Abstract
Nigeria is a country blessed with sun almost throughout the year but like the cliché, too much of everything is not good. The ability of the architect to be able to produce designs of buildings that will serve the needs of his client long after the building has been built proves to be a major challenge for him, and the needs of the client has risen far above just the provision of shelter. Nowadays, the client is becoming increasingly aware of the fact that his shelter can actually be comfortable to live in all throughout the season of the year and not just being a shelter over his head. Even, were the client not aware of the fact that his building should support his comfort all through the year which happens to be most of the body of clients- for now, it would still be the responsibility of the architect to provide a suitable and enduring abode for his client.
One of the major challenges of the modern day architect especially in Nigeria, is the ability to keep the sun out of the building for most part of the year and to allow it in for the other part of the year. In an effort to tackle this, comes the creation of sun shading devices.
This term paper will take a look at the various types of sun-shading devices that are available both locally and internationally and a critical look will be given to computer software that are used for the design of some of these devices and how effective they are in designing efficient sun-shading devices.
1 Introduction
The architect prides himself as a creative person sharing in God’s divinity by his ability to create designs of structures out of nothing as it were. All through the centuries, from Michael Angelo through Mies Van Der Rohe to Frank O. Gehry, the architect has struggled with himself and nature to create that perfect design. Though what that perfect design is, is still subject to a lot of debate among architects, but it is without doubt that the perfect building among other things should be so well thought out that not only will it support the comfort of the inhabitants all year round, but also support responsible construction, maintenance and deconstruction with regards to environmental sustainability.
The use of sun-shading device as a means of regulating the internal temperature of buildings is a common way of achieving this and while a sun-shading device in all its form helps to keep the incursion of solar heat from the building spaces, it also helps to keep sky glare out.
2 STEPS FOR DESIGNING SUN-SHADING DEVICES
SHADING DESIGN
Design of sun-shading devices is quite complex and undertaking such manually can be tedious, though not impossible. What is most important is the understanding of the mechanics of solar positions as well as the sun path diagram.
UTILIZATION OF SOLAR SEASONAL VARIATIONS
The position of the sun at a particular point in the sky and at a particular time of day tends to vary according to seasonal changes in the year. At some point in the year, there is longer day and shorter night, a period characterized by the sun taking longer to set and longer to rise, while at some other point in the year, there is shorter day and longer night when it seems as if the sun sets more quickly than it rises. The understanding of the mechanics of the sun’s movement across the sky at what period of the year and at what time of the day helps to utilize these characteristics to maximum advantage - typically to exclude as much solar radiation as possible in wet and hot season whilst letting as much through as possible during cold and dry season of the harmattan, which is important for the design of a good sun-shading device. This variation in the length of the sun’s journey across the sky is quite noticeable in the tropical region where the seasons are more or less limited to two, dry and wet seasons. The various steps to be taken in the design of sun-shading devices include:
1. THE DETERMINATION OF WHEN SUN-SHADING IS REQUIRED:
The period when shading is required is determined by observing the over-heated and under-heated periods. These periods are determined using an appropriate thermal index. The lower and upper comfort limit of the day is determined, then the time of the day when both periods fall is also recorded. Shading is done at the time of the lower comfort limit through-out the upper comfort limit and then stopped when it drops below the lower comfort limit.
2. THE POSITION OF THE SUN WHEN SHADING IS REQUIRED:
It is important to determine the position of the sun when shading is required so as to get the azimuth and altitude of the sun at each time on the cut-off date. Getting to know the motion of the Sun is very important for a proper solar systems design and the choice of proper location for solar collectors or photovoltaic modules. The solar path is described with the Sun path diagram. The Sun path diagram is an indispensable tool in the early photovoltaic system design phase for shadowing determination.
Figure 1; diagram showing the various positions of the sun in relation to the building using a sun-path diagram.
3. THE DIMENSION AND PROPORTION OF THE SUN-SHADING DEVICE:
The dimension needed for the effective shading of a sun-shading device is determined by calculating the Horizontal Shadow Angle which is angle that measures the effectiveness of the vertical member of the shading device and represented by delta, while also calculating the Vertical Shadow Angle for the horizontal shading member represented by the angle epsilon. These angles cast by the various shading members show how much they prevent the incursion of solar radiation through the windows. By calculating the shadow angles needed for a perfect shade, the dimensions can be obtained.
4. THE AESTHETIC AND STRUCTURAL DESIGN OF THE SHADING DEVICE:
In designing the shading device, its aesthetic value must be considered as it won’t do have an ugly contraption that resembles an after-thought to mar the entire effect and design concept of the building, while also taking into consideration the structural stability of the proposed device with respect to its ability to stand the various adverse effects of external weather conditions as these shading devices would eventually be installed outside the building. Any of the common Computer Aided Draughting software such as AutoCAD, REVIT, 3D Studio Max, and ArchiCAD and so on, are sufficient in the design of these shading devices.
