Simulation analysis of thermal performance of insulating glass with built-in louvers.

1. The introduction

Built-in louver insulating glass is a new energy-saving glass product that installs venetian blinds in the insulating glass, taking into account heat preservation and sunshade performance. It uses magnetic control to control the closing device and lifting device to operate the louvers in the insulating glass. The angle of the venetian blinds is used to control the light and radiant heat entering the room, meeting the needs of heat insulation and indoor lighting. Compared with other sunshade products, the built-in louver insulating glass has multiple excellent performances such as thermal insulation, sunshade and daylighting, sound insulation and environmental protection, safety and reliability, dustproof and privacy. Closing the venetian blinds during the day in summer can reduce the solar radiant heat entering the room and reduce the indoor air conditioning load; in winter, adjusting the louver angle or closing the curtains during the day can make full use of sunlight and use solar radiation heat to increase the indoor temperature. Closing the venetian blinds at night can reduce the indoor heat Loss, increase the thermal insulation performance of glass windows.

According to the regulations on thermal design of civil buildings, my country is divided into five climate zones: severe cold region, cold region, hot summer and cold winter region, hot summer and warm winter region, and mild region. The performance indicators of external windows in different climate zones are different. In general, the north emphasizes heat preservation, while the south emphasizes sunshade. However, as people's requirements for indoor light and heat environment further increase, both the north and the south put forward requirements for heat preservation and sunshade of doors and windows. A single glass with good thermal insulation performance or good sunshade performance cannot meet the dual requirements of thermal insulation and sunshade in different seasons and directions in different regions of my country. The built-in louver insulating glass has become suitable for different areas in my country due to its excellent thermal insulation performance and adjustable heat insulation and lighting performance. New energy-efficient glazing for climate zones.

The research on the built-in louver insulating glass mostly focuses on its own performance research, and there is no research on the photothermal performance of the venetian blind at different glass positions. LIJIANG Glass conducted an experimental study on the heat transfer coefficient of the built-in louver insulating glass. The results showed that using Low-E glass and filling inert gas can effectively improve the thermal insulation performance of the sample; The coefficient can be reduced by 0.48W/(m2・K), and the heat preservation effect is obviously improved. LIJIANG Glass introduced the energy-saving significance of the shading coefficient of hollow glass products with built-in louvers, and analyzed and compared the heat gain coefficient of glass products obtained by the actual measurement method and the calculation method. Using the door and window shading calculation software WINDOW and the energy consumption simulation software Energy-plus, the key structural parameters that affect the thermal performance parameters of the built-in louver shading insulating glass products are analyzed. The key influencing factors affecting its thermal performance, and the influence of the two on thermal performance is interactive. The influence of louver state, louver color and interlayer filling gas on the thermal performance of the built-in movable louver insulating glass is analyzed. The analysis results show that the color of the louver has little effect on its thermal performance, and the different types of filling gas only affect the heat transfer coefficient. Different angles affect both the heat transfer coefficient and the shading coefficient. In addition, it also introduces the application of insulating glass windows with built-in louvers in hot summer and cold winter regions, emphasizing its excellent performances such as energy saving, dimming, sound insulation, and safety. Data analysis is not included in the paper.

The objects of the above-mentioned research and analysis are all double-layer insulating glass, and do not involve triple-layer insulating glass and vacuum composite insulating glass, and the research content does not involve the study of the surface temperature of each layer. This study covers the current typical types of insulating glass such as built-in louver double-glass Low-E insulating glass, built-in louver triple-glass Low-E insulating glass, and built-in louver Low-E vacuum insulating glass. The research content includes heat transfer coefficient , shading coefficient, visible light transmittance and other optical and thermal properties, and analyzed the surface temperature of each layer of the built-in louver insulating glass, aiming to provide more comprehensive data reference for the design, manufacture and use of built-in louver insulating glass products and suggestion.

2. The calculation description

2.1 The boundary conditions

The computational boundary conditions are set as:

(1) Winter calculation conditions: indoor air temperature Tin=20℃, outdoor air temperature Tout=-20℃, indoor convective heat transfer coefficient hcjn=3.6W/(㎡・K), outdoor convective heat transfer coefficient hc5OUt=16W/( ㎡・ K), indoor average radiation temperature Trm, in= Tin, outdoor average radiation temperature Trm,°ut= Tout, solar irradiance Is=300 W/㎡;

(2) Summer calculation conditions are: indoor air temperature 1 25°C, outdoor air temperature Tout=30°C, indoor convective heat transfer coefficient hc5in=2.5W/(㎡・K), outdoor convective heat transfer coefficient hc?out=16W/ (㎡・K), indoor average radiation temperature 1 mountain 『5 outdoor average radiation temperature Trm, 0Ut=T0Ut, solar irradiance k=500 W/㎡;

(3) The calculation of shading coefficient and total sunlight transmittance adopts summer standard calculation conditions.

2.2 Software Description

The simulation mainly uses WINDOW 7.0 and THERM 7.0 software. WINDOW and THERM are a series of software developed by the Lawrence Berkeley Laboratory in the United States. They are one of the most important optical and thermal calculation software for architectural glass in the world. They have the calculation function of vacuum glass.

