The habitat of two deserts in India: hot-dry desert of Jaisalmer (Rajasthan) and the cold-dry high altitude mountainous desert of Leh (Ladakh)

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Energyand Buildings23 (1996) 217-229

The habitat of two deserts in India: hot-dry desert of Jaisalmer (Rajasthan) and the cold-dry high altitude mountainous desert of Leh (Ladakh) Arvind Krishan Centre fi~r Advanced Studies in Architecture School of Planning and Architecture, New Delhi 110 002. India

Abstract This paper explores the possibility of developing a design methodology and criteria for climatically responsive buildings and settlements for the two desert conditions of India, i.e. hot-dry desert of Jaisalmer (Rajasthan) and cold-dry desert of Leh (Ladakh), through a study of the indigenous architecture of these areas. The method explained, in detail, in the paper is based essentially on development of a mathematical model after co-relation of the monitored thermal performance and computer simulation of indigenous buildings. This paper limits its presentation to the stage of thermal performance data and analysis. Keywords: India; Architecture;Desert;Climate ; Habitat

1. Introduction

Jaisalmer and Leh are two cities unique as artifacts of human endeavor in climates of extremes. They offer effective solutions to the extreme climates and the terrain. The indigenous architecture evolved through the entire spectrum of individual building to settlement pattern, responds through form, thermal mass, spatial hierarchy/activity pattern, material and construction. This research is conducted to achieve the following objectives.

3. Hypothesis Since indigenous settlements and built form have evolved over a long period of time, they provide effective solution to the environmental conditions. By monitoring and analyzing the thermal performance/built form relationship--if mathematical models can be developed through computer simulat i o n - i t should be possible to evolve designs for new climatically responsive buildings and settlements through inter- and extrapolation of these mathematical models.

4. Method

2. Objectives

The three main objectives of this research and development work are: (i) to establish, through the study of evolutionary process of indigenous architecture, the organic link between the built and unbuilt form, human need and life style, and the optimum use of natural resources; (i i) to devise guidelines and criteria of planning and design of climatically responsive buildings and settlements, and (iii) to develop planning and design process/methodology and design tools/aids for ;architects and planners. 0378-7788/96/ $15.00 © 1996ElsevierScienceS.A. All fightsreserved SSDI O378-7788( 95 )OO947-V

The method consisted of the following factors: (i) recording of the physical form and construction of the buildings and settlements; (ii) analysis of the climate stress through Eco-chart, degree days, CET and Mahooney tables; (iii) study of the thermal performance of the buildings through on-site monitoring; (iv) analysis of the thermal performance of the buildings through time-lag and decrement factor evaluations; (v) computer simulation of the buildings for thermal and airflow characteristics to evolve mathematical models, and (vi) development of a methodology and criteria for the design of new buildings through inter- and extrapolation of mathematical models.

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A. Krishan / Energy and Buildings 23 (1996) 217-229

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5. H a b i t a t of J a i s a l m e r

5.1. Settlement pattern Jaisalmer is situated at 26°55 ' North latitude and 75°55 ' East longitude at 241.7 m above mean sea level. It was founded in the year 1156 AD by Maharwal Jaisal Singh who

was looking for a secure location for the state capital. He thus founded this fort city on one of the hilly outcrops of the Arawali range called 'Trikut' because of its triangular shape. The landscape of surrounding region is flat, rocky and barren; the region is characterized by sparse vegetation and acute scarcity of water. In certain areas namely, 'Sam' around Jaisalmer, there are shifting sand dunes. Water is most scarce and a very valuable resource. In times of frequent draughts there is no water available for kilometers at a stretch. For this reason this site was selected since it has the availability of subsurface water. The entire fort is built on a height, it generally follows the triangular geometry of the site (Fig. I ). City is served by a triangular fortification and is characterized by narrow winding streets with densely built construction on both sides. It has reasonably large open spaces to serve the community. The house planning and design is characterized by a courtyard-type house with an underground level. The house opens on to narrow 'streets through a hierarchy of spaces that becomes the interface between the street and the house. The entire city ranging from the small house to the Palace of the King is built in locally available light yellow Jaisalmer's stone which is basically a sand stone.

