Hydrogel glass, a new glass that can selectively block the sun’s heat without blocking its light, reducing energy consumption

After the summer that much of the world has suffered this year, many people are thinking of better ways to cool buildings. Chinese researchers have enhanced humble windows with hydrogel glass, a material that can selectively block the sun’s heat without blocking its light.

Normal glass is designed to let visible light through and illuminate the room, but its interactions with infrared light, which is felt as heat, are less desirable.

The glass lets in the near-infrared radiation of sunlight, but prevents mid-infrared light from leaving the room, causing the building to heat up. In summer, that sweltering heat leads people to turn on the air conditioning more often, which means more energy consumption.

To try to counteract this problem, scientists at Wuhan University have experimented with new window materials that interact with light differently. A hydrogel coating a few millimeters thick on the glass has been designed to reflect more of the near-infrared light from the outside and let more of the mid-infrared light from the inside escape, while remaining just as transparent to visible light.

The idea is that visible light photons can penetrate more than 1 m into water, while photons in the near-infrared part of the spectrum can only penetrate a few millimeters. Since hydrogels are mostly water, this makes them a useful and selective barrier.

In tests, the team found that the hydrogel emitted up to 96% of infrared light directly into space, as these wavelengths are not blocked by the atmosphere. This would help keep the interior of a building cooler, similar to other cooling systems. radiative cooling. Normal glass, meanwhile, emits around 84%.

It is important to note that hydrogel glass does not appear dimmer than regular glass; in fact, it lets in slightly more light. Depending on the thickness of the hydrogel layer, lets in up to 92.8% of the visible light in the roomcompared to 92.3% for normal glass.

The team tested the performance of hydrogel glass on 20 x 20 x 20 cm model houses, with thick, insulated walls and a large window. The sensors indicated that hydrogel glass windows reduced the interior temperature by up to 3.5 °C.

The team claims that this material could help reduce energy consumption for cooling, which would benefit both the environment and users’ pocketbooks. Also, hydrogels are common and cheap, so should be relatively easy to implementwhich could be an advantage over other more complex smart windows.


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