4.7 Buildings in New Delhi, India
The main points:
• A well-designed mud structure with arches, domes etc. performs similarly to a well-designed and insulated modern concrete/brick structure.
• Asbestos shhet roofing and fibre concrete roofing are hot in daytime and cool at night. In winter they are clearly too cool. Additional insulation would be appropriate.
Source: Development Alternatives, New Delhi, monitoring by Dr.-Arun Kumar, Vaidyanathan Geeta, Sanjay Prakash
4.7.1 Geographical location and climatic characteristics
New Delhi is located on the plain at an altitude of 200 m above sea level and a latitude of 28o North.
The climate is characterized by a hot and dry season in early summer determined by hot winds from the Thar desert in Rajasthan, with temperatures between a mean maximum of 32°C and 43°C and a mean minimum of 21°C to 27°C. In winter the cold, northern winds from the Himalayans dominate the climate. The temperature fluctuates between 20°C - 27°C in daytime and 4°C - 10°C at night. In between these two extremes there is a period of moderate temperatures. This includes the monsoon period during which the humidity is very high and most of the precipitation falls.
4.7.2 The monitored buildings
During the two climatically extreme seasons several building systems were monitored.
Various rooms of the headquarter building of “Development Alternatives” have been examined. The complex is located in the vicinity of a green belt in the Institutional Area of southern Delhi. The overall character of the building is determined by its strong roof forms which are a result of the materials used, mainly unburnt earth in the form of adobe and stabilized soil blocks. Many different systems have been applied in the building such as domes, vaults and also flat roofs. The walls are made of soil blocks laid in mud mortar, 23 to 35 cm thick. Floors are made using various options: sandstone slabs on concrete beams, prefabricated concrete jack arches or concrete slabs. Window openings are relatively small, just sufficient for natural lighting. They are arranged to allow a proper cross-ventilation. (Description of the building project see [ 160 ] )
By comparing the thermal performance, two rooms give interesting results:
A room with a Nubian vault made with adobe blocks of 12-cm thickness, rendered on the inside with a lime-based plaster of a natural brown color and on the outside with a regular 15 mm cement plaster over a chicken wire mesh as a waterproofing membrane. The room is exposed to the outside on three sides, the side walls face north and south. The outer shell is painted white and contributes to the solar radiation reflectance.
A room with a roof made of jack arches of 12 cm thick stabilized soil blocks. The arches rest on concrete beams and are covered with 10 cm lime and brick bat concrete, followed by a coat of marble dust in lime water and then a nominal layer of cement-based plaster. Further waterproofing has been achieved using a bitumen based compound. The outer shell has been painted white.
Only a small portion of the walls is exposed to the outside, on the S-W side and on the S-E side.
Fibre Concrete Roofing (FCR) / Corrugated Asbestos Cement roofing (ACC)
The Micro Model Unit of the Indian Institute of Technology was also selected for this study. It is located in a fairly low density area with a lot of open space. The monitored room is oriented along the east-west axis and is exposed on three sides to the weather. The structure consists of a load bearing frame made of burnt brick with soil block infill, 23 cm thick, rendered with mud plaster. The windows are fairly large, because the room is used as an architectural studio which requires good natural lighting. The roof consist of a timber structure covered with 8 mm thick Fibre Concrete Tiles. There is no ceiling. The floor slab is of concrete.
A similar structure with a corrugated asbestos cement roofing was also monitored. However, the performance was similar to that of FCR.
This is a conventional concrete and brick structure with flat roof. The building accommodates the Working Women’s Hostel “Prabhatara” and is located in a residential area. It consists of a concrete slab and frame structure with 23 cm thick brick walls, Fare faced on the outside and cement plastered on the inside. The room selected is located on the top floor with the east and north walls exposed, while the south side opens onto a corridor. The west wall is shared by an adjoining room.
The roof is a flat concrete slab, 10 cm thick, with a waterproofing 20 cm thick, including the base concrete and brick tile finish. The window opens towards the corridor on the south side which is open at each end. The space below the test room is an open passage.
4.7.3 Climatic performance and conclusions
• The indoor temperatures are generally very high compared to the performance monitored in the Dominican Republic (4.1.5). This can be attributed to the fact that while the Dominican Republic is a coastal area, New Delhi is land-locked and there is no appreciable cool night breeze flowing from the sea, as would be the case in coastal areas.
• The light roof (FCR / ACC) becomes hot in the daytime and cools down at night (damping effect 0.7) compared to heavy structures (damping effect 0.3). The daytime temperature is similar to the outdoor temperature.
• The jack arch room is generally hotter than the vault room, probably because the former is a more enclosed room. The ratio of surface area to volume being smaller for the Jack arch roofed room, the heat loss at night is less, resulting in the room being hotter.
• A well constructed conventional building (Prabhatara)performs similarly to the earth construction with vault or jack arch.
• Heavy structures have almost no temperature variance between day and night.
• Light roofs become slightly warmer in the daytime, but much cooler at night.
During this study, some isolated recordings of the surface temperatures have also been carried out. These could not be included in the presentation because they are not comprehensive enough. However, in addition to its importance with regard to thermal comfort, it has been clearly shown that surface temperature readings would provide more reliable information about the qualities of a wall or roof system because the air temperature and its time lag is heavily influenced by the variables of door and window openings.
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