The anti-condensation design of building doors and windows.

1. The introduction

The dew point temperature refers to the temperature at which air is cooled to saturation under the condition that the water vapor content and air pressure do not change. To put it figuratively, the temperature at which water vapor in the air turns into dew is called the dew point temperature, and a temperature drop below the dew point is a necessary condition for water vapor to condense. Condensation refers to the phenomenon that condensed water appears on the surface when the surface temperature of the object is lower than the dew point temperature of the nearby air. The dew point is the critical temperature point at which the surface of the object begins to condense to form droplets or ice. When the temperature of the surface of the object is equal to or lower than the dew point temperature, condensation will occur on the surface, which will cause the surface of the object to become moldy and black for a long time. 

Mildew is a common natural phenomenon. It often appears in food. Food contains certain starch and protein and contains more or less water. The growth and development of mold require the existence of water and warm temperature. When the water activity value rises after being exposed to moisture, the mold will absorb the water in the food and then decompose and consume the nutrients in the food.

2. Condensation on doors and windows

Door and window condensation is the condensation of dew or water mist on the indoor surfaces of doors and windows. When the surface temperature of the solid (glass, window sash, window frame) is lower than the dew point temperature of the surrounding humid air, the water vapor in the air turns into liquid water and condenses on the cold solid surface, resulting in condensation. When the temperature of the condensation part continues to reach above 13C and the relative humidity reaches above 80%, mildew is prone to occur

2.1 Main parts where condensation occurs in door and window engineering

2.1.1 Condensation on the frame

The heat insulation performance of the frame profile does not meet the requirements, and a cold bridge is formed on the profile part, resulting in condensation (Figure 1). For aluminum alloy heat insulation profiles, the heat insulation performance of the profile is directly related to the width and shape of the profile heat insulation strip. If the width of the heat insulation strip of the profile is small, it cannot meet the local winter heat preservation performance requirements.

^{Figure 1 The condensation on the frame profile 1}

2.1.2  Condensation on the glass

The phenomenon of glass condensation (Figure 2, Figure 3) in most cases is that the overall thermal insulation performance of the outer window is poor, resulting in a decrease in the indoor temperature and the formation of condensation on the glass surface. Another situation is that the indoor humidity is relatively high. This situation is mainly due to the good sealing performance of doors and windows. Especially in winter, the windows cannot be frequently opened for ventilation, resulting in high indoor humidity, especially in the kitchen and balcony. more locations

^{Figure 2 The phenomenon of glass condensation 1}

^{Figure 3 The phenomenon of glass condensation 2}

2.1.3 Condensation at the joint between the frame and glass

Condensation at the joint between the glass and the frame (Fig. 4, Fig. 5). First, the insulating glass spacer is made of aluminum alloy, resulting in a cold bridge;

As shown in Figure 5, there is no condensation in the middle of the glass, and only condensation occurs on the edge

^{Figure 4 The condensation at the joint between the frame and glass 1}

^{Figure 5 The condensation at the joint between the frame and glass 2}

2.1.4 Condensation at the junction of the frame and the opening

Condensation occurs at the joint between the door and window frame and the installation hole (Fig. 6, Fig. 7, Fig. 8, and Fig. 9). One is that the thermal insulation of the installation gap of doors and windows is not properly handled, resulting in cold bridges, condensation, and even mildew; the other is that the waterproofing of the installation parts is not properly handled, resulting in water leakage.

^{Figure 6 The mildew occurs at bay window and balcony window installations 1}

^{Figure 7 The condensation and mildew on the installation part on the side of the window frame}

^{Figure 8 The condensation occurs at bay window and balcony window installations 1}

^{Figure 9 The condensation and mildew occurs at bay window and balcony window installations} 

2.1.5 The mildew

Mildew on the wall means that under the appropriate temperature and humidity, the mold uses the carbon source and nitrogen source in the skin layer of the wall to parasitize on the surface of the wall and reproduce in large numbers, usually showing black color's, green color's, red color's, Yellow color's, and other forms, as shown in Figure 6~Figure 9.

In southern part of the northern hemisphere, the summer temperature is high, the relative humidity is high, and the duration is long. The average relative humidity of the hottest month is 78%~83%, which is a typical high-temperature and high-humidity area. Mildew on the wall is prone to occur after dampness and water accumulation.

2.2 Four main conditions for mildew

2.2.1 Appropriate temperature

22°C~35°C is considered to be the optimum temperature for mold growth. Most buildings (especially air-conditioned buildings) are usually right in this temperature range.

2.2.2 Existence of moisture

In building envelope materials, the liquid moisture provided by condensation is more effective for mold growth than the water vapor contained in the surrounding air. Usually, the relative humidity in the material is 80%, as the critical moisture content to prevent mold growth.

