Smart windows can control the amount of heat entering the room
DATE:2024-07-08 15:18:10
Read:
SHARE:
On May 14, 2024, scientists in China published an article on the development of smart energy-saving windows in the journal Nature Sustainability, announcing the development of electrochromic windows that can effectively reduce building energy consumption.
Principle of Smart Windows
According to the different electromagnetic radiation spectrum, sunlight can be divided into visible light, ultraviolet light, infrared light and other wavelength ranges of radiation. In daily life, visible light is the part that can be perceived by the human eye and can be used for indoor lighting. Nearly half of the energy in solar radiation lies in the infrared range, and the infrared portion can be used to heat objects.
In this study, scientists have developed an electrochromic window that can effectively reduce energy consumption in buildings. The window can automatically adjust its transmission and reflection characteristics for visible, near-infrared and mid-infrared light according to environmental changes such as indoor and outdoor temperatures or solar radiation - in other words, the window intelligently adjusts its own transmittance and reflectance, thereby controlling the amount of light and heat that enters the room, and ultimately improving the building's energy efficiency.
To avoid heat exchange between the indoor and outdoor environments, the researchers designed the window with a low-emissivity ITO/polyethylene (PE) substrate on the indoor side, which reflects most of the external heat radiation and reduces its impact on the indoor environment. At the same time, the outside of the room is a high emissivity quartz substrate, which can efficiently emit and absorb radiation, and therefore can effectively emit indoor thermal radiation to the outside environment, thus eliminating the need for external equipment such as air conditioners to lower the temperature in the room.
Meanwhile, the interior of the window contains lithium ion (Li⁺) and vanadium oxide/tungsten oxide (VO2/WO3) materials. Vanadium oxide and tungsten oxide act as transition metal oxides, and they are able to undergo reversible redox reactions in the presence of an electric field. By applying different applied voltages, Li⁺ can diffuse into the VO₂ and WO₃ layers, respectively, and combine to form different chemicals.
Li⁺ that enters the VO₂ layer can undergo a chemical reaction to form the tetragonal phase LixVO2, which has the characteristics of a metallic phase with a rapidly increasing refractive index, leading to a drastic change in the near-infrared light transmittance. In contrast, Li⁺ enters the WO₃ layer to form LiyWO3, which exhibits absorption of visible and infrared portions due to the reduction of tungsten ions, leading to a rapid decrease in transmittance. Therefore, the combined use of these two materials enables complex and diverse color change effects.
During the cold winter months, the cold outside temperatures activate the bright heated state of the material - in which the windows become more transparent - to facilitate the entry of near-infrared and visible light. Conversely, in the hot summer months, the bright-cooled and dark states of the material are activated, where bright-cooled means that the window also remains transparent in this state, but serves primarily to allow visible light to enter while reducing the entry of near-infrared light (heat), and the dark state means that the window becomes opaque or semi-transparent in this state to minimize the entry of both visible and near-infrared light.
As a result, such windows can save significant amounts of energy in heating and cooling, making them a sustainable option for windows in a variety of climates around the globe. The researchers conducted experiments outdoors using the new smart windows developed. The results show that the windows with the new electrochromic structure can achieve continuous cooling throughout the day with a maximum temperature drop of up to 14°C compared to conventional windows.
What other building materials are conducive to energy efficiency?
Since modern times, engineers have been using a wide range of insulation materials in buildings to keep them warm in winter and insulate them in summer, and they can actually reduce energy consumption. These materials include mineral wool, rock wool, glass wool, foam and porous polymers, expanded perlite and its products, calcium silicate insulation products, and various composite thermal insulation materials.
In addition, engineers have been using a variety of new materials over the years, including:
1 Silicate composite insulation mortar
This is a new type of wall thermal insulation material, with selected seafoam and aluminum silicate fiber as the main raw materials, compounded in depth by a variety of processes. Its distinctive features are good thermal insulation performance, easy construction (direct coating), and solved the problem of cracking of the cover layer at the plate splicing.
2 Cement polystyrene board
Made of polystyrene foam scraps or waste polystyrene foam, plus cement, water, foaming agent and foam stabilizer and other materials, mixing, molding, maintenance and become. It has the advantages of light weight, small thermal conductivity, good heat preservation and insulation, certain strength and toughness, water resistance, flame retardant, convenient construction, firm adhesion, easy plastering and low price.
3 "Chameleon" building materials
Scientists have designed an intelligent "chameleon" building materials that can freely change temperature. This material contains a solid-liquid internal two conformations can be freely converted between the layer, respectively, can retain infrared energy to make the temperature rise of solid copper and infrared emission to make the temperature drop of the electrolyte aqueous solution. Therefore, when the external temperature changes, chemical changes can occur within the material, thus changing the emissivity of the material for infrared thermal radiation to realize the regulation of temperature, which can greatly save the energy consumption of heating.
