Calculation method for thermal performance of built-in sunshade insulating glass

Built in sunshade insulating glass is a new type of energy-saving glass product. This article briefly introduces the characteristics, thermal calculation theory, and software use of built-in sunshade insulating glass products, and provides thermal calculation examples!

 

1. Product Introduction

 

Built in sunshade insulating glass is a building material with good insulation, thermal insulation, and sunshade performance.

 

The built-in sunshade insulating glass consists of two layers of glass panels and one sunshade layer, separated by an air layer at a certain distance. The basic structure is shown in the following figure.

 

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The built-in sunshade structure can be divided into blinds, folding blinds, honeycomb blinds, scroll blinds, and combination blinds, as shown in the following figure.

 

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The standard for built-in sunshade insulated glass products is JG/T 255 "Internal Sunshade Insulated Glass Products", which requires the heat transfer coefficient to be tested according to GB/T 8484, and the solar heat gain coefficient to be tested according to ISO 19467 or JG/T 440.

 

The thermal performance of built-in sunshade insulating glass needs to be calculated and analyzed to determine its energy-saving effect under different climate and environmental conditions. Mainly includes:

 

(1) Thermal performance calculation: According to the principle of heat transfer, the heat transfer coefficient and solar heat gain coefficient of the built-in sunshade insulating glass can be calculated to determine its insulation performance;

 

(2) Optical performance calculation: The built-in sunshade insulating glass sunshade layer can change the visible light transmission characteristics, thereby affecting the indoor lighting effect. Therefore, it is necessary to determine its visible light transmission characteristics;

 

(3) The influence of air layer on thermal performance: The thickness of air layer will affect the thermal performance of insulated glass. Through calculation and analysis, the optimal air layer parameters can be determined to achieve the best insulation effect.

 

The calculation and analysis of the thermal performance of built-in sunshade insulated glass is an indispensable part of building design. It can help us understand the thermal performance of built-in sunshade insulated glass, optimize design schemes, and improve building energy efficiency.

 

2. Computational Theory

 

The thermal calculation of built-in sunshade insulating glass can refer to "8 Sunshade System Calculation" in JGJ/T 151-2008 "Thermal Calculation Code for Building Doors, Windows, Glass Curtain Walls".

 

The calculation of the shading system in this regulation only applies to flat shading devices that are parallel or approximately parallel to the glass surface, including internal shading, external shading, and intermediate shading. The photothermal performance of the shading device is calculated based on the optical properties, geometric shape, and location of the shading device material.

 

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Calculate the confirmed model according to the following formula:

 

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The calculation formula is quite complex and lacks operability, so we won't explain it in detail here. Interested friends can refer to the specifications on their own.

 

The author has researched and compiled corresponding calculation tables, and the results are highly consistent with WINDOW software, as shown in the following figure.

 

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In practical operation, it is recommended to use software calculation, which will be emphasized below.

 

3. Software usage

 

The WINDOW software from Lawrence Berkeley Laboratory in the United States has a built-in function for calculating the photothermal performance of sunshade insulated glass.

 

In the Glazing System interface, select Shade or frit from Glass/Shade or frit, as shown in the following figure.

 

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Select the corresponding material from the sunshade material library and calculate the photothermal performance parameters of the built-in sunshade insulating glass, as shown in the following figure.

 

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For louvers, three states are usually considered:

(1) Open: blade angle is 0 °;

(2) Close: The blade angle is 90 °;

(3) Half open: The blade angle is 45 ° (or 30 ° and 60 °).

 

For materials that are not available in the database, spectral parameters need to be tested and then imported into Window software through Optics. The test data includes the spectral transmittance, front reflectance, and back reflectance of glass and louvers within the wavelength range of 300-2500 nm, as well as the surface emissivity of glass and louvers.

 

4. Calculation Example

 

Taking 6mm transparent glass+19A built-in louvers+6mm transparent glass as an example, the louvers are made of the default first material of the system, and the three states are as follows:

 

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When the louver is at 0 °, the calculation result is shown in the following figure.

 

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When the louvers are at a 45 ° angle, the calculation results are shown in the following figure.

 

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When the louvers are at a 90 ° angle, the calculation results are shown in the following figure.

 

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The thermal parameters of the 6mm transparent glass, 19A built-in louvers, and 6mm transparent glass are as follows:

 

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It can be seen that as the louver angle changes from horizontal to vertical, the heat transfer coefficient K value, solar heat gain coefficient SHGC value, and visible light transmittance Tv value of the built-in louver insulated glass all show a significant downward trend.

 

5. Conclusion

 

Built in sunshade insulating glass is a product that installs sunshade devices inside the insulating glass. The structure of the built-in sunshade curtain can be divided into louver curtain, folding curtain, honeycomb curtain, scroll curtain, and combination curtain. The product standard is JG/T 255-2020 "Built in Sunshade Hollow Glass Products".

 

The thermal calculation of built-in sunshade insulating glass can refer to "8 Sunshade System Calculation" in JGJ/T 151-2008 "Thermal Calculation Code for Building Doors, Windows, Glass Curtain Walls".

 

The WINDOW software from Lawrence Berkeley Laboratory in the United States has a built-in sunshade hollow glass thermal performance calculation function. Taking 6mm transparent glass+19A built-in louvers+6mm transparent glass as an example, the thermal performance of the blade at different angles was calculated.

 

As the louver angle changes from horizontal to vertical, the heat transfer coefficient K value, solar heat gain coefficient SHGC value, and visible light transmittance Tv value of the built-in louver insulated glass all show a significant downward trend.