SOLAR GEOMETRY (AND SOLAR RADIATION)

Transcription

1 SOLAR GEOMETRY (AND SOLAR 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 under design conditions Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Solar Radiation: A Resource or a Problem? force mitigating element: building envelope resultant radiation is an environmental force; it can be an asset or a liability depending upon site/project//context/opr 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 Mitad del Mundo, Quito marking the equator Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 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 8 4

5 Greenwich, England prime meridian Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Solar-Site Context summer spring/fall NORTHERN HEMISPHERE winter the sun follows defined and predictable paths on a daily and annual basis Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 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 11 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 12 6

7 Altitude Angle Patterns << site latitude for any given month and time, altitude angle varies with latitude Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 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 14 7

8 Azimuth Angle Patterns azimuth angle varies with month and time of day; range is most extensive in summer Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Solar Position Relative to Site conceptually simple, but three-dimensional Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 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 upcoming slide Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 South, Souther, Southiest 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 18 9

10 Magnetic Deviation solar reference magnetic deviation compass reference magnetic deviation magnetic deviation varies with site location Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Magnetic Deviation zero deviation line designing for east-central Indiana is not too deviant Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Solar versus Clock Time LST CT + DST local solar time = clock 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 21 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 22 11

12 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 23 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) to generate a diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 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 25 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) to generate a diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

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

15 Online Solar Position Data susdesign.com/sunangle/ Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Why Architects Should Understand Solar Geometry abcnews.go.com/ Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15