Public Flats With Implementation of Cross Ventilation In West Jakarta

Flats are a strategy that can be implemented to address housing needs on limited land, one of which is public flats. There is a problem with the lack of airflow rate which makes occupants use artificial ventilation to increase the airflow rate in flats units. Natural ventilation can solve airflow problems, with minimal energy use. The use of the cross-ventilation method is more effective than the use of one-sided ventilation. This study aims to discuss the size and location of the openings that can affect the airflow rate in flat’s units so that public flats with good airflow can be created using a quantitative simulation method. The simulation was carried out using the Rhinoceros software and the Butterfly plug-in with a model of an apartment unit with a different configuration of the size and location of the openings. The results of the simulation can be used to design residential flats with different heights, such as with an opening configuration ratio of 2:1:2.5 for a height of 9-24m and 2.5:1:2 for a height of 1-16m.


Introduction
Nowadays, development in big cities is increasing rapidly.Jakarta as the capital city of Indonesia is no exception.Developments in terms of infrastructure such as residential buildings and office buildings, are accelerating along with the increase in population which makes the city more crowded.According to the Central Bureau of Statistics [1], the density of Jakarta is ranked first with a population of 15,900 people/km 2 in 2019, and 15,978 people/km 2 in 2021, followed by West Java with 1379 people/km 2 in 2021.
Especially in 2021, West Jakarta, whose population density per km 2 is ranked second among other parts of Jakarta with a population density of 19,608 people/km 2 , and Kalideres sub-district, which has 471,436 people in 2019.
The problem that arises from this population density is the increasing need for housing, but the availability of land for housing in big cities is very limited and unaffordable.This leads to residential development that is not in accordance with city planning regulations, such as the creation of urban villages that are densely packed, irregularly located, poorly provided facilities, and buildings and requirements that do not meet eligibility standards.This condition causes the city to be unsustainable and not prosperous for the people who live in it.
The goal of Sustainable Development Goals (SDGs) 11 is to create cities and settlements that are inclusive, safe, resilient, and sustainable [2].This means ensuring that all people have equal access to the facilities and services needed to live well in cities and promote sustainable and environmentally sound development in cities and settlements.In order to achieve Sustainable Development Goals (SDGs) 11 points, the creation of flats is one of the strategies that can be used.Based on the Decree of the State Minister of Housing and Settlement Number: 10/KPTS/M/1999, flats are a strategy that can be used to overcome the problem of lack of land to build adequate residential facilities.Flats have also long been a solution to housing needs in urban areas where land is limited, and house prices are not affordable for some people, especially low-income people [3].The construction of flats is aimed at low-income people, so the operational costs of flats must be cheap but still have to provide comfort for the residents [4].
According to the World Health Organization [5], good air circulation can improve health because poor air quality is thought to be one of the main causes of the increased spread of infectious diseases and death.Therefore, the use of natural ventilation in flats is something that needs to be considered in designing flats.According to the Indonesian Minister of Health, No. 1405/MENKES/SK/XI/2002 the air velocity in the room must reach 0.1-0.25m/s.Indoor air velocity is often below the standard.This causes the accumulation of pollutants in the enclosed space.There are various diseases caused by poor indoor air quality, such as; 1) Sick Building Syndrome (SBS), and 2) Building Related Illness (BRI) [6].One way to increase the airflow into the building is to maximize the natural ventilation system used for air exchange in the building [4].
Previous research shows that the Sombo Flat units have met the regulations regarding ventilation/air circulation, but some residents consider it still inadequate, therefore the efforts they make are the addition of supporting facilities such as fans with the aim that air circulation can run optimally [3].Most residents of the Daan Mogot Flats in West Jakarta feel the heat so it becomes uncomfortable when they are in the room, so they use artificial air conditioning such as fans or air conditioners to be comfortable [7].The use of natural ventilation is also important and has a significant impact on energy savings [8]."Vertical housing as an energy-efficient building is the best solution for today's poor social settlements" [9].In order to achieve energy efficiency, it is important to use passive design elements, including orientation, opening size, and solar shading devices (Firmandhani and Pandelaki, 2020).
In general, the use of wind-driven cross-ventilation is more efficient than the use of single-sided ventilation [10].The configuration of larger outlet openings with smaller inlet openings increases the velocity at the inlet, thereby reducing the pressure inside the building and obtaining better ventilation rates [11].Ventilation efficiency was found to be highest for configurations with both openings in the center, and a 45 o orientation [12].
With this how is the design of public flats that get a good airflow rate with the use of cross-ventilation natural ventilation?so that it can design public flats with a space program that can meet the needs of the population, and with the use of cross ventilation so that good air circulation is created.

