Many manufacturers who visited the insulating glass processing plant heard the technical term "warm edge" through the introduction of the insulating glass manufacturer and processor. For glass deep-processing practitioners who don't know much about energy-saving doors and windows and insulating glass technology, "warm edge" may still be a relatively unfamiliar term. What exactly is the warm edge technology of insulating glass? Now let's learn about it through the following article.

#### 1. Overview of insulating glass warm edge technology

1.1 Definition of Warm Edge Technology

For the definition of warm-edge technology, an earlier statement is any kind of spacer as long as its thermal conductivity is lower than that of aluminum metal, it can be called a warm-edge system. This statement reflects the characteristics of warm-edge spacers to a certain extent, but it is not rigorous and clear enough. The German standard DINV 4108-4:2002-02 gives a clear and authoritative definition of the warm edge system, see formula 1:

Σ (d×λ) = d1×λ1 + d2×λ2+....+dn×λn ≤ 0.007 W/K (Formula 1)

Among them: d is the thickness of the material used, and the λ value is the thermal conductivity of the material used. For a spacer, if formula (1) is true, that is, the calculation result is less than or equal to 0.007 W/K, it is called a warm edge system; if formula (1) is not true, that is, the calculation result is greater than 0.007 W/K, then Defined as a cold edge system. This definition has been adopted by European standards and ISO standards. According to this definition, the interval bar can be quantitatively determined.

For example: According to the thermal conductivity of the material is as follows: polypropylene is 0.22 W/(m·K), stainless steel is 17.0 W/(m·K), and aluminum is is 160.0 W/(m·K). Putting the above data into the formula, the calculation result of a certain spacer is 0.002 W/K, which is less than 0.007 W/K, so it is defined as a warm edge system; the calculation result of the aluminum spacer is 0.112 W/K, which is much larger than 0.007 W /K, so it is defined as a cold edge system.

#### 2. Energy-saving principle of warm edge technology

The heat transfer coefficient of a complete external window system is composed of three parts: the glass, the window frame, and the linear heat transfer coefficient of the edge of the hollow glass, as shown in Figure 1.

Figure 1 Schematic diagram of the heat transfer principle of the whole window

The heat transfer coefficient calculation formula of the whole window is shown in formula 2:

Uw =（Af*Uf+Ag*Ug+Lg*Ψg)/(Af+Ag)

Where:

• Uw —heat transfer coefficient of the whole window;
• Uf  —heat transfer coefficient of window frame;
• Ug —heat transfer coefficient of glass;
• Aw—whole window area;
• Af —window frame area;
• A—glass area;
• Lf—The length of spacer bar
• Ψ—the linear heat transfer coefficient of the edge of the hollow glass.

Figure 2 The heat transfer coefficient of the whole window 1

The value of Ψ in the formula, that is, the linear heat transfer coefficient of the edge of the hollow glass, describes the heat loss rate through the edge of the hollow glass. The larger the value of Ψ, it means that the heat loss through the edge of the insulating glass will increase; reducing the value of the linear heat transfer coefficient Ψ can effectively reduce the heat transfer coefficient of the entire window. It can be seen that a relatively low value of the edge linear heat transfer coefficient is very critical to the improvement of the thermal insulation performance of the entire window. The size of the Ψ value is mainly determined by the material of the spacer used. Choosing a reasonable spacer with a lower linear heat transfer coefficient is an important method to reduce the value of the linear heat transfer coefficient Ψ. This is the principle that warm-edge spacers are more energy-efficient than traditional aluminum spacers.

2.1 Research on the influence of warm edge technology on the performance of insulating glass

Taking the TGI spacers widely used in the market as an example, the performance analysis and research of warm-edge insulating glass using thermal calculation software for building doors and windows and glass curtain walls is divided into three aspects:

• The heat transfer coefficient U of the warm-edge technology for the whole window;
• Research on the influence of warm-edge technology on the anti-condensation performance of insulating glass;
• Research on the influence of warm-edge technology on the thermal stress of glass.

2.2 Research on the influence of warm edge technology on the heat transfer coefficient of the whole window

For an aluminum alloy profile node, traditional aluminum spacers and warm-edge spacers are used to calculate the heat transfer coefficient. The calculation results are shown in Figure 5.

Figure 2 Calculation results of heat transfer coefficients for nodes with cold edges spacer

Figure 3 Calculation results of heat transfer coefficients for nodes with warm edges spacers

Figure 5 Calculation results of heat transfer coefficients of fan nodes with different intervals

It can be seen from Figure 5 that after the aluminum alloy window frame sash node adopts warm-edge spacers, the heat transfer coefficient of the entire node is reduced from 3.58 W/(m² ·K) to 3.12 W/ compared with traditional aluminum spacers. (m² ·K), reduce 0.46 W/(m² ·K); calculated by 30% of the frame window ratio, the heat transfer coefficient of the whole window can be reduced by about 0.14 W/(m² ·K). When designing doors and windows and curtain walls, some people think that the U value of the door and window profiles and the U value of the hollow glass is designed, and the two are weighted according to the area, and the U value of the entire window can be obtained. This is wrong. It can be seen from the formula for calculating the U value of doors and windows (Equation 2) that the linear heat transfer coefficient of the joint between the profile and the glass needs to be considered for the U value of the entire window. The strip has a significant effect on the heat transfer coefficient of the entire window.

