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Unit 2 Building Response to Sun & Sky.pdf
- 1. Climate & The BuiltEnvironment Unit 2: Building response to Sun & Sky MSAJAA-2021A 171022 BUILT ENVIRONMENT - Thermal Comfort SOURCES OF HEAT GAIN ● Three major sources of unwanted heat- ● Direct solar impacts on a building - Windows Skylights Heat transfer Infiltration of Exterior high temperatures - Materials & Elements of the structure Internal heat produced by appliances, equipment & inhabitants 2 BUILT ENVIRONMENT - Thermal Comfort 3 BUILT ENVIRONMENT - Thermal Comfort SOURCES OF HEAT GAIN 4
- 2. BUILT ENVIRONMENT -Thermal Comfort 5 BUILT ENVIRONMENT - Thermal Comfort THERMAL COMFORT ZONE The optimum thermal condition can be defined as the situation in which the least extra effort is required to maintain the human body’s thermal balance ● Greater the effort that is required, the less comfortable the climate is felt to be ● Maximum comfort condition can usually not be achieved ● Differs somewhat with individuals - depends also on the clothing worn, the physical activity, age and health condition ● Geographical location plays a role because of habit of individuals ● Can be regulated by HVAC 6 BUILT ENVIRONMENT - Thermal Comfort REGULATING MECHANISM 7 BUILT ENVIRONMENT - Thermal Comfort REGULATING MECHANISM 8
- 3. BUILT ENVIRONMENT -Thermal Comfort REGULATING MECHANISM ● Temperature difference between air and surfaces not to exceed 10 - 15°C if comfort is still to be maintained. ● Range of conditions within which at least 80% of the people would feel comfortable is termed as “comfort zone” COMFORT ZONE IN DIFFERING AIR AND SURFACE TEMERATURES 9 BUILT ENVIRONMENT - Thermal Comfort REGULATING MECHANISM 10 BUILT ENVIRONMENT - Thermal Comfort REGULATING MECHANISM Thermal mass - Measure of a material to store or retain heat energy ● High density materials - Concrete, bricks & tiles-high thermal mass ● Lightweight materials - Timber & metal have low thermal mass ● Buildings with high thermal mass iron have temperature variations naturally, ranges more consistent with the ideal human comfort zone ● Reduced need for artificial heating and cooling, resulting in less energy use 11 SUN PATH Seasonal Variations Refers to the seasonal and Hourly positional change of the Sun and length of Daylight as Earth rotates and orbits around the Sun Accurate location and specific knowledge of Sun’s path is essential for- ● Building orientation ● Daylighting ● Summer shading ● Landscaping ● Solar Collector Area for technologies based on solar energy 12
- 4. SUN PATH Seasonal Variations ●The sun rises in the east and sets in the west. ● Because the earth rotates on an axis that is tilted, however, the sun doesn’t stay exactly in the east or west. ● In summer, it rises north of east, travels high across the southern sky, and sets north of west. In winter, it rises south of east, travels low across the southern sky, and sets south of west. How high it gets in the summer and how low in the winter depend on how far you are from the Equator 13 SUN PATH Seasonal Variations 14 SUN PATH Northern side ● India being in Northern hemisphere - Sun does not touch the North side at all ● No direct solar radiation from the North - Coolest side with no direct harsh effects ● Daylight is available for the entire duration of Sun from the North - mostly remains uniform throughout the duration based on the sky conditions ● Best direction that require ample daylight but no heat gain ● North light is usually used in Industrial Design or Drawing studios ● Courtyards are not preferred in the North as direct sunlight is not available and hence the diffused radiation is even lower 15 SUN PATH Southern side ● Solar radiation is available in both Summers & Winters ● In Summers, the Sun angle is high - large duration of Sun - 14 Hours ● In winters, since the Sun angle is low, lesser duration of Sun - 9 Hours ● Maximum Solar radiation is only from the South ● Sufficient daylight during entire duration of sun-lit hours in Winter ● Summers bring heat and glare and require careful design considerations ● Can be used for living and working areas - bedrooms, kitchens, offices with adequate heat gain control 16
