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
| Jul 25, 2016
Top 35 Engineering/Architecture Firms
AECOM, Jacobs, and Thornton Tomasetti head Building Design+Construction's 2016 ranking of the largest engineering/architecture firms in the United States.
| Jul 25, 2016
Top 100 Architecture Firms
Gensler surpasses $1.1 billion in revenue, topping Building Design+Construction’s annual ranking of the nation’s largest architecture firms, as reported in the 2016 Giants 300 Report.
Healthcare Facilities | Jul 25, 2016
AIA selects seven winners of healthcare building design award
The National Healthcare Design Awards recognizes functional hospital projects that solve aesthetic, civic, urban, and social concerns. Recipients were selected in three categories this year.
Industrial Facilities | Jul 25, 2016
Snøhetta, Bjarke Ingels among four finalists for S.Pellegrino bottling plant design
A committee will evaluate proposals in September.
Architects | Jul 22, 2016
5 creative approaches to finish standards
With the right mindset, standards can produce great design for healthcare facilities, as VOA's Candace Small explores.
Retail Centers | Jul 21, 2016
MVRDV designs Seoul entertainment district with gold entrance and curtain façade
The 9,800-sm complex will have retail and nightclub space. A plaza separates the two concrete buildings.
Healthcare Facilities | Jul 20, 2016
Process mapping simplifies healthcare design
Charting procedures and highlighting improvement opportunities can lead to developing effective design strategy simulations. GS&P’s Ray Wong writes that process mapping adds value to a project and bolsters team and stakeholder collaboration.
Architects | Jul 20, 2016
AIA: Architecture Billings Index remains on solid footing
The June ABI score was down from May, but the figure was positive for the fifth consecutive month.
| Jul 19, 2016
2016 GIANTS 300 REPORT: Ranking the nation's largest architecture, engineering, and construction firms
Now in its 40th year, BD+C’s annual Giants 300 report ranks AEC firms by discipline and across more than 20 building sectors and specialty services.
Architects | Jul 18, 2016
17 buildings designed by Le Corbusier added to UNESCO World Heritage List
The sites are spread across seven counties and were built over the course of 50 years. Le Corbusier, an architect, designer, and urban planner, was a founder of modern architecture.