities, such as Central Business District (CBD), dominate the cases of increasing surface temperatures in Jakarta [6].The effects of thermal comfort on areas with high intensity of activities include inconvenience and health problems of the residents, decreased productivity, high energy use in the areas, and indications of poor environmental quality [7].
Sentra Primer Barat is one of the CBD areas in Jakarta which plays a strategic role as a centre of trade, services, offices, and government [8].With strategic direction of development, it is estimated that there will be an increase in the intensity of human activities in the region in the future.Consequently, the development of this region must be able to overcome current issues and anticipate more intense conditions in the future in the context of thermal comfort.It is important to review the comfort of the area both in the present and in the future by using a design scenario of the Urban Design Guidelines (UDGL) document.Unlike existing studies, this research will focus on comparing the current conditions with the planned conditions in terms of thermal comfort, offering valuable insights into the potential impacts of urban development and design interventions on the microclimate and thermal conditions.By conducting a comprehensive comparison, evidence-based recommendations can be made to optimize urban design and planning strategies, ultimately enhancing thermal comfort and creating a sustainable and comfortable urban environment in the area, aligning with the UDGL's goal of creating wellorganized public spaces that prioritise user comfort and sustainable development [9].
Two objectives of this study are (a) to review microclimate factors (air temperature, wind speed, humidity, Tmrt (Mean Radiant Temperature)) as well as elements of the city that affecting the factors in each of the conditions (b) to review the implications of microclimate factors on thermal comfort in the area under both conditions.This analysis will provide an understanding of the implications for thermal comfort of the region with different characteristics of the two conditions.It is expected that the planned conditions can provide improvement compared to the current conditions, so that future challenges of more intense thermal comfort can be properly addressed.

Study Area
The scope of the area in this study is Sentra Primer Barat CBD Area, West Jakarta.The Sentra Primer Barat has an area of 124 Ha and is located in Kembangan district, West Jakarta administrative city.The Sentra Primer Barat area in its development was planned as a high-intensity trade, services, and mixed area for national and international service and as the centre of West Jakarta local government [8].Based on the direction of its development, the area also plays a strategic role as it was designated as a primary activity centre, a city service centre, and as a provincial strategic area of economic interest [10].

Simulation on Envi-Met
In this research, the researchers adopted a quantitative approach, which emphasises data collection and analysis using numerical information.The focus was to compare two conditions or to establish links between factors within experiments [11].This method was taken by analysing a simulation result using the Envi-Met program to find out air temperature, wind speed, relative humidity, and thermal comfort index of the area.
In preparation for simulation, initial data must be provided.The model area's dimensions are influenced by its spatial resolution.The simulation grid was 250x180 cells horizontally and 70 cells vertically, with each cell measuring 6.5x6.5x6.5 (in meter), resulting in a total area of 1,625x1,170x455 meters.This resolution enables analysis of small-scale interactions among buildings, surfaces, and vegetation for various scenarios over a 12-hour period.Simulation start dates weren't tied to specific calendar dates but rather to model-time references due to the utilization of year-average climate data.Main climate parameters such as temperature range, humidity, wind speed, and direction were kept constant to solely evaluate scenario (current-planned) impacts on urban microclimate.Climate data used for simulation was sourced from the Wunderground website, obtained from the nearest meteorological station, Rawa Buaya Station.The data encompassed average microclimate factors for the study area in 2022.The following presents the configuration of the data used in both conditions.The study employed a thermal comfort comparison in outdoor spaces, the examination was done by developing two conditions.The first model was using current conditions by digitization and the second one was a future scenario written in the UDGL document (Figure 1).The conditions will be seen: in the morning, afternoon, and evening.The periods chosen were crucial hour at these periods, which were 07.00, 12.00, and 17.00.This study models microclimate factors and assesses the thermal comfort index of the study area that will be conducted using urban microclimate modelling in ENVI-Met application.The ENVI-Met is a model that uses a three-dimensional grid-based model to simulate wind speed, humidity, temperature, and an index measuring thermal comfort created in one region [12].The ENVI-Met requires input data such as site location, climatic elements applicable to the study area, type of cover material, type of 1313 (2024) 012035 IOP Publishing doi:10.1088/1755-1315/1313/1/0120354 vegetation, shape, and shape of building typology.The Envi-Met program is a collection of several application features that have their respective functions according to workflow stages and tasks [13].There are six main application features that make up the core program of the Envi-Met.Applications available on the Envi-Met are: a. Envi-Met Headquarter, an application that is the initial setting used to determine the location of the simulation data storage.b.Spaces, an application that describes the design area to be simulated in a predetermined input area.c.EnviMet-Guide, an application that becomes the basis for input for climate data, simulation time, or other settings related to simulation output.d.EnviMet-Core, a module calculation centre of the Envi-Met program.In it, there are settings for geometry, atmosphere, vegetation, soil system, building and biometeorology models.e. BIO-Met, a post-processing application to calculate human thermal comfort index based on the simulated data.This feature directly interacts with settings of the parameters of people, thermal comfort index, and their calculation range.f.Leonardo, an application to process simulation results into 2D and 3D maps.

