Notes on Principles and Applications of Building Science - Module 1: Solar Geometry

Overview

• Focus on the relationship between Earth and the sun, solar path diagrams, and implications for building design.

Key Concepts

Earth-Sun Relationship

• Climate driven by solar energy input.
  • Key Aspects:
    1. Apparent movement of the sun (solar geometry).
    2. Energy flow from the sun (heat and light).
• Importance of managing solar energy in building design.

Solar Geometry

• Heliocentric View: Sun at center; Earth orbits sun with a constant axial tilt of 23.5°.
• Key Dates:
  • Northern Solstice: June 21-22 (longest day, shortest night).
  • Southern Solstice: December 21-22 (shortest day, longest night).
  • Equinoxes: March and September (day and night are equal).
• Understanding solar geometry crucial for climatic building design.

Solar Angles

• Altitude Angle: Angle of sun above the horizon. Higher angle = sun more directly overhead.
• Azimuth Angle: Angle from a reference direction (usually North) to the sun’s position.

Example Locations

• Sagar: 34.1° N, 74.8° E
  • Summer solstice: sun rises in the Northeast, sets in the Northwest.
  • Winter solstice: lower sun angle, rises in the Southeast.
• Trivandrum: 8.5° N
  • Closer to the equator, different sun movement patterns.

Sun Path Diagrams

• Essential for building design and shading analysis.
• Helps visualize solar movement in relation to building orientation.

Longitude and Time Zones

• Solar time vs local time:
  • Local solar noon differs based on longitude.
  • India operates on one time zone (82.3° E), causing discrepancies across the country.
• Calculation Example:
  • Mumbai (73° E): Local noon occurs later than IST.
  • Diar (95° E): Local noon occurs earlier than IST.

Solar Radiation

• Two main measures:
  1. Radiance (W/m²) - instantaneous solar energy flow.
  2. Irradiance (Wh/m²) - energy quantity over a time period.
• Sun's radiation peaks at 550 nm wavelength.
• Factors affecting solar radiation on buildings: angle of incidence, atmospheric conditions, duration of sunshine.

Design Implications

• Importance of understanding solar geometry in building orientation and facade design.
• Impacts of different latitude on solar exposure.
• Shading Devices: Crucial for managing solar heat gain.
• Example Calculations:
  • Solar temperatures on different building orientations and effects of absorptivity (light vs dark surfaces).
  • Use of reflective coatings and shading systems to reduce solar temperature.

Conclusion

• Recap of solar geometry principles and their implications on building design.
• Importance of solar path diagrams for effective building orientation and design strategies.