A DISCUSSION ON THE DESIGN PRINCIPLES OF A PATENTED PORTABLE DIRECT SUNLIGHT LIGHT-DUTY UNIVERSAL HELIODON MOUNTED ON A CAMERA TRIPOD

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1 , Volume 8, Number 4, p , 2011 A DISCUSSION ON THE DESIGN PRINCIPLES OF A PATENTED PORTABLE DIRECT SUNLIGHT LIGHT-DUTY UNIVERSAL HELIODON MOUNTED ON A CAMERA TRIPOD K.P. Cheung Department of Architecture, The University of Hong Kong, Hong Kong, China (Received 10 October 2012; Accepted 11 January 2013) ABSTRACT Heliodons are physical tools developed to study and test the solar performance of physical building models by simulating direct sunlight to impinge onto building models, for various desirable combinations of latitude, day, and time. In the learning process of architecture students and in professional architecture design processes, small and light weight working models are always made first for studying various design objectives including solar performance. The preferred one or two optional designs will then be further developed and formed into physical models of larger size with more details, and developed into computational models, for in-depth and detailed study of various design objectives including solar performance. This paper discusses the design principles of a patented portable direct sunlight light-duty universal heliodon mounted on a camera tripod which is affordable, easily stored up and assembled for use. The patented heliodon is useful for testing the direct sunlight effect of small foam board or card board models of buildings, or building components. The universal capability of a heliodon attributes to its adjustment flexibility to test the model for all simulated desirable combinations of latitude, day, and time, for any simulated place in the world where the actual building will be built, from most north places to most south places. The patented heliodon was initially designed for outdoor operation, using direct sunlight available at any place, any time in the world, as the light source, to avoid light source error of artificial light. Furthermore, this heliodon can be mounted on a camera tripod commonly used for holding cameras, eliminating the special provision of a heliodon stand which is a key factor affecting the cost and storage space, and hence the portability and affordability of the heliodon. 1. INTRODUCTION Heliodons are physical tools developed to study and test the solar performance of building models by simulating direct sunlight to impinge onto building models, for various desirable combinations of latitude, day, and time. The adjustable variables of heliodons are [1-3]: - the latitude variable, which defines the sun paths in relation to the geographical location [Fig. 3, Fig. 3a], - the seasonal variation, which relates to the declination of the sun on a given day [Fig. 3, Fig. 3a, Table 1], - hourly change of the sun from East to West during the day. The heliodons developed so far could be broadly categorized into two categories: - a fixed light source (single lamp or multiple lamps) [2,7-9], or a moving light source [1,2] with the building model rotated and/or tilted, - the building model is placed horizontally and stationary, and the light source moves [4-6, 10-13]. Since the first heliodon developed in 1931 [1, Fig. 1], traditionally heliodons are tools located in architectural school laboratories, occupying a room, and not convenient for practicing architects to use, because it takes time and effort to transport the building models to the laboratories. For convenient and popular use of heliodons, the size, portability, and affordability of the heliodon are also important factors. A patented portable direct sunlight light-duty universal heliodon [14, Fig. 2] addressing these issues has been developed, and its design principles are discussed in this paper. 98

2 Fig. 1: Dufton & Beckett Heliodon of 1931 [1, 2, 16, Table 1] Note that d is the solar declination angle [Fig. 3, Table 1], and L is latitude in Northern Hemisphere shown in the above configuration. Fig. 2: The patented portable direct sunlight light-duty universal heliodon [14] - View showing outdoor operation using direct sunlight as the light source, mounted on a camera tripod set at two possible combinations of latitude, day, and time: [Fig. 7, Fig. 4, Fig. 5, Fig. 8] - For Northern Hemisphere : 10 am, Apparent Solar Time, 45 degree latitude, 5 May or 7 August, noting that the top point of the globe is the north pole [Fig. 3] - For Southern Hemisphere : 2 pm, Apparent Solar Time, 45 degree latitude, 4 Feb or 7 November, noting that the top point of the globe is the south pole [Fig. 3a] 99