5.2. Street layout

Fig. 2. Fort street layout of Jaisalmer.

All major streets are oriented almost in the east-west direction at right angles to the direction of dust storms (Fig. 2).

A. Krishan / Energy and Buildings 23 (1996) 217-229

219

enclosed room and an underground space used for storage and living. Variations of the courtyard house occur in the form of a simple single storey house and elaborate havelies. A haveli (Fig. 4) belonging to the Vyas family has been studied in detail and monitored for thermal performance. The more elaborate havelies (Fig. 4) are normally two- to threestorey structures with an underground living space.

5.4. Climatic context

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The climate of Jaisalmer (Fig. 5) is a typical hot-dry desert climate. There is very little and unreliable rain fall (average annual precipitation < 200 mm). Two seasons are predominant, summer and winter. In summer, the day-time temperature can reach upto 45 °C (some peak conditions of 50 °C have also been observed) and down to 25 °C at night. Similarly in winter, the temperature varies between 25 and 5 ° C. The diurnal range of temperature is between 15 and 20 °C. Relative humidity in summer can be less than 10% in day time. The sky is mostly clear and solar radiation is intense throughout the year. During the summer months the wind velocity is usually high and there are dust storms during May and June.

5.5. Climatic stress analysis

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The climate pattern and variation, represented in the Ecochart (Fig. 5), indicates that the critical period for the design of buildings is the summer period which is characterized by high ambient temperatures, high speed dust winds and a very low humidity. The winter conditions are relatively mild. Whereas the absolute values and patterns of day temperature, humidity, etc., become the broad indicator of the climatic stress the conversion of these parameters into a measure of human comfort is not yet directly achieved because of clothing and activity level conditions. Various thermal comfort indices such as tropical summer, CET, degree days and Mahooney tables have been used to assess the climatic stress. All these evaluations lead to the conclusion that the zone can be described as very hot in the summer and moderately cool in the winter.

Fig. 3. (a) Typical street in Jaisahner. (b) Mutual shading in a typical street section in Jaisalmer.

5. 6. Thermal performance of buildings The famous havelies with jharokhas and decorative facades are located on these streets (Fig. 3(a)). The streets are relatively narrow and winding (Fig. 3 ( b ) ) . The height of the building compared with the width of the streets is large to create shaded cool environment for the pedestrians, and social activities on the streets.

5.3. Generic house The generic house-type in Jaisalmer is courtyard-type of house with unenclosed verandah around the courtyard, a rear

The thermal performance of the typical haveli-type building is represented by the monitored temperature variations for both the summer and the winter conditions, see Fig. 6(a) and (b). The results are: (i) The thermal performance of the haveli is very good, in this type of building the maximum fluctuation of ground floor temperature was not more than 3.0 °C while the outdoor temperature fluctuation was in the order of 15 °C. The max-

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imum indoor temperature was 8 to 9 °C lower than the corresponding outdoor temperature. (ii) Ventilation fenestrations which are normally kept open throughout the day causes the building to be warmed up but they increased the air movement providing a greater sensible comfort. (iii) The combined effect of a greater time-lag and a small decrement factor reduces the heat flux entering the building. (iv) The courtyard system ensures ventilation through the building even during the calm outdoor conditions. (v) Due to shadow patterns, the buildings receive minimum radiation from direct solar exposure. In the summer, this serves in reducing peak heat flux into the building. In the winter, the building stays comfortable even when the lower altitude of the sun does not allow a direct solar penetration.

