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
| Jun 26, 2013
New York’s ‘Scaffold Law’ may be altered to place larger burden on workers
New York's Scaffold Law, which “places the burden of responsibility on the contractor to prove that the job site was safe for workers,” could be facing a major change.
| Jun 26, 2013
Commercial real estate execs eye multifamily, retail sectors for growth, says KPMG report
The multifamily, retail, and hospitality sectors are expected to lead commercial building growth, according to the 2013 KPMG Commercial Real Estate Outlook Survey.
| Jun 25, 2013
Mirvish, Gehry revise plans for triad of Toronto towers
A trio of mixed-use towers planned for an urban redevelopment project in Toronto has been redesigned by planners David Mirvish and Frank Gehry. The plan was announced last October but has recently been substantially revised.
| Jun 25, 2013
First look: Herzog & de Meuron's Jade Signature condo tower in Florida
Real estate developer Fortune International has released details of its new Jade Signature property, to be developed in Sunny Isles Beach near Miami. The luxury waterfront condo building will include 192 units in a 57-story building near high-end retail destinations and cultural venues.
| Jun 25, 2013
DC commission approves Gehry's redesign for Eisenhower memorial
Frank Gehry's updated for a new Dwight D. Eisenhower memorial in Washington, D.C., has been approved by the Eisenhower Memorial Commission, reports the Washington Post. The commission voted unanimously to approve the $110 million project, which has been gestating for 14 years.
| Jun 21, 2013
AIA report: Greater collaboration, stiffer competition among top trends in architecture
A new 34-page report from AIA highlights key trends in the architecture marketplace and their impact on business and growth.
| Jun 20, 2013
Virtual meetings enhance design of University at Buffalo Medical School
HOK designers in New York, St. Louis and Atlanta are using virtual meetings with their University at Buffalo (UB) client team to improve the design process for UB’s new School of Medicine and Biomedical Sciences on the Buffalo Niagara Medical Campus.
| Jun 19, 2013
Architects upbeat about the construction market
Following the first reversal into negative territory in ten months in April, AIA's Architecture Billings Index bounced back in May, reaching 52.9.
| Jun 19, 2013
NSF Sustainability begins verifying EPDs that can be used for LEED V4
NSF Sustainability has verified Environmental Product Declarations (EPDs) for nylon carpet styles and colors manufactured by Mannington Commercial and for J+J Flooring Group’s Kinetex® flooring product and Invision brand modular styles that use eKo® backing.
| Jun 19, 2013
Florida is latest battleground over LEED standards centered on certified wood
A nationwide battle over forest certification standards continues to be played out nationally and in Florida with legislation passed this month.