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.
CLICK IMAGE TO ENLARGE
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
| Nov 15, 2013
Metal makes its mark on interior spaces
Beyond its long-standing role as a preferred material for a building’s structure and roof, metal is making its mark on interior spaces as well.
| Nov 14, 2013
Fan of Frank Lloyd Wright? Here's your chance to run his architecture school
The Frank Lloyd Wright School of Architecture has launched a search for a new director. Deadline for applications is January 6, 2014.
| Nov 13, 2013
Government work keeps green AEC firms busy
With the economy picking up, many stalled government contracts are reaching completion and earning their green credentials.
| Nov 13, 2013
First look: Renzo Piano's addition to Louis Kahn's Kimbell Art Museum [slideshow]
The $135 million, 101,130-sf colonnaded pavilion by the famed architect opens later this month.
| Nov 11, 2013
4 trends driving the recovering commercial construction sector
Jones Lang LaSalle research reveals a four-point “new look” for the post-recession construction industry.
| Nov 8, 2013
Oversized healthcare: How did we get here and how do we right-size?
Healthcare facilities, especially our nation's hospitals, have steadily become larger over the past couple of decades. The growth has occurred despite stabilization, and in some markets, a decline in inpatient utilization.
| Nov 8, 2013
Can Big Data help building owners slash op-ex budgets?
Real estate services giant Jones Lang LaSalle set out to answer these questions when it partnered with Pacific Controls to develop IntelliCommand, a 24/7 real-time remote monitoring and control service for its commercial real estate owner clients.
| Nov 8, 2013
S+T buildings embrace 'no excuses' approach to green labs
Some science-design experts once believed high levels of sustainability would be possible only for low-intensity labs in temperate zones. But recent projects prove otherwise.
| Nov 8, 2013
Net-zero bellwether demonstrates extreme green, multifamily style
The 10-unit zHome in Issaquah Highlands, Wash., is the nation’s first net-zero multifamily project, as certified this year by the International Living Future Institute.
| Nov 8, 2013
Walkable solar pavement debuts at George Washington University
George Washington University worked with supplier Onyx Solar to design and install 100 sf of walkable solar pavement at its Virginia Science and Technology Campus in Ashburn, Va.
