Learning the harmony of indoor air quality from traditional housing. Case Study Batak Karo, Indonesia.

Air quality in buildings is an important principle for a sustainable building to create comfort and health for living things and the environment. This study wants to explore how the air quality in traditional housing can be feel comfortable. How the building was designed for passive cooling in harmony with environment surrounding. The combination of qualitative and quantitative descriptive approach was used to analyse the traditional Batak Karo house (Mecu Houses, The Computational Fluid Dynamic (CFD) was used to know how the air movement inside the house. The Mecu house as a vertical building design proposal. This study focuses on elements of air quality in buildings by using the theory from Iwamura Sustainability of Housing, Embedded in the Local Context. The results of this study showed that the traditional Batak Karo House has the pleasant indoor air quality that achieved from the unique type of roof and openings inside the roof.


Introduction
Air quality in buildings greatly affects comfort and health in buildings, this air quality can be influenced by air circulation factors and ambient air velocity.Poor air quality can have an impact on human health and other living things.Nature from time to time creates changes in climatic conditions due to environmental, social, and economic needs.Since nature is still abundant, humans can take advantage of natural products from climatic conditions.
In the past, human ancestors had sustainable ideas for survival, especially the house which has been a place of residence for generations until now [1].Traditional housing has a collection of knowledge, practices, and beliefs developed through an adaptive process or adjustment from a generation to another [2].The house as a place for shelter has various forms taking into account the climate in each area, generally some have a round and rectangular shape, also the height of the floor is raised up from the ground (stilts) and some are directly on the ground.The traditional forms show a sustainable purpose to respond to natural climates such as air which is always side by side with humans.Responding to the natural climate means responding to the air that goes in and out (cross-ventilation) in buildings to become regular, giving healthy and comfortable survival.
Since industrial revolution, the comfortable housing has been designed with using an air condition.This situation that ignoring the natural environment, due to human negligence in building cities without providing green open spaces as a breath of air for the environment.The most significant energy-using equipment for any commercial building is air conditioning equipment, with an average energy use of above 62%, followed by lights and sockets, lifts and escalators and other electrical 1301 (2024) 012009 IOP Publishing doi:10.1088/1755-1315/1301/1/012009 2 equipment [3].This condition can affect the air quality in large urban environments which results in discomfort and the temperature of the surrounding area becomes high.We can learn how traditional housing has been designed with good air circulation.Air quality in traditional housing Batak Karo has also been applied the passive cooling techniques.The natural conditions of Batak Karo house has produced the specific shape which expressed a depiction of the life and beliefs of the Karo people.This traditional Karo housing can respond well to the natural climate.The air quality in this Karo Batak traditional building has a natural potential with an air temperature of 16°C -27.0°C [4], an altitude of 200 -1500 m DPL [5].
The Karo Siwaluh Jabu Traditional House, which has been established for more than 200 years, has a unique shape and has good air circulation in the room because it has door openings in the east and west directions which are symmetrical, the walls have window openings in each room, also in the lower and upper structures of the building there are small gaps on four sides for wind circulation from above in the building structure.This makes the sun's heat that is received indirectly affect the user, and the livestock that are on the stilt structure, the outside air link and the Karo customary house can certainly take advantage of natural potential such as circulation and air quality inside and outside the building.This high room can also make the air fresher.The condition of the people who have switched to modern buildings is that there are still many who receive impacts on health because the building model does not pay attention to air circulation in hot rooms and there is no air circulation.In contrast to the Karo traditional house which has implemented the principle of comfort in the building, fresh air circulation enters the building.
The traditional house with the Siwaluh Jabu means Waluh 8 and Jabu Rumah which means that there are 8 extended families can live together in the house.These gathered occupants may generate more heat inside the house.This study wanted to explore and analyze, is the Karo house still can give the pleasing air quality for its occupants.

