SOLAR GEOMETRY (AND RADIATION)

Transcription

1 SOLAR GEOMETRY (AND RADIATION) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Solar Radiation Components glass will reflect some incoming radiation; absorb some; and transmit some SHGF (above) is solar heat gain factor a measure of the quantity of solar energy that will pass through a sheet of single-pane clear glass at a given time of the year for a given orientation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Solar Radiation: A Resource or a Problem? force mitigating element: building envelope result radiation is an environmental force; it can be an asset or a liability depending upon site/project/intent/context Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Solar Context Distance Sun Earth the solar constant is a mean value of the solar radiation intensity found at the edge of the Earth s atmosphere solar constant (Btuh/sq ft) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Solar Context Tilt the tilt of the Earth s axis, relative to the sun s position accounts for the seasons (as solar angle of incidence changes) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Site Context Latitude Muncie s latitude is approximately 40 deg N (a convenient latitude often used in design data tables) latitude locates a site in the north-south context, relative to the equator Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Site Context Longitude Muncie = apx. 85 deg W longitude locates a site in the east-west context, relative to the prime meridian (in Greenwich, England) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Greenwich, England prime meridian Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Solar-Site Context summer spring/fall winter NORTHERN HEMISPHERE the sun follows defined and predictable paths on a daily and annual basis Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Solar Angles Altitude ALTITUDE ANGLE the angle between a horizontal ground plane and the line describing the position of the sun in the sky vault Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Altitude Angle Patterns noon noon altitude angle; describes height of the sun in the sky varies with month and time of day Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Altitude Angle Patterns << site latitude for any given month and time, altitude angle varies with latitude Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Solar Angles Azimuth AZIMUTH ANGLE the angle between south and the position of the sun in the sky vault as projected onto the horizontal ground plane Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Azimuth Angle Patterns azimuth angle varies with month and time of day; and is most extensive in summer Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Solar Position Relative to Site conceptually simple, but three-dimensional Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Solar Position Conventions Azimuth angle is usually measured from South (in architecture) but sometimes from the North in other disciplines (or in the Southern hemisphere) South is always solar South; not magnetic South or plan South see next slide Altitude angle is measured from the horizontal Times are always expressed as solar time see following slide Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 South, Souther, Southest Plan South is usually an arbitrary designation used for convenience Solar South is by definition the position of the sun at solar noon Solar South marks the center of symmetry of the daily solar path Solar South differs from Magnetic South (as read on a compass) by the local magnetic deviation value Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Magnetic Deviation solar reference magnetic deviation compass reference magnetic deviation magnetic deviation varies with site location Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Magnetic Deviation zero deviation line designing for east-central Indiana is not too deviant Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Solar versus Clock Time CT CT (clock time) = local solar time + equation of time value + (4)(local standard time meridian local longitude) +/- daylight saving time adjustment example, Muncie, June 21: latitude adjustment = (4)(75-85) = -40 minutes; DST adjustment = 60 minutes; ET adjustment = -3 minutes bottom line: solar and clock time are rarely identical, and can differ by +/- an hour; this matters when solar loads are combined with clock-based loads Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Clock Time Influences equation of time US time zones (political devices) and time zone reference meridians; the sun is not influenced by politics Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Sunpath Information The sun s location at any time can be accurately predicted. Such information is readily available in several formats: Graphic sunpath diagrams: Horizontal projection diagrams (including the SBSE Sun Angle Calculator) Vertical projection diagrams Sunpeg diagrams Tabular data (as in the ASHRAE Handbook) Online calculators (interactive databases) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 Sunpath Diagrams horizontal projection sunpath diagram l-e-s-s.co.uk/guides/physics/solargeometry.htm sun paths for selected days can be projected downward onto a horizontal plane (the plane is a surrogate for the Earth s surface) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Sunpath Diagrams Pilkington Sun Angle Calculator available from SBSE Via CERES sun paths for multiple latitudes are provided, with usability enhancements Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Sunpath Diagrams vertical projection sunpath diagram sun paths for selected days can be plotted on a vertical surface (acting as a surrogate for the site horizon) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Sunpath Diagrams sunpeg diagram primarily used to properly orient a scale model to the sun (real or simulated); the shadow cast by the peg (gnomon) shows date and time Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 Tabular Solar Position Data Mechanical and Electrical Equipment for Buildings (10 th ed) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Online Solar Position Data susdesign.com/sunangle/ Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

15 for the upcoming QUIZ Focus on the material above for the topical quiz associated with these notes while not disregarding the very important information below. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Shading Devices The term shading device describes an element of the building design intended to reduce the amount of solar radiation falling on, or making its way into, a building; there are several broad categories of such devices External devices Are the most thermally-effective approach; these block radiation before it can engage glazing or opaque wall/roof surfaces; many types of external device are available Integral devices Next most effective approach; these engage radiation within the building envelope; various glazings or window inserts are available Internal devices The least thermally-effective approach; these engage radiation only after it is within the building; many popular examples (such as drapes or blinds) are available Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15

