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This summer, new horizons have sprung up all over the country. In the high temperature of more than 40 degrees, the room facing south dare not even open the curtains during the day, otherwise there is only one word, hot!

In fact, glass windows can be said to be the least energy-efficient components in buildings. Admittedly, compared with the ancient paper windows, glass windows not only keep out the cold and the wind, but also ensure the adequate lighting of natural light on the interior, which is really a great invention. But at the same time, the glass has turned the interior into a "greenhouse" regardless of winter and summer, making your French window balcony a sauna. At times like this, I really want to jump into the swimming pool and take a dip.

Why is the glass room so hot while the swimming pool is so cool? In addition to the high specific heat capacity of water, the temperature itself is low, but also because the optical properties of water and glass are different. For glass, in addition to the visible light that provides lighting, near-infrared light is also transmitted through the glass, heating the room. At the same time, the high reflection of the glass in the mid-infrared band limits the heat dissipation of the building. This "Greenhouse Effect" increases the energy consumption of cooling, while for water, the transmittance of near-infrared light is much more.

The electromagnetic radiation spectrum. In visible light, from purple light to red light, the wavelength becomes longer and the energy becomes lower; the longer wavelength than red light is infrared light, which is divided into near, medium and far infrared according to the wavelength from short to long. In the past few decades, people have been committed to manipulating the optical properties of windows to save energy consumption of buildings. For example, add a visible transparent coating with high emissivity (emission) in the medium infrared region to ordinary glass, but this can not stop the heating of the room by near-infrared light; another example is Low-E glass, which can reflect near-infrared light to reduce indoor heat, but the low emissivity of medium infrared light will cause heat accumulation, and the low transmittance of visible light increases the demand for indoor lighting. Is there a kind of glass that can have both high near-infrared light blocking rate and higher mid-infrared thermal emissivity while maintaining the visible light transmittance of the glass and ensuring indoor lighting?

Recently, a team of Liu Kang researchers at Wuhan University proposed a new type of hydrogel glass composed of a layer of hydrogel and a layer of ordinary glass, the results of which were published in the journal Frontiers of Optoelectronics. Compared with traditional glass, this kind of hydrogel glass has higher visible light transmittance, stronger near-infrared light barrier and higher mid-infrared thermal emissivity, which can enhance indoor lighting and reduce indoor temperature.

Screenshot of web page | Ref. [1] during the preparation of hydrogel glass, polyacrylamide (PAAm) hydrogel precursor solution is polymerized directly on the glass surface, and the double-layer adhesive structure shown in the lower right corner of the following figure is obtained. One layer is ordinary glass and the other is hydrogel.

Comparison of optical properties between ordinary glass and hydrogel glass. Reference [1] the hydrogel layer is composed of a small amount of cross-linked polymer and a large amount of liquid water, so it has optical properties similar to that of water. it allows visible light to pass through and block near-infrared light. In addition, the transmittance of the hydrogel can be controlled by its thickness to obtain the ideal transmission spectrum.

In order to test the photomodulation ability of hydrogel glass, the research team placed the hydrogel layer on the silicon solar cell encapsulated with commercial glass and found that the solar cell with hydrogel glass has higher photocurrent density and efficiency than the cell encapsulated with ordinary glass. In addition, the hydrogel layer enhances the thermal emissivity of the wavelength in the atmospheric infrared transparent window, which may reduce the temperature of the solar cell in operating mode.

Subsequently, the research team designed a cabin model with a length, width and height of 20 cm, installed hydrogel glass and ordinary glass, and carried out outdoor experiments. The results show that in sunny days, the indoor illuminance of the house using hydrogel glass is slightly higher than that of the house using ordinary glass, and the indoor temperature is always lower than that of the house using ordinary glass.

Therefore, this new type of hydrogel glass window can not only reduce the power consumption of lighting, but also reduce the energy consumption of refrigeration equipment. After simulating and calculating eight representative cities under different climatic conditions, the research team pointed out that compared with ordinary glass, hydrogel glass can save 2.37 MJ / m2 of building cooling and lighting energy per year, which is suitable for different cities all over the world.

reference

[1] Fu, J., Feng, C., Liao, Y., Mao, M., Liu, H., Liu, K. Broadband light management in hydrogel glass for energy efficient windows. Front. Optoelectron. 15,33 (2022).

[2] https://www.eurekalert.org/news-releases/962335

Research team

Communication author Liu Kang: research fellow, School of Power and Machinery, Wuhan University; Liu Huidong: specially appointed Associate Research fellow, School of Power and Machinery, Wuhan University

(co) first author Fu Jia: school of Power and Machinery, Wuhan University; Feng Chunzao: school of Power and Machinery, Wuhan University

Paper information

Publish periodical Frontiers of Optoelectronics

Released on August 5, 2022

Paper title Broadband light management in hydrogel glass for energy efficient windows

(DOI: https://doi.org/10.1007/s12200-022-00033-4)

This article comes from the official account of Wechat: I am a scientist iScientist (ID:IamaScientist), compiled by Bamboo, edited by Jin Xiaoming, typesetting by Yin Ningliu

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