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Sun Shade Calculator for Lahore, by Sarah Khan

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- 1. Sun Shade Calculator for Lahore Sarah Khan
- 2. Energy Efficiency and Sustainability Introduction Energy efficiency is an integral part of architecture. One of the simplest and most basic passive techniques, that is universally applied for hot climates such as that of Pakistan, is that of solar shading.
- 3. Energy Efficiency and Sustainability Introduction This presentation gives an overview of the existing methods of providing shade from the Sun. Additionally, a new technique is proposed and the verification of the reliability of this new method is also undertaken. Finally, there is an explanation of the diversity and limitations of its application, its scope and future prospects.
- 4. Energy Efficiency and Sustainability Introduction The building sector in Pakistan is a major consumer of energy resources, with its lighting, heating and air-conditioning loads (especially in extreme climatic zones of the country). EXISTING ENERGY USE 1 ENERGY CONSERVATION POTENTIAL 2 Savings can be achieved through a general ‘green’ building approach, using insulation, correct orientation, solar shading, etc. <ul><li>taken from “ A quick design approach towards energy efficiency” , Sabahat Alamgir PLEA 2008 – 25th Conference on Passive and Low Energy Architecture, Dublin </li></ul><ul><li>These figures can be downloaded from http://www.enercon.gov.pk/ </li></ul>25% Average 30% Building 20% Agriculture 20% Transport 25% Industry 3% Others 52% Building 1% Agriculture 17% Transport 27% Industry
- 5. Windows & Energy Efficiency Introduction The control or otherwise of solar radiation is an important part of building design. In a relatively hot climate it represents one of the most significant sources of potential summer heat gains. <ul><li>These figures have been taken from the article “ Shade screens and window treatments” by Arizona Public Service Company (APS);1999. Retrieved May, 2005 from www.apsc.com. Arizona is 34 o N Latitude, so study may be loosely comparable to Lahore (nearly 32 o N). </li></ul><ul><li>The contribution of the ceiling to the total heat gain is lower for Arizona, because of the use of proper roof insulation /attics etc. ; features that are missing in local architecture. Therefore, this figure would be significantly higher in case of Lahore/Pakistan. </li></ul>1 2
- 6. External Vs. Internal Shades Introduction Both external and internal shades control heat gain. External shades are more effective than internal shades because they block the solar energy before it enters the window. (In fact, stopping the sun’s heat before it penetrates windows and openings is up to seven times more effective than using interior blinds or curtains. 1 ) When using an internal shade, such as blinds or a curtain, the short-wave radiation (light) passes through the glass and hits the shade. Depending on the colour of the shade, some percentage will be reflected straight back out the window, but the rest will be absorbed by the shade itself, effectively heating it up. Some part of the incoming short-wave radiation will also already have converted into long-wave radiation (heat waves). Thus, even though internal and external shades seem to be doing the same job, their effect on the performance of the building is quite different. 1 A quote by U.S. Department of Housing and Urban Development, taken from the article ’Shade screens and window treatments’, by Arizona public service APS company,1999.Retrieved from www.apsc.com; May,2005.
- 7. The Problem Introduction The efficient design of a window shade - that which allows the Sun to penetrate in winter but not in summer - is a basic requirement that every architect aspires to achieve.
- 8. Existing Methods Introduction <ul><li>Graphical Method </li></ul><ul><li>The old traditional method using sun-path diagrams – it has been incorporated into most computer software now. </li></ul><ul><li>Computer Softwares </li></ul><ul><li>There are some computer software available attempting to remedy this problem; however, even they find limited applicability because: </li></ul><ul><li>• Extremely high prices of the few available software; most practices choose not to buy one. </li></ul><ul><li>The software is complicated to use; the software are specialised and need training to learn them. The whole process can be quite time-consuming and cumbersome. </li></ul>
- 9. The Proposed Solution Introduction <ul><li>The proposed solution is the design of a method that should be: </li></ul><ul><li>simple and quick to use; </li></ul><ul><li>Should avoid lengthy side-calculations / climatic considerations to be done every time. </li></ul><ul><li>Should be capable of calculating the shade parameters for a variety of shade types ; </li></ul><ul><li>Should operate in a user-friendly environment ; </li></ul><ul><li>Input Data needed should be simple and quick, and few input parameters be required; </li></ul><ul><li>It should be available for free . </li></ul>
- 10. The Proposed Solution Introduction The proposed solution is a software /calculator that is different from the available software, in that it is a Specific software, as opposed to all the existing General software. While a generalized software can respond to any global location; it can be quite time-consuming and complicated and therefore would always require extensive pre-calculations. A specific software on the other hand may not have global appeal but it can significantly ease the situation for a specified target audience. It becomes simpler for the user as it is possible to programme into it almost all the pre-calculations that would otherwise be required of the user.
