Speaking of building energy saving, people naturally think of doors and windows.
Because, the energy loss of ordinary single-layer glass windows accounts for more than half of the energy consumption of building insulation in winter or cooling in summer. Therefore, what kind of glass is used for doors and windows, or how to transform existing glass, is the top priority of the entire building energy conservation project.
At present, there are two types of single glass on the market that can play a role in thermal insulation: stained glass and coated glass.
Stained glass, as the name suggests, is colored glass, including brown, gold, green, blue, gray and other series. This type of glass has low light transmission. According to national standards, the minimum value of visible light transmission is allowed to be 18%-25%, so It can block part of the heat energy in the visible light of the sun.
Coated glass is divided into sunlight control coated glass and low emissivity coated glass. Because a layer of metal is coated on the glass surface, it has a certain control effect on the sunlight in the wavelength range of 0.35 microns-1.8 microns; that is, the coated glass can reduce the transmittance of sunlight in this wavelength range, so Can be insulated. The low-e coated glass has a higher reflectance to far infrared.
In addition to glass forums, there are also thermal insulation films and thermal insulation coatings that use a single piece of glass as a base material to be constructed on the glass surface. At present, there are many varieties of thermal insulation films, many brands, many places of production, and they are also widely used in automobiles. Since there is no national standard for thermal insulation film, various brands have various functions in the promotion of functions. Various terminology seems to be right and wrong, causing consumers to fall into the clouds.

In fact, the heat insulation film also reduces the transmission of sunlight to the glass by a metal object formed on the surface of the polyester plastic film to play a heat insulation effect.

Thermal insulation coating liquid is rare in the market, mainly because the coating liquid has certain requirements on the construction environment and construction means from liquid to film formation. Poor construction will have a certain impact on the aesthetics of the coating liquid after film formation, although its separation The thermal function is not reduced. Similar to the thermal insulation film, the thermal insulation coating liquid is also insulated by reducing the transmission of sunlight to the glass by the metal ions in the coating liquid.

