Solar Geometry Concepts and Principles University of Oregon January 16, 2007
Environmental Control Systems I – Winter 2007
WORKSHOP REMINDER “Sun Angle Calculator” Friday, January 19 Baker Lab (235 Pacific) 12:00 -12:30 Dianne Ahmann
Cluny Museum, Paris, France
Courtyard in Cambridge, UK
Sundial in near the Campo di Fiore, Rome, Italy
Rustic sundial in Heritage Park Calgary, Canada
The Solar Cat Book, Jim Augustyn
SOLAR RADIATION COMPONENTS
Plane of the ecliptic (equatorial plane)
DECLINATION
0°
-23 ½°
+23 ½°
0°
LATITUDE Latitude is related two angles, measured in degrees, "minutes of arc" and "seconds of arc" denoted by the symbols [ 째, ', " ]
Eugene 44째 7' N
LONGITUDE or MERIDIANS Earth rotates about axis in 24 hours (360o/24 hrs), 15o/hour Eugene 123째 13' W
GREENWICH
LOOK-UP Latitudes and Longitudes http://www.bcca.org/misc/qiblih/latlong.html
U.S. TIME ZONES
WORLD TIME ZONE MAP
TRIVIA QUESTION How can someone on an east coast state call a person on a west coast state and it be the same time?
Sun’s position determined by . . .
ALTITUDE
AZIMUTH
ALTITUDE of the sun at solar noon:
altitude = 90 – latitude + or - declination
Rectilinear sunpath chart
Equidistant sunpath chart
Sunpeg diagram
If you are located on the WEST side of magnetic variation zero (Michigan) - the compass will point to the EAST of true north.
SOLAR SOUTH • Defined by the position of the sun at solar noon • Marks the center of symmetry for the daily solar path • Differs from magnetic South by the magnetic deviation value • Plan South is totally arbitrary
SOLAR TIME depends on: • Speed around the sun (equation of time) • Location within the longitude • Daylight savings time
Calculate solar time: Solar time = Local time + E + 4 (Lst - Lloc) (E = equation of time)
Eugene = 123oW longitude o
Minneapolis = 93 W longitude
EQUATION of TIME
Stone ruins of the Tholos Delphi, Greece
38 separate exposures (and 1 foreground exposure) were recorded on a single piece of film between January 12 and December 21 at 6:00 am
The Solar Cat Book, by Jim Augustyn Ten Speed Press, 1979
CONVENTIONS • Azimuth angle is usually measured from South (in architecture) … but sometimes from the North • South is always “solar” South (not magnetic South or plan South) • Altitude angle is measured from the horizontal • Times are always “solar” times
Baker Lab ShadowTracker
Water Resources Control Board Sacramento, CA
PROFILE ANGLE • Shadow Angle • Architect’s Angle • conceptual The angle cast by the leading edge of an exterior shading device at particular times of the day, in a plane normal to the building.
SHADING DEVICE DESIGN
Shading design using trigonometry
SHADING PERFORMANCE Historic (and useful) performance metric Shading Coefficient (SC) SC =
solar heat gain to a building through glazing “x� solar heat gain to a building through reference glazing
SC • SC is dimensionless (percent or decimal value) • SC applies only to glazing (not frame) • Reference glazing is single, clear glass • SC may be found in manufacturers’ literature, from handbooks (ASHRAE), or derived from calculations • Overall SC may be assembled – SC total = (SC1)(SC2)(SC3) …
SHADING PERFORMANCE New (and also useful) performance metric Solar Heat Gain Coefficient (SHGC) SHGC = The fraction of solar radiation admitted through a window or skylight, both directly transmitted, and absorbed and subsequently released inward
SHGC • SHGC is dimensionless (percent or decimal value) • SHGC applies to glazing and frame/mullions • SHGC is a measured value (National Fenestration Rating Council—NFRC—tests products) • Overall SHGC is a problematic issue • SHGC ≠ SC • SHGC ≈ (SC)(0.87)
NFRC