Exterior Solar Screen
This article is about both exterior and interior solar screens.
Residential solar screens are either roller shade or fixed panels, which can be installed on either the exterior or interior of a window. Solar screens reduce solar heat gain, UV damage, and glare while permitting significant view and light transmission.
Screen materials include: PVC-coated polyester, PVC-coated fiberglass, and metallicized PVC-coated fiberglass (reflective metal finish on one side). The difference in the first two is largely thickness and durability; polyester screens are coated with PVC using an extrusion process resulting in thicker yarns (PVC coated fiberglass is drip coated and heat cured). The PVC coatings improve the durability of the screen and allow wide variation in optical properties and aesthetics, particularly with color variation.
Screens with a reflective metal finish represent a relatively new approach designed to improve the performance of interior solar screens by reducing solar heat gain (reflective side facing out) in summer and reducing radiant heat loss in winter (reflective side facing in). Reflective screens are more commonly used in commercial buildings.
Since screen fibers or strands are essentially round, they can refract light, increasing diffuse light entering a space. The percentage of sunlight absorbed, reflected, or transmitted by a solar screen is determined by two properties—the openness factor and the color of the screen.
Openness factor is simply the combined area of the screen that is open space, rather than filled with screen mesh. Higher percentages of openness mean less dense weave, more total view, and less shading and solar heat gain reduction. But screen color changes the portions of sunlight reflected, absorbed and transmitted; color affects glare and solar heat gain reduction as well.
Openness factors range from as high as 25% to as low as 1%, color can range from white to black. For the same color of screen, the openness factor can change the shading performance by between 5 and 25%; color can change the shading performance by as little as 5% or as much as 100%. Darker colors generally provide the best combination of solar heat gain/glare reduction and visibility.
Overall Thermal Performance
The primary thermal performance of solar screens is reducing solar heat gain, as reflected in shading coefficient (SC) numbers. The screen industry has historically used shading coefficient rather than solar heat gain coefficient—SHGC; the mathematical relationship between the two is: 0.87 X SC = SHGC).
Shading coefficient numbers for solar screens range from 0.50 – 0.70 for interior installations; 0.14 – 0.33 for exterior installations (based on openness factor and color as discussed above). The impact of solar screens on cooling costs and thermal comfort can range from substantial to modest, depending on the climate, performance properties of the screen, geographic location, and the cardinal orientation of the solar screen.
Interior reversible screens are designed with a metallic highly reflective side and black absorbent side to face metallic side in during heating and metallic side out during cooling. Their impact on solar shading is reduced because of their location on the interior. Their impact on reducing heat loss is modest and dependent on configuration. Metallic true screens maintain ventilation in the summer but no airtightness during the winter. One reflective screen product has a laminated plastic sheet component that can improve the air tightness of leaky windows during the winter but provides no ventilation during the summer.
- Reduced solar heat gain through windows (many different screens are available with widely varying solar heat rejection properties)
- Reduced glare
- Excellent UV protection (75-99%)
- Among the most economical solutions to solar shading/heat gain issues (fixed panel)
- Adjustability (roller shade)
- Reduced view and clarity (fixed panels)
- Fixed panels have same impact regardless of time of day/season
- Exterior installation not appropriate for outward swinging windows; interior installation has much less significant shading benefit
- About the same impact as insect screens, depending on color
- Silver side of reversible metallic screens may be distracting, particularly at night
- Go with black screens for best shading/cooling performance (exterior application)
- Evaluate screens with various openness factors and color at different light levels to ensure optimal combination of visual transmittance, view, glare control and shading (see, for example, this solar screen openness-factor-vs-color simulation tool)
- Effective use of roller screens is best suited to more expensive, motorized installations
- In climates with heating season, take down solar screens to increase solar gain and reduce heating costs
When To Consider
- Solar gain through window results in overheating or uncomfortable glare
- Homeowners are unwilling to block key views with awnings or other window attachments
- Large areas of glass would be prohibitively expensive and/or awkward to replace or fit with other window retrofits, such as storm windows or insulating blinds
- There is concern about fading of artwork, furnishings, carpet, etc.
- Climates with moderate to significant cooling requirements
- High glare context (lots of sky exposure/neighboring glass buildings)
When to consider this retrofit—Ownership
|Apartment Renter - Long Term|
|Apartment Renter - Short Term|
|x||Live in a Condo*|
|x||Live in a Historical District*|
* Condominium regulations or historic building codes may require the use of higher VT and lower reflectance window films that maintain appearance from the outside.
When to consider this retrofit—Window conditions
|x||Existing window new or in good shape|
|Existing window needs replacing (rot, safety, fogging, etc.)|
|x||Existing window single-glazed|
Existing window double-glazed, no low-e
|x||Existing window double-glazed with low-e (non-low-E films only)|
|x||Manufacturer or supplier (motorized)|
- Window unit air sealing
None (fixed panels) or motorized/automated
|Ease of Installation
(low = easier)
Average Total Cost for 30 by 60 inch window
|Motorized Roller Shade||$500|
Energy Modeling Tools for Professionals
|x||EnergyPlus-based modeling tools|
“Effect of Shading Devices on Residential Energy Use in Austin, Texas” (University of Texas at Austin)