3 Table 1: Mean value of the solar declination [Ref. 15, for l99l, noon UT (GMT), adapted from Ref. 16] DAY JAN FEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC Note: Declination to north of the Equator is positive, to south is negative; thus for 11 Jan l99l, solar declination angle was 21 deg 50 min south of the Equator. 2. THE DESIGN PRINCIPLES OF THE PATENTED PORTABLE DIRECT SUNLIGHT LIGHT-DUTY UNI- VERSAL HELIODON The Dufton & Beckett Heliodon of 1931, [1, Fig. 1] which is well illustrated and discussed in many books, and the patented portable direct sunlight light-duty universal heliodon [Fig. 2], are in fact both designed on the same basic solar-geographical principles listed below. The patented heliodon now reported, however has a more extensive coverage on application ranges, exhibiting its universal capability: - The components simulate the sun-earth system for Northern Hemisphere [Fig. 3]. However, in the patented heliodon now reported, the sun-earth system for Southern Hemisphere is also simulated [Fig. 3a]. - It is assumed that sunlight is practically parallel, and impinges at same angles onto the buildings,and hence building models, located at surface of earth, and fictitiously at the centre of the earth, because the distance of the earth from the sun (about 150 million km) is much greater than the diameter of the earth (about 12,756 km), and the diameter of the sun (about 1,380,000 km), in the ratio of about :1: The day scale surface of The Dufton & Beckett Heliodon of 1931 [1, Fig. 1], shows the simulated days for Northern Hemisphere application, and the lamp holder and the day scale is detached from the model platform 100

4 base frame. However, in the patented heliodon now reported [Fig. 1, Fig. 4, Fig. 5, Fig. 6], the simulated days are marked on the day scale for both Northern Hemisphere application, and Southern Hemisphere application, and the day scale is integrally attached to the model platform base frame. For both heliodons, the straight lines marking the various days, hence the corresponding solar declination angle [15, 16, Table 1] are set parallel to the axis of rotation of the model platform; the same axis being the simulated earth axis, the axis of rotation for change of time of a day [Fig. 1, Fig. 2, Fig. 3, Fig. 3a, Fig. 7, Fig. 8, Fig. 9]. - Apparent solar time is used as the basic time scale. However, in the patented heliodon now reported, the outer circular time scale ring is for Apparent Solar Time indication. Also an additional inner time scale ring is provided for local standard time indication, following established adjustment procedures [10,17, Table 2, Fig. 15]. In both time scales, the leading hour number is for use in Northern Hemisphere application, and the following hour number is for Southern Hemisphere applications, thus, 10/14 means 10 am for Northern Hemisphere application and 14:00, or 2 pm for Southern Hemisphere application [2,7,10,15, Fig. 7, Fig. 11, Table 2, Fig. 15]. - The model platform of The Dufton & Beckett Heliodon of 1931 [1, Fig. 1], is basically set for Northern Hemisphere. However, in the patented heliodon now reported, the model platform can be set to any desirable latitudes of both the Northern Hemisphere and the Southern Hemisphere [Fig. 1, Fig. 2, Fig. 7, Fig. 8, Fig. 9]. - The model is tilted and moved during heliodon operation. - The light source used in The Dufton & Beckett Heliodon of 1931 [1, Fig. 1], is commonly an artificial lamp placed sufficiently far away from the heliodon, yet giving sufficient illumination onto the building model being tested. However, in the patented heliodon now reported, direct sunlight which is moving, is the preferred light source. Because of its portability and its integral provision of the day scale onto the rotating simulated earth-latitude-time system assembly, NOW forming an integrated simulated earth-latitude-time-day system assembly, all mounted on a camera tripod, will enable quick, efficient, and accurate operation procedures to be carried out, yielding accurate results of good light quality. [Fig. 2, Fig. 7, Fig. 8, Fig. 9, Fig. 9a, Fig. 10] Of course, an artificial light source can be used for the patented heliodon now reported [Fig. 12], but errors will result, because no artificial light source can truly simulate direct sunlight. Note that in the photos showing the operation of the patented heliodon, the latitude scale component of the patented documents [14, Fig. 2] has been replaced by an enhanced latitude component [Fig. 9, Fig. 9a, Fig. 11, Fig. 11a, Fig. 12], based on the same solar-geographical principle. Table 2: [adapted from Ref. 10] Adjustment for Local Standard Time (LST) : Illustration on the steps to adjust the Inner time ring of the patented heliodon to read Local Standard Time RELATIVE TO Apparent Solar Time (AST), shown by the outer time ring Apparent solar time of local meridian of Hong Kong University 12:00 noon (AST) 12:00 noon (AST) at 114 deg.8 min. East Equation of Time (if slow, add; if fast, subtract) [ 17, Table 3] 8 Nov 16.3 min(sun fast) 20 Feb 13.8 min (sun slow) Mean Solar Time of Meridian [17] 11:43.7 [a.m.] 12:13.8 [p.m.] Correction for difference between local meridian (114 deg min 23.5 min min. East) of Hong Kong university and the related time zone meridian at 120 deg. East at rate of 1 deg.=4 min. (If standard time zone meridian lies to West, subtract the correction, if to East, add) [17] Hong Kong Standard Time (watch time, or mobile phone time) 12:7.2 [p.m.] 12:37.3 [p.m.] For example, to read Hong Kong Standard Time at 8 Nov, the 12:7.2 mark of the Inner LST Time Scale Ring of the heliodon has to be adjusted to match the 12:00 noon mark of the Outer AST Time Scale Ring. To read Local Standard Time (LST) on the Inner Circular Time Scale Ring, RELATIVE TO Apparent Solar Time (AST) read by the Circular AST Outer Time Scale ring : For the day 20 Feb, the 12:37.3 mark of the Inner LST Time Scale Ring [i.e. Hong Kong Standard Time] of the heliodon has to be adjusted to match the 12:00 noon mark of the Outer AST Time Scale Ring [Fig. 15]. 101

