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.
CLICK IMAGE TO ENLARGE
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
| Aug 7, 2012
Pioneering revival
Financial setbacks didn’t stop this Building Team from transforming the country’s first women’s medical school into a new home for college students.
| Aug 7, 2012
Shedding light on the arts
Renovating Pietro Belluschi’s Juilliard School opens the once-cloistered institution to its Upper West Side community.
| Aug 7, 2012
How to win more state and local government projects
With a huge building stock at their disposal, state and local governments can be attractive clients, especially in these difficult economic times.
| Aug 7, 2012
McCarthy tops out LEED Platinum-designed UCSD Health Sciences Biomedical Research Facility
New laboratory will enable UCSD to recruit and accommodate preeminent faculty.
| Aug 7, 2012
Pankow names Lum new CEO
Lum joined Pankow in 1980 in Hawaii and has held leadership roles in Pankow’s Honolulu and Northern California regional offices and was appointed president of the firm in 2009.
| Aug 7, 2012
Suffolk Construction builds new Boston Tea Party Ships & Museum
Construction management firm links history with the future by building museum using state-of-the-art virtual models and BIM technologies.
| Aug 7, 2012
Essex Builders to build church in Somerville, Mass.
The project’s design documents were prepared by Boston Bay Architects and reflect the church’s mission to serve the broader community as well as worship.
| Aug 6, 2012
Johnson Controls GWS appoints Genemaras as COO
Genemaras brings a wealth of experience in international business operations.
| Aug 6, 2012
Welton promoted to principal in Thornton Tomasetti’s Denver office
Welton serves as the manager of the firm’s Denver office and has more than 30 years of structural engineering experience across a range of project types including sports, commercial and residential.
| Aug 6, 2012
Kibby has joins the Harmon team
Kibby has over 24 years of experience in the glazing industry, coming to Harmon from Architectural Wall Systems where he worked in business development.
