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
Multifamily Housing | Feb 18, 2015
Make It Right unveils six designs for affordable housing complex
BNIM is among the six firms involved in the project.
Office Buildings | Feb 18, 2015
Commercial real estate developers optimistic, but concerned about taxes, jobs outlook
The outlook for the commercial real estate industry remains strong despite growing concerns over sluggish job creation and higher taxes, according to a new survey of commercial real estate professionals by NAIOP.
Museums | Feb 18, 2015
Foster + Partners' National Museum of Marine Science and Technology breaks ground in Taiwan
The museum will be home to an aquarium, exhibition space, and waterfront views.
University Buildings | Feb 18, 2015
Preparing for the worst: Campus security since Virginia Tech
Seven years after the mass shootings at Virginia Tech, colleges and universities continue to shake up their emergency communications and response capabilities to shootings and other criminal threats.
Office Buildings | Feb 18, 2015
Why the mobile workplace isn't always mobile
Perkins+Will’s Janice Barnes addresses the nuance in mobility types and explains the importance of defining terms upfront.
University Buildings | Feb 17, 2015
BD+C exclusive: How security is influencing campus design and construction
Campus crime—whether real or perceived—presents Building Teams with more opportunities for early-stage consultation with university clients.
Architects | Feb 17, 2015
Architecture billings dip in January, severe weather likely to blame
“This easing in demand for design services is a bit of a surprise given the overall strength of the market over the past nine months,” said AIA Chief Economist Kermit Baker.
Multifamily Housing | Feb 17, 2015
California launches pilot program to finance multifamily retrofits for energy efficiency
The Obama Administration and the state of California are teaming with the Chicago-based MacArthur Foundation on a pilot program whose goal is to unlock Property-Assessed Clean Energy financing for multifamily housing.
Sponsored | Building Team | Feb 17, 2015
Why diversity matters
Companies in the top quartile for gender or racial and ethnic diversity are more likely to have financial returns above their national industry medians.
Multifamily Housing | Feb 17, 2015
Young Millennials likely to return home
Ninety percent of individuals born between 1980 and 1984 and who hold a Bachelor’s degree left home before they were 27 years hold. However, half of this group later returned to their parents’ home, according to a study by the National Longitudinal Study of Youth.