5 Table 3: Mean value of the equation of time, in minutes at Apparent Solar noon [adapted from The Nautical Almanac 1991, HMSO, UK. Ref. 16] DAY JAN FEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC Note: Apparent Solar Time + Equation of Time = Mean Solar Time (fictional). The bold faced numbers indicate days in which the sun is slow, [25 Dec -15 April, 14 Jun-1 Sept] and normal fonts indicate days in which the sun is fast [2 Sept-24 Dec, 16 Apr-13 Jun]. 102

6 Fig. 3: The sun-earth system primarily set for Northern Hemisphere - Solar Geometric Parameters Illustrated on the Globe shown for noon time of Apparent Solar Time System [7, 14]. For studying places on Southern Hemisphere, it is advisable to rotate the diagram and replace the model platform to the desirable latitude of Southern Hemisphere, so that the South Pole is at the top of the page. Notes: 1. N-S is the axis of the earth for Northern Hemisphere. S-N is the axis of the earth for Southern Hemisphere. 2. In the diagram L is drawn equal to L for minimizing lines on the diagram, i.e. L=L =45 degree. 3. For Northern Hemisphere: At latitude L, the horizontal plane is making an angle φ= L with the N-S axis if the earth. At Equator, L=L 0, the horizontal plane is normal to the equatorial plane, and parallel to the N-S axis. At North pole, L=90 degree, the horizontal plane is parallel to the equatorial plane, and normal to the N-S axis. 4. For southern Hemisphere: At latitude L, the horizontal plane is making an angle φ= L with the S-N axis of the earth. At Equator, L =L=0, the horizontal plane is normal to the equatorial plane, and parallel to the S-N axis. At South pole, L =90 degree, the horizontal plane is parallel to the equatorial plane, and normal to the S-N axis. 103

