Many modern buildings use glass curtain walls, large glass and floor-to-ceiling glass doors (balconies), which not only improve the room landscape, but also increase the solar radiation heat introduced into the room and increase the electricity consumption of room air conditioning. Air conditioning is the first killer of building energy consumption, accounting for 20% to 50% of building energy consumption.
In order to solve the above problems, the United States has developed a solar thermal insulation film, which has the functions of heat insulation, energy saving, ultraviolet protection, beauty and comfort, safety and explosion protection, and effectively and conveniently solves many problems caused by glass, just like the car film will stick the glass together when the car collides.
The film pasted on the surface of automobile glass, commonly known as automobile film and explosion-proof film, was originally called solar film, so as the name implies, automobile film is used to deal with the scorching sun and ultraviolet rays in summer. Explosion-proof membrane has explosion-proof function besides heat insulation and light isolation. High-quality explosion-proof film uses special polyester film as the base material, and the film itself has strong toughness and is equipped with special pressure-sensitive adhesive. When an accident occurs, the broken glass will be stuck by the car film and will not splash and hurt people. Automobile explosion-proof membrane also has the function of one-way perspective and reducing glare. The birth of the solar film completely changed our naked life in the sun, but the heat insulation principle of the solar film did not come from the special project research in the laboratory. On the contrary, it came from the accidental discovery of the great inventor Thomas Alva Edison, who is known as the "king of invention in the world". 1888, after Edison invented the phonograph, he turned his attention to the research and development of movies. In the experiment, he took a series of photos and projected them on the curtains in rapid succession to create the illusion of movement, and the carrier of these photos is what we all know as "film". At this time, he found a very interesting phenomenon, that is, the film that was also irradiated by the strong light and heat of the electric lamp. The darker the color, the more it can block and absorb the heat emitted by the electric lamp, so Edison wrote this discovery in his work notes. It was this accidental discovery that laid the theoretical foundation for the early solar films.
In modern solar film production technology, aluminum, gold, copper, silver and other metals are often made into multi-layer dense and highly insulated metal films by vacuum spraying or magnetron sputtering technology. In general, shell electrons (free electrons) in metallic materials are not bound by nuclei. When the light wave irradiates, the electric field of the light wave makes the free electrons absorb the energy of the light, produce oscillation with the same frequency as the light, and then release the light with the same frequency as the original light, which is called light reflection. The higher the conductivity of metal, the shallower the penetration depth and the higher the reflectivity. These metal layers will selectively reflect all kinds of heat energy in the sun, including infrared, ultraviolet and visible light heat energy, and then the color on the film will absorb the solar heat radiation and release it to the outside for the second time, and take away part of the heat with the outdoor airflow, thus effectively playing the role of heat insulation.
The metal reflective materials of riot film mostly use highly conductive materials such as gold, silver, aluminum and copper. The reflectivity of several metal reflective films at different wavelengths is as follows:
Metal species 800 nm reflectivity% 650 nm reflectivity% 500 nm reflectivity%
Aluminium 86.7 90.5 9 1.8
Silver 9.2 98.8 97.9
Gold Gold 98.0 95.5 47.7
Copper 98. 1 96.6 60.0
Ultraviolet band: The wavelength is between 280-380nm, which has the characteristics of strong penetration, and can deposit melanin on human skin and deepen the color. Excessive ultraviolet radiation can lead to skin cancer, which can lead to the fading of carpets, curtains, fabrics and furniture paints.
Visible spectral band: the wavelength is between 380 and 780 nm, and it is characterized by a unique spectrum visible to the naked eye. The visible spectrum band can be further divided into different colors (red, orange, yellow, green, indigo and purple), which has no direct harm to human body.
Infrared spectral band: The wavelength is between 780 and 2500 nm (nanometer), which is characterized by that we can directly feel the "invisible" heat of sunlight, which contains the most energy, so the heat is also high.
Some people think that the calculation method of the total thermal insulation rate of solar energy, that is, the thermal insulation rate, is as follows:
Thermal insulation = 53% infrared x-blocking rate +3% ultraviolet x-blocking rate +44% visible x-blocking rate.
But this is actually unscientific. According to GB/T2680 "Method for Measuring the Performance of Window Glass in Building Glass Optical Grade", the total solar energy transmittance is the sum of the direct sunlight transmittance and the secondary transmittance to the indoor side. In the calculation of total solar energy transmittance, the weights used in each band from 300nm to 2500nm are different, so it is not appropriate to simply press the ratio of 3%, 53% and 44%.
Only by understanding this standard can we deeply understand the real thermal insulation rate of solar films.