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
| May 15, 2014
Biking to work up by 60 percent, according to Census Bureau report
Many U.S. cities are seeing an increase in bicycle commuters, according to new a U.S. Census Bureau report. While bicyclists still account for just 0.6% of all commuters, some of the nation's largest cities have more than doubled their rates since 2000.
| May 15, 2014
'Virtually indestructible': Utah architect applies thin-shell dome concept for safer schools
At $94 a square foot and "virtually indestructible," some school districts in Utah are opting to build concrete dome schools in lieu of traditional structures.
| May 15, 2014
First look: 9/11 Memorial Museum opens to first-responders, survivors, 9/11 families [slideshow]
The 110,000-sf museum is filled with monumental artifacts from the tragedy and exhibits that honor the lives of every victim of the 2001 and 1993 attacks.
| May 14, 2014
New study shows employees aren't happier working in green buildings
People working in buildings certified under LEED’s green building standard appear no more satisfied with their workplace environments than those in conventional buildings, according to new research from the University of California, Berkeley, and the University of Nottingham.
| May 14, 2014
Construction growth looking up: Gilbane Spring 2014 Economic Report
Construction spending for 2014 should finish 6.6% higher than in 2013, with nonresidential work contributing substantially.
| May 14, 2014
Prefab payback: Mortenson quantifies cost and schedule savings from prefabrication techniques
Value-based cost-benefit analysis of prefab approaches on the firm's 360-bed Exempla Saint Joseph Heritage Project shows significant savings for the Building Team.
| May 13, 2014
First look: Nadel's $1.5 billion Dalian, China, Sports Center
In addition to five major sports venues, the Dalian Sports Center includes a 30-story, 440-room, 5-star Kempinski full-service hotel and conference center and a 40,500-square-meter athletes’ training facility and office building.
| May 13, 2014
Drexel University case study report: Green Globes cheaper, faster than LEED
GBI’s Green Globes certification process is significantly less expensive to conduct and faster to complete than LEED certification, says Drexel prof.
| May 13, 2014
Steven Holl's sculptural Institute for Contemporary Art set to break ground at VCU
The facility will have two entrances—one facing the city of Richmond, Va., the other toward VCU's campus—to serve as a connection between "town and gown."
| May 13, 2014
Universities embrace creative finance strategies
After Moody’s and other credit ratings agencies tightened their standards a few years ago, universities had to become much more disciplined about their financing mechanisms.