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
Architects | Mar 9, 2017
Watch Frank Lloyd Wright and Buckminster Fuller discuss architecture in animated video shorts
Given more time, Wright wanted to rebuild the country and change the nation.
Architects | Mar 6, 2017
Demolished Frank Lloyd Wright buildings get new life with photorealistic renderings
Architect David Romero recreated the Larkin Administration Building and the Rose Pauson House with detailed, fully colored renderings.
Building Team | Mar 6, 2017
AEC firms: Your website is one of the most important things you'll build
Don’t believe it? You’d better take a look at the research.
Architects | Mar 3, 2017
Hoffmann Architects’ Leadership Elected President of Three Industry Organizations
Maureen Dobbins, Lawrence Keenan, and Arthur Sanders to lead chapters of BOMA, AIA, and ICRI.
Office Buildings | Mar 2, 2017
White paper from Perkins Eastman and Three H examines how design can inform employee productivity and wellbeing
This paper is the first in a planned three-part series of studies on the evolution of diverse office environments and how the contemporary activity-based workplace (ABW) can be uniquely tailored to support a range of employee personalities, tasks and work modes.
Building Team | Mar 1, 2017
Intuitive wayfinding: An alternate approach to signage
Intuitive wayfinding is much like navigating via waypoints—moving from point to point to point.
Architects | Mar 1, 2017
Rafael Aranda, Carme Pigem and Ramon Vilalta receive the 2017 Pritzker Architecture Prize
2017 marks the first time that three architects together are honored with the prize.
Architects | Feb 27, 2017
AIA selects four individuals to receive the 2017 Associates Award
The AIA Associates Award is given to individual Associate AIA members to recognize outstanding leaders and creative thinkers for significant contributions to their communities and the architecture profession.
Architects | Feb 24, 2017
14 architects selected to receive the 2017 Young Architects Award
Young Architects are defined as professionals who have been licensed 10 years or fewer regardless of their age.
Architects | Feb 20, 2017
Take an architecture class taught by Frank Gehry
The starchitect will be teaching a course for MasterClass, an online education platform.