5. 7. Built form and micro-climate The built form and micro-climate are interactive. The buildings influence the micro-climate around them as much as the micro-climate around the buildings can influence the thermal performance of the buildings. Temperatures in different areas have been measured corresponding to the ambient day temperature. These measurements indicate that street temperatures in the summer were lower in the day time and at night. The peak street temperature was 2.5 to 3.5 °C lower than ambient conditions whereas in winter it was 2 °C higher. The night temperature in winters were alleviated by 3 to 5 °C while a corresponding summer temperature were alleviated by 1.5 to 3.5 °C. This indicates the response of form of the street, it influences the micro-climate conditions in a beneficial manner both in summer as well as winter conditions. The

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densely built street with narrow winding pattern and orientation eliminates the high velocity and high temperature daytime wind.

5.8. The passive climatic control----deductions and conclusions for Jaisalmer 5.8.1. Dense compact settlement In Jaisalmer the layout of town is the first control mechanism against the climate. The compact settlement generates a large thermal mass attenuating the external ambient conditions (Fig. 7). The street orientation ensures that the building facades are either shaded by jharokhas (balcony) or chajjas (sun shade) projections, or by the opposite buildings.

5. 8. 2. Sun control by orientation and projections In summer, the major east-west street orientation should have solar exposure on street from 9:30 am to 2:30 pm with corresponding solar altitude varying from 54 ° to 86°, small projections can therefore help shade the surface completely. The north face of the building on the opposite side of the street will receive radiation before 8 am and after 4 pm with solar altitude less than 35 °. Therefore, buildings on the opposite streets provide the shade on the north face.

For minor streets along north-south orientation, one may observe a solar exposure in east face in summers till 11.30 am and in west face after 12.30 pm. The solar altitude during this period is 0 ° to 79 °, when the narrow streets of the buildings get shade before 10.30 am and after 1.30 pm; therefore, the solar radiation incident on the east and west facades is for no more than one hour for which care is taken by the construction of thick walls.

5.8.3. Control of heating by texture on surfaces The heat inside the building in Jaisalmer is controlled by the use of textures. This is organized at three levels. Firstly, at the town scale the buildings are of unequal height with parapets and high walls, creating uneven sky lines and a desired shading of each other. Secondly, the building facades have large number of projections like jharokhas and chajjas that provide shade to the facades. Thirdly, the front part of the facade which remains exposed are controlled by creating deeply carved patterns. Use of such devices minimizes the heat gain by providing shading due to texture. Such devices also result in increased connvective transfer of heat because of an increased surface area. In summer, in day time, when the major heat source is the sun, the exposed textured surfaces

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6. Habitat of Leh (Ladakh) 6.1. Settlement patterns

Fig. 7. Street section with shadow projections at different times, 21st June. will be cooler than plain surfaces. In evening, when ambient conditions are cool, the increase in surface area helps in cooling them faster. Howew.'r, an extended surface will warm up faster than a plain surface under winter conditions due to low solar altitude, therefore, the location in context of these surfaces is very important.

5.8.4. Thick construction with use of stone in walls and timber and mud in floors Due to the typical thermal lag available, because of thick constructions which also have a large thermal capacity, the outside conditions are attenuated to provide comfort conditions in inside the buildings. The combined effect of large thermal capacity of the thick construction with large surface area, is to increase the long wave radiative loss from the buildings. 5.8.5. Ventilation---courtyord In the warm conditions prevailing in Jaisalmer and due to scarce availability of water, the only effective means to achieve thermal comfort is to increase ventilation through the space by drawing air from ~.he cooler areas. In densely built constructions it is relatively difficult to obtain ventilation since the temperature differences are usually not great. In Jaisalmer this combined effect of courtyard and internal vertical shafts is used for creating ventilation. The clear vertical ducts and stair cases combined with the courtyard are used to deflect wind down into the houses. Coupled with high thermal inertia of massive construction, these shafts temper the air before it enters a living space.

