Quick Answer
Choose a south window size that spans 10-15% of the wall area to allow for sufficient natural light and passive solar heating. A larger window size can lead to overheating, while a smaller one may not provide sufficient warmth. Consider the orientation and climate of your location when determining the ideal window size.
Determining Window Size Based on Latitude
When choosing the right south window size, consider the latitude of your location. In general, windows in the southern United States should be smaller than those in the northern states. For example, a home in Miami, Florida (latitude 25.79° N) should have a south window size of around 8-12% of the wall area, while a home in Minneapolis, Minnesota (latitude 44.97° N) should have a south window size of around 12-18%. This is because the sun’s rays are more intense in the southern states, making it easier to overheat.
Calculating Window Size Based on Insolation
To calculate the ideal south window size, you can use the insolation data for your location. Insolation is the amount of solar radiation that hits a surface per unit area. For example, in Phoenix, Arizona (latitude 33.45° N), the insolation is around 5.8 kWh/m²/day. Based on this data, you can calculate the ideal window size using the following formula: Window Size (m²) = Insolation (kWh/m²/day) x 0.1. In this case, the calculation would be Window Size (m²) = 5.8 kWh/m²/day x 0.1 = 0.58 m² or approximately 6.25 square feet.
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