Definition indoor air quality
 According to the United State Department of Labor, Indoor Air Quality describes a favorable and productive environment for building occupants, providing a sense of comfort, health, and well-being.Significant increases in worker productivity have also been shown when air quality is adequate.This includes temperature, humidity, lack of outside air (poor ventilation), mold and bacteria, or exposure to other chemicals (Occupational Safety and Health 4) [6]. According to the United States Environmental Protection Agency, Indoor Air Quality (IAQ) refers to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants.Understanding and controlling common pollutants indoors can help reduce your risk of indoor health concerns.Health effects from indoor air pollutants may be experienced soon after exposure or, possibly, years later.[7].
The definition of indoor air quality is everything that humans need for their survival and well-being depends, directly or indirectly, on the natural environment.Benchmarks on air quality around buildings inside and outside, especially those related to the health and comfort of building users.
This study will focus on the physical quality by detecting the air movement to find the housing comfort.

Understanding of indoor air quality for housing
A Healthy housing has been developed in Japan through the project called an environmental symbiotic housing [9].It was developed from the viewpoint of preserving the global environment by conserving energy and resources, and how-to live-in harmony with both the natural and man-made environment, as well as to provide residents with a healthy life that is rich in convenience, thereby encouraging them to participate in the construction process, and thereby protecting the environment.From all the aspects of the environmental symbiotic housings, this study will focus only on aspect of Healthy & Comfortable Living Environment (Health & Amenity): [9].
 Enjoying the benefits of the natural Environment;  Safe, healthy and pleasant indoor environment;  Design for beautiful harmony;  Design for a rich community lifestyle.

The Location and Climate of Batak karo Housing
It is a district in the province of North Sumatra, general location and geography.The location and natural conditions of Tanah Karo Regency are located between 2° to 3.2° latitude North and 98° to 99° East Longitude, namely to the north of Lake Toba which is famous for its beauty [10].The position of Karo Regency is at an altitude of 200-1,500m DPL.To the north it is bordered by Langkat Regency and Deli Serdang Regency, to the east by Simalungun Regency, to the south by Dairi and Toba Samosir Regencies, and to the west by Nangroe Aceh Darusalam Province.
The climate in the Karo area is tropical, has two dry and rainy seasons, the rainy season starts from August to January and then again in March to May, while the dry season is in February, June, July.The air temperature in the Karo district is between 15.6°C and 23.0°C with an average humidity of 89.12%.

The Physical Condition of Batak Karo Housing.
Became a symbol of the cultural heritage of the Karo people together with Dokan Village, Lingga Village and Peceren Village.Dokan Yang village located in Karo land has a cool atmosphere.The preservation of Karo culture in this village is marked by the establishment of the Siwaluh Jabu Traditional House which still retains its original architecture and is hundreds of years old.Siwaluh Jabu comes from the word 'Siwaluh' which means eight and 'Jabu' means family.When interpreted as a whole, it is eight families and is inhabited by eight families in one house.In the beginning, this village was built by a village leader with the surname Ginting.The development of the village was originally carried out by the Ginting community, who are the original residents of this village.Dokan itself has a distant meaning, the mention or name of Dokan village comes from the people who come to Dokan village [11].
The Karo traditional house is one of the traditional houses located in the highlands of North Sumatra.This traditional house has a unique characteristic which has a floor height of two meters from the ground and has a roof height of up to 12 m.The wall's slope of this house ranges from 15-20 degrees from the line where this traditional house has a terraced roof.The structure of the supporting pillars of this house uses drasi wood that creaks solidly on a stone that has been perforated.This method is believed to be a barrier to the earthquake at that time [12].

Building Orientation.
The Karo house has a rectangle form plan, but the house is facing to the four side, there is no called as front or back house.The Karo house has two doors, one facing east and the other facing west.The house configuration was built following the flow of the river, then one door faces the headwaters of the river and the other faces the river mouth [10].The general form of this typology of traditional buildings is in accordance with the Karo custom, with square and rectangular shapes, one of which functions as a place to live.In addition, the walls of his house do not stand perpendicular, but at an angle of 120°.Magnificent because it has a high and large dimension.It is about 17 meters long, about 12 meters wide, and about 12 meters high.All these dimensions are supported by 20 wooden foundation pillars which only stand on stone bases [13].

