Case study on condensation on the inner surface of insulating glass in construction engineering.

Due to its good optical and thermal properties, insulated glass is widely used in residences, hospitals, schools, shopping malls, and other places that require indoor environments. According to a survey by relevant foreign glass organizations, the failure rate of insulating glass after two years of use is 3% to 5%, and 63% of the failure cases are due to condensation on the inner surface of the insulating glass. The dew point of insulating glass refers to the temperature when the air humidity sealed in the air layer reaches a saturated state. When the temperature of the surface layer is lower than this temperature, the water vapor in the air layer will condense or frost on the inner surface of the glass. The international industry standard "Insulating Glass" clearly stipulates that the dew point of insulating glass should be N-40°C and the expected service life should be at least 15 years. According to this regulation, insulating glass for construction should not have condensation or frosting problems on the inner layer during daily use. The reason for this phenomenon can be attributed to the increase in the dew point of the inner layer of the insulating glass. Therefore, dew point has become a necessary indicator to judge the quality of insulating glass. This article starts from the actual case of insulating glass condensation failure in engineering and detects the dew point of the failed product on site.

1. Project Overview

This project is a high-end commercial housing complex in Shanghai City on China, with a total construction area of approximately 900,000㎡. It is a multi-format urban complex under an internationally renowned brand that integrates commercial centers, offices, and business hotels. There are 18 residential buildings in total, with a maximum building height of 90.275m, a floor area ratio of 1.81, and a greening rate of 36%. The project started construction in 2012 and was completed in 2014. It was delivered in the same year and the occupancy rate reached 80%. The light-transmitting parts of this project mainly use insulating glass with thicknesses of 6+ 12A+6 (mm), 6 + 0,76 + 6 + 12A + 6 (mm), and 5 + 0.76 + 5 + 9A + 5 (mm). The length and width are between 540~2220mm, which is a super large glass.

2. Problem Description

After moving in July 2014, the owners gradually discovered that some of the insulating glass had fogged up, and water droplets gradually appeared on the walls. The insulating glass where this phenomenon occurs is distributed on the balcony, master bedroom, secondary bedroom, study room, and kitchen on each floor. This phenomenon occurs in the insulating glass used in houses facing north and south, and it occurs randomly in the insulating glass used in opening fans and fixed fans, with no rules to follow. The owner has cleaned the outer surface of the insulating glass many times, but the problem has not improved. And as time goes by, this phenomenon becomes more and more serious. Gradually, part of the insulating glass has lost its sense of transparency, seriously affecting the lighting inside the building.

Because the developer provides a warranty on the glass of the house. In this regard, both the developer and the community property management expressed their willingness to replace the atomized insulating glass for free. However, during the use of the house, because there are no rules to follow, the owners are restless and worried that there are problems with other insulating glass and even potential safety hazards. The developer has not encountered the same problem before and it has passed the inspection when the house was handed over. The developer actively helps the owners deal with this problem and does not want to harm the brand due to the quality problems of the insulating glass. During the on-site inspection, it will be found that there is indeed fogging and frosting on the inner surface of some insulating glass. There are no obvious impact marks on the inner and outer surfaces of the glass where fogging and frosting occur, and there are no signs of damage caused by external force.

3. Reasons Analysis

The schematic diagram of the insulating glass structure is shown in Figure 1. If there is visible moisture in the insulating glass on site, the insulating glass has failed. To find the cause of the problem with the insulating glass in the residential area, the business entrusted a third-party testing company to provide technical support. The technicians first conducted an on-site survey of the insulating glass in the community and found that this phenomenon was consistent with the condensation and frosting phenomenon produced during the dew point test of the insulating glass. The failure of the dew point is largely related to the manufacturing environment and the use environment of the glass. It is inseparable from the glass processing and lamination process, desiccant, sealant, and other edge materials. The quality of edge sealing materials directly affects the service life of insulating glass. In the change of temperature and humidity environment, the surrounding water vapor continuously penetrates the insulating glass cavity, causing the desiccant to absorb moisture until it fails.

^{Figure 1 The Schematic diagram of insulating glass structure 1}

The reasons why the insulating glass dew point does not meet the standard can be analyzed from the following reasons:

