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
| Oct 8, 2014
Massive ‘healthcare village’ in Nevada touted as world’s largest healthcare project
The $1.2 billion Union Village project is expected to create 12,000 permanent jobs when completed by 2024.
| Oct 8, 2014
First look: Woods Bagot unveils plans for new Christchurch Convention Center
The locally-inspired building is meant to serve as a symbol of the city's recovery from the earthquake of 2011.
| Oct 8, 2014
Denver transit project wins design-build Project of the Year honor
The Denver Union Station Transit Improvement Project is among 25 projects honored by the Design Build Institute of America for excellence in design-build project delivery.
| Oct 7, 2014
Analysis: Student loans will cost housing industry $83 billion in 2014
More than 410,000 single- and multifamily home sales will be lost in 2014 due to student loan debt, according to analysis by John Burns Real Estate Consulting.
Sponsored | | Oct 7, 2014
Boost efficiency with advanced framing
As architects continue to search for ways to improve building efficiencies, more and more are turning to advanced framing methods, particularly for multifamily and light commercial projects.
| Oct 7, 2014
Economic gains are rallying rents in Raleigh, N.C.
The greater Raleigh, N.C., market appears to be getting back on its feet again, which is good news for rental property owners.
| Oct 7, 2014
Structured, not stirred: The architecture of cocktails [infographic]
In this downloadable graphic, technologist Shaan Hurley dissects 37 cocktails and analyzes their architectural makeup.
| Oct 6, 2014
Moshe Safdie: Skyscrapers lead to erosion of urban connectivity
The 76-year-old architect sees skyscrapers and the privatization of public space to be the most problematic parts of modern city design.
| Oct 6, 2014
Houston's office construction is soaring
Houston has 19 million square feet of office space under construction, 54% more than a year ago, and its highest level since the booming 1980s, according to local news reports.
| Oct 6, 2014
Design activity at architecture firms finally back to pre-recession levels: AIA report
Gross billings at architecture firms have increased by 20% since 2011, according to a new report by the AIA.