3. COMPUTER SOFTWARE FOR SUN-SHADING DEVICES
The importance of the determination of the sun’s position is paramount to the effectiveness of the sun-shading devices. The sun’s position can be determined using the following means; by calculation, by computer software, from tables, by experimental means, by sun-path diagrams. It unnecessary to state the obvious fact that the fastest and most accurate of all the means listed above is the various computer software designed for the purpose of tracking and recording of the positions of the sun at various times of the day which helps in the design of the shading devices. The various computer programs include:
I. “Solar Pathfinder” - The Solar Pathfinder has been the standard in the solar industry for solar site analysis for decades. Its panoramic reflection of the site instantly provides a full year of accurate solar/shade data, making it the instrument of choice. The Solar Pathfinder is
- a powerful non-electronic instrument that includes:
- has a printed Manual (online version also available)
- has Sun-path Diagrams (latitude & application specific)
- has an angle estimator (for determining altitude and azimuth)
- has white marking pen with extra leads
- and has a tool box specifically designed for the Pathfinder
Solar Pathfinder™ gives an entire year’s solar potential for a given site in just seconds.
Solar Pathfinder Assistant is companion software that generates monthly sun-paths for each specific site latitude instead of relying on the stock latitude band diagrams.
II. “SunEye” - The Solmetric SunEye (patent pending) is a hand held electronic device that allows users to instantly assess to total potential solar energy given the shading of a particular site. It Identifies the shading pattern early in the process thereby reducing the expense of system and home design and improves the efficiency of the final system or house.
III. “Solmetric iPV” - is an iPhone based site evaluation tool, providing full solar site analysis in an affordable hand held package.
IV. “HORIcatcher” - HORIcatcher is an easy and fast tool to take outdoor pictures of the horizon. The pictures can be used to determine the solar energy input, sunshine duration and sun exposure reduced by obstacles like trees, houses or mountains. HORIcatcher is supplied with a digital camera.
V. “HORIZON” – this software simulates sun path diagrams for arbitrary latitude.
VI. “Pilkington Sun Angle Calculator” - This handy tool provides a relatively simple method of determining solar geometry variables for architectural design, such as designing shading devices or locating the position of the sun relative to a particular latitude and time.
VII. “Sun path chart” - this program creates sun path charts in Cartesian or polar coordinates for "typical" dates of each month (i.e.; days receiving about the mean amount of solar radiation for a day in the given month).
VIII. “Shadow Analyser” - Shadow Analyzer is an advanced parametric CAD tool for professionals in the area of Solar Energy Engineering and Architecture.
IX. “pvPlanner” - Simulation tool for planning and optimization of photovoltaic systems using climate and geographic data at high temporal and spatial resolution and new generation high performance algorithms.
X. “METEONORM” - Global Meteorological Database for Solar Energy and Applied Meteorology. METEONORM is a comprehensive climatological database for solar energy applications: a meteorological database containing comprehensive climatological data for solar engineering applications at all points of the globe between the polar circles; a computer program for climatological calculations; a data source for engineering design programs in the passive, active and photovoltaic application of solar energy with comprehensive data interfaces; a standardization tool permitting developers and users of engineering design programs access to a comprehensive, uniform data basis.
XI. “Autodesk ECOTECT Analysis” - is an industry leading building analysis program that allows designers to work easily in 3D and apply all the tools necessary for an energy efficient and sustainable future.
XII. “Sombrero” - A PC-tool to calculate shadows on arbitrarily oriented surfaces. For both, active use of solar energy (domestic hot water, photovoitaics) as well as for passive solar architecture, shading or lighting of planes plays an important role SOMBRERO provides quantitative results for the shading of collectors or windows by buildings, trees, overhangs or the horizon.
XIII. “Focus Solar” - Focus Solar is a leading provider of solar energy information services for the design, planning, and performance monitoring of PV systems. The specialty of Focus Solar is the use of weather satellites for solar energy applications. PV system planners and developers derive a unique value from the combination of geophysical science and PV engineering.
XIV. “Geomodel” - high resolution solar radiation and temperature data for any location or region, solar maps, and simulation tools for solar energy technologies (PV, CSP, CPV, solar heating/cooling).
Conclusion
The advancement of technology has aided the architect in his bid to design the perfect building, from the materials used to the method and means applied. The use of sun-shading devices has become more acceptable in building construction circles and it is only natural that computer software be developed to assist the architect in providing a very comfortable abode in terms of the way solar energy to buildings is managed.
The various software that has been provided by software designers mostly assist in tracking the movement of the sun across the sky. This helps the architect to determine the proportion and dimensions of the sun-shading device to be used.
References
1. Denis Lenardic (May, 2011): Solar Radiation Estimation and Site Analysis.
2. Ogunsote, O.O. (1986). "MOTOLA, STRESS and SHADE -Educational Software for Tropical Countries". Paper Presented at the Seminar On Computer Aids: Computers and Climatic Data