Analysis of the causes and control measures of dew condensation inside the insulating glass
An internal condensation is a typical form of insulating glass sealing failure. Many glass deep-processing manufacturers often encounter such as what is the typical condensation phenomenon of insulating glass, what is the dew point of insulating glass, and the relationship between dew point and temperature and relative humidity problems. As a manufacturer of insulating glass automation equipment for many years, Jinan LIJIANG Glass will focus on how to test the dew point of insulating glass, the influencing factors, and control measures of the dew point insulating glass.
1. The dew condensation inside the insulating glass
An internal condensation is a typical form of insulating glass seal failure. According to a survey, the failure rate of insulating glass after two years of use is 3% to 5%, and 60% of the failures are caused by condensation inside the insulating glass. The typical phenomenon is shown in the figure below.
Figure 1 The dew condensation inside the insulating glass 1
Condensation of the insulating glass will reduce the transparency of the glass, affect the thermal insulation effect, and the accumulation of water vapor will also cause mildew, and in severe cases, the outer glass will fall off.
Figure 2 The dew condensation inside the insulating glass 2
The condensation performance of insulating glass is characterized by dew point, so what is the dew point of insulating glass?
2. What is the dew point of 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, and is an important indicator to reflect the sealing performance of insulating glass. When the temperature of the glass surface in the hollow layer is lower than the dew point of the air in the air layer, the water in the air will condense or frost on the inner surface of the glass. There is a one-to-one correspondence between dew point and air temperature and relative humidity. The higher the relative humidity, the higher the dew point temperature; conversely, the lower the relative humidity, the lower the dew point temperature.
So can we determine the air dew point by air temperature and relative humidity?
3. The relationship between dew point and temperature and relative humidity
The relationship between dew point and air temperature and relative humidity can be obtained in several ways: psychrometric diagram, look-up table method, formula method, etc.
Enthalpy hygrogram method. The dew point temperature can be determined by querying the dry bulb temperature, relative humidity, enthalpy line, etc. of the enthalpy-humidity diagram. The typical enthalpy-humidity diagram is shown in the figure below.
Figure 3 The Enthalpy hygrogram method of insulating glass dew point 1
Look-up table method. Calculate the dew point temperature at a certain temperature and relative humidity by querying the partial pressure of saturated water vapor at different temperatures. The partial pressure of saturated water vapor at different temperatures under standard atmospheric pressure is shown in the table below.
Table 1 Partial pressure of saturated water vapor at different temperatures at standard atmospheric pressure
Taking the relative humidity of 50% at 20 °C as an example, the partial pressure of saturated water vapor is 2337.1 × 50% = 1168.55, and the corresponding temperature is about 9.3 °C, which is the corresponding dew point temperature. formula method. Calculate according to the formula given in "5.2 Dew Point Temperature Calculation" in the international industry standard "Thermal Calculation Regulations for Building Doors, Windows, Glass Curtain Walls".
Under a certain air relative humidity f, the water vapor pressure e of the air can be calculated as follows:
in this formula:
e--water vapor pressure of air
f--relative humidity of the air
E--Saturated water vapor pressure of air
The dew point temperature of air can be calculated as follows:
T--dew point temperature of air
e--water vapor pressure of air
a、b--parameter，a=7.5，b=237.3.
These are three methods for determining the dew point temperature summarized by Jinan LIJIANG Glass, the psychrometric method, the table look-up method, and the formula method. Through theory, the dew point temperature at a certain temperature and relative humidity can be determined, which provides a theory for the control of condensation inside the insulating glass.
So how to quickly judge the dew point of insulating glass in practice?
4. What are the dew point test methods for insulating glass?
The dew point test method for insulating glass is specified in the international industry standard "Insulating Glass" and the international industry standard "Construction Quality Acceptance Standards for Building Energy-saving Projects". The international industry-standard "Insulating Glass" provides the requirement that "the dew point of insulating glass should be <-40 ℃", and the corresponding test method is given in the "7.3 Dew Point Test".
Sample: 510 mm×360 mm, 15 pieces;Test conditions: 23 ℃±2 ℃, relative humidity 30%~75%, placed for at least 24 hours;Test equipment: dew point meter, the measuring surface is made of copper material, the measuring range can reach -60 ℃, and the accuracy is ≤ 1 ℃. The international industry-standard "Acceptance Standards for Construction Quality of Building Energy-saving Projects" provides the test method for the sealing performance of insulating glass, namely the dew point test method, in "Appendix E Test Method for Sealing Performance of Insulating Glass".
Figure 4 The insulating glass dew point detector 1
Dew point meter: the height of the measuring tube is 300 mm, and the diameter of the measuring surface is 50 mm;
Thermometer: The measuring range is -80 ℃~30 ℃, and the accuracy is 1 ℃.
Samples: 10 samples per group, should be placed in laboratory environment conditions for more than 24 hours before testing.
Conditions: 25 ℃±3 ℃, relative humidity 30%~75%.
What needs to be emphasized here is that the "sealing performance of insulating glass" in "5.2.2" and "6.2.2" of the international industry standard "Construction Quality Acceptance Standards for Building Energy Conservation Projects" and the international industry standard "Insulating glass sealing performance" during the re-examination of the performance of curtain walls and doors and windows The sealing performance mentioned in "Glass" is different.
The sealing performance of insulating glass in the international industry standard "Acceptance Standards for Construction Quality of Building Energy-saving Projects" is tested according to "Appendix E", which is actually to try the dew point of insulating glass; "Sealing durability performance" and "hermetic sealing durability performance" are in a parallel relationship with "dew point". When the international industry standard "Insulating Glass" is used for project acceptance, the sealing performance of insulating glass is the dew point.
5. Insulating glass dew point influencing factors and countermeasures
The factors affecting the dew point of insulating glass mainly include the following aspects:
5.1 The relative humidity of the production environment. The production environment's relative humidity mainly affects the desiccant's adequate adsorption capacity and residual adsorption capacity. When the relative humidity of the insulating glass laminate space is high, on the one hand, there is a large amount of water vapor in the air layer of the insulating glass, and on the other hand, the residual adsorption capacity of the desiccant will be reduced, especially when the desiccant is exposed to the air for too long.
5.2 The insulating glass desiccant filling quantity and quality. Some manufacturers will using the manual filling desiccant processes, rather than using the automatic desiccant filling machine, the manual processing can't guarantee a stable filling amount, resulting in insufficient absorption capacity of the desiccant; some inferior desiccants cannot effectively absorb water molecules, or react with water molecules to cause spacer corrosion.
5.3 The insulating glass edge sealing quality. Most of the insulating glass water vapor seals rely on butyl rubber, some of which are difficult to guarantee when manually applying butyl rubber, rather than using the automatic butyl rubber coating equipment, which will lead to sealing failure; some secondary sealants are doped with white oil, which dissolves the butyl rubber and causes flow oil and water vapor. Leakage; the edge of the Low-E glass is not removed or the treatment is incomplete, the edge sealant is not reliably bonded, and the moisture intrusion causes the oxidation of the film, etc.
It can be seen from this that the relative humidity and the exposure time of the desiccant in the air during the production of insulating glass are strictly controlled, and the high-quality desiccant and stable and reliable filling process are selected to ensure the quality of butyl rubber and secondary sealant materials and glue, and timely and effective quality inspection, adopts a more intelligent automatic producing solution for insulating glass is the key to controlling the dew point of insulating glass.
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