Case analysis of dew condensation on the inner surface of insulating glass

Insulating glass is widely used in residences, hospitals, schools and shopping malls and other places that indoor environment requires good optical and thermal properties. According to China domestic surveys, the failure rate of insulating glass after two years of use is 3% to 5%, and 63% of the failure cases are due to dew condensation on the inner surface of the insulating glass. The dew point of insulating glass refers to the temperature at which the humidity of the air 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 Chinese standard GB/T11944–2012 “Insulating Glass” clearly stipulates that the dew point of insulating glass should be >-40 ℃ and the expected service life should be at least 15a. According to this regulation, the insulating glass for construction should not have the problem of dew or frost on the inner layer in daily use. The reason for this phenomenon can be attributed to the rise of the dew point of the inner layer of the insulating glass. Therefore, the dew point has become a necessary indicator for judging the quality of insulating glass. This paper starts from the actual case of dew condensation failure of insulating glass in engineering, and detects the dew point of the failed product on site.

1. Project Overview

The project is a high-end residential commercial housing community in Shanghai, with a total construction area of about 900,000 square meters. It is a multi-format urban complex that integrates commercial centers, offices, and business hotels under an internationally renowned brand. There are 18 residential buildings, the highest building height is 90.275m, the floor area ratio is 1.81, and the greening rate is 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 the 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). Dimension of length and width between 540~2220mm, it belongs to jumbo size glass.

2. Problem Description

After checking in in July 2014, the owners found that some of the insulating glass was fogged, and the phenomenon of water droplets hanging on the glass gradually appeared. The insulating glass where this phenomenon occurs is distributed in the balcony, master bedroom, secondary bedroom, study room and kitchen on each floor. This phenomenon occurs regardless of the insulating glass used in the north or south facing housing, and it happens randomly to the insulating glass used for the opening window and the fixed window, and there is no rule to follow. The owner has cleaned the outer surface of the insulating glass several times, but the phenomenon has not improved. And with the passage of time, the phenomenon has become more and more serious. Gradually, some of the insulating glass has lost its transparency, which seriously affects the lighting in the building.

Since the houses purchased by these households are all well-decorated houses, the developer provides a quality guarantee for the house glass. In this regard, both the developer and the community property expressed their willingness to replace the foggy insulating glass for free. However, in the process of using the house, because there are no rules to follow, the owners are restless, worrying that there are problems with other insulating glass, and even potential safety hazards. The developer has never encountered the same problem before, and the developer has actively helped the owner to deal with this problem through testing when the house was handed over, and did not want to hurt the brand because of the quality of the insulating glass. The survey site will find that there is indeed fog and frost 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 occurs, and there is no damage caused by external force.

3. Cause Analysis

The schematic diagram of the insulating glass structure is shown in Figure 1. There is visible moisture in the insulating glass on site, the insulating glass is invalid. In order to find the cause of the problem of insulating glass in this residential area, the developer entrusted a third-party testing company to provide technical support. The technicians first conducted a field survey of the insulating glass in the community, and found that this phenomenon was consistent with the condensation and frosting phenomenon produced in the dew point test of the insulating glass. The unqualified dew point is largely related to the manufacturing environment and use environment of the glass, and is inseparable from the glass pressing process, desiccant and sealant and other edge materials. The quality of the edge sealing material directly affects the service life of the insulating glass. In the change of temperature and humidity environment, the surrounding water and gas continuously penetrate into the insulating glass cavity, so that the desiccant continuously absorbs water until it fails.

Dew point failure can be analyzed from the following reasons:

• According to the spacer material and sealing method of insulating glass, the mandatory certification of safety insulating glass for construction is divided into polysulfide sealing groove aluminum double-sealed insulating glass, silicon glue sealing groove aluminum double-sealing insulating glass, polyurethane sealing groove aluminum double-sealing insulating glass, compound butyl rubber strip sealing insulating glass, hot-melting butyl rubber sealing groove aluminum insulating glass. Nowadays, the most widely used safety insulating glass for construction is polysulfide sealing groove aluminum double-sealed insulating glass, and silicon glue sealing groove aluminum double-sealed insulating glass. In the use of sealant, the quality of the sealant for insulating glass is not good or the thickness and width of the sealant are too small, which will affect the adhesiveness of the sealant. In many cases, the workers do not pay enough attention to processing, the operation is not standardized, and bad sealing technology leads to uneven colloid coating, discontinuity, etc., which will cause the sealant to produce turbidity, discoloration, a large number of bubbles, chalking, intermittent, and glue flow. And the phenomenon that the volatile content in the glue is too high and fogging. The viscosity of the sealant and the glass will be greatly reduced, so that the insulating glass cavity is no longer sealed, and a large amount of water vapor penetrates into the insulating glass cavity, causing the insulating glass to fail, and the sealing effect is poor and the service life is short.
• Processing technology. Insulating glass for construction is a product in which two or more pieces of glass are evenly spaced for effective support, and the periphery is bonded and sealed, so that a dry gas space is formed between the glass layers. The control of the production and processing process is not strict, and there is contamination on the glass surface or the spacer, which leads to a decrease in the adhesion after pressing. Improper operation by the operator will directly lead to the poor assembling effect of the insulating glass and the failure of sealing. After a period of use, the insulating glass will be cracked or unglued, which will lead to condensation and fogging of the insulating glass over time.
• In the selection of desiccant, the unqualified molecular sieve is used as the desiccant, and the result is likely to cause salt precipitation in the spacer, thereby corroding the spacer and causing the molecular sieve to fail and increase the moisture content. The water absorption capacity of the desiccant also affects the moisture content in the insulating glass cavity to a certain extent. Or in the process of processing, the desiccant is exposed to the air for long time, causing the desiccant to fail or partially fail. The factory does not pay attention to the process supervision, the desiccant absorbs too much water, and the sealed insulating cavity has failed.

4.On-site investigation and testing analysis

In order to investigate the condensation and frosting phenomenon of the insulating glass in this community, the technicians first inspected the use of the sealant on site, and found that the sealant strip did not produce a large number of bubbles, chalking and discontinuity, and the outer sealant was uniform and neat and did not exceed the glass edge. However, it is obvious that the thickness and width of the inner sealant are too small. The sealant that does not meet the specified technical requirements affects its adequate bonding and sealing effect with the glass. Secondly, the processing technology and the outside of the glass were observed. There is no obvious scratch on the outer surface of the glass, there is a little stain on the inner surface of the glass, and there is no flow of sealant. Since the project has been put into use for a period of time, it is impossible to determine whether the stains are contamination when the insulating glass is pressing at the factory, or it follows the penetration of water vapor due to the deterioration of the sealing performance in the later stage.

In addition, it is impossible to directly verify the failure of the desiccant without destroying it. It can only be recommended to send a part for inspection later to test the durability of the water vapor seal. The spacer material was visually inspected on site, no distortion, smooth and clean surface, no stains, spots and flake oxidation. There is no foreign matter in the hollow cavity.

Finally, a testing plan was formulated according to the on-site conditions. Since it is difficult to accurately identify the production or delivery batches of glass used in the project installation, the dew point project determined the number of sampling groups to be 1901 pieces according to the test plan and the actual operational conditions on site, and the test volume covered 1,901 pieces. Most of the floor technicians in the community marked the glass of the dew point test sample on the spot, injected ethanol into the dew point tester, and then added dry ice to make the temperature drop below -60℃, after maintaining the contact time, remove the dew point tester, immediately observe the surface if there is such as frost or condensation occurs, and continuously increase the test temperature until -40°C. 1528 pieces of glass with thickness and quantity of 6+12A+6(mm), 437 pieces of glass with 6+0.76+6+12A+6(mm), 16 pieces of glass with 5+0.76+5+9A+5(mm) piece. Due to the high-level safety hazards, the operation of technicians and the placement of equipment and all tests are carried out indoors. In terms of staffing, 2 groups of technicians are arranged, each with a total of 4 devices. Each tester is responsible for one instrument alone, and the cooperating personnel are assigned by the client. Two groups of personnel enter the site in turn, and it is estimated that 4 devices enter the site at the same time. Every day (working time 9:00-17:00), the glass can be tested about approx. 220 pieces, under the condition of ensuring the work intensity and the accuracy of the results, it will take about 18d to complete the test. After arriving at the scene, each equipment is equipped with 1 auxiliary personnel. Before the test, the entrusting party shall number the glass of each window and door in the project, and describe the position of each numbered glass. Numbered and described door and window drawings shall be provided to each tester. The specific test sequence will be fully discussed by both parties before entering the venue. After the detection is completed, the results are summarized in Table 1.