2.3 Research on the influence of warm edge technology on the anti-condensation performance of insulating glass

For insulating glass, aluminum spacers and warm-edge spacers are used for thermal calculation. Take the 5+16 A+5 Low-E glass configuration as an example. The air temperature on the outdoor side is -20℃, and the air temperature on the indoor side is 20℃. Under these conditions, the calculation results are shown in Figure 6.

Figure 6 The calculation results of the temperature inside the insulating glass interior of the warm-side spacer and the aluminum spacer

As can be seen in Figure 6, the edge temperature of the insulating glass of the warm-edge spacer is 0.6°C, while the edge temperature of the insulating glass of the aluminum spacer is -4.5°C, that is, the temperature of the insulating glass edge of the warm-edge spacer is higher than that of the aluminum spacer. The temperature is about 5°C higher. Under the premise of ensuring no condensation, the indoor air temperature in the northern part of the winter remains unchanged at 16°C. The calculation result of the indoor relative humidity is shown in Figure 7.

Figure 7 Calculation of indoor relative humidity under different dew point conditions 1

As can be seen in Figure 7, when the indoor air temperature is 16°C, the indoor relative humidity can be increased from 23.07% to 35.12% without condensation. While the indoor living comfort has been significantly improved, the possibility of condensation on the interior surface of the window is reduced, the pollution of the interior decoration surface and the mold on the wall are reduced, and the indoor environment is effectively improved.3. Research on the influence of warm edge technology on glass thermal stress

Tempered glass self-explosion, coating, and thermal stress burst of insulating glass are the main safety hazards in the application process of domestic door and window curtain wall glass. In addition to defects such as nickel sulfide impurities and cracks in the glass body, the stress change caused by temperature difference is an important inducement for glass rupture. Take the calculation result in Figure 3 as an example, calculate the glass stress according to the formula in JGJ113-2009, the formula is:

σh=0.74 Eα μ1 μ2 μ3 μ4 (Tc-Ts) (Equation 3)

In the formula:

• σh——glass end face stress, N/mm2;
• E——The elastic modulus of glass, which is taken as 0.72×105 N/mm2;
• α——The linear expansion coefficient of glass, which is taken as 10-5/℃;
• μ2——curtain coefficient;
• μ3——Glass area coefficient;
• μ4——Edge temperature coefficient;
• Tc——The temperature in the middle of the glass;
• Ts——The edge temperature of the glass.

To simplify the calculation, the shading coefficient, curtain coefficient, glass area coefficient, and edge temperature coefficient are all taken as 1.0, and the glass edge temperature difference (Ts1-Ts2) is taken as 5℃, then the stress difference is:

Δσh=0.74 Eα μ1 μ2 μ3 μ4 (Ts1- Ts2)=0.74×0.72×105 N/mm² ×10-5/℃×1.0×5℃=2.66 N/mm²

That is, compared with aluminum spacers, when the temperature of the glass edge is increased by 5℃, the glass stress can be reduced by 2.66.N/mm²  can reduce the possibility of glass spontaneous explosion and thermal stress bursts caused by temperature difference stress during glass use.

#### 3. Research on the Application of Warm Edge Insulating Glass Project

As an important part of insulating glass, the warm edge technology in the glass curtain wall should meet the requirements of the "Glass Curtain Wall Engineering Technical Code" . Article 3.4.1 of the "Code" clearly stipulates that when insulating glass is used for the glass curtain wall, it shall meet the following requirements in addition to the relevant provisions of the current national standard "Insulating Glass" :

1 Insulating glass gas layer The thickness should not be less than 9mm;

2. The insulating glass should be double-sealed.

One seal should use a butyl hot melt sealant. The second sealant for insulating glass for the hidden frame, semi-hidden frame, and point-supported glass curtain wall should use silicone sealant; the second sealant for insulating glass for open frame glass curtain wall should adopt polysulfide insulating glass sealant, or Use silicone sealant. The second seal should be mixed and glued with a special glue machine.

3. The partition aluminum frame of the hollow glass can be of continuous bending type or pin type, and no hot-melt type spacer tape shall be used. The desiccant in the partition aluminum frame should be filled with special equipment.

Therefore, hot-melt butyl warm-edge insulating glass products cannot be applied to building curtain walls because they do not meet the secondary sealing requirements, so most of them are used in residential buildings. The spacers (such as TGI spacers) with double-channel sealing structures meet the requirements of the "Code" and can be applied to the doors and windows of residential buildings and the large-area glass curtain walls of public buildings.

#### 4. The conclusion

In summary, compared with aluminum spacers, the research conclusions are as follows:

1. Warm edge technology can reduce the heat transfer coefficient of the entire window, which is an effective way to improve the thermal performance of the entire window;
2. Warm edge technology can greatly increase the edge temperature of the insulating glass and improve the anti-condensation performance of the insulating glass;
3. Warm edge technology can effectively reduce the possibility of glass spontaneous explosion and thermal stress bursts caused by temperature difference stress during the use of glass;
4. The warm edge spacer with a double-sealed structure can be used in residential building doors and windows and glass curtain walls of public buildings.

The application of hot-melt butyl warm-edge spacers is subject to certain restrictions in the specification.