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
| Apr 10, 2014
Collegiate sports becoming greener: Survey
A survey conducted from May through June 2013 by the University of Arizona Office of Sustainability and published by the Natural Resources Defense Council (NRDC)* finds that more collegiate athletic teams are adopting green and sustainable practices in operation of their sports facilities.
| Apr 10, 2014
Submit Your Project for a Bluebeam eXtreme Award!
Bluebeam is holding the second annual Bluebeam eXtreme Awards at the 2014 Bluebeam eXtreme Conference in Hollywood, Calf.
| Apr 9, 2014
How patient-centered medical homes can help healthcare providers and patients
Beyond reducing the number of uninsured Americans, the Affordable Care Act is driving new types of healthcare facilities, especially patient-centered medical homes.
| Apr 9, 2014
Colossal aquarium in China sets five Guinness World Records
With its seven salt and fresh water aquariums, totaling 12.87 million gallons, the Chimelong Ocean Kingdom theme park is considered the world’s largest aquarium.
| Apr 9, 2014
Gregory Hodkinson appointed head of Arup Group
Hodkinson has spent his professional career at Arup and brings more than 40 years' experience in large-scale projects to the new role, including several in the US and Canada.
| Apr 9, 2014
5 important trends shaping today’s hotel construction market
AEC firms, developers, and investors worldwide are bullish on hotels. Our hospitality Giants share what’s new in this fast-morphing sector.
| Apr 9, 2014
Steel decks: 11 tips for their proper use | BD+C
Building Teams have been using steel decks with proven success for 75 years. Building Design+Construction consulted with technical experts from the Steel Deck Institute and the deck manufacturing industry for their advice on how best to use steel decking.
| Apr 8, 2014
Gehry, Foster unveil plans for Battersea Power Station redevelopment [slideshow]
Phase 3 of the massive redevelopment of the London landmark will include more than 1,300 residential units, a 160-room hotel, and 350,000 sf of retail space.
| Apr 8, 2014
Fire resistive curtain wall helps The Kensington meet property line requirements
The majority of fire rated glazing applications occur inside a building to allow occupants to exit the building safely or provide an area of refuge during a fire. But what happens when the threat of fire comes from the outside? This was the case for The Kensington, a mixed-use residential building in Boston.
| Apr 8, 2014
First look: Zaha Hadid reveals design for dreamy sculptural hotel
Hadid's design, which will become the fifth hotel tower in the City of Dreams entertainment hub in Macau, features a latticed exoskeleton enveloping the building's exterior.