Table 1 Summary of the dew-point test results

Among the 1,608 samples in Block 19, 1,484 samples had dew point <-40℃, and 124 samples had dew point ≥-40℃, which showed condensation and frost, and the failure rate reached 7.71%; Among the 288 samples in Block 20, 245 samples had dew point <-40℃, and 43 samples had dew point ≥-40℃, which showed condensation and frost, and the failure rate reached 14.93%. Among the 1896 samples installed in total, 1729 samples had dew point <-40℃, and 167 samples had dew point ≥-40℃, which showed condensation and frosting, and the failure rate reached 9.66%. On-site inspection of 90 uninstalled samples showed that the dew points were all <-40°C, and no condensation or frost occurred. If there is frost or condensation on the inner surface of the glass sample, the dew point is ≥-40℃ after inspection, which cannot meet the standard. It can be seen that the frosting and dew condensation of the insulating glass is directly related to the failure of the dew point of the product.

5. Solutions

After a large number of field tests, the project was indeed a quality problem of insulating glass, which led to serious condensation and frost problems during use. The developer also replaced the insulating glass for the owners free of charge.

Judging from the situation on site, some insulating glass have problems of substandard dew point even after two to three years in high-end residential areas , but conditions are limited, and it is difficult to confirm whether it is a quality problem of processing, or whether the product is caused by various factors after used two years later. problem. Therefore, the contractor is advised to pay attention to the follow issues when purchasing insulating glass:

(1) Product qualification.

Since the product certification of architectural (safety) insulating glass products began in July 2006, insulating glass manufacturers have been forced to carry out product certification. Insulating glass manufacturers must screen-print or paste CCC logos on the products they sell. The CCC mark is applied to the accompanying documents (such as the certificate of conformity). When purchasing a product, you must first check whether there is a CCC mark, and check whether the purchased product is within the scope of the company’s ability to pass the compulsory certification and whether the certification certificate is valid through the Internet according to the company information, factory number or product certification certificate. At the same time, for the main materials such as sealant and desiccant that affect the product life, the supplier should be confirmed with the manufacturer, and the relevant qualifications of the supplier should be confirmed by checking the certificate.

(2) Admission Inspection

When entering the site, check the appearance quality of the product. The insulating glass must not have stains, inclusions and splashes of sealant that hinder the perspective. Some samples can be appropriately taken and sent to third-party laboratories to verify their quality. The testing company can conduct quality control testing on newly-entered insulating glass. Most of the failures of insulating glass are due to the continuous penetration of water vapor from the edge into the hollow cavity in the environment, and the desiccant eventually loses its water vapor adsorption capacity due to continuous adsorption of water molecules. Due to the change of ambient temperature, the thermal expansion and contraction of the gas in the hollow cavity make the sealant in a state of stress for a long time, and ultraviolet rays and moisture in the environment accelerate the aging of the sealant and accelerate the water vapor entering the hollow cavity. Therefore, the insulating glass cannot reach the expected service life. For example, in this project, the dew point does not meet the standard after only two years of use. For the long-term service life of insulating glass, related tests such as water vapor sealing durability, gas sealing durability, and water vapor permeability of edge sealing materials can be carried out in the laboratory to verify the insulating glass sealant’s ability to block water vapor permeation, molecular sieve The adsorption capacity and the process control level of the insulating glass production process can solve the customer’s worries.

6. Conclusion

After a series of investigations and guidance by on-site and professional technicians, the project has not encountered any quality problems of insulating glass so far.

However, because the project started testing after the problem was discovered, it was already an “ex-post” treatment. Due to the limitations of the site conditions, the cause of the specific failure could not be thoroughly investigated. The on-site dew point detection only represents the dew point performance of the product in the current state (a few years after the project is installed and used), and it cannot explain whether the problem is caused by the aging of the insulating glass over time.

At present, in the production process of insulating glass, manufacturers of different scales have a large gap in the level of production technology, and there is a certain gap in the level, resulting in the quality of the final product. The fluctuation is very large, so it is recommended to carry out systematic quality inspection before the material enters the site, and test the product’s water-vapor sealing durability and other indicators that affect the product’s long-term performance, so as to improve the overall quality of insulating glass and reduce the impact caused by insulating glass.

Source from www.chinaglassnet.com

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