Volume 8, Issue 6 - June 2007


Preventing the Great Escape
by Jim Plavecsky

With energy conversation and ecological thinking becoming ever-important, consumer interest in energy saving technology is at an all-time high. Vinyl, wood and thermally-broken aluminum frames have taken over. Low-E coatings are more popular than ever. Warm-edge technology is a given. However, gas-filling, although very popular, remains somewhat controversial. Several lawsuits have caught the attention of the industry (see sidebar) and these have led to a heightened concern among manufacturers with respect to gas-fill rates and long-term gas retention. Homeowners want to be reassured that their windows are gas-filled to the proper level. And once that is accomplished, what about gas retention? The minute an insulating glass (IG) unit is gas-filled, the gas starts trying to escape. It is inevitable that it eventually will. The question is “How do we make this a very long time?”

Measurement Dilemma
A decade ago, manufacturers were filling IG units with gas without worrying about actual fill-rate levels. Also, there was not a big concern about how long the gas would stay in the unit. After all, homeowners could not see the gas, so there was no way for anyone to really question how much gas was inside a window or how long it would stay there. I actually had one client, however, who wanted to add an odorant to his argon. He would make it smell like roses, and he wanted to add a valve on the window so that the homeowner could check to see if the argon was in the window. Ah yes, the occasional smell of roses was the reassurance that the homeowner needed. The only problem with this is that each time that one would check for the smell of roses, a portion of argon was being released from the unit. Also, a hole had to be drilled through the unit to install the valve. There was a big concern that the integrity of the sealed unit was compromised. The area around the valve was a possible leakage concern. What the industry needed was simply a quick and non-destructive way of measuring argon content in an IG unit making it easier for us to ensure the homeowner that he or she is getting a properly-filled window. 

Enter Sparklike
Sparklike’s Gasglass instrument now offers the manufacturer a quick and non-evasive technique for measuring the argon content of an IG unit. High voltage (50,000 volts) is used to excite the argon atoms contained in the IG unit. When excited, argon emits light, which is measured by the instrument’s spectrometer. The amount of light emitted correlates to the amount of argon contained within the unit, and the resulting argon percentage is shown on the display instantly. Now, the IG fabricator can quickly check the effectiveness of the gas-filling equipment and workmanship practices employed. The latter cannot be overemphasized. 

Many fabricators seal a unit leaving one corner open or create a separate opening through which a filling/sniffling wand is placed. Argon or krypton flows into the unit through the filling wand while the sniffling port sucks air from the cavity and analyzes for oxygen. The absence of oxygen indicates the unit is full and shuts off the flow of argon or krypton. Once the unit is filled, the area where entry was made needs to be sealed with the application of a gas impermeable sealant. This is a critical workmanship step. Hot sealant is applied against sealant that has already cooled, and care must be taken to make sure that this is a high integrity patch. If not, when the unit expands and contracts, a fissure could develop resulting in rapid gas loss. For this reason, some fabricators have invested in gas-filling presses which seal the unit inside of a cavity while being flooded with argon. The advantage of this method is that the argon is trapped within the unit as it is sealed so that no entry gap is required. There are no concerns with how well the entry gap has been sealed because there is no entry gap.

Handy Solution
What is better yet is that this device is portable. It fits into a briefcase. So, not only can it be used to measure argon content in the factory, but it can also be used to measure argon content in units that have been installed for long periods of time. This can help us determine real-world gas retention. 

This is especially important because when argon permeates through the IG sealing system, it does so faster that air permeates from the outside to within the unit. Each gas behaves independently from the others and permeates through a polymeric sealant at its own rate. Scientists use the laws of entropy to describe these types of movements. Argon is present in air naturally at a concentration of slightly under one percent. So when we pack a large umber of argon gas particles into a confined space, we are adding order to the world. Entropy change has often been defined as a change to a more disordered state at a molecular level. Gas wants to migrate from areas of high concentration to areas of lower concentration, and the greater the disparity in concentration, the faster the gas movement. For each gas, this rate is related to the difference in the amount of that gas on each side of the barrier. Air is a mixture containing 78-percent nitrogen, less than 21-percent oxygen, and less than 1-percent argon. If an IG unit is filled with 95-percent argon, the ratios of each gas from the high concentration side to the low concentration side are shown in the table. A larger ratio indicates a greater disparity, and, therefore, a greater driving force for gas migration. As you can see, the driving force for argon to return to its natural state is the greatest compared to the other gases. Therefore, it will move faster from inside to outside while the other gases are entering the IG unit at a slower pace. 

Strains and Stresses
Over a long period of time, this can result in a negative pressure differential inside the unit and lead to unit deflection, especially with thinner glass. When the glass deflects, it reduces the gap between the two panes of glass resulting in an increase in heat transfer. The insulation value of the IG unit diminishes. Glass deflection also puts strain on the edge of the IG unit and this can increase the likelihood of stress cracks and sealant failure. The glass deflection also results in visible glass distortion as the IG unit becomes somewhat of a concave lens. Temperature extremes make matters worse. High temperatures increase permeation rates as the molecules of each gas become excited and move faster. Extremely low temperatures can reduce the effectiveness of the sealants as flexibility is reduced. Ultraviolet (UV) light can also degrade the effectiveness of sealants causing them to harden and crack. This could result in a loss in sealing capabilities. Ideally, IG spacer-sealant systems should combine components which are highly-resistant to gas permeability and also are very resistant to UV degradation. A traditional dual seal system combines a polyisobutylene sealant on the sides of the spacer in combination with a silicone or other structural sealant on the backside of the spacer. Other IG fabricators use a highly-resistant structural silicone foam spacer combined with a highly gas impermeable secondary sealant on the backside. The sealant is shielded from UV exposure as it is imbedded into the sash, while the spacer facing the inside of the IG unit acts as a UV shield. 

IG and window fabricators should be very concerned with the type of spacer-sealant combination used in the IG unit as well as the workmanship practices in place during unit fabrication. Fabricators of IG units exhibiting high rates of gas permeability and gas loss have much more to lose than the gas itself. The end result could result in high warranty expense, lawsuits, negative publicity and loss of reputation. These are all big reasons to prevent the great escape! 

Jim Plavecsky is the owner of Windowtech Sales Inc., a sales and consulting firm specializing in the door and window industry based in Columbus, Ohio. 


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