- 5. SUN PATH Sun pathDiagram ● Solar radiation is available in both Summers & Winters ● In Summers, the Sun angle is high - large duration of Sun - 14 Hours ● In winters, since the Sun angle is low, lesser duration of Sun - 9 Hours ● Maximum Solar radiation is only from the South ● Sufficient daylight during entire duration of sun-lit hours in Winter ● Summers bring heat and glare and require careful design considerations ● Can be used for living and working areas - bedrooms, kitchens, offices with adequate heat gain control 17 SUN PATH Altitude Angle Solar Altitude Angle (θ) is the vertical angle at the point of observation, between the horizon plane and the line connecting the sun to the observer. Azimuth Angle Solar Azimuth Angle (α) is the angle at the point of observation measured at the horizontal plane between the north direction and the vertical plane containing the sun. Azimuth angle is measured clockwise from North towards East. North: (α ) = 0˚ or 360˚ East : (α ) = 90˚ South : (α ) = 180˚ West : (α ) = 270˚ 18 SUN PATH Sun path study - Stereographic Diagram ● Convenient way of representing the annual changes in the path of the Sun through the sky on a single 2D diagram ● Most immediate use is that the solar azimuth and altitude can be read off directly for any time of the day and month of the year ● Also provide a unique summary of solar position that the architect can refer to when considering shading requirements and design options. ● There are several methods of projections to present the apparent movement of the sun on the sky hemisphere. By using any of these projection methods, the apparent three-dimensional movement of the sun can be represented on a two dimensional chart which is called SOLAR CHARTS or SUN PATH DIAGRAM. ● Most commonly used projections are EQUIDISTANT and STEREOGRAPHIC Projection Methods. 19 SUN PATH Sun path study - Stereographic Diagram ● Sun path diagram prepared by the aid of the equidistant projection gives easy and direct reading to the users. On this diagram - ● Circle with 90 mm radius represents the sky hemisphere on the horizontal plane. ● Center of the circle represents observation point. ● Perimeter scale gives the azimuth angles (α). ● Concentric circles give the altitude angles (θ). 20
- 6. SUN PATH Sun pathstudy - Stereographic Diagram ● Group of curves extending from East to West show the sun path at various dates. The two extreme curves show sun path in two solstices., June 21 and December 21. Sun paths for other days lie between these extremes. ● Vertical radius represent solar noon. Group of curved lines on both sides of the vertical radius represent solar hours between sunrise and sunset ● Sunrise and sunset times can be read from the intersection of sun path curve and the peripheral circle. ● On equinox days, March 21 and September 21, the sun rises at 6:00 am & sets at 6:00 pm. In summer, the sun rises earlier and sets later, in winter it rises late and sets earlier. 21 SUN PATH Sun path study - Stereographic Diagram Steps to read the Sun position from a stereographic sun-path diagram- Step 1 - Locate the required hour line on the diagram. Step 2 - Locate the required date line, remembering that solid are used for Jan-Jun and dotted lines for Jul-Dec. Step 3 - Find the intersection point of the hour and date lines. Remember to look for the intersection of the dotted with dotted lines. Step 4 - Draw a line from the very centre of the diagram, through the intersection of the circle around from the intersection point to the vertical North axis, on which is displayed the altitude angles Step 5 - Read the azimuth as an angle taken clockwise from North. In this case, the value is about 62° 22 SUN PATH Sun path study - Stereographic Diagram Step 6 - Trace a concentric “C” Step 7 - Interpolate between the concentric circle lines to find the intersection point sits exactly on the 30° line. 23 SHADING DEVICES Any device, external or internal that shades the opening of a built space by casting its shadow on the same can be termed as a Shading Device 24