- 11. The Objectives Introduction <ul><li>To develop a software for Lahore that is capable of calculating the shade parameters for a variety of shade types. </li></ul><ul><li>To compare the efficiency of the developed software with the existing methods. </li></ul><ul><li>To test the software’s accuracy. </li></ul><ul><li>To explain its use. </li></ul>
- 12. Design Parameters: Climatic analysis Software Development <ul><li>Determination of the over-heated period for Lahore. </li></ul><ul><li>The rule given by Olgay and Olgay is to provide shading for all those times when outdoor air temperature exceeds 70 o F (21 o C) in regions of 40 o Latitude. For every 5 o latitude change towards equator, elevate limiting temperature by 0.75 o F. This translates into an average temperature of 71.3 o F , or 22 o C for Lahore. </li></ul>. 50 . 18 1.Taken from “Man,Climate and Architecture” by B. Givioni. London:Applied Science publishers. 1969 ;pp220.
- 13. Design Parameters:Climatic analysis Software Development <ul><li>Determination of the over-heated period for Lahore. </li></ul>The final dates selected are from 21 st March – 21 st September. The shade designed provides full protection over the time period selected. However, we have to consider how much Sun we will get in winter, when some heat penetration is usually desirable. Unfortunately, a shading device will not suddenly stop working after a certain date (unless it is retractable). It will usually partially obscure the window all year round, more so in summer and less so in winter. This is where the trade-off begins - the amount of which depends on the relative heating and cooling stresses in the environment. Max. & Average outdoor temperature Graph 1 1.Graph taken from “Building Climatology” by Dr. Riaz Hussain Mirza. Bulletin IES/75;pp14. 2. Weather data derived from combined data taken from Lahore Met Office, and Yahoo Weather Services. 2
- 14. The Method Software Development <ul><li>Determination of the over-heated daily time-period for Lahore. </li></ul><ul><li>The time of the day for which shading is to be designed is determined by a number of factors; the orientation, the client/user requirements, etc. Basically, it is at the discretion of the designer. </li></ul><ul><li>However, shading design has some physical limitations. It is generally designed up to 3pm, sometimes 4pm, as beyond that shading is not realistically possible through external fixed shades. </li></ul><ul><li>The time-period selected for this software is from 10am to 4pm; with a 2pm option given if so desired/required by the designer. </li></ul>
- 15. Calculations Software Development <ul><li>Determination of equations for calculating shade parameters. </li></ul><ul><li>Trigonometric equations are used to calculate the solar angles and shade profiles; these equations are then programmed into a mathematical environment to create the required software. The design steps for the calculations include: </li></ul><ul><li>Determination of solar altitude and azimuth angles for the over-heated period. (The cut-off solstice dates.) </li></ul>These angles can be read off sunpath diagrams; they can also be calculated through equations, or through freely-available solar angle calculators.
- 16. Calculations Software Development <ul><li>Determination of equations for calculating shade parameters. </li></ul><ul><li>Determination of the shading profile angles; the HSA (Horizontal Shadow angle) and the VSA (the Vertical Shadow angles.) </li></ul>These are determined using the equations: HSA=Azimuth-orientation VSA=tan -1 (tan(altitude)/cos(HSA))
- 17. Calculations Software Development <ul><li>Determination of equations for calculating shade parameters. </li></ul><ul><li>Determination of equations for different types of shades. </li></ul><ul><li>The equations available in literature are for a simple horizontal & vertical shade. </li></ul>1. Equations taken from“The Architect’s Handbook of Formulas, Tables and Mathematics.” by David Ballast. Prentice Hall, 1998. pp 5-7. 1 Depth = height tan HSA Width = depth x tanHSA Depth= width of window tan HSA Height=depth x tan VSA
- 18. Calculations Software Development The equations for other shade types were derived from these basic ones, and programmed into the calculator. For example, for angled walls and angled horizontal louvers, the equations are: Length ‘l’ = (h/n) sin ( b- VSA) sin (180 – a – b + VSA) width = depth x sin a sin (180 – b ) where H=height of opening a = angle of inclination of shade, b = angle of inclination of wall Additional checks were introduced in the software to give a value of zero for the orientations when a shade is not required. a b
- 19. The Medium Software Development <ul><li>The software basically consists of a simple excel spreadsheet. </li></ul><ul><li>Reasons and advantages: </li></ul><ul><li>It is perhaps the most readily available and accessible medium </li></ul><ul><li>Most people already use it for other work </li></ul><ul><li>There is no need to acquire new skills to use it, no time spent learning a new software </li></ul>
- 20. The Layout The Software shadecalculator.xls
