Shading devices are used in order to reduce heat gain in a building, moreover two common strategies are adopted for the same namely, facade shading and fenestration shading.Sun shading devices are any mechanical equipment or textiles that are used internally or externally or in both. The primary objective is to create a soothing micro-climate which is cool in the summers and warm in the winters.
- Facade Shading
It is always advisable to block direct heat gain in a building by means of external shading devices or facade shading. If the critical surface of the facade can be shaded the cooling load can be reduced drastically .It is observed in sun path analysis that maximum heat occurs through roof, then walls to the west and east. Therefore, these facades need appropriate shading devices that can cut incident radiation. The western and eastern walls of buildings are subjected to very low angle solar radiation due to lower altitude position of sun.Therefore vertical shading is required in these sides.There are various types of facade shading techniques some of which are as follows –
- Roof Pergola
- Space Frame
- False Wall / Jaali
- Green Wall
- Window pergola
- Fenestration Shading
It is very important to shade the fenestrations in a building as it is a major source of heat gain in a building.Use of external shading devices is a efficient way to prevent unwanted heat gain during summers. However the shading device need to be optimized according to the sun path, solar angle, so that it can keep the summer heat away and winter sunshine in .
There are many types of shading devices used for fenestration shading broadly classified as –
- Vertical Type (V)
- Horizontal Type (H)
- Mixed (M)
- Method of Shading Design
Two methods for appropriate shading device for fenestration are –
- Sun Path Analysis
- Use Of Shading Norms
The design of any shading device, particularly horizontal shades, depends greatly on the exact path of the Sun through the sky. Thus, shading device strategies need to be tailored to the orientation of each window. Whilst some orientations are easy to shade, others are much more difficult as the Sun can be almost direct-on at certain times of the day.
The table below indicates the appropriate types of shading device for use on each orientation of a building.
|Equator-facing||Fixed Horizontal Device|
|East||Vertical Device/Louvres (moveable)|
|West||Vertical Device/Louvres (moveable)|
- Sun Path Analysis
The main aim of sun path analysis is to find out critical window angles or shadow angles on respective fenestrations in order to calculate the appropriate depth of shading devices, the angle of incident radiation of sun i relation to building elevation must be established.The angle of incidence on the vertical surface is represented by following two components.
- Horizontal Shadow Angle (HSA)
- Vertical Shadow Angle (VSA)
The performance of shading devices is specified by these two angles, and both of these are measured from a line perpendicular to elevation.
Horizontal Shading Angle (HSA) characterizes a vertical shading device. It is a angle between the wall normal and the line joining the outer edge of the vertical shade to the center of the wall normal. The horizontal shadow angle (HSA) is relevant for vertical shading devices such as fins. It is easy to determine: It’s theangle between the normal of the window pane and the azimuth of the sun.
The calculation is also performed only for a certain period during the day, typically near solar noon since that is when it’s most important to increase solar gain in the winter and reduce gain in the summer (because the sun is most intense then). In fact, it is not usually possible to design a horizontal overhang that works in the early morning or late afternoon because the sun is low in the sky in both the summer and winter.
Vertical Shading Angle (VSA) characterizes a horizontal shading device. It is the angle between the wall normal with the line joining the outer edge of horizontal shade to the center of normal.The vertical shadow angle (VSA) is a little bit more difficult. If we imagine a virtual plane between the bottom left-hand and right-hand corners of the window and the sun, then the VSA is the angle this plane formes with the ground plane. The VSA is required when designing horizontal shading devices such as overhangs.
The vertical exterior louver and egg-crate solar shading devices, are primarily useful for east and west exposures. These devices also improve the insulation value of glass in winter months by acting as a windbreak.
- Shading Design with help of HSA and VSA
Once the required horizontal or vertical window angles are calculated, it is easy to determine the size of shading device.in the figure below , the required horizontal window angle H is shown. Ab is the resulting vertical louver normal to wall. Ab can also be replaced by an inclined louver AC without any effect on masking angle AB. The size of inclined louver AC is less than that of normal louver AB.
- Use of Table
- P- It denotes the outward projection of louver system perpendicular to wall. All other dimensions are given in terms of P.
- B _ It is the angle of inclination of louver away from normal to the wall. A value of B=0 signifies vertical or horizontal louver normal to wall.
- Spacing- It is horizontal or vertical distance between corresponding points of adjacent vertical or horizontal lovers respectively.For the same value of P , it always increases with increase in angle of inclination of louver.
- The spacing between individual louvers is given in terms of their outward projection for various angles of inclination, the net performance remains unaltered.
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