7 Fig. 3a: The sun-earth system- primarily set for Southern Hemisphere - Solar Geometric Parameters Illustrated on the Globe shown for noon time of Apparent Solar Time System [7, 14]. For studying places on Northern Hemisphere, it is advisable to rotate the diagram and replace the model platform to the desirable latitude of Northern Hemisphere, so that the North Pole is at the top of the page. Notes: 1. S-N is the axis of the earth for Southern Hemisphere. N-S is the axis of the earth for Northern Hemisphere. 2. In the diagram L is drawn equal to L for minimizing lines on the diagram, i.e. L =L=45 degree. 3. For Southern Hemisphere: At latitude L, the horizontal plane is making an angle φ= L with the S-N axis of the earth. At Equator, L =L=0, the horizontal plane is normal to the equatorial plane, and parallel to the S-N axis. At South pole, L =90 degree, the horizontal plane is parallel to the equatorial plane, and normal to the S-N axis. 4. For Northern Hemisphere: At latitude L, the horizontal plane is making an angle φ= L with the N-S axis of the earth. At Equator, L= L =0, the horizontal plane is normal to the equatorial plane, and parallel to the N- S axis. At North pole, L=90 degree, the horizontal plane is parallel to the equatorial plane, and normal to the N-S axis. 104

8 Fig. 4: The Front view of the patented heliodon assembly set at 12:00 Apparent Solar Time and 90 degree latitude, showing The combined N. Hemisphere-S. Hemisphere Day Selector of the patented heliodon. For Northern Hemisphere application, the north pole is at the top of the globe [Fig. 3]. For Southern Hemisphere application, the south pole is at the top of the globe [Fig. 3a]. See Fig. 8 for Right Side View. 105

9 Fig. 5: The combined Northern Hemisphere-Southern Hemisphere Day Selector of the patented heliodon, showing the principles of determining the marking positions of the day[s] onto the Day Selector scale [Fig. 4, Fig. 8, Fig. 6] in relation to the dimensions of the gnomon, and solar declination angle [Table 1] corresponding to each day. Fig. 6: The Design of Day Selector Scale using the sundial principle for setting the desirable day, showing the trigonometric relationship of the actual height of the tip of the gnomon and solar declination angles [Table 1, Fig. 4, Fig. 5, Fig. 8]. 106

10 Fig. 7: The top view of the patented light duty universal heliodon [14, Fig. 2], set at 12:00 of Apparent solar time, 90 degree latitude. Notes: 1. The model platform can be adjusted to the desirable latitude angle, and locked. The north, south direction for Northern Hemisphere and Southern Hemisphere are in opposite direction. 2. The OUTER Circular Apparent Solar Time ring is fixed, while the INNER Circular time ring can be turned, following established steps [2, 7, 10, Table 2] to read local standard time 3. The globe is added to help users to understand the sun-earth system simulated. For Northern Hemisphere application, the north pole is at the top of the globe [Fig. 3]. For Southern Hemisphere application, the south pole is at the top of the globe [Fig. 3]. 107

11 Fig. 8: Right Side view of the patented heliodon assembly [14, Fig. 1], set at 12:00 of Apparent solar time, 90 degree latitude, showing The combined N. Hemisphere-S. Hemisphere Day Selector. For Northern Hemisphere application, the north pole is at the top of the globe [Fig. 3]. For Southern Hemisphere application, the south pole is at the top of the globe [Fig. 3a]. See Fig. 4 for the Front View. 108

