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 7, 2013
Progressive steel joist and metal decking design [AIA course]
This three-part course takes a building owner’s perspective on the range of cost and performance improvements that are possible when using a more design-analytical and collaborative approach to steel joist and metal decking construction.
Sponsored | | Oct 7, 2013
Bridging the digital divide between the BIM haves and have nots
There's no doubt that BIM is the future of design. But for many firms, finding a bridge to access rich model data and share it with those typically left on the sidelines can be the difference between winning a bid or not.
| Oct 7, 2013
How to streamline your operations
The average U.S. office worker generates two pounds of paper each day, according to the EPA. Ninety percent of that trash is made up of printed materials: marketing reports, project drafts, copy machine mistakes, and unwanted mail. Here are a few ways AEC firms can streamline their management processes.
| Oct 7, 2013
Reimagining the metal shipping container
With origins tracing back to the mid-1950s, the modern metal shipping container continues to serve as a secure, practical vessel for transporting valuable materials. However, these reusable steel boxes have recently garnered considerable attention from architects and constructors as attractive building materials.
| Oct 4, 2013
Sydney to get world's tallest 'living' façade
The One Central Park Tower development consists of two, 380-foot-tall towers covered in a series of living walls and vertical gardens that will extend the full height of the buildings.
| Oct 4, 2013
Nifty video shows planned development of La Sagrada Familia basilica
After 144 years, construction on Gaudi's iconic Barcelona edifice is picking up speed, with a projected end date of 2026.
| Oct 4, 2013
Mack Urban, AECOM acquire six acres for development in LA's South Park district
Mack Urban and AECOM Capital, the investment fund of AECOM Technology Corporation (NYSE: ACM), have acquired six acres of land in downtown Los Angeles’ South Park district located in the central business district (CBD).
| Oct 4, 2013
CRB opens Atlanta office
Georgia’s status as a burgeoning hub for the life sciences industry has fueled CRB’s decision to open an office in Atlanta to better serve its clients in the market. CRB is a leading provider of engineering, design and construction services for customers in the biotech, pharmaceutical and life sciences industries.
| Sep 27, 2013
NYC releases first year-to-year energy performance data on commercial properties
A new report provides information on energy performance of New York City's largest buildings (mostly commercial, multi-family residential). It provides an analysis of 2011 data from city-required energy “benchmarking”—or the tracking and comparison of energy performance—in more than 24,000 buildings that are over 50,000 square feet.
| Sep 27, 2013
ASHRAE/IES publish first standard focused on commissioning process
ANSI/ASHRAE/IES Standard 202, Commissioning Process for Buildings and Systems, identifies the minimum acceptable commissioning process for buildings and systems as described in ASHRAE’s Guideline 0-2005, The Commissioning Process. Standard 202 is ASHRAE’s first standard focused on the commissioning process.