SUN AND THE DESIGN PROCESS

In the design of buildings that makes use of the principles of passive cooling, one essential consideration is to understand SOLAR GEOMETRY because the suns rays upon hitting the earth vary with time and latitudes.SOLAR GEOMETRY - describes the relationship between the sun and earth or more importantly the relationship of solar radiation, the product of the sun with any location on the earth.In concept, a specific site is made static and the sun allowed to move from east to west across the sky. This is technically called CELESTIAL SPHERE.Sun Control Warm Climates excessive solar gain result in high cooling energy consumption. Cold Climates south facing windows contribute to passive solar heating.

RELATIONSHIP OF THE SUN AND EARTHSUN Main source of light and heat . It is the closest star to earth Core- 15M degrees Celsius Distance to Earth = 150M Kms. - Apparently moves across the sky at a rate of 15.04 deg/hr.

EARTH The earth revolves in an orbit around the sun. It takes 365.25 days to complete one revolution around the sun. Rotates about its polar axis at 360.99 degrees per day as it revolves around the sun.

The period of rotation of the earth in its axis is 23 hours 56 minutes and 4 seconds.

The Earths polar axis is inclined at 23deg 47 from a vertical to the earths orbital planeInclination causes seasonal changes on earth.

SOLSTICE - either of the two points on the ecliptic at which the sun is overhead at the tropic of Cancer or Capricorn at the summer and winter solstices.

(Astronomy) either the shortest day of the year (winter solstice) or the longest day of the year (summer solstice)

SUMMER SOLSTICE - lies on the Tropic of Cancer at 2327 north latitude.

WINTER SOLSTICE - lies on the Tropic of Capricorn at 2327 south latitude.

EQUINOX - means "equal day and night

-occurs twice a year, when the tiltof theearths axis is inclined neither away from nor towards thesun the center of the Sun being in the same plane as the Earth's equator

-At an equinox, the Sun is at one of two opposite points on the Celestial spherewhere the celestial equator(i.e. declination 0) andeclipticintersect. These points of intersection are calledequinoctial points: classically, thevernal pointand theautumnal point.

Note : The inclination of the polar axis reaches its maximum on June 21 during the summer solstice where the sun would be at its farthest northern position. Therefore, June 21st is considered longest day.

During the winter solstice, the inclination draws towards the sun on December 21. The sun is at its nearest northern position. It is on this day where we experience the shortest day.

As equinox means equal, on March 21 and September 21, both northern and southern hemisphere experience equal amount of solar radiation. During this period the sun rises and sets directly to the position of east to west, respectively.

THE SUN PATHThe position of the sun is determined by two angles: SOLAR ALTITUDE ANGLESOLAR AZIMUTH ANGLE

SOLAR ALTITUDESolar Altitude is the angular height of the sun measured from the Horizon. Above the horizon is positive, below is negative. The sun directly in the centre of the sky has a Solar Altitude of 90 degrees.SOLAR AZIMUTHSolar Azimuth is the angular position of the sun measured around the Horizon with North being 0 degrees, East 90 degrees, South 180 degrees and West 270 degrees.

LATITUDES

FACTORS THAT DETERMINE THE AMOUNT OF SOLAR RADIATION ON EARTHThe position of the sun according to time and dayThe position of the sun according to the seasonClouds and atmospheric obstructionsThe angle of slope of the stationThe height of the stationThe situation of the station with regards to its surroundings

THE SOLAR CHARTS