Pre-inflating/pre-deflating

IGUs initially can be made with a preset positive or negative pressure, induced by pre-inflating or pre-deflating during fabrication. This is achieved by removing or injecting gas to increase or decrease the volume by a specific amount, which mimics the effect of the atmospheric pressure typical of the installation site. This allows the glass to be manufactured at one elevation and adjusted to the desired cavity condition at its pre-determined destination. Pre-inflating/deflating is a method used to adjust a unit for its elevation at the final destination. In many cases, however, it does not compensate for changes in elevation during transit to the final location. Depending on the application, pre-inflating/deflating may help lower the effect of elevation changes during transit or it may make them worse.

Pre-inflated or pre-deflated IGUs will likely have a convex or concave shape during glazing if they are installed at an elevation that is the same as where they were manufactured. The degree of concavity/convexity can vary significantly depending on the size, aspect ratio, and degree of pre-inflation/pre-deflation.

This method does have some limitations and may not work for all IGU configurations due to increased stress on the glass. Pre-inflated/pre-deflated windows may be unable to operate until they reach the design elevation. This is especially true of horizontal and vertical sliding windows that are convex after adjustment. Pre-inflated/pre-deflated IGUs also can cause challenges related to installation of external muntin bars.

Adjustment of IGUs for change in elevation may induce additional stress on the edge seal from the time of manufacture until it reaches its final installed elevation. Many IGUs can handle this added stress, but the degree of stress, the size of the IGU, the spacer, the sealant, and the glass all need to be considered to determine when pre-inflation/pre-deflation is appropriate.

Temperature manipulation

Here, the environment is controlled through heating or cooling of the entire IGU prior to sealing and/or gas filling, affecting the volume according to the gas pressure equation. Temperature manipulation also will cause convex or concave conditions in the IGU at the time of installation.

Bladder relief system

Specifying the use of a flexible container, also known as a ‘bladder’ system, can counter pressure differentials due to elevation changes between the points of manufacture and installation. These pressure changes can be intensified by internal heating of the IGU due to the radiant effects of the sun, which are common at higher elevations. A bladder system acts as a mechanism for relieving this accumulated pressure differential over a brief period. It can be temporary, such as for use during transport, or permanent upon installation at the final construction site.

A bladder is attached to the IGU cavity, typically via an access tube, to control the internal pressure during shipping. Commonly made of coated plastic or foil, the bladder is removed once the IGU has reached the jobsite and then is sealed. Be aware bladder access tubes may not be of sufficient diameter to enable pressure equalization over such short periods of extreme pressure changes experienced during transit. Such IGUs should be treated as if there were no access tubes and packaged to effectively manage glass and edge seal stress.

Permanent bladder application is like what is used for transportation, but the bladder stays active to occasionally equalize pressure as needed throughout the life of the IGU. It can be used for a single IGU or in parallel with multiple IGUs.

When installing IGUs using a flexible container/bladder system, the installing contractor or glazier should take care to confirm:

• The IGU is glazed in accordance with the bladder manufacturer’s written recommendations.
• The IGU is fabricated with a bladder system that will remain permanently operational for the life of the IGU, and all tubing connections do not leak.
• For IGUs fabricated with bladder systems, where the bladder will be removed and access tubes sealed at installation, the IGU and/or bladder manufacturer’s written instructions for removal must be provided. Proper removal of the bladder should ensure no damage occurs to the IGU’s edge seal, and the access tube itself is properly sealed.