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
Multifamily Housing | Sep 12, 2019
Meet the masters of offsite construction
Prescient combines 5D software, clever engineering, and advanced robotics to create prefabricated assemblies for apartment buildings and student housing.
Cultural Facilities | Sep 11, 2019
The Kennedy Center expands for the first time since its 1971 debut
The REACH, with three pavilions on a generous lawn, adds openness and light to this performance space.
Architects | Sep 11, 2019
Buoyed by construction activity, architect compensation continues to see healthy gains
The latest AIA report breaks down its survey data by 44 positions and 28 metros.
Multifamily Housing | Sep 10, 2019
Carbon-neutral apartment building sets the pace for scalable affordable housing
Project Open has no carbon footprint, but the six-story, solar-powered building is already leaving its imprint on Salt Lake City’s multifamily landscape.
Giants 400 | Sep 9, 2019
Top 70 Industrial Sector Architecture Firms for 2019
AECOM, Stantec, Ware Malcomb, FSB, and Macgregor Associates top the rankings of the nation's largest industrial sector architecture and architecture engineering (AE) firms, as reported in Building Design+Construction's 2019 Giants 300 Report.
Giants 400 | Sep 9, 2019
2019 Industrial Sector Giants Report: Managing last mile delivery
This and more industrial building sector trends from Building Design+Construction's 2019 Giants 300 Report.
Codes and Standards | Sep 9, 2019
Free app calculates maximum allowable heights and areas for buildings
A free app that calculates the maximum allowable heights and areas for buildings of various occupancy classifications and types of construction has been released.
Retail Centers | Sep 6, 2019
Another well-known retailer files for bankruptcy: Here's the solution to more empty anchor stores
Where can you find the future of retail? At the intersection of experience and instant gratification.
Giants 400 | Sep 5, 2019
Top 110 Hotel Sector Architecture Firms for 2019
Gensler, WATG, HKS, HBG Design, and Steelman Partners top the rankings of the nation's largest hotel sector architecture and architecture engineering (AE) firms, as reported in Building Design+Construction's 2019 Giants 300 Report.
Architects | Sep 5, 2019
AIA launches landmark initiative to drive climate action
AIA Board of Directors approves member-led resolution to rally architects in mitigating and adapting the built environment.