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
| Jan 2, 2013
Trends Report: New facilities enhance the quality of campus life
Colleges and universities are building state-of-the-art student unions, dining halls, and other non-academic buildings to enrich the campus experience, boost enrollment, and stay competitive.
| Jan 2, 2013
M&A activity at U.S. AEC firms up slightly
Total mergers and acquisitions in the AEC industry hit 171 in 2012, up slight from the 169 deals in 2011.
| Jan 2, 2013
Global data center market to ‘slow’ to 14.3% this year
Total global investment in data centers is expected to slow down somewhat this year but still increase at a respectable 14.3%, according to DCD Intelligence.
| Jan 2, 2013
Construction jobs made gains in 2012, even with a slow Q4, says Gilbane report
The construction sector in the nine states with 50% of construction employment was up 169,000 jobs from February to September 2012, following a lost of 137,000 jobs from September 2011 to January 2012.
| Dec 21, 2012
ABI gains for fourth straight month
Positive business conditions for all building sectors.
| Dec 17, 2012
CSM Group names recipient of the CSM Architect Fellowship Grant
With the money from the grant, Harlow has chosen to use it entirely for the Chapter of American Institute of Architecture Student’s Freedom by Design Program at Andrews University.
| Dec 9, 2012
AIA: Laboratory design, building for breakthrough science
To earn 1.0 AIA/CES learning units, study the article carefully and take the exam.