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
| Jul 22, 2013
Transportation Facility Report [2013 Giants 300 Report]
Building Design+Construction's rankings of design and construction firms with the most revenue from airport terminals and other transportation-related facilities, as reported in the 2013 Giants 300 Report.
| Jul 22, 2013
Convention Center Report [2013 Giants 300 Report]
Building Design+Construction's rankings of design and construction firms with the most revenue from convention center projects, as reported in the 2013 Giants 300 Report.
| Jul 22, 2013
Cultural Facility Report [2013 Giants 300 Report]
Building Design+Construction's rankings of design and construction firms with the most revenue from cultural facility projects, as reported in the 2013 Giants 300 Report.
| Jul 22, 2013
International Report [2013 Giants 300 Report]
Building Design+Construction's rankings of design and construction firms with the most revenue from international projects, as reported in the 2013 Giants 300 Report.
| Jul 19, 2013
Top BIM Construction Firms [2013 Giants 300 Report]
Turner, Clark Group, DPR top Building Design+Construction's 2013 ranking of the contractors and construction management firms with the most revenue from BIM-driven projects.
| Jul 19, 2013
Top BIM Engineering Firms [2013 Giants 300 Report]
Jacobs, URS, SAIC top Building Design+Construction's 2013 ranking of the engineering and engineering/architecture firms with the most revenue from BIM-driven projects.
| Jul 19, 2013
Top BIM Architecture Firms [2013 Giants 300 Report]
Gensler, HOK, HDR top Building Design+Construction's 2013 ranking of the architecture and architecture/engineering firms with the most revenue from BIM-driven projects.
| Jul 19, 2013
BIM 2.0: AEC firms share their vision for the great leap forward in BIM/VDC implementation [2013 Giants 300 Report]
We reached out to dozens of AEC firms that made our annual BIM Giants lists and asked one simple question: What does BIM 2.0 look like to you? Here’s what they had to offer.
| Jul 19, 2013
Reconstruction Sector Construction Firms [2013 Giants 300 Report]
Structure Tone, DPR, Gilbane top Building Design+Construction's 2013 ranking of the largest reconstruction contractor and construction management firms in the U.S.
| Jul 19, 2013
Reconstruction Sector Engineering Firms [2013 Giants 300 Report]
URS, STV, Wiss Janney Elstner top Building Design+Construction's 2013 ranking of the largest reconstruction engineering and engineering/architecture firms in the U.S.