In addition to the above single glass can be insulated, a reasonable combination of several pieces of glass can also be insulated, this is hollow glass. For ordinary insulating glass, the single glass itself cannot be insulated, but after the combination of two single layers or three double layers, the interlayer air is evacuated and the inert gas is injected, which also has a certain insulation effect. The insulating mechanism of insulating glass is to use the evacuated interlayer to reduce the secondary heat transfer from the outer glass to the room after absorbing heat, but its more obvious role is still sound insulation.
To assess the thermal insulation effect of glass, first of all, we should look at the physical indicators. Some popular thermal insulation terms and explanations on the market, such as infrared cut rate, infrared reflectance, heat blocking rate, thermal insulation rate is equal to infrared cut rate, etc., to pass on a plausible concept to people, thermal insulation is only infrared cut.
In fact, the heat we want to isolate is derived from solar radiation. The distribution of solar radiation energy with wavelength is called the solar radiation spectrum. The wavelength range of solar radiation is very wide, but most of its energy is concentrated between 0.17 and 4 microns. Among them, the visible light region accounts for 50%, and the infrared region accounts for 43%. , The ultraviolet region accounts for 7%. In the infrared region, most of them are concentrated below 1.8 microns, and only 3%-5% are distributed between 1.8-4 microns. Observations show that the solar radiation spectrum is not strictly a continuous spectrum. In addition to the different energy ratios carried by different wavelength bands, the energy ratio carried by wavelengths from short to long is very irregular. For example, in the infrared region below 1.8 microns, the energy carried by the different bands differ greatly. Therefore, if the average infrared transmittance is simply calculated, it is impossible to see how much solar thermal energy is blocked, and even how much infrared thermal energy is blocked cannot be reflected. Whether the glass can be insulated, it must be able to block visible light and infrared rays at the same time, the effect is obvious, after all, visible light accounts for the bulk of the solar thermal energy. To evaluate the physical index of the effect of thermal insulation glass, the index of our country is the shading coefficient, that is, the SC’s shading coefficient for external windows must be between 0.35 and 0.6 according to the requirements of [Energy Saving Design Standard for Public Buildings]. The lower the shading coefficient, the better the thermal insulation effect. When the shading coefficient of a single piece of glass with thermal insulation function is 0.6, if the direct reflection ratio of sunlight is about 6%, the direct transmission ratio of sunlight {0.35-1.8 microns} of glass is about 40%, that is, there is no In the case of calculating the secondary heat transfer, the glass only transmits about 40% of the solar thermal energy and blocks about 60% of the solar thermal energy.
In addition to the shading factor, the visible light transmittance of the glass should also be compared. Because, in building energy consumption, lighting energy consumption is 20-30%, when considering glass insulation and energy saving, it must also meet the lighting requirements as much as possible, otherwise, the visible light transmittance is too low will lead to insufficient natural lighting, even during the day Turning on the lights increases the energy consumption of lighting, and the heat release of the lighting causes indoor heat, which increases the cooling load of the air conditioner and increases the energy consumption of the air conditioner. When satisfying the above shading coefficient, the ideal choice is to increase the transmittance of visible light as much as possible. Like the example above, the lower the shading coefficient, the lower the visible light transmittance accordingly. When the shading coefficient of the single glass is 0.6, the visible light transmittance can be 45%, which is quite good; if the visible light transmittance can be increased to 50%-55%, then it proves that the insulating glass has a very high ratio of infrared thermal energy blocking, It can also transmit most of the visible light, and the heat insulation and light transmission functions are ideal. The national standard specifies the shading coefficient, but does not specify the visible light transmittance, which can be interpreted as giving a standard a lot of difficulty, a bit of heat and light transmission can not take into account the taste. The problem lies in this too. After all, solar thermal energy occupies a large portion of the visible light segment; but if the heat insulation effect is good, the shading coefficient reaches 0.35, and the visible light transmittance is only 15% or 10%, or even lower, which is lower than colored glass. , Which will make the glass lose its light transmission function.
Therefore, the visible light transmittance of the glass with heat insulation function should be considered together with its shading coefficient. If the shading coefficient is high, the visible light transmittance should be correspondingly high; if the shading coefficient is low, the visible light transmittance should also be low; but the minimum should not be low 18-25% standard for stained glass. Never have a high shading factor and a low visible light transmittance. Comparing these two indicators with several varieties of insulating glass, the conclusion is easy to come out. In the case of the same shading coefficient, the higher the visible light transmittance, the better the comprehensive function of its insulating glass. Among the thermal insulation glass listed above, in terms of thermal insulation effect, the colored glass is the worst, and the shading coefficient of the single glass cannot reach 0.6. The remaining coated glass, heat-insulated film glass, heat-insulated coated liquid glass, some of their respective models and varieties have a shading coefficient of less than 0.6, which is worth comparing.
Among these types of glass, the heat insulation film and heat insulation coating liquid can be applied on transparent glass, stained glass and coated glass, and the liquid can be applied after the film is applied. Regardless of any type of construction combination, the shading coefficient can be further reduced to improve the thermal insulation effect. These thermal insulation glasses also have their own weaknesses: if the light reflection ratio is too high, it is easy to cause light pollution; the wear resistance is poor; the dependence on the construction process is large, and improper construction will affect the service life and appearance of the finished product. These all depend on the user to choose according to the purpose and environment of use. Make full use of the heat insulation effect of heat insulation glass to eliminate some of their shortcomings. At this stage, it seems that processing into hollow glass can overcome some of the defects of the original heat insulation glass and comprehensively improve the function. Because insulating glass can overcome the weakness of poor wear resistance; but most importantly, as long as insulating glass is processed according to specifications, it can effectively reduce the secondary heat transfer from the outer glass to the room. The thermal insulation film glass and thermal insulation coating glass, which take up a large proportion of sunlight absorption, when they are made into double-layer or triple-layer insulating glass, the shading coefficient can be reduced by 0.1-0.15, while the visible light transmittance is only slightly reduced. That is, when the shading coefficient of some single-piece heat-insulating film glass or heat-insulating coating glass is 0.65-0.7, by processing into hollow glass, the shading coefficient of the entire glass window can be reduced to about 0.6, which is achieved Standard minimum requirements. However, the installation of insulating glass will increase the thickness of the wall, in addition to the cost of the window frame, it will also increase the load of the building. These must also be evaluated comprehensively.
The effect of heat insulation glass on energy saving is quite obvious, and the replacement or modification of building window glass is not complicated. In Guangzhou, a representative city with warm winters and hot summers, simulation calculations have been conducted. The window-to-wall ratio of the south facade of this public building is 0.42. When the window glass shading coefficient is 0.46, it saves 37.45% of electricity for air conditioning and cooling in summer. Faced with energy shortages and environmental pollution, how can we achieve the 65% building energy saving requirement in 2015, the whole society should make joint efforts to reduce the energy consumption of window glass.