The settlements of 'Spituk' and Leh are situated at a latitude of 34°9 ' N and longitude of 77°34 ' E at a height of 3514 m above mean sea level. These settlements developed essentially because Leh was a trading city on the crucial trading link between India and Tibet. The region is a valley lying between high altitude ( > 8000 m) snow-capped mountains. The river Indus flows through this valley. The landscape of the valley is barren with almost no vegetation, although good agricultural activity exists near the Indus river and its minor tributaries. The mountains are rocky and barren with the rock breaking and falling off frequently due to great change in the diurnal temperature. The soil of the area is characteristic of any dessert, i.e. it is basically very fertile and wherever a minimal amount of water is present vegetation occurs immediately. Climatically the region is characterized by a very large annual range of ambient temperatures with a minimum recorded as - 30 °C and maximum recorded as 37 °C. Low temperatures are also accompanied by high velocity cold winds which tend to get funneled in the valley when passing through the mountainous passes. The settlements respond to this harsh climate by optimising the use of solar exposure through form, placement, hierarchy of spaces, technology and material of construction and life cycle of the people, Fig. 8. .-?.... -e: .~.

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Fig. 9. Site plan ofLeh (Spituk); all levels are in m, datum level: 100 m. 6.2. Settlement o f 'Spituk' 'Spituk' is a very old monastic settlement dating back 700 years (Fig. 9). It is located on a carefully chosen hillock in the valley reasonably close to Indus river. The entire settlement has been developed on the southern steeply sloping face of the hillock to maximize the exposure to the Sun. The entire settlement is a very fine example of architectural planning and design where exposure to solar radiation is a primary determinate of the settlement pattern and its form. The design of all buildings is carefully controlled in their siting, orientation, plan-form and total three-dimensional configuration,

i.e. height, volume and form. In order to obtain maximum heat gain through solar exposure the hierarchy of spaces at the community level and individual house level have been so designed and provided such that maximum solar exposure is obtained. 6.3. Settlement o f old LEH Old Leh is the first settlement in this area which was established as a key link on the trade route to China. It is situated on the south slope of the mountain where the palace of erstwhile King is located (Fig. 10). The settlement is compact

A. Krishan/ Energy and Buildings 23 (1996) 217-229

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Fig. 10. Street layout of Old Leh.

with freely winding streets. Inspite of the settlements being compact the entire planning and design of the settlement and the individual buildings has been organized so as to provide maximum solar access to various spaces in the buildings and the community spaces within the settlement.

6.4. Generic house The generic house in 'Spituk' as well as Old Leh is a compact two- to three-storey house constructed in sun-dried mud blocks (Fig. I1). The walls are very thick, tapering in thickness from ground floor to the top with average thickness being almost 1 m. The doors and windows fenestrations are quite small. The houses provide hierarchy of spaces both enclosed and unenclosed where a good solar exposure is available. The buildings typically do not have any overhangs thus preventing any shading of the surfaces thereby maximizing the heat gain from direct solar radiation.

6.5. Climatic context The climatic context of Leh is a very cold-dry climate. There is very little rain fall, average annual precipitation is less than 115 mm. There is basically one season that is predominant in this area, i.e. winter which becomes very acute for a long period from November to March. The summer, i.e. June and July, do offer a comparatively mild climate. The diurnal range of ambient temperatures in winter is about 16 °C with the maximum mean recorded as - 2 . 8 °C (although a maximum of + 3.2 °C has also been recorded) and the minimum mean recorded as - 14 °C (although a minimum of - 3 0 °C has also been recorded). The summer diurnal range is above 15 °C with the mean maximum recorded as +24.7 °C (although + 3 7 °C has also been recorded). A diurnal range of 30 °C has also been observed by us in the month of October. The relative humidity drops to an average of 30% in summer and rises to an average of 50% in winter.

The winter period is characterized by a high cloudy cover and the summer period with a less cloudy number of days. Because the valley is surrounded by high mountain ranges, the clouds tend to get trapped in the valley creating long spells of cloud cover. During winter the cold winds can blow at a fairly high speed of 30 km/h for reasonably long periods of time.

