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Hot and dry climate case study.
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- 3. General remarks Hot-arid zonesor desert regions with scarce vegetation and saline soils are distributed throughout the world. 15% percent of the world’s population lives in arid zones. 1/3 of the world’s land mass and 22% of all potential arable land lies in the arid zone. Most of the world’s energy reserves (oil) are within or adjacent to these zones. INTRODUCTION
- 4. Deserts with hotand dry climates are warm all year round, and are extremely hot in the summer. Usually, they have very little rainfall, making the climate extremely dry, and hard for plants and animals to survive. Animals in the hot and dry desert also have special adaptations that allow them to survive. There are very few plants in hot and dry deserts. Often, the only things that can survive are short shrubs and trees. Plants that live in the desert have special abilities that allow them to live in such a hot and dry place. For ex : animals, like the camel, store fat in one particular area (such as their hump), providing surface area to dissipate heat. Many animals are also light in color.
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- 6. HOT AND DRYREGION IN INDIA HOT AND DRY REGION •The hot and dry climate in India prevails in north- western region of the country mainly from April to June and in the rest of the country from March to May . • Jaisalmer, Jodhpur ,Ahmedabad and Sholapur are some of the city that experience this type of climate. Ahmedabad Jodhpur Jaisalmer Sholapur
- 7. HOT AND DRYREGION IN THE WORLD Hot & Dry regions: Kutch, Algeria ,Peru ,Egypt ,Libya, Coober Pedy SA, Ahmedabad, Rajasthan, North Africa, Pakistan etc. kutch Egypt Libya Peru Coober pedy
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- 9. • A typicalhot and dry region is usually flat with sandy or rocky ground conditions, and sparse vegetation comprising cacti, thorny trees and bushes. • The mean monthly temperature remains 30 degree . • Due to intense solar radiation (values as high as 800-950 W/m2), the ground and the surroundings of this region are heated up very quickly during day time. i. In summer, the maximum ambient temperatures are as high as 40-45 C during the day and 20-30 C at night. ii. In winter, the values are between 5 and 25 C during the day and 0 to 10 C at night. iii. It may be noted that the diurnal variation in temperature is quite high, that is, more than 10 C.
- 10. •The climate isdescribed as dry because the relative humidity is generally very low, ranging from 25 to 40 %, • The hot and dry regions receive less rainfall – the annual precipitation being less than 500 mm. •Hot winds blow during the day in summers and sand storms are also experienced, the night is usually cool and pleasant. •A generally clear sky, with high solar radiation causing an uncomfortable glare, is typical of this zone. • A generally clear sky, with high solar radiation causing an uncomfortable glare, is typical of this zone. As the sky is clear at night, the heat absorbed by the ground during the day is quickly dissipated to the atmosphere. Hence, the air is much cooler at night than during the day.
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- 12. Objective Resist Heat Gain Promote Heat Loss 1. Decrease exposed surfacearea. 2. Increase thermal resistance. 3. Increase thermal capacity. 4. Increase buffer space. 5. Decrease air exchange rate. 6. Increase shading. 7. Increase surface reflectivity 1. Ventilation of appliances. 2. Increase air exchange rate. 3. Increase humidity level.
- 13. PHYSICAL MANIFESTATION Various Methodsto reduce heat gain in a building • Building orientation • Shading by neighboring buildings • Shading by vegetation • Roof ponds and garden •Solar chimney • Courtyard effect • Air vent and wind tower • Sensible and evaporative cooling •Shading by overhangs, louvers and awnings etc. • Air cooling by tunnels •Earth berming •Thermal storage •Opening and windows •Orientation of opening •Walls •Roofs •Shading of roof
- 14. •Building orientation Maximum solarradiation is interrupted by the roof (horizontal surface) followed by the east and west walls and then the north wall during the summer period, when the south oriented wall receives minimum radiation. It is therefore desirable that the building is oriented with the longest walls facing north and south, so that only short walls face east and west. Thus only the smallest wall areas are exposed to intense morning and evening sun. •Shading by Neighboring Buildings The buildings in a cluster can be spaced such that they shade each other mutually. The amount and effectiveness of the shading, however, depends on the type of building clusters.