12 Fig. 9: Testing of a cardboard model using the patented universal light duty heliodon mounted on a camera tripod [14], placed outdoor, with a weak state of direct sunlight of 1 Jan 2013, 3.15 pm, Hong Kong Local Time, as the light source, set at two possible combinations of latitude, day, and time: [Fig. 4, Fig. 5, Fig. 7, Fig. 8] Fig. 10: Enlarged view of the direct sunlight effect on a cardboard model, tested by the patented universal light duty heliodon mounted on a camera tripod [14], placed outdoor, with a weak state of direct sunlight of 1 Jan 2013, 3.15 pm, Hong Kong Local Time, as the light source, set for the conditions mentioned in Fig For Northern Hemisphere : 10 am, Apparent Solar Time, 45 degree latitude, 5 May or 7 August, noting that the top point of the globe is the north pole [Fig. 3] - For Southern Hemisphere : 2 pm, Apparent Solar Time, 45 degree latitude, 4 Feb or 7 November, noting that the top point of the globe is the south pole [Fig. 3a] Note: In the above photo, the latitude scale of the patented documents [14, Fig. 2] has been replaced by an enhanced latitude scale [Fig. 9a, Fig. 11, Fig. 11a, 12], based on the same solar-geographical principle. Fig. 11: Enlarged view of the Enhanced Latitude Scale [Fig. 11a] of the demonstrated prototype of the patented heliodon, which replaces the same component shown in the patented documents, [14, Fig. 2], both designed on the same solar-geographical principle. The attitude is set at 45 degree. Apparent Solar Time (AST) is set at 10 a m for Northern Hemisphere, same as 2 p m [i.e. 14 hour] for Southern Hemisphere, in the outer time scale ring, which thus reads 10/14 [Fig. 7]. Inner time scale ring, used for setting Local Standard Time-LST [Table 2], meets the outer AST time scale ring at the same markings, as LST is not used in the test. Fig. 9a: The patented heliodon set for the conditions mentioned in Fig. 9, showing enlarged view of the components, with the latitude scale of the patented documents [14, Fig. 2] now replaced by an enhanced latitude scale [Fig. 9, Fig. 11, Fig. 11a, Fig. 12], based on the same solar-geographical principle. 109

13 Fig. 11a: The Enhanced Latitude Scale [Fig. 11] of the demonstrated prototype of the patented heliodon, which replaces the same component shown in the patented documents, [14, Fig. 2, Fig. 8] both designed on the same solar-geographical principle. Fig. 12: Illustration of setting up the patented portable direct sunlight light-duty universal heliodon [14], incorporating Enhanced Latitude Scale [Fig. 11, Fig. 11a], indoor using a tungsten lamp as the light source at 3 m from the heliodon, inheriting light source error on light quality and deviation from being parallel. 110

14 Fig. 13: Testing of a cardboard model of a building façade using the patented universal light duty heliodon mounted on a camera tripod [14], placed outdoor, with a strong state of direct sunlight of 5 Jan 2013, 2.45 pm, Hong Kong Local Time, as the light source, set at two possible combinations of latitude, day, and time: - For Northern Hemisphere : façade facing South, 10 am, Apparent Solar Time, 45 degree latitude, 22 Dec, Winter Solstice in Northern Hemisphere, noting that the top point of the globe is the north pole [Fig. 3] - For Southern Hemisphere : façade facing North, 2 pm, Apparent Solar Time, 45 degree latitude, 21 Jun, Winter Solstice in Southern Hemisphere, noting that the top point of the globe is the south pole [Fig. 3a] Fig. 14: Enlarged views (Front view at Left, Back Side view at Right) of direct sunlight effect on cardboard model of a building façade using the patented universal light duty heliodon mounted on a camera tripod [14], placed outdoor, with a strong state of direct sunlight of 5 Jan 2013, 2.45 pm, Hong Kong Local Time, as the light source, set for the conditions mentioned in Fig

