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
| Aug 4, 2016
Top 110 Multifamily Architecture Firms
Perkins Eastman, CallisonRTKL, and Solomon Cordwell Buenz top Building Design+Construction’s annual ranking of the nation’s largest multifamily building sector architecture and A/E firms, as reported in the 2016 Giants 300 Report.
| Aug 3, 2016
GREEN BUILDING GIANTS: Sustainability leaders turn to wellness and technology to get an edge
AEC leaders in green building are stepping up to a higher level of innovation and to be a green leader today, you have to dig deeper into data.
| Aug 2, 2016
Top 130 Green Building Architecture Firms
Gensler, Stantec, and HOK top Building Design+Construction’s annual ranking of the nation’s largest green building sector architecture and A/E firms, as reported in the 2016 Giants 300 Report.
Architects | Aug 2, 2016
Bradley Lukanic named CannonDesign's CEO
In his new role, Lukanic takes helm of an experienced leadership team crafting and achieving optimal short- and long-term strategies and business outcomes
| Aug 1, 2016
K-12 SCHOOL GIANTS: In a new era of K-12 education, flexibility is crucial to design
Space flexibility is critical to classroom design. Spaces have to be adaptable, even allowing for drastic changes such as a doubling of classroom size.
| Jul 29, 2016
AIRPORT FACILITIES GIANTS: Airports binge on construction during busy year for travel
Terminal construction will grow by nearly $1 billion this year, and it will keep increasing. Airports are expanding and modernizing their facilities to keep passengers moving.
| Jul 29, 2016
Top 35 Airport Terminal Architecture and A/E Firms
Corgan, HOK, and Gensler top Building Design+Construction’s annual ranking of the nation’s largest airport terminal architecture and A/E firms, as reported in the 2016 Giants 300 Report.
Architects | Jul 28, 2016
Connecting the dots: Architecture and design in a changing world
What do Tesla, Airbnb and Amazon have in common? They’re all shifting the paradigm for quality of life and the built environment, as CallisonRTKL senior associate VP Jayson Lee explains.
| Jul 26, 2016
ENGINEERING GIANTS: Firms continue to push innovation
Trends include 3D printing, modular hospitals, and fluid dampers.
| Jul 26, 2016
Top 80 Architecture/Engineering firms
Stantec, HOK, and Callison RTKL once again top Building Design+Construction's 2016 ranking of the largest architecture/engineering firms in the United States.