Back
Principle of Smart Windows
According to the different electromagnetic radiation spectrum, sunlight can be divided into visible light, ultraviolet light, infrared light and other wavelength ranges of radiation. In daily life, visible light is the part that can be perceived by the human eye and can be used for indoor lighting. Nearly half of the energy in solar radiation lies in the infrared range, and the infrared portion can be used to heat objects.
In this study, scientists have developed an electrochromic window that can effectively reduce energy consumption in buildings. The window can automatically adjust its transmission and reflection characteristics for visible, near-infrared and mid-infrared light according to environmental changes such as indoor and outdoor temperatures or solar radiation - in other words, the window intelligently adjusts its own transmittance and reflectance, thereby controlling the amount of light and heat that enters the room, and ultimately improving the building's energy efficiency.
To avoid heat exchange between the indoor and outdoor environments, the researchers designed the window with a low-emissivity ITO/polyethylene (PE) substrate on the indoor side, which reflects most of the external heat radiation and reduces its impact on the indoor environment. At the same time, the outside of the room is a high emissivity quartz substrate, which can efficiently emit and absorb radiation, and therefore can effectively emit indoor thermal radiation to the outside environment, thus eliminating the need for external equipment such as air conditioners to lower the temperature in the room.
Meanwhile, the interior of the window contains lithium ion (Li⁺) and vanadium oxide/tungsten oxide (VO2/WO3) materials. Vanadium oxide and tungsten oxide act as transition metal oxides, and they are able to undergo reversible redox reactions in the presence of an electric field. By applying different applied voltages, Li⁺ can diffuse into the VO₂ and WO₃ layers, respectively, and combine to form different chemicals.
Li⁺ that enters the VO₂ layer can undergo a chemical reaction to form the tetragonal phase LixVO2, which has the characteristics of a metallic phase with a rapidly increasing refractive index, leading to a drastic change in the near-infrared light transmittance. In contrast, Li⁺ enters the WO₃ layer to form LiyWO3, which exhibits absorption of visible and infrared portions due to the reduction of tungsten ions, leading to a rapid decrease in transmittance. Therefore, the combined use of these two materials enables complex and diverse color change effects.
During the cold winter months, the cold outside temperatures activate the bright heated state of the material - in which the windows become more transparent - to facilitate the entry of near-infrared and visible light. Conversely, in the hot summer months, the bright-cooled and dark states of the material are activated, where bright-cooled means that the window also remains transparent in this state, but serves primarily to allow visible light to enter while reducing the entry of near-infrared light (heat), and the dark state means that the window becomes opaque or semi-transparent in this state to minimize the entry of both visible and near-infrared light.
As a result, such windows can save significant amounts of energy in heating and cooling, making them a sustainable option for windows in a variety of climates around the globe. The researchers conducted experiments outdoors using the new smart windows developed. The results show that the windows with the new electrochromic structure can achieve continuous cooling throughout the day with a maximum temperature drop of up to 14°C compared to conventional windows.
What other building materials are conducive to energy efficiency?
Since modern times, engineers have been using a wide range of insulation materials in buildings to keep them warm in winter and insulate them in summer, and they can actually reduce energy consumption. These materials include mineral wool, rock wool, glass wool, foam and porous polymers, expanded perlite and its products, calcium silicate insulation products, and various composite thermal insulation materials.
In addition, engineers have been using a variety of new materials over the years, including:
1 Silicate composite insulation mortar
This is a new type of wall thermal insulation material, with selected seafoam and aluminum silicate fiber as the main raw materials, compounded in depth by a variety of processes. Its distinctive features are good thermal insulation performance, easy construction (direct coating), and solved the problem of cracking of the cover layer at the plate splicing.
2 Cement polystyrene board
Made of polystyrene foam scraps or waste polystyrene foam, plus cement, water, foaming agent and foam stabilizer and other materials, mixing, molding, maintenance and become. It has the advantages of light weight, small thermal conductivity, good heat preservation and insulation, certain strength and toughness, water resistance, flame retardant, convenient construction, firm adhesion, easy plastering and low price.
3 "Chameleon" building materials
Scientists have designed an intelligent "chameleon" building materials that can freely change temperature. This material contains a solid-liquid internal two conformations can be freely converted between the layer, respectively, can retain infrared energy to make the temperature rise of solid copper and infrared emission to make the temperature drop of the electrolyte aqueous solution. Therefore, when the external temperature changes, chemical changes can occur within the material, thus changing the emissivity of the material for infrared thermal radiation to realize the regulation of temperature, which can greatly save the energy consumption of heating.