- 15. • Shading byVegetation •Shading by trees and vegetation is a very effective method of cooling the ambient hot air and protecting the building from solar radiation. • The solar radiation absorbed by the leaves is mainly utilized for photosynthesis and evaporative heat losses. A part of the solar radiation is stored as heat by the fluids in the plants or trees. • The best place to plant shady trees is to be decided by observing which windows admit the most sunshine during peak hours in a single day in the hottest months. • Usually east and west oriented windows and walls receive about 50% more Sunshine than the north and south oriented windows/walls • Reflecting Surfaces If the external surfaces of the building are painted with such colors that reflect solar radiation (in order to have minimum absorption), but the emission in the long wave region is high, then the heat flux transmitted into the building is reduced considerably.
- 16. This solar chimneydraws air through a geometrical heat exchange to provide passive home cooling. •Solar Chimney •A solar chimney utilizes the stack effect, but here the air is deliberately heated by solar radiation in order to create an exhaust effect. •One should distinguish between the stack effect ventilation due to the building itself, and that due to a solar chimney. • In the former case, one tries to keep the increment in the building temperature as small as possible and hence the stack effect is weak. • In the case of a solar chimney, there is no limit to the temperature increment within the chimney,since it is isolated from the used spaces. The chimney can therefore be designed to maximize solar gains and the ventilation effects. •Courtyard Effect •Due to the incident solar radiation in the courtyard, the air in the courtyard becomes warmer and rises up. To replace it, cool air from the ground level flows through the louvered openings of the room, thus producing the air flow.
- 17. •Sensible and EvaporativeCooling •The heat loss from air results in a decreased air temperature, but no change in the water vapor content of the air. Air in the upper part of a wind tower is sensibly cooled. •When water is introduced into a system, evaporative cooling occurs. Such cooling involves a change in both the water-vapor content and the temperature of the air. When unsaturated air comes in contact with water, some water is evaporated, thus lowering the temperature of the air and increasing its water-vapor content. Fountain Air Vent or wind tower •A typical vent is a hole cut in the apex of a domed or cylindrical roof. Openings in the protective cap over the vent direct wind across it. When air flows over a curved surface, its velocity increases resulting in lowering of the pressure at the apex of the curved roof, thereby, inducing the hot air under the roof to flow out through the vent. In this way, air is kept circulating through the room under the roof. Air vents are usually placed over living rooms, often with a pool of water directly under the vent to cool the air, which is moving up to the vent, by evaporation.
- 18. •Shading by overhangs,louvers and awnings Well-designed sun control and shading devices, either as parts of a building or separately placed from a building facade, can dramatically reduce building peak heat gain and cooling requirements and improve the natural lighting quality of building interiors. The design of effective shading devices will depend on the solar orientation of a particular building facade. For example, simple fixed overhangs are very effective at shading south-facing windows in the summer when sun angles are high. Different types of shading devices.
- 19. • Air Coolingby Tunnels The use of earth as a heat sink or a source for cooling/heating air in buried pipes or underground tunnels has been a testimony to Islamic and Persian architecture. The air passing through a tunnel or a buried pipe at a depth of few meters gets cooled in summers and heated in winters (Fig. 10). Parameters like surface area of pipe, length and depth of the tunnel below ground, dampness of the earth, humidity of inlet air velocity, affect the exchange of heat between air and the surrounding soil. Working principle of earth air tunnel.
- 20. •Earth berming In anearth sheltered building or earth beamed structure the reduced infiltration of outside air and the additional thermal resistance of the surrounding earth considerably reduces the average thermal load. Further the addition of earth mass of the building acts like a large thermal mass and reduces the fluctuations in the thermal load. Besides reducing solar and convective heat gains, such buildings can also utilize the cooler sub-surface ground as a heat sink. Hence with reference to thermal comfort, an earth sheltered building presents a significant passive approach. Working principle of earth berming during summer and winter conditions.
