Solar GeometryConcepts and Principles

University of OregonJanuary 16, 2007

Environmental Control Systems I – Winter 2007

WORKSHOP REMINDER

“Sun Angle Calculator”

Friday, January 19Baker 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 inHeritage Park

Calgary, Canada

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SOLAR RADIATIONCOMPONENTS

Plane of the ecliptic(equatorial plane)

+23 ½° -23 ½°

0°

0°

DECLINATION

LATITUDELatitude is related two angles, measured in degrees, "minutes of arc" and "seconds of arc" denoted by the symbols [ °, ', " ]

Eugene 44° 7' N

LONGITUDE or MERIDIANSEarth rotates about axis in 24 hours (360o/24 hrs), 15o/hour

Eugene 123° 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 QUESTIONHow 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

Minneapolis = 93oW 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

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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