Efficiency

Energy Star Most Efficient Criteria Released

The U.S. Environmental Protection Agency (EPA) recently released the proposed recognition criteria for 2019’s Energy Star Most Efficient windows.

As of July 2018, 419 window product lines are recognized as Most Efficient from more than 40 product brand owners, according to the EPA.

The agency says only windows for residential buildings are eligible for Most Efficient recognition. Commercial windows, doors, skylights and tubular daylighting devices are excluded.

According to the EPA, the window must be “Energy Star certified consistent with applicable Energy Star Partner Commitments and the requirements set forth in the latest version of the Energy Star Program Requirements and Eligibility Criteria for Windows.”

Additionally, products must be independently certified to meet the North American Fenestration Standard/Specification (NAFS) with a Performance Grade of 15 or higher. They must also have a U-factor of 0.20 or lower in all climate zones, plus a solar heat gain coefficient (SHGC) of 0.20 or higher in the Northern climate zone; a SHGC of 0.40 or lower in the North-Central zone; and a SHGC of 0.25 or lower in the South-Central and Southern zones.

Technology

Material Could Help Windows Power Homes, Control Temperature

Researchers in China say they have created a window-compatible film that could double the energy efficiency of an average house-hold by combining coatings that block unneeded parts of sunlight with thin solar cells that turn windows into miniature electricity generators.

Their work appears in the journal Joule.

“Building-integrated photovoltaics are a great example of a market where silicon photovoltaics, despite their cheapness and performance, are not the most appropriate due to their dull appearance and heaviness,” says senior author Hin-Lap Yip, a professor of materials science and engineering at the South China University of Technology. “Instead, we can make organic photovoltaics into semi-trans-parent, lightweight and colorful films that are perfect for turning windows into electricity generators and heat insulators.”

To construct a prototype capable of simultaneously outputting electricity and preventing excessive heating, the researchers needed to balance harvesting light for electricity generation, blocking it for heat insulation, and transmitting it as a window normally would. They put together a device that let the visible portions of sunlight through, turned back the infrared light (a cause of heating), and converted the near-infrared region in between into an electric current.

Calculations suggest that in theory, installing windows outfitted with dual electricity-generating and heat-insulating properties could cut an average household’s reliance on external electric sources by more than 50 percent. Although that estimate assumes that every square inch of every window would be paneled with multifunctional solar cells, it only requires a slight uptick in power-conversion performance from the 6.5-percent figure realized by Yip, Huang and their colleagues.

“For this demonstration, we are not even using the best organic photovoltaics that are out there in this field,” says Yip. “Their efficiency is improving rapidly, and we expect to be able to continuously improve the performance of this unified solar-cell window film.”

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