1. The introduction
With the accelerated implementation of the "carbon peak" goal in the entire building field, ultra-low energy consumption buildings and near-zero energy consumption buildings will achieve a huge breakthrough in the total implementation area in new and renovated projects. Building exterior windows are the weakest components of ultra-low energy consumption buildings and near-zero energy consumption buildings in energy conservation, and the building energy consumption lost through exterior windows accounts for more than 51%. To promote the application of high-energy-saving exterior windows in ultra-low energy consumption buildings and near-zero energy consumption buildings, the "Near-Zero Energy Consumption Building Technical Standard" stipulates that the summer solar heat gain coefficient (SHGC) of the exterior windows of public buildings in hot summer and cold winter areas is <0.15, and the summer solar heat gain coefficient index is significantly lower than the solar heat gain coefficient of 0.25~0.30 in the energy-saving design standard of ordinary buildings.
Built-in blind insulating glass is a new type of energy-saving glass product that installs blinds inside insulating glass. It has the advantages of thermal insulation, sunshade, and lighting, sound insulation and environmental protection, safety and reliability, dustproof, and privacy. It is currently used in ordinary energy-saving buildings, and there is little research on how to improve its application in near-zero energy-consumption buildings. The research on the thermal insulation performance of built-in blinds insulating glass is mostly focused on the position of blinds and the angle of blinds. At present, there is no research on the thermal insulation performance of built-in blinds insulating glass with different blind reflectivity and blind angles.
LIJIANG Glass uses WINDOW7 software to study the thermal performance of built-in blinds double-glass, triple-glass Low-E insulating glass, and built-in blinds Low-E vacuum insulating glass. The results show that the shading coefficient and solar heat gain coefficient of the product are closely related to the thermal performance of the glass on both sides of the blinds. When the thermal resistance of the inner glass of the blinds is large, its thermal insulation performance is best. LIJIANG Glass used simulated solar light sources to study the effects of different blind usage states on the energy-saving performance of built-in blind insulating glass products. The results showed that the usage state of built-in blind insulating glass has a great impact on its energy-saving performance. When the blinds are closed, they can block about 65% of the solar radiation heat. The energy-saving performance improvement ratio when the blinds are closed and when the blinds are folded is consistent with the heat transfer coefficient improvement ratio under the corresponding state. LIJIANG Glass also studied the key parameters affecting the thermal performance of built-in blind insulating glass. The results showed that the air layer thickness and blind angle are the key factors affecting the thermal performance of built-in blind insulating glass. The above research and analysis on the impact of built-in blinds sunshade insulating glass on thermal insulation performance did not involve the blinds' solar reflectivity, nor did it involve how to improve the thermal insulation performance of built-in blinds sunshade insulating glass to meet the relevant index requirements of near-zero energy buildings.
This paper first tests the solar reflectivity of different blinds, and then uses WINDOW7 software to simulate and analyze the thermal insulation performance of three-glass two-cavity built-in blinds insulating glass with different blinds solar reflectivity and blinds angles, summarizes the influence of blinds solar reflectivity and blinds angle on the thermal insulation performance of built-in blinds insulating glass, and conducts a feasibility analysis on the application of high reflectivity and high shielding built-in blinds insulating glass in near-zero energy buildings.
2. Solar reflectivity of different blind coatings
Ordinary white paint, silver paint, and heat-reflective paint with high solar reflectivity on the market are sprayed on the blinds to make three kinds of blind samples (see Figure 1), and Lambda950 UV, visible, and near-infrared spectrophotometers are used to test the solar reflectivity of these three blinds. The results show that the solar reflectivity of ordinary white paint, silver paint, and heat-reflective paint are 65.15%, 70.55%, and 87.13% respectively.
(a) Ordinary white paint
(b) Silver paint
(c) Heat reflective paint
Figure 1 Shutter samples sprayed with different paints
3. Calculation instructions
WINDOW7 is a series of software developed by the Lawrence Berkeley Laboratory in the United States, which can calculate the optical properties and heat transfer properties of glass and sunshade products. The software can simulate and calculate the solar heat gain coefficient, shading coefficient, and heat transfer coefficient of glass and sunshade products based on parameters such as the optical properties of glass and shutters, shutter width, shutter opening angle, blade spacing, and distance between blades and glass.
The boundary condition parameters for the calculation of solar heat gain coefficient in summer are set as follows: indoor air temperature Tin = 24℃, outdoor air temperature Tout = 32℃, solar radiation intensity Is = 783W/㎡, indoor average radiation temperature Trm, in=24℃, outdoor average radiation temperature Trm, out32℃, outdoor wind speed W = 2.75m/s, indoor convection heat transfer coefficient hc,in = 2.5W/(㎡·K), outdoor convection heat transfer coefficient hc.out = 15W/(㎡·K).