15 It is expected that this reported patented heliodon will help educate effectively the architecture and building students, and will be a convenient, portable and affordable tool to be used by the building and architecture profession, and the general public on solar architecture design, thus arousing the general public in wider acceptance and demand on more integration of solar design into buildings, contributing to building a sustainable world. Fig. 15: Illustration on setting the Inner time ring of the patented heliodon to read Local Standard Time (LST) on the Inner Circular Time Scale Ring, RELATIVE TO Apparent Solar Time (AST) read by the Circular AST Outer Time Scale ring : For the day 20 Feb, the 12:37.3 mark of the Inner LST Time Scale Ring [i.e. Hong Kong Standard Time] of the heliodon has to be adjusted to match the 12:00 noon mark of the Outer AST Time Scale Ring [Table 2]. In the time rings, one small division represents a difference of 5 minutes of time. 3. CONCLUSION The Dufton & Beckett Heliodon of 1931, [1, Fig. 1] used a separate day scale for holding the lamp which simulates the sun and its varying positions over the year, i.e. solar declination [Table 1], allowing light source error, while the adjustable earth-latitude-time system assembly is detached. However the reported patented heliodon incorporates an integral Day Selector Scale onto the earth-latitude-time system assembly, NOW forming an innovative integrated simulated earth-latitude-time-day system assembly, all mounted on a camera tripod. This assembly makes the patented heliodon portable, conveniently to be taken to anyway using various light sources, primarily with sunlight as the light source for obtaining accuracy of shadow boundaries and good lighting quality over the tested model surfaces. Since direct sunlight is practically parallel, using artificial light source will induce the inheriting light source error on light quality and deviation from being parallel. Since the components are demountable and can be stored inside a box about the size of an A4 paper [297 mm x 210 mm, OR inch x inch ] of 100 mm thick [ 4 inch thick], and the common camera tripod is used as the support, the reported patented heliodon has demonstrated the convenience of its storage and transportation, and its affordability for students and architects. REFERENCES 1. A.F. Dufton and H.E. Beckett, Orientation of buildings-sun planning by means of models, Royal Institute of Building Architects Journal, p. 509 (1931). 2. K.P. Cheung, C.Y. Chu, L.M. Lo, C. Siu and S.K. Sin, A light duty universal direct sunlight heliodon, Architectural Science Review, Vol. 39, No. 4, pp (1996). 3. T.A. Markus and E.N. Morris, Buildings, climate and energy, Pitman, London, pp (1980). 4. S.V. Szokolay, Solar geometry, PLEA Note 1, c/o Department of Architecture, The University of Queensland, Australia, p N.M. Lechner, A new sun machine: A practical teaching, design, and presentation tool, Proceedings of American Solar Energy Society, p. 145, Figs. 1,3,4,5 (1993). 6. Olgyay & Olgyay, Solar control & shading devices, Princeton University Press, New York, pp. 26, 27, 42, 43 (1957). 7. K.P. Cheung and S.L. Chung, A heavy duty universal sunlight heliodon assembled from precision machining tools, Architectural Science Review, Vol. 42, No. 3, pp (1999). 8. K.P. Cheung and S.L. Chung, An elaboration on the design and operation principles of a heavy duty universal sunlight heliodon assembled from precision machining tools, Proceedings of ISES Solar World Congress, Jerusalem, 4-9 July 1999, International Solar Energy Society (1999). 9. Laboratoire de Lumiere Naturelle, Programme interdisciplinaire LUMEN, Lumière naturelle et énergétique du bâtiment, Projet OFEN, The Manual, Laboratoire d Energie Solaire et de Physique du Bâtiment EPFL, CH-1015 Lausanne,Switzerland, pp (1994). 10. K.P. Cheung, H.M. Kam, S.L. Chung and C.F. Lam, A 23-lamp heliodon, Architectural Science Review, Vol. 42, No. 1, pp (1999). 11. K.P. Cheung, A table top heliodon developed for use in an architect s design studio, International Journal on Architectural Science, Vol. 2, No. 4, pp (2001). 112

16 Engineering/summary_of_output/journal/IJAS/V2/ p pdf 12. K.P. Cheung, H.M. Kam and C.F. Lam, A Multi- Lamp Heliodon for Architectural Schools, International Journal on Architectural Science, Vol. 1, No. 1, pp (2000). Engineering/summary_of_output/journal/IJAS/V1/ p pdf 13. K.P. Cheung, and S.L. Chung, A Table Top Heliodon with a Moving Light Source for Use in an Architect's Office, International Journal on Architectural Science, Vol. 3, No. 2, pp (2002). Engineering/summary_of_output/journal/IJAS/V3/ p pdf 14. Kwok Pun Cheung, US Patent No. US B1. A Universal Heliodon-Sundial, patent issued by US Patent Office on 25 February also searchable at K.P. Cheung, An alternative solar chart and its use in a case study, Architectural Science Review, Vol. 40, No. 1, p (1997) 16. The Nautical Almanac l99l, HMSO, UK, pp A.N, Strahler, Physical georgraphy. 6 th edition, John Wiley and Sons, New York, pp (1975). 113