3.1 Sealant. 

According to the spacer material and sealing method of the insulating glass, the safety insulating glass for construction is compulsorily certified into polysulfide sealing groove aluminum double-pass sealing insulating glass, silicone rubber sealing groove aluminum double-pass sealing insulating glass, polyurethane sealing groove aluminum Type double-channel sealed insulating glass, composite butyl rubber strip sealed insulating glass, hot melt butyl rubber sealed groove aluminum insulating glass. Nowadays, the two types of safety insulating glass used in buildings are polysulfide-sealed aluminum double-pass sealed insulating glass and silicone rubber-sealed aluminum double-pass sealed insulating glass. When it comes to the use of sealant, if the quality of the sealant for the insulating glass is poor or the thickness and width of the sealant are too small, it will affect the adhesion of the sealant. In many cases, workers do not pay enough attention to the construction, the operations are not standardized, and the lack of technology during glue application leads to uneven colloid coating. (The problem of uneven artificial coating can be solved by using LIJIANG Glass fully automatic insulating glass sealing robot line or butyl extruder coating equipment. ) discontinuity, etc. will cause the sealant to produce turbidity, discoloration, a large number of bubbles, powdering, discontinuity, sealant sealing flow, and fogging due to too high volatile content in the sealant. The viscosity between the sealant and the glass will be greatly reduced, causing the insulating glass cavity to no longer be sealed. A large amount of water vapor will penetrate the insulating glass cavity, causing the insulating glass to fail, with a poor sealing effect and short service life.

3.2 Processing technology. 

Insulating glass for construction is a glass product in which two or more pieces of glass are evenly spaced with effective support and bonded and sealed around the edges so that a dry inert gas space is formed between the glass layers. The control of the production and construction process is not strict, and there are stains on the glass surface or spacer strips, resulting in a decrease in adhesion after joining the sheets. Improper operation by the operator will directly lead to poor insulating glass joining effect and sealing failure. (The problem of poor insulating glass joining can be solved by using the LIJIANG Glass outer plate pressure-inflated automated insulating glass production line.) After being used for some time, the insulating glass will glass may crack or debond, which may lead to condensation and fogging of the insulating glass over time.

3.3 Molecular Sieve Desiccant. 

In the selection of desiccant, if an unqualified molecular sieve is used as the desiccant, the result is likely to cause salt precipitation in the spacer bars, thereby corroding the spacer bars, causing the molecular sieve to fail and the moisture content to increase. The water absorption capacity of the desiccant also affects the moisture content in the insulating glass cavity to a certain extent. During the processing, the desiccant is exposed to the air for too long, causing the desiccant to fail or partially fail, and the factory does not pay attention to process supervision. (The use of LIJIANG Glass automatic insualting glass molecular sieve filling machine can solve the problem of insulating glass molecular sieve desiccant poor filling effect) The desiccant absorbs too much water and the sealing in the hollow cavity has failed.

4. On-site investigation and detection analysis

To investigate the condensation and frosting phenomenon on the insulating glass in this community, technicians first inspected the use of sealant on site and found that there were not a large number of bubbles, powdering, and discontinuities in the sealing strips. The exterior sealant was even and tidy and did not extend beyond the glass. However, the thickness and width of the inner channel sealant are too small. Sealants that do not meet the specified technical requirements affect their adequate bonding and sealing effect with the glass. Secondly, the processing technology and glass surface were observed. There are no obvious scratches on the outer surface of the glass, there are some stains on the inner surface of the glass, and there is no leakage of sealant. Since the project has been put into use for some time, it is impossible to determine whether the stains are caused by contamination when the insulating glass sheets are assembled at the factory, or whether they are due to water vapor penetration due to the decreased in sealing performance at a later stage.

Furthermore, it is impossible to directly verify the failure of the desiccant without destroying it. We can only recommend that a part be sent for inspection later to test the durability of the water vapor seal. The spacer material was visually inspected on site and found to be free of distortion, the surface was smooth and smooth, and there were no stains, spots, or flaky oxidation. There are no foreign objects in the insulating glass cavity.

Finally, a testing plan was formulated based on the on-site conditions. Since it was difficult to accurately identify the production or delivery batch of glass used during project installation, the dew point project determined the number of sampling groups to be 1901 pieces based on the testing plan and actual on-site operability conditions. The test volume covered Most floors in this complex. The technician marked the glass of the dew point test sample on-site, injected ethanol into the dew point meter, and then added dry ice to reduce the temperature to below -60°C. After maintaining the contact time, remove the dew point meter and observe the surface immediately, such as Frost or condensation, and continuously increase the test temperature to -40℃. The thickness and quantity are 1528 pieces of glass of 6+12A+6 (mm) and 437 pieces of glass of 6+0,76+6+12A+6 (mm). 16 pieces of glass, 5+0.76+5+9A+5 (mm). Due to the safety hazards of high-rise buildings, the operation of technicians, the placement of equipment, and all tests were conducted indoors. In terms of staffing, 2 groups of technicians were arranged, with a total of 4 pieces of equipment in each group. Each tester is responsible for one piece of equipment, and the cooperating personnel are appointed by the client. Two groups of personnel take turns to enter the site. It is estimated that if four pieces of equipment enter the site at the same time, the glass can be tested for about 10 hours every day (working hours 9:00-17:00) 220 pieces, take about 18 days to complete the test while ensuring the work intensity and accuracy of the results. After arriving at the scene, each piece of equipment will be assigned an auxiliary person. Before testing, the client should fixedly number the glass of each window and door in the project, and describe the location of each numbered glass. Numbered and described drawings of windows and doors should be given to each tester. The specific test sequence will be fully discussed by both parties before entering the site. After the test is completed, the results are summarized in Table 1.