6.6. Climatic stress analysis The climatic pattern and variation as represented in the Eco-chart (Fig. 12) indicates that a critical period for the design of buildings is the prolonged winter period which is characterized by low ambient temperatures, high cold wind and relatively low relative humidity. The winter conditions may thus be classified as harsh cold-dry conditions. The number of degree days ( refer Eco-chart) indicates that the heating load on the buildings is very high. Degree days as well as Mahoony tables have been used to asses the climatic stress in this region. All these lead to the conclusion that this zone can be described as a cold-dry zone and the prolonged winter period is the critical period for design.

6. 7. Thermal performance of buildings The thermal performance of the typical Ladakhi houses is represented by the monitored thermal variation for both winter and late October condition (Fig. 13(a) and ( b ) ) . The winter monitoring is still in progress. The results are: (i) The thermal performance of the typical Ladakhi house is very good even against the very harsh winter climate. Whereas the ambient conditions fluctuate between minimum low of - 20 to - 5 °C in winter and a minimum low temperature of 3 to 14.7 °C in summer. The internal temperatures stay very stable and at best fluctuate between 12 and 15 °C;

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although this is not in the comfort zone, yet stability in indoor temperature allows the temperature to be increased by a minimum auxiliary energy source, mostly in the kitchen which is, for this purpose, centrally located within the main living spaces. (ii) The thick mud walls provide a large thermal mass leading to a large time-lag and small decrement factor, thereby effectively attenuating the external ambient conditions. (iii) Small window and door fenestrations provide the minimum aperture area for ingress of cold winds. (iv) Windows are typically splayed in the thick mud walls so as to provide minimal area of exposure on the outside and much larger area on the inside face of the wall. The mythical answer to this, given by the local people is that this keeps the evil spirits out of the dwellings. But there is a scientific reason behind this, i.e. the splayed window allows a greater distribution of daylight inside the space, thereby minimizing the use of auxiliary energy for lighting spaces in day time.

Fig. 14. ( a)- (f) Solaraccess and solaxpenetrationstudy. On the other hand the compact settlement of Leh offers first control mechanism by its compactness. Yet it provides the maximum solar exposure through the spatial hierarchy in the buildings by the way of placement and design of spaces in the buildings. 6.8. Passive climatic control: deductions and conclusions

6. 7.1. Settlement patterns

The settlement patterns are the first level of control against the climate. Whereas 'Spituk' offers an open settlement maximizing the heat gain from solar exposure, it eliminates the cold winds effectively by the very careful choice of the site. Since the north-east face of the hillock on which this settlement is situated completely cuts off the cold winds which blow predominantly from this direction. The spatial hierarchy, siting and orientation of the buildings are very fine example of maximizing solar exposure.

6.8.1. Control o f heat by thermal mass

The heat inside of the building is captured and controlled by the large thermal mass of the building provided by thick mud walls and large thermal capacity traditional Ladakhi flooring which is built from timber and thick mud. 6.8.2. Fenestration pattern

The fenestration pattern is designed such as to minimize the ingress of cold winds but to allow the maximum heat gain from solar exposure during the time the sun is available.

A. Krishan / Energy and Buildings 23 (1996) 217-229

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6. 9. Solar access----a primary element of design

Settlement of Spituk is a 'very fine example in site planning and architecture. Since the sun is the only source of heat and light in this region, the entire settlement, i.e. the built form, open space and circulation system are designed to respond to the sun's movement, in order to the maximize solar access. A photographic study of the model of Spituk at different times of the day and year is a clear evaluation of the solar penetration, see Figs. 14 and 15.

7. Basis of paper

Research work is done by Centre for Advanced Studies in Architecture, School of Planning and Architecture, New Delhi 7.1. Research team Professor Dr Arvind Krishan, Professor and Chief Investigator, Professor M.R. Agnihotri, Advisor, and Pashim Tewari and Kunal Jain, Research Associates.