4. Research plan
4.1 Glass structure
To study the influence of different blinds' solar reflectivity and blinds angle on the solar heat gain coefficient of three-glass two-cavity built-in blinds insulating glass, electric built-in blinds insulating glass with blinds located in the outer hollow cavity and magnetically controlled built-in blinds insulating glass with blinds located in the inner hollow cavity are designed. The structure is shown in Figure 2. Among them, the electric built-in blinds insulating glass adopts electric control to lift and flip the blinds, and the magnetic control built-in blinds insulating glass adopts magnetic control to lift and flip the blinds.
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(a) Magnetic control three-glass
(b) Electric three-glass
Figure 2 Two structures of three-glass two-cavity built-in blinds insulating glass
4.2 Parameter setting
The air layer thickness of the blinds in the built-in blinds insulating glass is 25mm, and the blinds angles are set to 45. , 60. , 68. , 75. and 80. , respectively. According to the test results of the solar reflectivity of different blind coatings, the blind's solar reflectivity is set to 55%, 65%, 70%, 80%, and 87% respectively. Different blind angles and different blinds' solar reflectivity are selected to simulate the solar heat gain coefficient of the built-in blind insulating glass.
5. Results and analysis
5.1 Simulation analysis of thermal insulation performance of electric built-in blinds insulating glass
5.1.1 Simulation results of solar heat gain coefficient of electric built-in blinds insulating glass with different solar reflectivity
The blind angle has two states: 68° and 80°, and the blind solar reflectivity has five parameters: 55%, 65%, 70%, 80%, and 87%. The simulation results of the thermal insulation performance of electric built-in blinds insulating glass with different blind solar reflectivity are shown in Table 1.
As can be seen from Table 1, the higher the blind solar reflectivity, the lower the solar heat gain coefficient of the electric built-in blinds insulating glass; the larger the blind angle, the more the solar heat gain coefficient of the electric built-in blinds insulating glass is reduced. When the louver angle is 68°, the solar heat gain coefficient of the electric built-in louver insulating glass with a louver solar reflectivity of 87% is 10.1% lower than that of the louver solar reflectivity of 55%; when the louver angle is 80°, the solar heat gain coefficient of the electric built-in louver insulating glass with a louver solar reflectivity of 87% is 28.5% lower than that of the louver solar reflectivity of 55%, and the reduction is significant.
Table 1 Thermal insulation performance of electric built-in louver insulating glass with different louver solar reflectivity at louver angles of 60° and 80°
5.1.2 Solar heat gain coefficient of electric built-in louver insulating glass with different louver angles
The louver solar reflectivity has two parameters of 70% and 87%, and the louver angle has five states of 45., 60., 68., 75. and 80. The simulation results of the thermal insulation performance of electric built-in louver insulating glass with different louver angles are shown in Table 2.
Table 2 Thermal insulation performance of electric built-in blinds insulating glass with different blinds angles when the blinds solar reflectivity is 70% and 87%
It can be seen from Table 2 that the larger the blind angle, the lower the solar heat gain coefficient of the electric built-in blinds insulating glass; the higher the blind's solar reflectivity, the greater the influence of the blind angle on the solar heat gain coefficient of the electric built-in blinds insulating glass. When the blind's solar reflectivity is 70%, the electric built-in blinds insulating glass with a blinds angle of 80. is 59.44% lower than that with a blinds angle of 45.; when the blind's solar reflectivity is 87%, the electric built-in blinds insulating glass with a blinds angle of 80. is 66.97% lower than that with a blind angle of 45.
5.1.3 Analysis of simulation results of solar heat gain coefficient of electric built-in blinds and insulating glass
In electric built-in blinds and insulating glass, a large blind angle can increase the shading rate of the blinds, so that the heat of sunlight entering the room through the blinds and glass is reduced. The high blinds’ solar reflectivity can make most of the solar heat irradiated on the blinds reflected to the outside, and a small part is absorbed by the blinds. The solar heat absorbed by the blinds is much greater than the thermal resistance of the insulating glass inside the blinds. The heat absorbed by the blinds is finally only a small amount transferred to the room, which greatly reduces the solar heat gain coefficient of the electric built-in blinds and insulating glass.
4.1.4 Feasibility analysis of the application of electric built-in blinds and insulating glass in near-zero energy buildings
Through the simulation results of the solar heat gain coefficient of electric built-in blinds and insulating glass with different blinds’ solar reflectivity and different blinds’ angles, it can be seen that when the blinds’ angle is 75. ~80. When the solar heat gain coefficient of the electric built-in blind insulating glass with a blind solar reflectivity of 70% and 87% is less than 0.15, it meets the index requirements of the summer solar heat gain coefficient in GB/T 51350-2019. When developing electric built-in blinds insulating glass suitable for near-zero energy consumption buildings, silver paint blinds and heat reflective paint blinds can be selected, and high-shielding blinds can be used to achieve the solar heat gain coefficient of the electric built-in blinds insulating glass in line with the application requirements of near-zero energy consumption buildings.
