Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 11 00 16, India
The traditional architecture is known for providing comfortable indoor climatic conditions to its occupants via passive and natural methods. Today, the architecture is completely isolated from the outdoor and completely dependent on artificial means for cooling/ heating of the indoor areas even if the outside conditions are pleasant. It therefore becomes very important to understand the passive methods and apply them in today's buildings for energy conservation. Various passive cooling concepts, their application in the buildings and their respective impact have been reviewed and summarized. This paper, thus makes an effort to review and investigate some examples of vernacular architecture and its building elements from India tracing the respective passive cooling potentials. It has been found that natural ventilation and daylight should be the prime element in building design in order to achieve effective passive cooling and reduce the dependence on artificial means of cooling. Evaporative cooling, courtyard planning with landscaping and water features are the most common elements found in the Indian vernacular architecture.
Keywords: Vernacular Architecture, Day Light, Openings, Passive Cooling
Traditional buildings are time tested and well known for energy conservation. It therefore becomes necessary to understand and incorporate the passive technologies used in vernacular architecture in present day architecture since today's buildings are completely dependent on mechanical devices for heating/ cooling and providing comfortable indoor thermal conditions. It has been estimated that about 40 % of the world's energy is dedicated towards the building sector (Development 2009). Lifetime energy requirements of a building include the energy used in that building right from the construction stage to its occupancy and also include the energy that is necessary to sustain and maintain the building throughout its life which is dependent on selection of site, orientation of building, building material, shading devices, façade treatments, openings, windows, form and space utilization, courtyard planning, skylights, structure etc. Hence, incorporating these methods with passive solar techniques will help reduce the lifetime energy requirement of a building substantially. The combination of various passive heating and cooling techniques in order to achieve comfortable thermal temperature conditions has always been visible in vernacular architecture.
Vernacular term refers to the construction done by the local people using traditional technologies, using locally available material in accordance with the environmental context. It offers a good solution to the climatic constraints. With incorporation of passive solar design, about 1-
With combination of various passive cooling concepts as listed in in Table 1, energy saving potentials may be increased tremendously as summarized in Table 2.
2. Indian Vernacular Architecture
Various passive cooling strategies have been discussed in Table 1 and 2. The following section comprises of few examples from the traditional Indian architecture and how these concepts have been implemented since long.
2.1 Planning type
Indigenous planning layout was followed for places and simple small dwellings as seen in Shahjahanabad, Jaisalmer and many other cities in India. This type of a dense clustering layout ensured that the buildings were not exposed to the outer sun. This prevents the solar gain and the hot winds from entering the premises and also allows the cold wind to circulate within the building (Figure 1).
2.2 Evaporative cooling and landscaping
Concept of evaporative cooling is extensively used in ancient architecture for example Amber Fort, Rajasthan, India comprises of a garden which has been positioned just at the center of the lake to modify the microclimate for comfortable outdoor sitting during summers. Also, this concept can be seen in Red Fort, New Delhi where the entire building has been surrounded by water body and landscaping or by a water garden in Deegh Palace, Bharatpur, India or green area in Imambara, Lucknow (Figures 2a, 2b and 5). This was done in order to reduce the surrounding temperatures using landscaping. The small spaces were constructed to keep them sheltered from sun by the neighboring buildings. In case of large open spaces, plantation and water pools were used as landscaping element to protect them from the solar gains.
2.3 Radiative cooling and Courtyard planning
Courtyard planning is visible in havelis and forts of Rajasthan, India for cooling effect (Figure 3). Courtyards were the main architectural element used in planning generally integrated with water bodies, vegetation and usually open to sky to enhance evaporative cooling, provision of shade and infuse maximum daylight in the buildings. In Shahjahanabad, India, the lower floors are used to spend the hot days while the nights are spent on the terrace taking advantage of the radiative cooling. The rooftops are sprinkled with water for evaporative cooling effect. Whereas during the winters, the days are spent on the sunny rooftops and the nights in the enclosed rooms. The buildings in Shahjahanabad, India were designed to allow the heavy cool air to enter the building. There was no provision of parapet wall towards the courtyard and solid parapets were constructed towards the street. Large openings are provided towards the courtyard to take advantage of radiative cooling so that the cool air is passed through the interiors.
