Block the Sun Before it Enters Your Windows

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.