The method of study
The research method used is quantitative because the data obtained/sought is systematic, so assistance is needed from simulations such as CFD software.The data obtained is divided into primary data derived from simulations using Rhinoceros software with Ladybug and Butterfly plug-ins, and observations on the site by measuring wind using an anemometer, and secondary data derived from literature, such as Fisika Bangunan book by Prasasto Satwiko; Technical Requirements for the Construction of Flats; SNI-03-6572-2001.
The research stage is divided into two, the first is: searching for data on wind speed and direction, as well as dry temperature on the selected site, using Rhinoceros with Ladybug and Butterfly plug-ins; simulating the air flow rate on the selected site by taking into account the surrounding conditions; determining the optimal building orientation so that the airflow rate standards are met.And the second stage is: airflow rate data on the site is used as initial data to simulate the room; modeling with crossventilation configurations based on literature studies conducted by Moey, Sing, Tai, Go, & Sia.The configurations used are 3 configurations that have the best results from 6 existing configurations; simulate with the cross-ventilation configuration that has been made to produce data with air flow rate analysis.

Analysis of wind and temperature on the site
To analyze the wind on the site, data is required first.Wind data is obtained using Rhinoceros software and Ladybug plug-ins, and input data are obtained from Ladybugtools' EPW Map (epwmap (ladybug.tools))as in Figure 1.The EPW Map data uses the closest location to the site, namely in Jakarta Soekarno Hatta Intl AP :: 967490 :: ISD-TMYx.Wind data is also obtained by direct measurement on site using an anemometer, which is used to validate the data obtained from using Rhinoceros software and Ladybug plug-ins.The airflow at each height has a different speed, therefore a calculation simulation is carried out.The simulation produces airflow velocity data at every 8m height which will become airflow velocity data on the unit at a certain height.Calculation of speed at a certain height can be obtained through calculations where the average airflow rate at a height of 2m reaches 1.69 m/s.The wind speed can be seen in Figure 2 and Table 1.The calculation can be done with the wind speed formula at a certain height.The simulation results obtained prove that the west direction simulation shows the best results for the best airflow rate, and from the east direction is not good because the airflow rate has been split before hitting the site, which results in reduced airflow speed.So as to get the results of building orientation as in Figure 3 where the shape of the building is "U" shaped towards the west, so that the wind from the west can be caught by the building and can produce good airflow for the dwelling unit.

Airflow rate simulation of the room
Making cross-ventilation simulation which will be applied to the room layout according to the results obtained.The simulation is carried out with a room that has a width of 4m and a height of 3m with a configuration with reference to optimizing openings to increase the airflow rate in the cross-ventilation room listed in the book Sun, Wind & Light by DeKAY Mark is as follows:  The average pressure velocity is 0.56 m/s and -11.17Pa.

: 2
The average pressure velocity is 0.67 m/s and -14.34 Pa.

: 2.5
The average pressure velocity is 0.67 m/s and -14.14 Pa.

: 1
The average pressure velocity was 1.12 m/s and 3.43 Pa.

Cross Opening Opening ratio
Airflow rate Pressure Description 1 : 1 The average pressure velocity was 0.84 m/s and -8.03 Pa.

: 2
The average pressure velocity is 0.71 m/s and -13.45 Pa.
The results of the simulations from Table 3 have a configuration based on Table 2 carried out with different opening locations and also opening configurations state that the smaller opening compared to other openings will make the pressure smaller, and it causes the air flow rate to be faster.Therefore, the airflow rate and airflow can be regulated or directed so that it can be more thorough in the room.The location of cross openings produces better air distribution than the location of perpendicular openings and makes the pressure not as strong as perpendicular openings.This results in the outgoing air flow rate will be less than the perpendicular opening location.The wind speed generated from the simulation can be calculated by the air flow formula due to differences in wind pressure.

