Before innovations in glass, films, and coatings in the past decade, a typical residential window with one or two layers of glazing allowed roughly 75 to 85 percent of the solar energy to enter a building, which has a negative impact on summertime comfort and cooling bills, especially in hot climates.
Instructions: Click on the hot spots in the image below to see the properties of a normal window.
External Window Shading
External window shading devices such as awnings, roof overhangs, shutters, and solar screens, and internal shading devices such as curtains and blinds, can control the entry of solar heat. Although external window shading devices are about 50 percent more effective than internal devices at blocking solar heat, they do have some disadvantages.
Instructions: Click on the hot spots in the image below to see the disadvantages of external window shading.
Internal Shading Devices
The table below shows the percentages of the radiant energy that different types of internal shading devices transmit, reflect, or absorb.
| Shade Type | Transmitted energy (percent) | Reflected energy (percent) | Absorbed energy (percent |
|---|---|---|---|
| Roller Shades | 25 percent | 15 - 80 percent | 20 - 65 percent |
| Vertical Blinds | 0 percent | 23 percent | 77 percent |
| Venetian Blinds | 5 percent | 40 - 60 percent | 35 - 55 percent |