Figure 7. Mecu house plan
The form is symmetrically both on East and West.There are the openings on both side of the roof that can be for air circulation.The walls have window openings in each room, also the lower and upper structural parts of the building.

Enjoying the benefits of the natural Environment
There are 4 air vents 1 above and 3 below Air that is constantly changing due to good cross ventilation provides good health benefits The building responds to air coming in and out of the natural environment, creating a comfortable atmosphere due to horizontal and vertical ventilation circulation.There are openings as air vents on the door windows which keep the air in the room changing which has a good impact on health, while at the top it is able to flow indoor smoke pollution out of the building.

Safe, healthy and pleasant indoor environment
Mecu House Wind Circulation Analysis.The shape of the roof can protect the house from exposure to hard air The shape of this building can control strong winds by directing it directly to the ventilation ramps which produce a venturi effect so that the air entering the building makes the atmosphere comfortable.
This shape will be the shape of the plane surface of the proposed room design module.

Design for beautiful harmony
Mecu House Air Circulation Analysis cm/s Mecu House So in this piece of space module there is ventilation under the stage floor.Roof pieces as plane surfaces in vertical buildings Air vents are made in harmony with this shape to produce a venturi effect.
The air that is directed through the cut shape from the west has 2 vents and on the east side there are also 2 vents which result in good cross ventilation.The air vents are located on the sides above and below to create a harmonious direction, so the air vents are adjusted to the shape of the roof of the mecu house as a wall in the proposed design.This traditional Karo house can respond to lighting as well as air which makes the house comfortable.Design for a rich community lifestyle Air quality in traditional buildings can be used in vertical buildings, which are able to provide new air in the room and provide comfort to the body.
Can be applied to buildings that have corridors and have atriums From the simulation results of the mecu house plan on the left using the velocity magnitude m/s, while the image on the right in the middle selection of the mecu house uses the velocity magnitude cm/s.but the wind speed data in this analysis is adjusted to the wind speed data in Karo Batak.
The wind that enters the house on the floor plan shows that the window doors have large enough openings that allow the wind to easily enter, provide fresh new air and remove old air, so that the air in the house is maintained

Conclusion
The harmony of Indoor air quality on Mecu house showed that the activities and the openings positions are the main attributes to push the air movement.Learning from the Mecu House, the cross ventilation has two positions.The first is the both door in West and East and 8 windows allow the wind cross through the room.The second is the position of the opening is located on top of the wall along the four side of the building.The main air moving from any direction and is crossing from four side of the building, thus makes the air quality able to provide comfort until now, so that the people who live inside are health and feel comfort.This must be considered as the genuine local wisdom from Mecu House to give the opening above the wall on four side of the building.
The second position of the opening is located inside the roof that facing to the west and east, because the house plan is rectangular thus it is only has two openings.But when we look at the Sianjung-anjung house that has a square plan, the opening inside the roof is located on four side of the top roof.
The unique of how Batak Karo House makes the opening, it can be adopted for the modern housing.We can make the air movement into the rooms or in the corridor rooms from any direction.Thus learning from the harmony of air movement in Batak Karo House can support the indoor air quality for health of the inhabitants.

Figure 2 .
Figure 2. Location map of Batak Karo Housing (source: taken from google maps 2023)

Figure 3 .
Figure 3. Karo House orientation (source: goggle map, 2023) 3.2.2.The Form of Batak Karo Traditional Roof.The form of Batak Karo dominated with the roof configuration.It has two types of roofs depends on house plan rectangular or square.Sianjung-anjung house has square plan with four faces looks equally.A sianjung-anjung house is a house that has four or more faces on the roof.And the Mecu house has rectangular plan.A mecu house is a house that has a simple shape, two faces.

Table 1 .
Qualitative Analysis of the Mecu House

Table 2 .
Quantitative Analysis of the Mecu House Computational Fluid Dynamic / CFD Analysis The Harmony of air Quality Passive cooling movement Batak Karo House Plan Part Of A Batak Karo House Simulation Perspective Of The Karo Batak House