3. The glass construction

In order to study the influence of built-in louvers on the thermal performance of different insulating glasses, five types of typical built-in louver insulating glasses were designed, namely: ordinary double-glass insulating glass (Fig. la), Low-E double-glass insulating glass (Fig. 1b) , common three-glass insulating glass (Figure 1c), Low-E three-glass insulating glass (Figure Id) and Low-E vacuum insulating glass (Figure le) The thickness is taken as 0.15 mm, and the thickness of other air layers is taken as 12 mm. The louvers are made of white metal with a surface emissivity of 0.9.

aOrdinary double glass insulating glass bLow-E double glass insulating glass cOrdinary triple glass insulating glass

5〃20-12

dLow-E triple glass insulating glass

Figure 1 Five types of typical built-in louver insulating glass

Since the above five types of glass still have different combinations when built-in louvers, taking Low-E double-glass insulating glass as an example, there are situations where the Low-E surface is on the second and third sides, so the research content is refined, see Table 1.

Table 1 Research content of five types of typical built-in louver insulating glass

4. Results and Analysis

4.1 Simulation analysis of optical and thermal performance of ordinary double-glazed insulating glass with built-in louvers...—Industrial

The simulation analysis of photothermal performance of ordinary double-glass built-in louver insulating glass adopts the glass configuration: 5+20A louver+5. The louvers are divided into three states: 0. , 45. and 90° o 0. When the louvers are horizontally parallel, that is, the louvers are opened; 45. When the louvers are at 45 to the horizontal plane. Angle, that is, the louvers are in a half-open state; 90. When the louvers are perpendicular to the horizontal plane, that is, the louvers are in the closed state. The calculation results of optical and thermal parameters of ordinary double-glazed built-in louver insulating glass in three states are shown in Table 2, the temperature distribution of inner and outer surfaces of each layer is shown in Table 3, and the layer 1, layer 2, and layer 3 in Table 3 are shown in Figure 2.

Table 2 Simulation results of optical and thermal performance of ordinary double-glazed insulating glass with built-in louvers

Table 3 Simulation results of surface temperature of each layer of ordinary double-glass built-in louver insulating glass

^{Figure 2 Schematic diagram of double glass temperature distribution layer}

It can be seen from Table 2 that as the louver angle increases, the heat transfer coefficient, shading coefficient, solar heat gain coefficient and visible light transmittance of ordinary double-glass built-in louver insulating glass all decrease. When the louvers are opened to closed, the original louver cavity is divided into two cavities, so the heat transfer coefficient will be significantly reduced; the shading coefficient and solar heat gain coefficient are secondary to the reflection and absorption of direct sunlight radiation by the louvers. Radiation-related, the louvers can reflect part of the sunlight while absorbing part of the radiation, and the absorbed radiation is converted into long-wave heat radiation. The glass is impenetrable to long-wave heat radiation, so it can only be taken away by convection and heat conduction of the glass on both sides of the louver , due to the large heat transfer coefficient of the outer surface of the outdoor glass, most of this part of the heat will be transferred to the outdoors, and a small amount will be transferred to the indoors. The shading coefficient and solar heat gain coefficient will gradually decrease as the louvers are gradually closed; the louvers are made of opaque metal From opening to closing, the visible light transmittance gradually decreases to 0.

It can be seen from Table 3 that the louver has a certain absorption effect on solar radiation, which will cause the surface temperature of the louver and the air temperature in the cavity to increase significantly. ) should be designed to prevent thermal bursting.

4.2 Low-E double-glazed insulating glass with built-in louvers

Low-E double glass built-in louver hollow glass photothermal performance simulation analysis adopts glass configuration as follows:

(1)5Low-E+20A shutter+5;

(2)5+20A louvers+5Low-E.

The calculation results of the optical and thermal parameters of the Low-E double-glass built-in louver insulating glass are shown in Table 4, and the temperature distribution of the inner and outer surfaces of each layer is shown in Table 5, and the layer 1, layer 2, and layer 3 in Table 5 are shown in Figure 2.

Table 4 Simulation results of optical and thermal performance of Low-E double-glazed insulating glass with built-in louvers

Table 5 Simulation results of surface temperature of each layer of Low-E double-glazed insulating glass with built-in louvers

It can be seen from Table 4 and Table 5 that when the position of the Low-E film layer changes, the optical thermal performance of the Low-E double-glass insulating glass with built-in louvers does not change significantly, and the surface temperature of each layer does not change significantly. This is because one side of the louver is a single piece of ordinary glass, and the other side is a single piece of Low-E glass, and the difference in optical and thermal performance between the two is not obvious. However, when the Low-E glass is located on the indoor side, the shading coefficient and solar heat gain coefficient of the Low-E double-glazed insulating glass with built-in louvers are low, and the surface temperature of each layer is also low. This is because the solar radiation heat absorbed by the louvers needs to pass convection. And heat conduction is transferred to both sides. Low-E glass is located on the indoor side and ordinary glass is located on the outdoor side, which is conducive to heat transfer to the outdoor side.