2.2.3 Adequate nutrition

Each building material contains nutrients to varying degrees.

2.2.4 Sufficient time

Mold growth depends on characteristics such as temperature, relative humidity, moisture content of the material, time, etc. When the ambient temperature is 50-50°C and the relative humidity is above 80%, it can cause mold growth in a few weeks or months.

3. Anti-condensation design

In winter, when the warm indoor air contacts the surfaces of doors and windows, the decrease in temperature will lead to an increase in relative humidity, which may cause condensation and mildew on the surfaces of doors and windows, damaged interior decoration, and affect indoor air quality and health. Regardless of the profile and glass that make up the doors and windows, or the structure of each node of the doors and windows, multi-cavity design is the basic principle of thermal insulation design.

3.1 Thermal insulation design of profiles

The thermal insulation design of profiles should be determined according to the overall thermal insulation performance design of doors and windows. The thermal insulation performance of the profile is directly proportional to the effective thermal insulation thickness of the profile. For multi-cavity door and window profiles, the effective heat insulation thickness of the profile and the multi-cavity design of the profile are effective means to increase the thermal resistance of the profile. The greater the thermal resistance, the stronger the profile’s ability to prevent heat transfer, which can reduce The cold bridge effect generated on the profile to avoid condensation the profile.

3.2 Glass insulation design

The multi-cavity insulating glass is the first choice for glass heat insulation design. On this basis, choose Low-E film or inert gas filling according to the actual needs of the overall energy saving of doors and windows. To obtain better heat insulation performance, you can choose composite glass composed of vacuum and insulated. To prevent condensation at the edge of the glass, warm edge adhesive strips should be used at the edge of the insulating glass to avoid the occurrence of cold bridges at the edge of the glass, and also, how to process warm edge adhesive strips by automatic insulating glass equipment is also more and more important for insulating glass design.

3.3 Thermal insulation design of node structure

The structural design of door and window joints is an important part of the energy-saving design of doors and windows, and its thermal insulation design also follows the principle of multi-cavity design. The node structure of doors and windows includes fixed nodes and open nodes. The heat insulation design of the fixed joint structure mainly exists at the edge of the glass inlaid notch, and the clearance at the edge of the glass mainly exchanges heat through convection, which is the main cause of cold bridges (Figure 5, measures should be taken during heat insulation design Block the glass clearance. To achieve better thermal insulation performance, multi-cavity thermal insulation design should also be carried out at fixed nodes. The thermal insulation design of an open cavity should follow the principle of multi-cavity design and separation of the cold cavity and hot cavity.

3.4 Thermal insulation design of installation nodes

When the door and window frame is installed and the wall is sealed and heat-insulated, the door and window should be as close as possible to the insulation layer or wrapped by the insulation layer, and the installation gap should be filled with insulation materials to achieve the purpose of reducing cold bridges. The installation position of doors and windows also has a great influence on the overall energy-saving performance of the building. Building insulation wall forms include external insulation, internal insulation, and sandwich insulation. The installation methods of building doors and windows mainly include centering, along the outside of the wall, along the inside of the wall, and outside hanging along the wall.

3.4.1 External insulation wall

See Table 1 for the linear additional heat transfer coefficient values of the external window openings of the external thermal insulation wall, and the best thermal insulation effect is installed along the outer side of the wall.

3.4.2 Inner insulation wall

See Table 2 for the linear additional heat transfer coefficient value of the thermal bridge at the outer window opening of the inner insulation wall, and the best insulation effect is installed along the inner side of the wall.

3.4.3 Sandwich insulation wall

The linear additional heat transfer coefficient of the window opening outside the sandwich insulation wall is shown in Table 3. When the window is installed along the outside of the wall, the thermal bridge loss at the window opening is small, and the result is slightly larger when the wall is installed in the center than when it is installed along the outside of the wall.Table 1 The linear additional heat transfer coefficient of the opening of the external window of the external thermal insulation wall at different installation positions (w/㎡ • k)

^{Table 1 The linear additional heat transfer coefficient of openings in different installation positions of external windows of external insulation walls}                                                                                                                                                                                                         _{w/㎡ • k}

^{Table 2 The linear additional heat transfer coefficient of openings in different installation positions of interior insulation walls and exterior windows}                                                                                                                                                                                                            _{w/㎡ • k}  

^{Table 3 The linear additional heat transfer coefficient of the openings of different installation positions of the outer window of the sandwich insulation}                                                                                                                                                                                           _{w/㎡ • k}

3.4.4 External hanging installation along the outside of the wall

The external hanging installation along the outside of the wall is mainly the installation of ultra-low energy passive doors and windows. The doors and windows are installed on the external insulation layer of the wall, which can effectively control the cold bridge, as shown in Figure 10.