16 External Shading Devices overhang blocked generally admitted external overhang; can be very effective with direct radiation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 External Shading Devices vegetation external tree; can be very effective (and, if deciduous, can act as a switch) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32 16

17 External Shading Devices an overhang is an altitude-responsive device a fin is an azimuth-responsive device overhang vs. fin external overhang (in section) and fin (in plan) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 33 Integral Shading Devices tinted glass increased heat convection reduced solar radiation transmission integral radiation-absorbing glass, increases glass surface temperature Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 34 17

18 Internal Shading Devices draperies complex thermal interactions internal draperies; radiation is only blocked once it is within the envelope; solar energy (heat) is allowed to enter the building Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 35 Shading Devices California State Office Buildings: San Jose Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 36 18

19 Shading Devices Dallas City Hall, TX shading by inherent building form Georgia Power offices, Atlanta Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 37 Shading Devices blinds placed between two sheets of glazing (integral) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 38 19

20 Shading Devices 1 = vegetation; 2 = overhang; 3 = blinds reverse shading (oops) layered shading Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 39 Shading Devices? New Capitol Old Capitol North >>> Florida State Capitol, Tallahassee, FL Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 40 20

21 Shading Device Design Establish design intent For example block sun in summer (the overheated period) Establish design criteria For example full shade, all day from May through September For example no shade from November through January For example no blockage of views Decide upon design method Design can evolve rationally through the use of various tools Or, design can be based upon trial and error using precedents Verify success of design in meeting criteria Numerous tools are available: physical models and heliodons, hand calculations and sketches, computer simulations Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 41 Shading Device Design Tools shading pattern provided by device type; projected onto sunpath diagram shading masks, these provide a pattern language for shading devices: from Solar Control and Shading Devices (Olgyay and Olgyay) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 42 21

22 Shading Device Design Tools lighter area indicates times of the year when device does NOT shade window shading mask for a south-facing overhang plotted on a vertical projection sunpath diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 43 Shading Device Design Tools shaded shaded no shade a shading mask for a specific overhang, showing period of sun penetration Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 44 22

23 Shading Device Design Tools not shaded shaded fisheye photo of sky vault from a site and similar image with sunpath superimposed: Design with Climate, Olgyay Solar Pathfinder tool Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 45 Shading Device Design Tools L overhang L set to provide full shade (from direct sun) during times of the year when the solar altitude angle is β (or greater) H overhang design using trigonometry (or, even easier, using a scale drawing) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 46 23

24 Shading Device Design Tools series of images courtesy of Alison Kwok, Univ. of Oregon shading device design analysis using a scale model and sunpeg diagram; what you see is what you ll get Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 47 Shading Device Design Tools shading device design analysis using a scale model and sunpeg diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 48 24

25 Shading Device Design Tools shading device design analysis using a scale model and sunpeg diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 49 Shading Device Design Tools shading device design analysis using a scale model and sunpeg diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 50 25

26 Shading Device Design Tools devices and inquisitive designers Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 51 Shading Device Design Tools fixed-table, moving sun fixed table, selectable suns fixed sun, moving table three types of heliodons (solar position simulators) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 52 26

27 Shading Device Design Tools photos from the Pacific Energy Center a heliodon provides information on shading performance and direct sun patterns; it provides no information on daylight factors Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 53 Expressing Shading Performance An historic (and still useful) performance metric for shading systems is: Shading Coefficient (SC) SC = solar heat gained through glazing x solar heat gained through reference glazing Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 54 27

28 Shading Coefficient (SC) The reference glazing is single-pane, clear glass As a ratio, SC is dimensionless (it is stated as a percent or more commonly as a decimal value) SC values may be found in manufacturers literature, in handbooks (such as from ASHRAE), or may be derived from calculations SC, as generally used, applies only to glazing (not to the opaque frame or mullions) An overall SC may be assembled from parts SC overall = (SC 1 )(SC 2 )(SC 3 ) where, SC 1 may be for an overhang, SC 2 for glazing, Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 55 Expressing Shading Performance A newer (and need-to-know for code compliance) shading performance metric is: Solar Heat Gain Coefficient (SHGC) SHGC = the fraction of incident solar radiation that is admitted through a window or skylight (including the frame) both that directly transmitted, and that which is absorbed and subsequently released inward Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 56 28

29 Solar Heat Gain Coefficient (SHGC) SHGC is a dimensionless value (it is stated as a percent or most commonly as a decimal value) SHGC applies to glazing and frame/mullions SHGC is a laboratory-measured value (the National Fenestration Rating Council NFRC tests and certifies products) Determining (figuring) an overall SHGC (considering site additions to shading) is a problematic issue SHGC SC SHGC (SC)(0.87) SHGC is self-referential; while SC references a base product for comparison Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 57 NFRC Window Label full solar spectrum if product is residential if product is non-residential visible spectrum label is removed from window after code inspection Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 58 29

30 Window Performance Indicators Florida Solar Energy Center SC glazing only a selective transmission product SHGC entire unit Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 59 be creative movable shading device (sail); Alpine House, Kew Gardens, UK Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 60 30