TABLE OF CONTENTS For many zones, the solar radiation transmitted through windows accounts for a significant fraction of the total peak heat gain. Generally, transmitted solar radiation is affected by three factors:
sunlit area of the window,
orientation of the glazing relative to the sun,
optical properties of the window unit.
This example deals with the first factor, sunlit area. Orientation and optical properties are discussed in other examples.
In the Northern Hemisphere, for zones with east-, west-, or south-facing fenestration, increases in window area usually result in measurably higher cooling loads. Consider changing the window area of the base case by 50% from 80 ft 2 to 120 ft 2. The new window area is shown in Table 3.8. It should be noted that the specified wall area in the input forms is the actual area. In order to keep the overall size of the surface the same, when the window area is increased, the associated wall area must be decreased.
| Area (ft 2) | Normal SHGC | LW Emiss Out | LW Emiss In | Transmittance of Inside Shade | Reveal (ft) | Overhang width (ft) | Distance from Overhang to Window (ft) | |
|---|---|---|---|---|---|---|---|---|
| South Window | 120.0 | 0.93 | 0.9 | 0.9 | 1.0 | 0 | 0 | 0 |
| East Window | 0.0 | 0.93 | 0.9 | 0.9 | 1.0 | 0 | 0 | 0 |
| North Window | 0.0 | 0.93 | 0.9 | 0.9 | 1.0 | 0 | 0 | 0 |
| West Window | 120.0 | 0.93 | 0.9 | 0.9 | 1.0 | 0 | 0 | 0 |
| Skylight | 0.0 | 0.93 | 0.9 | 0.9 | 1.0 | 0 | 0 | 0 |