4.2 Simulation analysis of thermal insulation performance of magnetically controlled built-in blinds insulating glass
4.2.1 Simulation results of solar heat gain coefficient of magnetically controlled built-in blinds insulating glass with different blind solar reflectivity
The blind angles are 68. , 80. The blind solar reflectivity is 55%, 65%, 70%, 80%, and 87%. The simulation results of the thermal insulation performance of magnetically controlled built-in blind insulating glass with different blind solar reflectivity are shown in Table 3.
Table 3 Thermal insulation performance of magnetically controlled built-in blinds hollow glass with different solar reflectivity at 68° and 80° blind angles
It can be seen from Table 3 that the higher the blind solar reflectivity, the lower the solar heat gain coefficient of the magnetically controlled built-in blinds hollow glass; the larger the blind angle, the more the solar heat gain coefficient of the magnetically controlled built-in blinds hollow glass decreases. When the blind angle is 68., the solar heat gain coefficient of the magnetically controlled built-in blinds hollow glass with a blind solar reflectivity of 87% is 18.6% lower than that of the blind solar reflectivity of 55%; when the blind angle is 80., the solar heat gain coefficient of the magnetically controlled built-in blinds hollow glass with a blind solar reflectivity of 87% is 28.2% lower than that of the blind solar reflectivity of 55%, with a significant decrease.
4.2.2 Simulation results of solar heat gain coefficient of magnetically controlled built-in blinds hollow glass with different blind angles
There are two parameters of blind solar reflectivity 70% and 87%, and the blind angle is 45. The simulation results of the thermal insulation performance of magnetically connected laminated blinds insulating glass with the same blind angles of 60°, 68°, 75°, and 80° are shown in Table 4.
Table 4 Thermal insulation performance of magnetically controlled built-in blinds insulating glass with different blind angles when the blind solar reflectivity is 70% and 87%
It can be seen from Table 4 that the larger the blind angle, the lower the solar heat gain coefficient of the magnetically controlled built-in blinds insulating glass; the higher the blind solar reflectivity, the greater the influence of the blind angle on the solar heat gain coefficient of the magnetically controlled built-in blinds insulating glass. When the blind solar reflectivity is 70%, the solar heat gain coefficient of the magnetically controlled built-in blinds insulating glass with a blind angle of 80° is 40.48% lower than that of the blind angle of 45°; when the blind reflectivity is 87%, the solar heat gain coefficient of the magnetically controlled built-in blinds insulating glass with a blind angle of 80° is 48.99% lower than that of the blind angle of 45°.
4.2.3 Analysis of simulation results of solar heat gain coefficient of magnetically controlled built-in blinds insulating glass
In magnetically controlled built-in blinds insulating glass, the blinds are swung to increase the shielding rate of the blinds, so that the heat of sunlight entering the room through the blinds and glass is reduced. The high blinds' solar reflectivity can also make most of the light and heat irradiated on the blinds reflected to the outside, and a small part is absorbed by the blinds. However, since the thermal resistance of the insulating glass outside the blinds is much greater than the thermal resistance of the single-layer glass inside, most of the absorbed heat will eventually be transferred to the room, so that the solar heat gain coefficient of the magnetically controlled built-in blinds insulating glass can be reduced, but the reduction is significantly lower than that of the electric built-in blinds insulating glass.
4.2.4 Feasibility analysis of the application of magnetically controlled built-in blinds insulating glass in near-zero energy buildings
Through the simulation results of the solar heat gain coefficient of magnetically controlled built-in blinds insulating glass with different blinds' solar reflectivity and different blinds angles, it can be seen that the blind's solar reflectivity is 87% and the blinds angle is 80. The solar heat gain coefficient of the magnetically controlled built-in blind insulating glass is the lowest, which is 0.203 (0.15), which does not meet the index requirements of the summer solar heat gain coefficient in GB/T 51350-2019.
5 Conclusions
(1) The solar reflectivity of the blinds and the blind angle are the key factors affecting the thermal insulation performance of the built-in blinds insulating glass. The higher the solar reflectivity of the blinds, the lower the solar heat gain coefficient of the built-in blinds' insulating glass. The larger the blind angle, the more the solar heat gain coefficient of the built-in blind insulating glass decreases. The solar heat gain coefficient of the electric built-in blind insulating glass can reach a minimum of 0.108, and the thermal insulation performance is excellent.
(2) When the blinds angle is 80. When the solar reflectivity of the electric built-in blinds and insulating glass is 70% or 87%, the solar heat gain coefficient of the blinds can be less than 0.15, which meets the index requirement of the summer solar heat gain coefficient of GB/T 51350-2019 (summer solar heat gain coefficient (%)). 15; the solar heat gain coefficient of the magnetically controlled built-in blinds and insulating glass is as low as 0.203, which does not meet the index requirement of the summer solar heat gain coefficient (%). 15.
(3) When the electric built-in blinds and insulating glass are used in near-zero energy buildings, silver paint blinds or heat-reflective paint blinds can be selected, and high-shielding blinds can be used to achieve a solar heat gain coefficient that meets the application requirements of near-zero energy buildings.
