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
Green | Aug 7, 2023
Rooftop photovoltaic panels credited with propelling solar energy output to record high
Solar provided a record-high 7.3% of U.S. electrical generation in May, “driven in large part by growth in ‘estimated’ small-scale (e.g., rooftop) solar PV whose output increased by 25.6% and accounted for nearly a third (31.9%) of total solar production,” according to a report by the U.S. Energy Information Administration.
Resiliency | Aug 7, 2023
Creative ways cities are seeking to beat urban heat gain
As temperatures in many areas hit record highs this summer, cities around the world are turning to creative solutions to cope with the heat. Here are several creative ways cities are seeking to beat urban heat gain.
Government Buildings | Aug 7, 2023
Nearly $1 billion earmarked for energy efficiency upgrades to federal buildings
The U.S. General Services Administration (GSA) recently announced plans to use $975 million in Inflation Reduction Act funding for energy efficiency and clean energy upgrades to federal buildings across the country. The investment will impact about 40 million sf, or about 20% of GSA’s federal buildings portfolio.
MFPRO+ New Projects | Aug 4, 2023
Nashville gets 'first-of-its-kind' residential tower
Global architecture firm Goettsch Partners announces the completion of Alcove, a new 356-unit residential tower in Nashville, Tenn., developed by Giarratana LLC.
Industrial Facilities | Aug 3, 2023
The state of battery manufacturing in the era of EV
One of the most significant changes seen in today’s battery plant is the full manufacturing process—from raw materials to the fully operational battery.
Government Buildings | Aug 2, 2023
A historic courthouse in Charlotte is updated and expanded by Robert A.M. Stern Architects
Robert A.M. Stern Architects’ design retains the original building’s look and presence.
Hotel Facilities | Aug 2, 2023
Top 5 markets for hotel construction
According to the United States Construction Pipeline Trend Report by Lodging Econometrics (LE) for Q2 2023, the five markets with the largest hotel construction pipelines are Dallas with a record-high 184 projects/21,501 rooms, Atlanta with 141 projects/17,993 rooms, Phoenix with 119 projects/16,107 rooms, Nashville with 116 projects/15,346 rooms, and Los Angeles with 112 projects/17,797 rooms.
Architects | Aug 1, 2023
Ware Malcomb announces hire of Jason Golub as Regional Director
In this role, Golub is responsible for the overall leadership and continued growth of the office.
Market Data | Aug 1, 2023
Nonresidential construction spending increases slightly in June
National nonresidential construction spending increased 0.1% in June, according to an Associated Builders and Contractors analysis of data published today by the U.S. Census Bureau. Spending is up 18% over the past 12 months. On a seasonally adjusted annualized basis, nonresidential spending totaled $1.07 trillion in June.
Healthcare Facilities | Aug 1, 2023
Top 10 healthcare design projects for 2023
The HKS-designed Allegheny Health Network Wexford (Pa.) Hospital and Flad Architects' Sarasota Memorial Hospital - Venice (Fla.) highlight 10 projects to win 2023 Healthcare Design Awards from the American Institute of Architects Academy of Architecture for Health.