4.3 Ordinary three-glass built-in louver insulating glass

The simulation analysis of photothermal performance of ordinary three-glass built-in louver insulating glass adopts the glass configuration as follows:

(1) 5+20A louvers+5+12A+5; 

(2) 5+12A+5+20A louvers+5.

The calculation results of optical and thermal parameters of ordinary three-glass built-in louver insulating glass are shown in Table 6, and the temperature distribution of the inner and outer surfaces of each layer is shown in Table 7. In Table 7, layer 1, layer 2, layer 3, and layer 4 are shown in Figure 3.

Table 6 Simulation results of optical and thermal performance of ordinary triple-glazed insulating glass with built-in louvers

Table 7 Simulation results of surface temperature of each layer of ordinary three-glass built-in louver insulating glass

It can be seen from Table 6 and Table 7 that when the louvers are located in the outer air cavity of ordinary triple-glazed insulating glass, the shading coefficient and solar heat gain coefficient are significantly lower than those of the louvers located in the inner air cavity, and the difference in heat transfer coefficient and visible light transmittance is small. The side surface temperature is about 6°C lower. When the louvers are placed in the ordinary three-glass insulating glass, one side is a single glass and the other side is an insulating glass. Since the thermal resistance of the insulating glass is about twice that of the single glass, when the louvers are located in the outer air cavity, the absorbed heat passes through the hollow The amount of glass entering the room is small, so its shading coefficient and solar heat gain coefficient are small.

4.4 Low-E triple-glazed insulating glass with built-in louvers

Low-E three-glass built-in louver hollow glass photothermal performance simulation analysis adopts glass configuration as follows:

(1) 5+20A shutter+5+12A+5 Low-E;

(2) 5Low-E+12A+5+20A Louver+5.

The calculation results of the optical and thermal parameters of the Low-E three-glass built-in louver insulating glass are shown in Table 8, and the temperature distribution of the inner and outer surfaces of each layer is shown in Table 9, and the layer 1, layer 2, layer 3, and layer 4 in Table 9 are shown in Figure 3.

Table 8 Simulation results of optical and thermal performance of Low-E triple-glazed insulating glass with built-in louvers

Table 9 Surface temperature of each layer of Low-E triple-glazed insulating glass with built-in louvers (simulation results)

It can be seen from Table 8 and Table 9 that the Low-E three-glass louver insulating glass is equivalent to one side of the louver being ordinary single glass, and the other side being Low-E double-glass insulating glass. Since the thermal resistance of Low-E double-glass insulating glass is about three times that of ordinary single glass, when the Low-E insulating glass is located on the indoor side, the shading coefficient and solar heat gain coefficient are significantly lower than those located on the outdoor side. The side surface temperature is also significantly lower.

4.5 Low-E vacuum built-in shutter insulating glass

Low-E vacuum built-in louver insulating glass photothermal performance simulation analysis adopts glass configuration as follows:

(1) 6+20A shutter + 6Low-E +0.15V+6;

(2) 6+0.15V+6Low-E+20A louver+6;

(3) 6Low-E+20A Louver+6Low-E+0.15V+6.

The calculation results of the optical and thermal parameters of the Low-E vacuum built-in louver insulating glass are shown in Table io, and the temperature distribution of the inner and outer surfaces of each layer is shown in Table 11. See Figure 4 for Layer 1, Layer 2, Layer 3, and Layer 4 in Table n.

Figure 4 Schematic diagram of temperature distribution layer of vacuum glass

Table 10 Simulation results of optical and thermal performance of Low-E vacuum built-in louver insulating glass

GlassConfiguration Louver Angle Heat Transfer Coefficient KW/(㎡·K) Shading Coefficient SC Solar Heat Gain CoefficientSHGC visible light transmittanceTy configuration one 0° 0.626 0.557 0.485 0.675 45° 0.592 0.161 0.140 0.135 90° 0.548 0.046 0.040 0.000 Configuration two 0° 0.624 0.664 0.578 0.675 45° 0.5 93 0.504 0.438 0.152 90° 0.552 0.368 0.320 0.000 Configuration three 0° 0.617 0.501 0.436 0.654 45 ° 0.570 0.160 0.140 0.127 90° 0.502 0.067 0.058 0.000
Table 11 Simulation results of the surface temperature of each layer of Low-E vacuum built-in louver insulating glass in °C

Glassconfiguration louversangle outdoorAirTemperature Layer 1 Surface Temperature Layer 2 Surface Temperature Layer 3 Surface Temperature Layer 4 Surface Temperature IndoorAirTemperature Outside Inside Outside Inside Outside Inside Outside Inside Configuration- 0° 30.0 37.6 38.3 41.8 41.8 45.2 45.4 30.9 30.8 25.0 45° 30.0 42.5 43.7 57.1 57.1 55.9 55.8 29.6 29.4 25.0 90° 30.0 40. 7 41.6 54.0 54.0 51.4 51.2 28.2 28.0 25.0 configurationTwo 0° 30.0 34.8 35.1 43.0 42.8 40.0 40.0 37.0 36.6 25.0 45° 30.0 36.1 36.5 64.3 64.2 60.7 60.7 47.8