Cross-ventilation simulation on room layout
The wind analysis data on the site and the results of the simulation of the opening configuration that has been obtained become a reference for making the layout of a flat unit with a size of 5.75 x 6m and has 2 bedrooms, 1 common room combined with a kitchen, and also a bathroom.This room layout which can be seen in Table 4 will be simulated using different opening configurations according to its needs.The simulation is run 500 times in each layout and the height of the room to be simulated is every 8m.The simulation is run to get the air flow rate and then analyze it so that it can be seen if the air flow rate does not meet the standard.The average pressure velocity is 0.77 m/s and -13.56 Pa.

: 1
The average pressure velocity was 1.24 m/s and 9.75 Pa.Based on the simulations from Table 5 carried out, it can be seen how the results of the simulation of air flow rates in residential units of public flats that use natural ventilation openings with the crossventilation method can be seen in Table 6.In layout 1 the air flow rate obtained has met the standard, but there are many points where it still does not meet the standard, so layout 1 cannot be used for residential units of flats.In layout 2 the flow rate obtained has met the standard, but at a height of 8m there are several points where the air flow rate is still below the standard, so this layout can be used for residential units of flats that have a height above 8m.And in layout 3, the airflow rate obtained at all heights meets the standard, but at a height above 16m, the air flow rate generated is too large so it will cause discomfort in the residential unit of this flat.This is due to the use of strategies on natural ventilation openings.By utilizing the existing airflow on the site and choosing the best building orientation, as well as the position of the openings and the size of the openings so that there is a pressure difference that keeps the air flow rate maintained and also the airflow that spreads throughout the room in the apartment dwelling unit.

Design Strategy
Based on the data that has been obtained, the mass of the building can be formed as shown in Table 7.After the building mass has been obtained, the strategy used in residential units uses residential units with layout 2 and layout 3. Layout 3 is used in residential unit 1 because layout 3 produces good air flow rates on floors 1 to 16, therefore it is used on floors 2 -5.This residential unit 1 which can be seen in Figure 4 uses windows with a nako model which can produce suitable openings and can also save space.And layout 2 is used in residential unit 2 because the flow rate in layout 3 produces airflow that is too fast so it will create discomfort in the room, layout 2 is used on floors 6-8.This residential unit 2 which can be seen in Figure 5 uses windows with a nako model which can produce suitable openings and save space.

Concluding Remarks
In order to get a state of the room that has an airflow rate with the use of cross-ventilation strategy is not enough just to make openings on two sides of the wall that face each other, there are aspects that affect the air flow rate.By making the size of one of the openings smaller, the airflow rate can increase, it is because of the pressure that makes the air flow rate increase.Airflow settings can also be adjusted by creating a barrier or the location of the vents that are not parallel, this air flow setting is used so that the spread of airflow is not only straight from the inlet to the outlet, but the airflow can spread throughout the room.
Combining the configuration of openings and also the location of openings in the room can produce configurations that can be used, such as: layout 3 for heights of 1-8m; layout 2 and 3 for heights of 9-16m; and layout 2 and layout 3 for heights of 17-24m, but at a height of 17-24m layout 3 several points have a large air flow rate.
The design strategy is carried out by making many openings in the mass of the building so that air can spread throughout the site and get the maximum air flow rate inside the residential unit, the use of Nako model windows is also used to produce suitable openings and can save space.

Figure 2 .
Figure 2. Airflow rate at a specific altitude.

Figure 3 .
Figure 3. Airflow in building orientation form.

Table 4 .
(a) Flat unit layout, (b) layout opening size of flat house units.Front opening size cm (width x height) Center opening size cm (width x height) Back opening size cm (width x height) 1 : 2.5

Figure 4 .
Figure 4. Unit 1 floor plan and details.

Figure 5 .
Figure 5. Unit 2 floor plan and details.

Table 1 .
Airflow rate data at a specific altitude.

Table 2 .
Inlet and outlet opening configuration.