2.4 Solar shading devices
Solar shading devices is another control medium for solar heat gains in form of horizontal (canopies, awnings, horizontal louvers, overhangs), vertical (vertical louvers, projecting fins), screening (movable insulations, vegetation etc.) or egg crate devices (jalis, grills). These devices reduce the heat gains and thus provides comfortable indoor temperature, reducing the cooling costs. They also act as an aesthetic element and also satisfy daylighting needs if properly designed. Mughal architecture used inclined and deep shades to cover more surface area with deep carvings which creates self-
Ancient buildings were able to keep themselves cool without using the movable screens or curtains rather with the use of some passive techniques as seen in Diwan-
2.5 Ventilation and daylighting
The details of the windows and the openings were also taken care of in the vernacular architecture. Examples included small windows (lesser than 100 mm in diameter) used in Amber fort, India in order to ensure the visibility without letting the light or air in (Figure 6a). Openings installed for ventilation purpose were seen in Shahjahanabad, India. These were installed near the floor level and near the roof level in order to let the cool air in from the bottom opening and let the hot air out from the top opening (Figs. 6b and 6c). At some places jalis (perforated stone or latticed screen) have been used to maintain privacy (Figures 4a, 6d and 6e), let the air and light enter the building and also allow the visual connectivity from inside to the outside surroundings (Figures 5d and 5e). Diffused light is allowed to enter the interiors during sunshine hours, and at the same time the interiors are not visible from the outside. For the outside view, small opening is provided at the eye level of the viewer in sitting position (Gupta 1984).
2.6 Trombe wall
Another planning tool widely seen in vernacular architecture is thick walls i.e., Trombe walls (Figure 4a). They can be seen in Shahjahanabad, Jaisalmer, India. The natural, ventilated air also enters the chambers at the same temperature. The Trombe wall of 600 mm thickness is also seen in all the buildings of Banaras Hindu University, Varanasi. The inside temperature range was found to be about 25-
2.7 Some examples of region specific architecture are:
o Passive cooling features of vernacular architecture for Kerela, India have been discussed by Dili et al. (Dili, Naseer & Varghese 2010). These included courtyard planning, verandah, scale and proportions, orientation of the building, local building materials (mud, laterite, granite, lime mortar, wood, bamboo, clay roofing, coconut palm leaves etc.,) steep sloped roofs, decorative jalis (for ventilation and daylight), strut comprising walls spaced by slats forming fenestration design thus creating comfortable indoor thermal conditions without input of an external cooling source. The temperature near the courtyards was found to be in the range of 3-
o Warli house, Maharashtra. These are mud plastered houses on framework of karvi walls. Suitable for hot humid climatic conditions.
o Bhunga, Rajasthan. These are generally mud structures with thatch roof, circular in form planned around atriums or courtyards in clusters with minimum exposure to sun. These structures have controlled entry of light, wind and sun due to small openings. Suitable for hot dry climatic conditions.
o Laterite structures, Goa. These are lime and earth structures with un-
Thus, from the above examples it can be clearly stated that to achieve natural harmony between climate, people and buildings, passive cooling concepts should be adopted to make the building self-
3. Results and Discussions
o Evaporative cooling is the most economic and the oldest passive cooling concept used.
o Natural ventilation should be the focus of any building design and results in an effective passive cooling technique. This reduces the dependence on artificial means of cooling leading to energy conservation.
o Allowing natural daylight in the buildings leads to reduction in artificial means of lighting. Therefore, the heat generated by the artificial lighting decreases, resulting into an indirect passive cooling concept.
o Vertical shadings should be used for east and west walls whereas horizontal for south facing because of overhead sun.
o Landscaping: Deciduous trees allows summer shading and natural daylight in winter months by shedding their leaves and thus should be planted in south and south-
o Radiative cooling: The long wave terrestrial radiation shows no correlation with the elevation while the short wave incoming radiation shows a proportionate decrease at the normal lapse rate. Thus, leading to an increase in the value of radiative cooling.
o Courtyard planning: The cooling power decreases with decrease in the difference between the ambient and sky temperature.
o Exterior Trombe walls (thick thermal mass) leads to a reduction in the decrement factor and thus, creates a time lag. The heavy structure is seen in the ancient buildings and is preferred for passive cooling. This mass acts as an insulator and a heat storage medium.
Based on the present study, the following conclusions have been drawn:
o It has been seen that passive cooling techniques like ventilation, window and wall shading devices, natural cross ventilation, trees, water bodies, courtyards and verandahs are very effective in maintaining the indoor comfort thermal conditions.
o Indigenous planning, courtyards, landscaping, local materials, movable screens, Trombe walls are the most common passive cooling techniques seen in Indian vernacular architecture and are found to be very efficient.
o Integrating evaporative cooling concept with wind towers is found to be very effective and may lead to a reduction of 12-
o Combination of Trombe wall, thermal insulation and cool roof may achieve savings of 46 % and 80 % in winter and summer months respectively.
o Evaporative cooling can reduce indoor temperature by 9.6 °C.
o Solar shading techniques alone can provide a fall of 6 °C in the room temperature.
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