Principles and Applications of Building Science

Module 1: Solar Geometry

Overview

• Focus on Earth-Sun relationship, sunpath diagrams, solar time, and local time differences.
• Implications of solar radiation on building design.

Key Concepts

1. Earth-Sun Relationship

   • Climate driven by solar energy.
   • Two aspects:
     • Apparent movement of the sun (solar geometry).
     • Energy flow from the sun (heat and light).

2. Solar Geometry

   • Heliocentric model: Earth orbits the sun, tilt of Earth = 23.5°.
   • Key Dates:
     • Northern Solstice (Summer Solstice): June 21-22 (longest day in Northern Hemisphere).
     • Southern Solstice (Winter Solstice): December 22 (shortest day in Northern Hemisphere).
     • Equinoxes: March (Spring) and September (Autumn).

3. Latitude and Its Effects

   • Example locations: Sagar (34.1° N) vs. Trivandrum (8.5° N).
   • Effects on Solar Path:
     • Higher altitude angles closer to the equator.
     • Different patterns of solar incidence on facades.

Solar Angles

1. Altitude Angle: Angle between the sun and the horizontal plane.
2. Azimuth Angle: Angle from North (or South) to the sun's position.
   • Calculated using declination, hour angle, and day of the year.

Sunpath Diagram

• Projection of solar movement to aid in building design.
• Components: Altitude and azimuth angles.
• Useful for determining shading devices and building orientation.

Longitude and Time Zones

• Difference between solar time and local time.
• India has a single time zone (82.3° E), but longitude affects local solar time.
• Calculation of local solar noon:
  • Mumbai (73° E): Local solar noon occurs later than standard time due to its position.
  • Diar (95° E): Local solar noon occurs earlier than standard time.

Solar Radiation

1. Measurements:

   • Radiance (W/m²): Instantaneous energy flow.
   • IR Radiation: Integrated energy quantity (e.g., per day).

2. Components:

   • Direct radiation vs. diffuse radiation.
   • Effects of angle of incidence, atmospheric depletion, and duration of sunshine on radiation intensity.

3. Building Facade Implications:

   • Solar temperature affects interior temperatures based on facade orientation.
   • Considerations for shading devices and wall color on solar incidence.

Design Implications

• Orientation of building facades critical for energy efficiency.
• Longer facades should ideally face North/South, with shorter facing East/West.
• Adjustments in facade orientation based on location-specific solar data.

Examples and Calculations

• Case studies of Sagar and Trivandrum illustrate solar incidence and building design implications.

Conclusion

• Recap of key points:
  • Earth and Sun relationship.
  • Solar path diagrams and their applications.
  • Longitude's effect on time zones.
  • Impact of solar radiation on building design and orientation strategies.