7. shading devices

Sun Shading Devices

CLIMATOLOGYROHIT KUMARASSISTANT PROFESSORMBS SPA 2016

Introduction Sun Shading Devices inhibit the solar radiation

(block, allow,, etc.) incident on a building and are used either internally or externally or in between the internal and the external building space.They can be any mechanical equipment (like

dynamic facades), projections (chajja), cantilevers, louvres, fins, jaalis, or even textiles. They can be fixed, manual and automatic moveableThe primary objective of creating a comfortable

internal environment, that is, cool in the summer and warm in the winter.

Importance of Sun Shading DevicesSolar radiation is an important factor of thermal

comfort. Sun Shading Devices improve internal environment in order to provide greater comfort for occupants. To reduce the heat gains during summer and promote

heat gain during winter, reduce the HVAC loads and therefore minimize energy costs. Use of shading device can improve building energy performance.To prevent glare (causing discomfort or disablility of

vision).To increase useful daylight availability.To create a sense of security- internal sun shading

devices like curtains help to beautify internal space and create a sense of privacy.

Use of shadingSolar controls should be considered for all glazed

openings exposed to direct sunlight.

Solar control is particularly important on south towest-facing facades, since the solar gains willcoincide with the hottest part of the day.

Solar control is also vital for lightweight buildingswith large areas of glazing.

Constraints of shading devices

Sun path and wind direction are usually different.Maintenance of air flow through the non-air-conditioned buildings during the cooler hours ofthe day.

There will be a need for admitting controlled levelsof diffused daylight.

In most cases there will be a requirement of viewsout of the window.

Solar shadingWhen sunlight hits a pane of glass, it splits into three components –Reflected : no effect on heating.Absorbed: glass heats up which would transfer heat by conduction and also emits heat (and) Transmitted: Heat up surface behind it.The proportion between the three components is

determined by the ‘angle of incidence’ and by thetype of glazing.

For most types of glazing, the transmitted componentis very small if the angle of incidence is larger than45º from the normal to the glazing.

If the angle is more than 60º , most of the radiation isreflected.

Types of Sun Shading Devices

On the basis of their position in a building:-

InternalExternal Interpane

Internal Sun Shading Devices

Limit the glare resulting from solar radiation. Usually are adjustable and allow occupants to

regulate the amount of direct light entering their space.

Cur

tain

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Vene

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Verti

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ouvr

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inds

Rol

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linds

Pleated blinds

Blackout blinds

External Sun Shading Devices

Most thermally efficient as it controls the amount of radiation entering the building externally.

Horizontal, Vertical or egg-crate devicesVegetation and other buildings can also act as

shading devices.

Horizontal Devices: to shade a window during hot summer months, but to allow sunlight to shine through a window in the winter, to help warm a building.

Vertical Devices: Primarily useful for east and west exposures to improve the insulation value of glass in winter months by acting as a windbreak.

Slanted Vertical Fin Vertical Fins

The egg-crate: A combination of vertical and horizontal shading elements commonly used in hot climate regions because of their high shading efficiencies. The horizontal elements control ground glare from reflected solar rays. The device works well on walls

Shading from External Environment

Shade from buildings

DESIGNING SHADING DEVICE1. Understand the sun path of the place.2. Select shading typeHorizontalVerticalEgg crate

3. Identify category FixedAdjustable

4. Calculate design dimensionsUnderstand horizontal and vertical shadow angles

1. Sun paths

2. & 3. Select Shading Type & CategoryOrientation Suggested Shading Type

North fixed or adjustable shading placed horizontally above window

East and West adjustable vertical screens outside window

NE and NW adjustable shading

SE and SW planting

Climatic zones Requirements

Hot and dry Complete one year round shading

Warm and humid Complete year round shading , but design should be made such that ventilation is not affected

Temperature Complete year round shading but only during major sunshine hours

Cold and cloudy No shading

Cold and sunny Shading during summer months only

Composite Shading during summer months only

Shading from External Environment

Shadow angles are formed by sun shadingdevices or projections on a wall exposed to thesun.Different design of sun shading devices formdifferent shadow angles. The performance of shading device isspecified by two angles : Horizontal shadow angle Vertical shadow angle

These angles depend on the position of thesun and the orientation where the window isfacing.

Horizontal shadow angleThe horizontal shadow angle (HSA) isrequired for (or cast by) vertical shadingdevices.It is the horizontal angle between thenormal of the window pane and the azimuthof the sun.

HSA = wall azimuth – solar azimuth

Horizontal shadow angle

Vertical shadow angle

The vertical shadow angle (VSA) is required for(or cast by) horizontal shading devices.It is the angle between the ground line andaltitude of the sun.


Actually it is measured on a vertical plane normal to theelevation considered.

If we imagine a virtual plane between the bottom left-hand andright-hand corners of the window and the sun, then the VSA isthe angle this plane forms with the ground plane.

tan VSA = tan(altitude) / cos(HSA)

Solar altitude angle & VSA

Solar altitude angle describes sun’s positionin relation to the horizon, while VSA describesthe performance of the shading device.Numerically, the two coincide when, the sun isexactly opposite the wall considered i.e. whensolar azimuth and wall azimuth angle are sameand HSA = 0.For all other cases, when the sun is sidewaysfrom the perpendicular, the VSA is always largerthan the solar altitude angle.

4. Shade DimensionsThese two angles, HSA and VSA, can then beused to determine the size of the shading devicerequired for a window.If the height value refers to the vertical distancebetween the shade and the window sill, thenthe depth of the shade and its width from eachside of the window can be determined usingrelatively simple trigonometry.

Shade Depth : The depth is given by:depth = height / tan(VSA)

Shade Width : The width is given by:width = depth x tan(HSA)

Disadvantages of Sun Shading DevicesDifficulties can be experienced in handling the

internal shading devices like curtains and blinds. In the use of shading devices like light shelves,

problems with low angle winter sunlight penetration can give rise to glare. If the building is highly stylized (e.g. Neoclassical or

glass cube), it may be impossible to reconcile external shading with the original style. Shading always blocks a part of the view. As a

minimum, it blocks the portion of the sky where the sun travels.Some shading methods are extremely specific to

compass orientation (azimuth). For example, fixed horizontal shading may leak sunlight into the building during the morning or afternoon unless it is

Presentation on Sun Shading Devices: Presenters: Binisha Gurung , Nishu Shrestha, Prabal Dahal, Rojina Nakarma, Suchitra Bhatta

Presentation: Solar control and shading

Hübe, Helena Bülow. "ESTIMATION OF THE PERFORMANCE OF SUNSHADES USING OUTDOOR MEASUREMENTS AND THE SOFTWARE TOOL PARASOL V 2.0." Lund University. Web. 28 Nov. 2014. <http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=699802&fileOId=711430>.

Bahr, Wassim. 1 Dec. 2009. Web. 28 Nov. 2014. <http://www.sesam‐uae.com/greenbuilding/presantation/5. Wassim Bahr, AUD.pdf>.

Mohammad Arif, Kamal. "A S Tudy on S Hading of B Uildings as a P ReventiveM Easure for P Assive C Ooling and E Nergy C Onservation in B Uildings." International Journal of Civil & Environmental Engineering, 1 Dec. 2010. Web. 28 Nov. 2014. <http://www.ijens.org/102406‐5252 IJCEE‐IJENS.pdf>.

Web. 3 Dec. 2014. <http://www.bembook.ipsa.us>.Web. 3 Dec. 2014. <http://www.usc.edu>.Web. 3 Dec. 2014. <http://www.earchitect.co.uk>.

References:

7. shading devices

Design