Table 1 Summary of dew point detection results

Among the 1,608 samples in Building 19 for this on-site inspection, 1,484 samples had a dew point of <-40°C, and 124 samples had a dew point of less than -40°C, showing condensation and frost. The failure rate reached 7.71%, 20 Among the 288 samples in Building No. 2, 245 samples had a dew point of V-40°C, and 43 samples had a dew point >-40°C, with condensation and frost appearing, and the failure rate reached 14.93%. Among a total of 1,896 samples installed, 1,729 samples had a dew point <-40°C, and 167 samples had a dew point of N-40°C, showing condensation and frosting. The failure rate reached 9.66%. On-site inspection of 90 uninstalled samples showed that the dew points were all V-40°C, and no condensation or frost occurred. If frost or dew appears on the inner surface of the glass sample, the dew point after inspection is 40 °C, which cannot meet the standards. It can be seen that the occurrence of frost and dew on insulating glass is directly related to the dew point of the product not reaching the standard.

5. Solutions

After a large number of on-site tests, it was found that the quality of the insulating glass caused serious condensation and frosting problems during use. The developer also replaced the insulating glass for free for the owners.

Judging from the on-site situation, even in high-end residential areas, some insulating glass has problems with dew points not meeting standards after two to three years. However, due to limited conditions, it is impossible to confirm whether it is a quality problem at the entrance or a product failure due to various factors after two years. question. Therefore, it is recommended that project purchasers should pay attention to the following issues:

5.1 Product Qualifications. 

Since the product certification of architectural (safety) insulating glass products was launched in July 2006, insulating glass manufacturers have been forced to undergo product certification. The companies must silk-print or affix the 3C logo on the product body for sale, or on its minimum outer packaging. And add the 3c mark to the accompanying documents (such as the certificate of conformity). When purchasing products, you must first check whether there is a 3C mark, and check online based on the company information, factory number product certification certificate, etc., whether the purchased product is within the capabilities of the company that has passed compulsory certification, and whether the certification certificate is valid. At the same time, for major materials such as sealants and desiccants that affect product life, you should confirm the supplier with the manufacturer and check the certificate to confirm the supplier's relevant qualifications.

5.2 Admission Inspection. 

Check the appearance quality of the product when entering the site. The insulating glass must not have stains, inclusions, or sealant splashes that hinder perspective. Some samples can be appropriately taken and sent to a third-party laboratory for inspection to verify their quality. The testing company can conduct quality control testing on newly imported insulating glass. Most insulating glass failures are due to the continuous penetration of water vapor in the environment from the edges into the hollow cavity. The desiccant eventually loses its water vapor adsorption capacity due to the continuous adsorption of water molecules. Due to changes in ambient temperature, the thermal expansion and contraction of the gas in the hollow cavity puts the sealant under stress for a long time, and ultraviolet rays, water vapor, etc. in the environment accelerate the aging of the sealant and accelerate the entry of water vapor into the hollow cavity. Therefore, the insulating glass cannot reach the expected service life. For example, in this project, the dew point did not meet the standard after only two years of use. Given the long-term service life of the insulating glass, relevant tests such as water vapor seal durability, gas seal durability, and edge sealing material water vapor permeability can be conducted in the laboratory to verify the ability of the insulating glass sealant to block water vapor penetration and the molecular sieve performance. The adsorption capacity and process control level of the insulating glass production process solve customers' worries.

6. Conclusion

After a series of on-site inspections and guidance by professional technicians, this project has not had any quality problems with the insulating glass so far. However, since the project only started testing after the problem was discovered, it was already a "post-facto" treatment. Due to the limitations of on-site conditions, the specific cause of the failure could not be thoroughly investigated. On-site dew point testing only represents the dew point performance of the product in its current state (several years after the project is installed and used), and cannot explain whether the problem is caused by the aging of the insulating glass over time. In the current production process of insulating glass, manufacturers of different sizes have a relatively large gap in the level of production technology, resulting in a certain gap in the quality of the final product. The profit-seeking behavior of some companies has also caused the quality of insulating glass to decline. Fluctuations are very large, so it is recommended that before the glass and other building materials enter the site, systematic quality testing should be carried out to test the water and air-sealing durability of the product and other indicators that affect the long-term performance of the product. Only in this way can the overall quality of insulating glass be improved and the quality of insulating glass belts reduced.

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