- 21. •Thermal Storage Thermal capacityeffects in the materials result in time delay as well as damping of the parameters in the environment. As a result temperature differences exist between the materials and the environment around them and this effect can be utilized for space cooling. •Walls •Good materials in hot-arid zones, combined with few openings and light colored outer surface. Takes best advantages of time lag, with heat emission at night. In regions with large diurnal temperature ranges and nigh especially in the absence of a ceiling - roofs should possess a large thermal capacity with an appropriate time lag to balance temperature variations. To achieve this they must be constructed of heavy materials. The use of exterior or interior insulation has to be considered carefully and its suitability depends on the particular requirements and technical possibilities •CAVITY WALLS Has many advantages, especially in hot-arid zones. Reflective surface in the cavity reduces radiant heat transfer. Ventilation of the cavity takes the heat away and reduces conductive heat transmission to the interior.
- 22. •Openings and windowsare necessary for natural lighting and ventilation, but heat gain in summer should be minimal. During the daytime, the absence of openings would be desirable, especially on the west side; or the openings should be as small as possible and be shielded from direct radiation and located high on the walls to protect from ground radiation . At night, the openings should be large enough to provide adequate ventilation for the dissipation of heat emitted by the walls and the roof. Hence larger openings should be closed during the day with insulated shutters and opened at night. Such systems are not always reliable because they require the attendance and readiness of the inhabitants. Other considerations such as desired privacy and safety may prevent the correct use of a system with shutters. •Openings and windows •Orientation and size of openings •Main openings should face north and south, but the latter should be shaded either by shading devices, roof overhangs or by deciduous trees. The size of the windows on the west and east sides should be minimized in order to reduce heat gains into the house in the early morning and late afternoon, or also be protected by particular shading devices. A moderate, south-facing glass area catches the solar radiation during the cold season, but should not be affected by direct radiation during the summer.
- 23. •Roofs •In hot-arid regionsthe vault, the dome and the flat roof are the traditional •The rounded form of a hemispherical vault (dome) has a larger surface area than its base. Solar radiation is thus diluted and re-radiation during the evenings is also greatly facilitated. Example of dome and vault structure •The flat roof is practical in areas where it seldom rains. It is also a good reflector and re-radiates heat efficiently, especially if it consists of a solid, white painted material. High solid parapet walls along the edge of the roof can on the one hand provide daytime shade and privacy, but can have the disadvantage of creating an undesired stagnant pool of hot air. The construction and exact placement of parapet walls should therefore be carefully examined. Example of flat roof
- 24. •Shading of roof •Shadingthe roof is a very important method of reducing heat gain. Roofs can be shaded by providing roof cover of concrete or plants or canvas or earthen pots etc. •Shading provided by external means should not interfere with night-time cooling. A cover over the roof, made of concrete or galvanized iron sheets, provides protection from direct radiation. Disadvantage of this system is that it does not permit escaping of heat to the sky at night-time . •A cover of deciduous plants and creepers is a better alternative. Evaporation from the leaf surfaces brings down the temperature of the roof to a level than that of the daytime air temperature. At night, it is even lower than the sky temperature. •Another inexpensive and effective device is a removable canvas cover mounted close to the roof. During daytime it prevents entry of heat and its removal at night, radiative cooling. Fig. 5 shows the working principle of removable roof shades. Painting of the canvas white minimizes the radiative and conductive heat gain
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- 26. Sangath Thaltej Road,Ahmedabad SANGATH means“moving together through participation”. Ar. BALKRISHNA VITHALDAS DOSHI