Microclimate Factor
Climate can be broadly defined as the intricate interplay of meteorological elements within a region [14].Koenigsberger et al. (2013) describe climate as the encompassing atmospheric conditions and specific environmental traits over a defined period [15].Lippsmeier (1997) categorizes climate into macroclimate and microclimate [16].Macroclimate involves overarching atmospheric events influenced by topography and human activities.On the other hand, microclimate pertains to localized conditions, like indoor spaces, streets, or parks.Brown and Gillespie (1995) explain microclimate as confined climatic conditions, influenced by factors like solar radiation, air temperature, humidity, wind, and precipitation [17].In alignment with these principles, this paper examines microclimate factors such as air temperature, humidity, wind speed, and solar radiation that reflected in Tmrt values in the study area.

Physiological Equivalent Temperature (PET)
Thermal comfort is a subjective condition where individuals experience satisfaction with the prevailing ambient temperature conditions, and it varies among different people [18].The consideration of thermal comfort is not limited to building design but also extends to regional or city planning.Creating a comfortable environment in an area is essential to encourage human activities and promote its active use.In the context of city planning, the assessment of thermal comfort in outdoor spaces becomes crucial in understanding the quality of the microclimate and supporting sustainable development [19].The Physiological Equivalent Temperature (PET) model is commonly used to quantify thermal comfort based on the energy balance of the human body [20].It represents the air temperature, both outdoors and indoors [21], at which the ambient air temperature is equivalent to the human body temperature during light activity (above standard metabolism) while wearing clothes with 0.9 clo insulation [22].The study will use standard PET values from Table 2 to assess the thermal comfort in the study area.

Air Temperature
Based on the microclimate simulations (Figure 3), the air temperature in the design for planned conditions' area is higher compared to the one for the current ones.The temperature can reach up to 33°C in the future design.Meanwhile in the current design, it only reaches 31°C.The increase in temperature can be attributed to various factors such as road orientation, building types, and vegetation conditions [24].The simulations show that roads with a downwind orientation tend to have cooler temperatures, as the wind flow provides a natural cooling effect.Additionally, buildings with a courtyard design allow for better ventilation and heat dissipation, resulting in lower temperatures inside the buildings.Furthermore, the simulations indicate that the current conditions experience a faster temperature drop compared to the planned conditions.This could be attributed to the presence of vegetation and water bodies in the area at the present time, which contribute to the natural cooling process through evaporation and temperature regulation [25].However, in the planned conditions, the impact of vegetation and water bodies on temperature reduction is not significant.Therefore, it is important to consider incorporating more extensive and effective vegetation as well as properly managing water bodies to enhance the environmental quality and mitigate the high temperatures in the area.

Wind Speed
In the context of wind speed, there is generally a similar pattern under all conditions, where wind speeds tend to be high in the morning and then decrease gradually until afternoon (Figure 4).The planned conditions shows that the average of wind speed decreases compared to the current conditions, from 1.5 m/s to 1.3 m/s.This change occurs due to environmental modifications such as changes in building patterns or the addition of design elements that can affect airflow [26].
Relatively high wind speeds occur in road corridors with a downwind orientation, while around buildings wind speeds are very low, the use of the right courtyard type can produce a tunnel effect.This effect can help speed up wind flow through the region and help in cooling the region.By utilizing this effect, a suitable courtyard-type design can help improve ventilation and airflow within the area.However, although the tunnel effect concept can be a potential solution, it has not been very visible in the design of the current conditions.To strengthen this effect, it is necessary to conduct further analysis of the possibility of making appropriate design modifications.This could involve adjusting the orientation and shape of the building, the arrangement of open spaces, or the addition of design elements that supports better air circulation.