- 7. SHADING DEVICES Why areShading devices needed? ● Impact of Solar radiation entering a room through windows ● Increase in air temperature by radiation absorbed on room surfaces ● Increase in the mean radiant temperature of occupants ● High intensities of radiation from direct sun can cause discomfort glare. 25 SHADING DEVICES Functions of Shading devices ● Stop solar radiation penetration into the building during hot periods. ● Allow solar radiation penetration into the building during cool periods. ● Should allow view to the outside from inside the building. ● Should allow daylight into the building. ● Provide some privacy whenever required. ● Protect the occupants of the building from glare. ● Should not interfere with air circulation through the windows. 26 SHADING DEVICES 27 SHADING DEVICES 28
- 8. SHADING DEVICES Shadow AngleProtractor: ● The shadow angle protractor gives a representation of the shadow angles on a horizontal plan in stereographic projection and to the same scale as the sun path diagram. ● Semi-circular protractor, shows two sets of lines- - Radial lines marked 0 at centre to -90 to the left and +90 to the right, to give readings of the horizontal shadow angle - Arcual lines coincide with the altitude circles along the centreline, but then deviate and converge at two corners of the protractor. These will give readings of the vertical shadow angle 29 SHADING DEVICES Performance Parameters of Shading devices ● Thermal performance ● Visual performance ● Acoustic performance ● Aesthetic performance Values of these parameters depend on - Independent variables Climate Site Building type Dependent variables Heat transfer Facade type Position of the blinds relative to the window 30 SHADING DEVICES - Types of Vertical Devices 31 SHADING DEVICES - Types of Horizontal Devices 32
- 9. SHADING DEVICES -Types of Compound Devices 33 SHADING DEVICES - Other types of H & V Devices 34 SHADING DEVICES - Design considerations For an OVERHANG design- h = D x Tan (Solar altitude) / cos (Solar azimuth – Window azimuth) For total shade at your target month/hour, set h to height of window from sill to head and solve for D, required overhang depth. For partial shade, set h to acceptable height of shadow (perhaps 2/3 of window height) and solve for D, required overhang depth. With a given overhang, set D to its depth and find h, the height of shadow it will cast at your target month/ hour. For a FIN design- w = D x Tan (Solar azimuth - Window azimuth) Solve for either W - width of shadow, or D - depth of fin, as with the overhang equation Be sure to observe proper signs If both solar and window azimuths are on the same side of the south vector, then both values are positive. If they are on opposite sides of south, then set one azimuth as negative. Solar azimuth - (-Window azimuth) = Solar azimuth + Window azimuth 35 SHADING DEVICES - Design considerations Factor method The following equation provides a quick method for determining the projection of a fixed overhang Projection = Window opening (height) / F F Factor from the table Select a factor according to the latitude. The higher values will provide 100% shading at noon on June 21st, the lower values until August 1 North latitude F factor 28 5.5 – 11.1 32 4.0- 6.3 36 3.0- 4.5 40 2.5- 3.4 44 2.0- 2.7 48 1.7- 2.2 52 1.5- 1.8 56 1.3- 1.5 36
- 10. SHADING DEVICES -Design considerations 37 DAYLIGHTING ● Practice of placing windows, skylights, other openings and reflective surfaces so that Sunlight - both direct & indirect can provide effective internal lighting for a built space. ● Special attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy use. ● Energy savings can be achieved from the reduced use of artificial lighting or from passive heating Sources ● Primary source is the Sun ● Light received from Sun is through direct solar illumination and Designmethods to enhance the light reception 38 DAYLIGHTING Why Daylighting? ● Improved Aesthetics of interiors ● Daylight has direct impact on User health - increasing productivity and maintaining circadian rhythm ● Humans need it for visual and psychological health ● Is a free resource and essential for human survival ● Reduces lighting and HVAC dependence thereby reducing electricity costs also 39 DAYLIGHTING National Lighting Code 40
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- 13. DAYLIGHTING 49 Overhead Daylighting Skylights -Domed, horizontal or slightly sling glazed openings in the roof Clerestories - Usually situated ata a high level ( near the ceiling of the room) - always above eye level. They provide an effective source of natural light an ventilation while reducing glare DAYLIGHTING 50