In recent years, sun shading has become a primary
consideration to reduce energy consumption in homes and buildings. Since windows are the largest consumer of
energy in a structure, blocking direct sunlight from entering windows can
dramatically improve the performance of any cooling system. Conversely, allowing the sun to enter during
the winter months can improve heating performance. A shading system that does both is the key to
lowering energy consumption and cost.
Interior vs. Exterior
Shading
Interior Shading
Interior window shades provide a benefit to occupants by
reducing glare, direct sunlight, and heat gain.
However, interior shading provides a minimal energy reduction. This is
because interior shades allow the sun to enter the home or building (Figure 1).
Figure 1
 |
| Interior Sunshade |
Once the sun breaks the plane of a window, heat gain is
generated. This heat is captured by
floors, furnishings, walls, etc. By
shading a window on the building interior, we are blocking the heat from
hitting these locations. Instead, the
heat is captured by the shade. But since
the sunshade is located within the structure, this heat must ultimately be
overcome by the cooling system.
Therefore, shading the interior of a window provides comfort
for the occupants, but little energy cost benefit.
Exterior Shading
Exterior window shades block the sun before it penetrates
the windows. Any heat gain is captured by the shading device and is dissipated
by outside air (Figure 2).
Figure 2
 |
| Exterior Sunshade |
By utilizing an exterior shade, we are provide the benefits to
occupants while adding energy savings due to reduced heat gain within the
building. Blocking the sun prior to the
window is the best way to improve cooling performance.
Summer and Winter Savings
Sun entering through windows during the summer months is
always an energy consumer due to increased cooling costs. But did you know that
in most climates, sun entering through windows during winter is a natural energy
saver? That sunshine heats the interior of the building or house and reduces
heating costs. So how do we block the
summer sun and let it enter during the winter?
The simple solution is to let nature to it for you. The sun angle during summer is much steeper
than it is during winter. By properly sizing and locating sunshades (see article), the sun can be blocked during
summer and allowed to enter during winter months (Figure 3).
Figure 3
 |
| Minimal Shading in Winter |
 |
| Full Shading in Summer |
Best Sun Shading
Practices
Window sunshades provide occupants with comfort in all
seasons. But blocking it before it hits window surfaces is far superior to any
interior shading. Also, by blocking the summer sun and allowing the entry of
winter sun, energy savings can be dramatically improved. Proper sizing and locating of exterior
sunshades is the key to capturing these benefits in one device.