- 27. Location: Thaltej Road,Ahmedabad 380054 Client: Balkrishna Doshi Architect: Balkrishna Doshi Period of construction: 1979-1981(2yr.) Project Engineer: B.S. Jethwa, Y. Patel Site area: 2346 m2 Total Built-up Area: 585 m2 Project Cost: Rs. 0.6 Million(6 crores )
- 28. •Cold northerly windsare responsible for a mild chill in January. •Avg. Annual Rainfall: 800mm •Highest temp. recorded: 48.5 °C •The weather is hot from March to June The avg. summer maximum is 43 °C The avg. minimum is 24 °C • From November to February, The avg. maximum temperature is 30 °C The avg. minimum is 13 °C •Climate Type Hot and Dry
- 29. 1. Forecourt 2. Pond 3.Amphitheatre 4. Entrance court 5. Reception 6. Workshops 7. Conference 8. Toilets 9. Architects office 10. Subterranean meeting room 11. Engineers 12. Design studio 13. Library 14. Studio •Plan of studios
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- 36. Sketch of “SANGATH“ by B.V Doshi 3D Modal of Sangath
- 37. •Design concept AndFeatures: 1. Design concerns of climate ( temperature or sunlight). 2. Main studio partly bellow the ground (sunken). 3. Extensive use of vaults. 4. Very less use of mechanical instrument. 5. Special materials are used resulting in a low cost building costing it. 6. Lot of vegetation & water bodies. 7. Continuity of Spaces. 8. Use of lot of diffused sunlight. 9. Complete passive design. 10. Grassy steps which Doshi uses as informal Amphitheatre.
- 38. •Earth berming 1. Mainstudio partly bellow the ground (sunken). Section BB Lounge Conference 2. Building is largely buried under ground to use earth masses for natural insulation. 3. Earth sheltered structure reduced infiltration of outside air and the additional thermal resistance of the surrounding earth considerably reduces the average thermal load.
- 39. •Extensive use ofvaults •3.5 cm thick RCC •8 cm ceramic fuses •3.5 cm thick RCC •6 cm thick water proofing •1 cm thick broken China mosaic finish. •Ceramics are temperature resistant. •Broken China mosaic is insulative and reflective surface. •The rounded form of a hemispherical vault (dome) has a larger surface area than its base. Solar radiation is thus diluted and re- radiation during the evenings is also greatly facilitated.
- 40. Heat from thesun is reduced by grassy mounds and the white reflective china mosaic that covers each vault. •Reflecting outer surface
- 41. •Stack effect Pressure Pressure • Thewarmer indoor air rises up through the building and escapes at the top either through open windows, ventilation openings. The rising warm air reduces the pressure in the base of the building, drawing cold air in through either open doors, windows, or other openings and leakage. •The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect.
- 42. •Lighting Indirect Lighting oUpper LevelLarge Openings-Facing North. oSkylights as projected masses from the roof. oSmall cut-outs on roof slab filled with hollow glass blocks.
- 43. •Design studios withsmooth floors and rough textured vaulted ceiling interiors. •The rough textured vaulted ceiling interiors in the main drafting room dispersed natural light into the space(does not produce glare).
- 44. •Shading by vegetation MinimizingSolar Radiation on South and West side : The structure is closely integrated with the outdoor spaces. Vegetation on site is almost left to grow into wilderness. The West and South façade is shaded by dense trees.
- 45. •Maximizing Wind Flow : Windfrom West and South-West side is taken in by just a positioning structures so as to create a central open space through which wind can flow unobstructed. •Wind flow and building form
- 46. Water Body: • Waterin the Sangath building is used as a major modifier of the microclimate. • Rainwaer and overflow of pumped water from the roof tank are harnessed through roof channels that run through a series of cascading tanks and water channels to finally culminate in a pond from where it is recycled back or used for irrigating vegetation. •Water cascades also provide interesting visual experiences.
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- 48. Terraced court leadingto main entrance areas; split level fountain
- 49. A temperaturedifference of about 8°C Time lag for heat transfer is nearly 6 hours 30% to 50% reduction in cooling energy •Performance
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