^{Figure 10 The external hanging installation along the outside of the wall}

3.5 Isotherm design

As shown in Figure 12, taking an indoor temperature of 20°C and a relative humidity of 50% as an example, when the air temperature drops to 12.6°C, the critical temperature for mold growth is reached, and when the temperature drops to 9.3°C, the air begins to condense. Therefore, we regard 13°C and 10°C as the two key control temperatures in the energy-saving design of doors and windows. See Figure 11 for the isotherm of the door and window joints, and Figure 12 for the critical temperature of mildew.

^{Figure 11 The isotherm of the door and window joints}

^{Figure 12 The critical temperature of mildew}

To consider anti-condensation and anti-mildew during the heat insulation design of door and window joints, a thermal simulation of heat transfer performance should be carried out, and an isotherm diagram should be drawn. The 10°C isotherm should not expose the indoor surfaces of doors and windows to prevent condensation on the surfaces of doors and windows. The 13°C isotherm should not expose the indoor surfaces of doors and windows to avoid mold growth. The anti-condensation design should be considered as a whole in the heat insulation design of doors and windows. The heat insulation design of the profiles, glass and joint structures that make up the doors and windows and the heat insulation design of the installation nodes should be considered comprehensively. The comprehensive heat insulation performance of each part constitutes the overall performance of the doors and windows. For thermal insulation performance, see Figure 13.

^{Figure 13 The kind of anti-condensation design and anti-mildew design}

4. Calculation and evaluation of condensation on doors and windows

4.1 Indoor humidity calculation options. In the dew condensation design, the indoor humidity is generally selected as 60%. The higher the humidity, the higher the requirements for the material selection of the whole window. For the same profile and the same glass configuration, in a climate environment with an indoor temperature of 20°C and an outdoor temperature of -13°C, the effects of different humidity on the condensation design are shown in Figures 14 to 17 and Tables 4 to 7, respectively.

^{Figure 14 The effects of different humidity on the condensation design 1}

^{Figure 15 The effects of different humidity on the condensation design 2}

^{Figure 16 The effects of different humidity on the condensation design 3}

^{Figure 17 The effects of different humidity on the condensation design 4}

^{Table 4 The condensation calculation results when the humidity is 30%}

^{Table 5 The condensation calculation results when the humidity is 40%}

^{Table 6 The condensation calculation results when the humidity is 50%}

^{Table 7 The condensation calculation results when the humidity is 60%}

4.2 When carrying out the energy-saving design of doors and windows, condensation calculation should be carried out according to various parameters such as local indoor and outdoor temperature and indoor humidity design requirements of the project. The calculation results must all meet the requirements before it can be determined that the condensation calculation and evaluation of the entire window meet the requirements. Require.

5. Mistakes in thermal insulation design

Under normal circumstances, the area of door and window frames accounts for about 25%, and the glass accounts for about 75%. It is believed that as long as glass with a small heat transfer coefficient is used, the overall heat transfer coefficient of doors and windows can be reduced. The hidden danger of condensation is caused by the linear heat transfer coefficient of the joint between the frame and the glass and the incoherence of the isothermal line between the glass and the frame. The door and window frame area accounts for about 25%, and the glass accounts for about 75%. Therefore, many companies adopt high glass and low frame allocation when designing the energy-saving performance of doors and windows.

To reduce the heat transfer coefficient K value of the whole window, it is considered that the glass area accounts for a large proportion. As long as the glass with a lower K value is selected, the heat transfer coefficient of the whole window can be quickly reduced, and the heat transfer coefficient of the frame is ignored. Energy-saving performance of the whole window However, the cold bridge effect and hidden dangers of condensation caused by the incoherence of the isotherm between the glass and the frame profile are ignored. During the actual use of doors and windows, the window frame and the edge of the glass will generate cold bridges, and the thermal insulation performance is not good, resulting in dew condensation. 

There are also a large number of enterprises that ignore the insulation of the installation gap between doors, windows, and openings. During installation and use, thermal bridges and condensation will occur at the joints of doors and windows.

6. Conclusion

Anti-condensation design is the deepening of the energy-saving design of doors and windows, and the anti-condensation design of doors and windows should be considered systematically. The energy-saving design of doors and windows should also be considered in the overall energy-saving design of the building. Therefore, the installation location has an important impact on the overall energy-saving performance of doors and windows.

^{For more information about LIJIANG Glass insulated glass production line and insulated glass producing machine, please click here to learn more}