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
| Mar 29, 2013
Shenzhen projects halted as Chinese officials find substandard concrete
Construction on multiple projects in Guangdong Province—including the 660-m Ping'an Finance Center—has been halted after inspectors in Shenzhen, China, have found at least 15 local plants producing concrete with unprocessed sea sand, which undermines building stabity.
| Mar 29, 2013
Pearce Brinkley Cease + Lee joins Clark Nexsen
Clark Nexsen, PC, headquartered in Norfolk, Va., has announced that the architecture firm Pearce Brinkley Cease + Lee (PBC+L) of Raleigh and Asheville, NC, has officially joined Clark Nexsen.
| Mar 29, 2013
Cuningham Group acquires NTD's healthcare practice, expands into key markets
The international design firm Cuningham Group Architecture, Inc. has announced that NTD Healthcare has the joined the company in a strategic expansion. A practice of NTD Architecture, NTD Healthcare joins Cuningham Group with three principals: Wayne Hunter, AIA, NCARB, ACHA and Phillip T. Soule, III, AIA, ACHA in San Diego, along with Maha Abou-Haidar, AIA in Phoenix.
| Mar 27, 2013
Small but mighty: Berkeley public library’s net-zero gem
The Building Team for Berkeley, Calif.’s new 9,500-sf West Branch library aims to achieve net-zero—and possibly net-positive—energy performance with the help of clever passive design techniques.
| Mar 27, 2013
RSMeans cost comparisons: college labs, classrooms, residence halls, student unions
Construction market analysts from RSMeans offer construction costs per square foot for four building types across 25 metro markets.
| Mar 26, 2013
Will Google Glass revolutionize the construction process?
An Australian architect is exploring the benefits of augmented reality in the design and construction process.
| Mar 24, 2013
World's tallest data center opens in New York
Sabey Data Center Properties last week celebrated the completion of the first phase of an adaptive reuse project that will transform the 32-story Verizon Building in Manhattan into a data center facility. When the project is completed, it will be the world's tallest data center.
| Mar 22, 2013
8 cool cultural projects in the works
A soaring opera center in Hong Kong and a multi-tower music center in Calgary are among the latest cultural projects.
| Mar 22, 2013
Earn $500 as a DOE proposal reviewer
The DOE'S Building Technologies Office this morning put out a call to the AEC industry for expert reviewers for its new energy-efficiency initiative for small commercial buildings, which make up more than 90% of the commercial building stock.