Window Orientation and Suitable Glass / Glass Circle

Window Orientation and Suitable Glass

Sunlight that feels pleasant in cold seasons becomes painful in summer heat. Glass that reduces such harsh sunlight is solar shading glass. Solar shading glass, when installed on windows receiving sunlight, softens sunlight and reduces heat near windows ※1. Sunlight entering indoors through windows changes according to positional relationship between windows and sun, so we consider effectiveness of solar shading glass from how sunlight hits according to window orientation, season, and time.

Simulation conducted for building with no surrounding buildings and windows only in one direction

Generally, when thinking of "windows with good sunlight," south-facing probably comes to mind first. So, assuming a building with only windows of 1700mm vertical × 1700mm horizontal on the south side as shown on the right, we consider shadows formed on indoor floors when simulating sun movement near Tokyo.
In winter (January 1) simulation, sunlight begins entering around 8～9 AM, and light reaches about 3m from windows at 12 PM, while in summer (August 1) simulation, even at 12 PM it only reaches about 50cm from windows.

South windows: sunlight reaches 50cm in summer, 3m in winter

Similarly, simulating when windows are on the west side, sunlight hits from around 1 PM until sunset in both summer and winter, but western sun reaches quite deep into rooms in both summer and winter.

West windows: sunlight reaches deep into rooms in both summer and winter

The lower the sun's altitude (angle), the deeper sunlight reaches into rooms

Basically, south windows receive light around noon when sun altitude is highest during the day, but this sun altitude changes with season. In winter, meridian altitude ※2 is low and sun draws a low orbit, so light enters indoors even during daytime, but in summer, sun draws a high orbit, so only areas near windows receive sunlight.

In contrast, west windows receive sunlight from afternoon to evening, and evening sun is at low angles regardless of season, so sunlight reaches deep into rooms regardless of season.

Therefore, when thinking about avoiding harsh summer sunlight, south side can be avoided by moving slightly away from windows, but avoiding sunlight entering from west windows is difficult. Also, east side has almost the same sunlight as west side, but since temperature is lower than evening, it is somewhat more bearable.

East windows: sunlight reaches deep into rooms the same as west windows.

From these points, ranking orientations needing solar shading glass becomes West ＞ East ＞ South. While solar shading glass has several types, generally those with higher solar shading effects tend to weaken winter sunlight as well, of course, and brightness also tends to become darker. Rather than simply matching glass, we recommend selecting glass according to windows considering sunlight, regional weather conditions, room use, and thermal insulation including the entire house ※3. North windows do not receive direct sunlight, so normally there is no need to consider solar shading ※4. (Used when matching building exterior or window color tones)

Types of Solar Shading Glass

Solar shading glass handled by our company includes Heat-Absorbing Glass, Heat-Reflecting Glass, laminated glass structure Cool Safer, insulating glass units using solar shading LowE LE Twin Glass (Solar Shading Type), and Heat Mirror Glass (Solar Shading Type) using solar shading heat mirror film. Please select according to use.

※1	Solar shading glass effects include not only "softening sunlight entering indoors" but also "reducing heat from sunlight transmitted indoors," so even if not near windows, air conditioning cost reduction effects can be obtained if sunlight hits glass.
※2	The altitude when sun is highest is called meridian altitude (angle between horizon and sun when sun rises to true south and is highest).
※3	In houses with high thermal insulation, rooms with good sunlight may require cooling even in winter due to room temperature rise. Since various factors such as your region, sunlight, overall room thermal insulation, volume, window orientation, and size affect this, please consider after consulting with house manufacturers and design offices.
※4	North-facing vertical windows almost never receive direct sunlight, but depending on surrounding conditions, reflected light from opposite windows, etc., may enter.
※	The above simulation is conducted under conditions with no eaves or surrounding buildings, etc., that block sunlight hitting windows. If there are objects that reflect or block sunlight in the surroundings, it may differ from the above.
※	Sun altitude in the above simulation assumes Tokyo, and content differs somewhat by region.