Relative Humidity (RH)
In general, humidity has a similar pattern to wind speed, where humidity tends to be high in the morning and then decreases over time, until it reaches its lowest point in the afternoon (Figure 5).In the planned conditions, there was also a decrease in average humidity from the current conditions, from 74% to only 72%.These changes can occur because of planned environmental changes, such as building additions or vegetation modifications.In addition, high humidity tends to occur in undeveloped areas, around vegetation, and near water bodies [27].
Undeveloped areas, such as parks or green areas, tend to retain higher humidity due to the presence of soil that can absorb and moisturize the surrounding air.Vegetation also plays a significant role in retaining moisture, because plants through the process of transpiration emit moisture into the surrounding air.In addition, the presence of water bodies such as rivers, lakes, or ponds can also contribute to the humidity in the region, due to the evaporation of water from the surface of the water.In the planned conditions, there is an increase in the average value of Tmrt from the current condition, from 50 °C to 60 °C in the area (Figure 6).This increase can be caused by several factors that affect the magnitude of Tmrt, such as material, shadowing areas, and vegetation [28].
Open spaces with pavement materials that are directly exposed to sunlight tend to have a higher Tmrt than areas protected by buildings or other structures.Direct exposure to sunlight causes an increase in thermal radiation received by objects in the area, which in turn increases Tmrt.Conversely, open spaces with green material tend to have lower Tmrt values than other areas.Shadowing areas, such as trees or buildings that provide shade, can help reduce Tmrt by providing protection from direct sunlight.Such shading reduces thermal radiation received by objects below and can provide a cooler environment.Vegetation can also affect Tmrt.Plants, especially large trees, can have a Tmrt lowering effect through microclimate temperature regulation.The evapotranspiration process that occurs in plants reduces the temperature of the surrounding air and can help lower Tmrt around the area.
Although factors that may affect Tmrt, such as open space, shadowing areas, and vegetation, are considered for the area of the planned conditions, the Tmrt values are still very high during the day and its decline is slow in the afternoon.This may occur for several reasons, such as lack of adequate vegetation or lack of design elements that can help reduce Tmrt effectively.

Physiological Equivalent Temperature (PET) Thermal Comfort Index Value
In the planned conditions, there is an increase in the Thermal Comfort Index (PET) when compared to the current conditions (Figure 7).The highest PET in the current conditions reach 44 °C, while in the design area it can reach 46 °C.This increase can be influenced by several factors, such as open space, settlement density, and building type [29].
In the current conditions, it is still relatively comfortable in the morning and evening with the PET index showing a green class.However, during the day, the area is already uncomfortable to move about, with the dominance of the red index class which indicates discomfort.Meanwhile, in the planned conditions, the area is still relatively comfortable only in the morning, and it is in the category of uncomfortable to a little uncomfortable in the afternoon and evening, with the dominance of the red and orange index classes.optimize air circulation.In addition, it is also necessary to consider the use of building materials with good thermal insulation capabilities, proper lighting arrangements, and efficient energy use strategies to reduce heat loads and improve energy efficiency.By making appropriate design improvements and adjustments, it is expected to create more comfortable thermal conditions.In addition, this can also have a positive impact on energy efficiency and comfort for the residents of the area.

Conclusions
The results of the analysis shows that there are differences in microclimate factors in two conditions, which is that the air temperature, Tmrt in the planned conditions increase, and that wind speed and humidity decrease.These have implications for the difference in thermal comfort between the current conditions and the planned conditions of the Sentra Primer Barat CBD Area.The thermal comfort index deteriorates in the planned conditions; thermal comfort is at a comfortable level only in the morning, and it tends to be uncomfortable in the afternoon and in the evening.Better planning and designs are needed to reduce high temperatures, optimize windspeeds, maintain appropriate humidity, and manage the Tmrt to achieve optimal comfort levels in the region.The main goal is to create a comfortable, cool, and sustainable environment for residents or users of the Sentra Primer Barat CBD area.

Figure 1 .
Study Area Conditions

Figure 3 .
Figure 3.Comparison of Potential Air Temperature

Figure 4 .
Figure 4. Comparison of Wind Speed

Figure 5 .
Figure 5.Comparison of Humidity3.1.4.TMRT (Mean Radiant Temperature)In the planned conditions, there is an increase in the average value of Tmrt from the current condition, from 50 °C to 60 °C in the area (Figure6).This increase can be caused by several factors that affect the magnitude of Tmrt, such as material, shadowing areas, and vegetation[28].Open spaces with pavement materials that are directly exposed to sunlight tend to have a higher Tmrt than areas protected by buildings or other structures.Direct exposure to sunlight causes an increase in thermal radiation received by objects in the area, which in turn increases Tmrt.Conversely, open spaces with green material tend to have lower Tmrt values than other areas.Shadowing areas, such as trees or buildings that provide shade, can help reduce Tmrt by providing protection from direct sunlight.Such shading reduces thermal radiation received by objects below and can provide a cooler environment.Vegetation can also affect Tmrt.Plants, especially large trees, can have a Tmrt lowering effect through microclimate temperature regulation.The evapotranspiration process that occurs in plants reduces the temperature of the surrounding air and can help lower Tmrt around the area.Although factors that may affect Tmrt, such as open space, shadowing areas, and vegetation, are considered for the area of the planned conditions, the Tmrt values are still very high during the day and its decline is slow in the afternoon.This may occur for several reasons, such as lack of adequate vegetation or lack of design elements that can help reduce Tmrt effectively.

8 Figure 6 .
Figure 6.Comparison of Tmrt 3.2.Comparison of Microclimate Factors and Their Implications for Thermal Comfort