Low-emissivity (low-e) glasses are critical to making today’s buildings brighter, more energy-efficient and more sustainable. By controlling solar heat gain and promoting daylighting, they help buildings use less energy for temperature control and lighting, while adding the human benefits associated with outdoor views and more pleasant working and living environments.
Here are five tips to help architects, engineers, and contractors understand and explain the differences among low-e glasses and their impact on building performance:
1. E = Emissivity. Emissivity refers to the relative ability of a material’s surface to radiate energy. Low-e glass has a microscopically thin coating that lowers the emissivity of the glass surface and is engineered to transmit energy from the visible light portion of the solar spectrum (between 380 and 780 nanometers), while reflecting energy from ultraviolet light (310 to 380 nanometers), which causes fading, and infrared light (above 780 nanometers), which makes buildings warmer.
2. Think of a thermos. A thermos works by using a silver lining to continuously reflect and maintain the temperature of the drink it contains. Low-e glasses function according to the same principal, using multiple layers of silver or other low-emissivity materials in the coating to keep heat inside a building or prevent it from entering. Similarly, thermoses and insulating glass units (IGUs) are both designed with air spaces that provide a layer of insulation between the inside and outside.
3. More slivers of silver. Low-e coatings incorporate multiple layers of silver (or other low- emissivity materials) to control the transmission and reflection of heat and light. Recent technical advances now enable glass manufacturers to deposit up to three layers of silver on the glass substrate, which has enhanced the solar control capability of low-e glasses without diminishing their ability to transmit light.
4. Passive for insulation. Passive low-e glasses are usually made using the pyrolitic process, which means the coating is applied while the molten glass ribbon is still on the float line. This produces a “hard” coat that is fused to the glass surface and highly durable, but which has a higher emissivity that a solar-control low-e glass. Passive low-e glasses have decent insulating capabilities, but because of the limitations of metal deposition on the float line, they permit more solar infrared energy (heat) to pass through their coatings and become trapped inside the building. Consequently, passive low-e glasses are often the best choice for cold, heating-dominated climates.
5. Solar control to reduce heat gain. Coatings for solar control, low-e glasses are applied to pre-cut sheets of glass in a vacuum chamber at room temperature. This gives glass manufacturers the ability to deposit more sophisticated coatings (with multiple layers of silver) on the glass substrate, which improves solar control of the infrared (heat) portion of the solar spectrum without substantially diminishing the transmittance of visible light. These coatings are the best choice for hot, cooling-dominated (and moderate) climates. The lower emissivity of solar control low-e glasses also provides better insulating values to maintain the interior temperatures.
To learn more about low-e glass and other topics related to designing, specifying and building with glass, visit the PPG Glass Education Center at http://educationcenter.ppg.
Related Stories
BIM and Information Technology | Feb 8, 2015
BIM for safety: How to use BIM/VDC tools to prevent injuries on the job site
Gilbane, Southland Industries, Tocci, and Turner are among the firms to incorporate advanced 4D BIM safety assessment and planning on projects.
Museums | Feb 6, 2015
Tacoma Art Museum's new wing features sun screens that operate like railroad box car doors
The 16-foot-tall screens, operated by a hand wheel, roll like box car doors across the façade and interlace with a set of fixed screens.
Office Buildings | Feb 6, 2015
6 factors steering workplace design at financial services firms
Grossly underutilized space and a lack of a mobility strategy are among the trends identified by HOK based on its research of 11 top-tier financial services firms.
Cultural Facilities | Feb 6, 2015
Architects look to ‘activate’ vacant block in San Diego with shipping container-based park
A team of alumni from the NewSchool of Architecture and Design in San Diego has taken over a 28,500-sf empty city block in that metro to create what they hope will be a revenue-generating urban park.
Multifamily Housing | Feb 6, 2015
Fannie Mae to offer lower interest rates to LEED-certified multifamily properties
For certified properties, Fannie Mae is now granting a 10 basis point reduction in the interest rate of a multifamily refinance, acquisition, or supplemental mortgage loan.
Airports | Feb 6, 2015
Zaha Hadid-designed terminal in Beijing will be world’s largest
The terminal will accommodate 45 million passengers per year, and will be a hub for both air and rail travel.
Codes and Standards | Feb 6, 2015
Obama executive order requires federal construction projects to consider flood damage caused by climate change
To meet the new standard, builders must build two feet above the currently projected elevation for 100-year floods for most projects.
HVAC | Feb 6, 2015
ASHRAE, REHVA publish guide to chilled beam systems
The guide provides tools and advice for designing, commissioning, and operating chilled-beam systems.
Cultural Facilities | Feb 6, 2015
Under the sea: Manmade island functions as artificial reef
The proposed island would allow visitors to view the enormous faux-reef and its accompanying marine life from the water’s surface to its depths, functioning as an educational center and marine life reserve.
Contractors | Feb 6, 2015
Census Bureau: Capital spending by U.S. businesses increased 4.5%
Of the 19 industry sectors covered in the report, only one had a statistically significant year-to-year decrease in capital spending: the utilities sector.