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South-facing glass is a vital element of a passive solar building. It allows the sun’s energy into the living space during the winter season. The admitted heat energy is absorbed and stored by thermal mass, then dispersed during nighttime to heat the room space. Hence, the south-facing glazing helps heat the house during the winter months and reduces the household energy consumption.
However, the size of the south-facing window needs to be optimized to make sure it serves its function. The optimum size of the south-facing window will permit an ample amount of heat energy into the house during the cold season and without causing overheating during the summer season.
The direction of such windows in the northern hemisphere should be toward the south, whereas it should be toward the north for buildings constructed in the southern hemisphere.
What is Glazing in Passive Solar Building?
Glazing is an architectural term used to describe the glass incorporated into the frame of a south-facing window.
Shading the south-facing window is a good strategy to maintain the cooling effect inside the house during summer. Proper shading can be provided by taking advantage of the sun’s angle during the winter and summer seasons.
The sun is lower during winter and higher during summer months, as illustrated in Figure-1 and Figure-2. The sun shines through the south-facing window during winter and warms the living spaces, but the overhang or shading system blocks the sun’s heat energy during summer, maintaining a comfortable temperature inside.
Double or triple glazing windows can be employed to prevent heat loss during nighttime. Generally, the south-facing windows should have a high solar heat gain coefficient of 0.55 or greater and a low U-factor of 0.35 or less to maximize heat gain and minimize heat loss.
Vertical windows permit sunshine into the passive solar building, but angled windows are more effective and allow a greater amount of heat energy. Nonetheless, the angled windows can overheat the house, so suitable shading must be provided.
Shading the angeled windows is more challenging than shading the vertical windows. Besides, vertical windows are less susceptible to damage and leakage, and less likely to cause overheating.
Criteria for Sizing South-facing Window
The total area of the south-facing glass should be specified carefully and accurately. This is because a larger area raises the temperature inside the house during summer. Therefore, the optimum size of south-facing glass is critical for implementing the design of a passive solar building.
The following limitations can be utilized to determine the suitable area of the south-facing window in a passive solar house:
- The size of the south-facing window, without the addition of thermal mass, for a sun-tempered house should be 7% of the total floor area of the house.
- The maximum area for a south-facing glass of a passive solar house should be 12% of the total floor area, regardless of how much thermal mass is added to the house. Beyond that, problems with fading fabrics and glare are likely to occur.
- The third criterion for determining the size of a south-facing glass is the total of all passive solar systems combined, which should not exceed 20% of the total floor area. Using larger south-facing glass than this limit can lead to overheating even in winters. For instance, passive solar system for 140 m2 house may consist of 14 m2 of direct gain glazing (Figure-4) and 11 m2of sunspace glazing (Figure-5). The total solar glazing is 25 m2 which is 18% of total floor area. So, the solar glazing area is well within the upper limit of 20% of total floor area.
South-facing glass is a vital element of a passive solar building. It admits the sun’s heat energy into the living space during the winter season. Hence, the south-facing glazing helps heat the house and reduce energy consumption.
1. The size of south-facing windows for a sun-tempered house should be 7% of the total floor area of the house, without the addition of thermal mass.
2. The maximum south-facing glass area for a passive solar house should be 12% of the total floor area, regardless of how much thermal mass is added to the house.
3. The third criterion for determining the size of south-facing glass is the total of all solar passive solar systems combined, which should not exceed 20% of the total floor area.
The provision of architectural features like an overhang or covering the south-facing window with tinted film to maintain visibility to the outside but reduce heat gain.