- 21. Verification Methods Analysis 1: Verification <ul><li>Three verification methods are used: </li></ul><ul><li>Comparison with the existing (Graphical) method. </li></ul><ul><li>Self Verification. </li></ul><ul><li>Computer simulation. </li></ul><ul><li>These methods test the shade calculator’s accuracy, as well as its efficiency, and give an insight into its application. </li></ul><ul><li>For the purpose of the verification test, a model window is selected. Its orientation is South (180 o ); its dimensions are 3’wide x 4’ high; the shade type selected is a simple horizontal shade. </li></ul>
- 22. The Graphical Method Results Analysis 1: Verification The shade parameters, as calculated by the Shade Calculator are:
- 23. The Graphical Method Results Analysis 1: Verification <ul><li>The overheated period is marked on the Sunpath diagram. (In red.) </li></ul><ul><li>The shading mask (in green) and shade protractor is also super-imposed on it. </li></ul><ul><li>The Shade Profile angles are read as: </li></ul><ul><li>Horizontal profile angle = 25 o </li></ul><ul><li>Vertical profile angle = 60 o </li></ul>59 o 25 o
- 24. Analysis 1: Verification The Graphical Method Results
- 25. Self-Verification Analysis 1: Verification The shade parameters, as calculated by the Shade Calculator through different sheets are identical, even though completely different formulae are used; The simple Horizontal shade calculator uses formulae available in literature. E.g. D=H/tanVSA The Horizontal shade calculator for angled walls and angled shade uses formulae derived through this research. E.g. D=Hxsin(b-VSA)/sin(180 o - a-b+VSA)
- 26. Computer Simulation Analysis 1: Verification The computer simulation results for the test window, showing Solar Shading patterns for the Summer equinox (21 st June; 12pm), as well as the Autumn equinox ( 21 st September; 4pm.) Ecotect
- 27. Application Analysis From the Specific to the General The designed software is for Lahore, i.e. 31.5 o N and 74.18 o E. The software is applicable to any area around the globe that falls into the 31.5 o N latitude band. The above analysis shows its applicability between 30.5 o N – 32.5 o N with considerable accuracy. For Pakistan, its applicability can extend to such cities as: Sheikhupura=31.42 o N Faislabad=31.25 o N Gujranwala=32.09 o N Dera Ismail Khan=31.65 o N 5.5% 60.65 50.4 230.7 48.6 30.0 o N 4.2% 60.35 50.3 230.3 48.3 30.5 o N 2.1% 59.80 49.9 229.9 47.9 31.0 o N 0% 59.28 49.4 229.4 47.6 31.5 o N 1.68% 58.81 49.0 229.0 47.3 32.0 o N 3.78% 58.33 48.6 228.6 47.0 32.5 o N 5.88% 57.78 48.2 228.2 46.6 33.0 o N % Error VSA (For South) HSA (For South) Azimuth Angle Altitude angle Latitude
- 28. Use
- 29. Examples of Shades & How to design them Use How to Calculate shade: Treat it as a Simple Horizontal shade on a curved wall. The McLaren Technology Centre Architect: Norman Foster. Location: Approx. three km north of Woking town centre, Surrey, UK. Diwan-e Khas, Lahore Fort
- 30. Examples of Shades & How to design them Use Autodesk trademark image for sustainable design using Autodesk software Publishers united limited; Anarkali. How to Calculate Shade: Simple Horizontal + drop down shade.
- 31. Examples of Shades & How to design them Use How to Calculate shade: (For the school) Vertical Louvres; Horizontal + Louvres + Simple Vertical Shade.) Greenwich Millennium Village primary school. (Edward Cullinan Architects.) IKEA
- 32. Scope, Limitations, and Future Work Conclusion <ul><li>The limitations of this software are three-fold; </li></ul><ul><li>Firstly, the calculator cannot be expected to calculate for all possible shade types. The basic shade types have been programmed in, with the more complex ones to be extrapolated from them by the architect. </li></ul><ul><li>Secondly, this calculator can simply give the output to the given set of input parameters; it cannot ‘suggest’ the most suitable shade type. That too, relies on the architects discretion. </li></ul><ul><li>Thirdly, similar shade calculators can be developed for other major cities of Pakistan – while the foundations for that have been laid down here, still this is beyond the scope of this work. </li></ul>
- 33. The Shade Calculator’s Future Conclusion The focus of this research was to produce a simple equation calculator that requires input of window parameters and orientation, etc. and gives results in terms of shade parameters. Comparison with existing softwares…just as accurate?
- 34. The Shade Calculator’s Future Conclusion The use of a familiar environment (Microsoft Excel) should hopefully ensure that it remains user-friendly and easy to operate. Making it city-specific ensured that most of the climatic data, and other related tedious calculations have already been fed into it; making the input requirements minimum. The end result is hopefully simple, easy to comprehend and simple to operate. The present computer-friendly generation of architects should find this an extremely easy and quick method of shade calculation, and this calculator should hopefully prove very useful and may promote a more pro-sustainable attitude from the designers.

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