Building Science 2 lec 2.pptx gg ggg

building science

1. Building Science 2 Lecture 2 Dr. Sara Abdelaziz Elgezary

2. Spatial system of climate Subdivision of regional Recommendations for passive cooled buildings Design approach, adapt to nature 2 8/27/2019 Add a footer

3. Climate system Earth's climate arises from the interaction of five major climate system components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere (living things ). Energy, water and different chemical elements are constantly flowing between the different components of the system. Climate is the average of weather , typically over a period of 30 years, and is determined by a combination of processes in the climate system 3 8/27/2019 Spatial system of climate

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5. Over time, the climate system's pattern can change due to internal variability and external forcings . These external forcings can be natural, such as variations in solar intensity and volcanic eruptions, or caused by humans. The emissions of heat-trapping greenhouse gases from industrial sources and their subsequent accumulation is currently causing global warming . Human activity also releases cooling aerosols , but their net effect is far less than that of greenhouse gases . Excessive Greenhouse Gases Lead to Warming Greenhouse gases like carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and methane (CH 4 ), trap heat in the atmosphere. With higher-than-natural concentrations, they lead to unnatural warming. 5 8/27/2019 Spatial system of climate

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7. Climate Spatial Zones: The classification is based on maximum and minimum temperatures and the temperature range as well as the total and seasonal distribution of precipitation. Simple summary of climatic zones: Polar - very cold and dry all year Temperate - cold winters and mmild summers Arid - dry, hot all year Tropical - hot and wet all year Mediterranean - mild winters, dry hot summers Mountains (tundra) very cold all year 7 8/27/2019 Add a footer

8. Climatic Zones The world has several climatic zones. These are summarized on the map below. 8 8/27/2019 Add a footer

9. Global Topography Note the location of mountain ranges and lowlands.  The pale blue lines are tectonic plate boundaries.  In general, air temperatures and total rainfall decrease as elevation increases. Regarding topography, mountains are a barrier to moisture carried by winds that cross water. More precipitation falls on the windward side of the mountain than on the leeward side of the mountain. The leeward side of the mountain is sometimes referred to as being in the rain shadow. 9 8/27/2019 Add a footer

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11. Ocean Currents (with Global Prevailing Winds) 11 8/27/2019 Add a footer

12. The world by region 12 8/27/2019 Add a footer

13. Maldives - Climate The climate of Maldives is warm year round, determined by the monsoons. However, being on the equator, the monsoons are mild and not as defined as in neighboring countries. Of the two monsoons, the southwest monsoon from May to October, brings some rain and wind. The northeast monsoon, from November to April, is the dry season with very little wind. The temperature varies little with an annual average daily maximum of 30.4 degrees Celsius and the minimum at 25.9 degrees Celsius. 13 8/27/2019 Add a footer

14. 14 8/27/2019 Add a footer This period starts in January and typically continues to approximately March/April. This period starts in May and ends somewhere in November.

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16. Heat gain in building: 16 8/27/2019 Add a footer

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19. Recommendations for passive cooled buildings The last two decade has witnessed a severe energy crisis in developing countries especially during summer season primarily due to cooling load requirements of buildings. The energy consumption in buildings is quite high and is expected to further increase because of improving standards of life and increasing world population. Air conditioning use has increasingly penetrated the market during the last few years and greatly contributes in the upsurge of absolute energy consumption . According to the World watch Institute, buildings consume about 40% of the world’s energy production. As a result, buildings are involved in producing about 40% of the sulfur dioxide and nitrogen oxides that cause acid rain and contribute to smog formation. Building energy use also produces 33% of all annual carbon dioxide emissions, significantly contributing to the climate changes brought about by the accumulation of this heat-trapping gas .In India, the building sector represents about 33% of total electricity consumption, with commercial sector accounting for 8% and 25 % respectively 19 8/27/2019 Add a footer

20. Passive cooling of buildings A ‘passive’ solar design involves the use of natural processes for heating or cooling to achieve balanced interior conditions. The flow of energy in passive design is by natural means: radiation, conduction, or convection without using any electrical device. Maintaining a comfortable environment within a building in a hot climate relies on reducing the rate of heat gains into the building and encouraging the removal of excess heat from the building. To prevent heat from entering into the building or to remove once it has entered is the underlying principle for accomplishing cooling in passive cooling concepts. This depends on two conditions: the availability of a heat sink which is at a lower temperature than indoor air, and the promotion of heat transfer towards the sink. Environmental heat sinks are: 20 8/27/2019 Add a footer

21. Outdoor air (heat transfer mainly by convection through openings) Water (heat transfer by evaporation inside and / or outside the building envelope) The (night) sky (heat transfer by long wave radiation through the roof and/or other surface adjacent to a building Ground (heat transfer by conduction through the building envelope) Passive cooling techniques can reduce the peak cooling load in buildings, thus reducing the size of the air conditioning equipment and the period for which it is generally required. 21 8/27/2019 Add a footer

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23. Some of the important cooling concepts like shading are: 23 8/27/2019 Add a footer Different types of shading devices.

24. 24 8/27/2019 Add a footer Roof shading by solid cover. 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 (the following figure)

25. 25 8/27/2019 Add a footer Roof shading by plant cover.

26. Covering of the entire surface area with the closely packed inverted earthen pots, as was being done in traditional buildings, increases the surface area for radiative emission. Insulating cover over the roof impedes heat flow into the building. However, it renders the roof unusable and maintenance difficult (Fig. 4). Broken china mosaic or ceramic tiles can also be used as top most layer in roof for reflection of incident radiation. 26 8/27/2019 Add a footer

27. 27 8/27/2019 Add a footer Roof shading by earthen pots.

28. 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. working principle of removable roof shades. Painting of the canvas white minimizes the radiative and conductive heat gain 28 8/27/2019 Add a footer

29. 29 8/27/2019 Add a footer Removable roof shades.

30. Shading by textured surfaces Surface shading can be provided as an integral part of the building element also. Highly textured walls have a portion of their surface in shade as shown in Figure .The increased surface area of such a wall results in an increased outer surface coefficient, which permits the sunlit surface to stay cooler as well as to cool down faster at night 30 8/27/2019 Add a footer Shading due to surface texture

31. Insulation Induced ventilation techniques Radiative cooling Evaporative cooling Earth coupling Desiccant cooling 31 8/27/2019 Add a footer

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33. 33 8/27/2019 Add a footer Working principle of earth air tunnel.

34. 34 8/27/2019 Add a footer Working principle of earth berming during summer and winter conditions

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37. Design approach, adapt to nature 37 8/27/2019 Add a footer

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44. Thank You 44 8/27/2019 Add a footer