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Peak Temperatures of
Your Climate
This refers to normal
peak summer air temperatures and corresponds
roughly to climate zones. The 109˚F
or less peak summer temperature would be true for much of the
Midwest. Most of southern US would use the 110˚F-119˚F level and the southwest deserts would use
120˚F or
more.
Glass Thickness
How Thick is your
glass? *Note* film may be applied to 1/2 inch thick glass only
if glass is tempered. If the glass is laminated, all layers
must be tempered.
Shadowing
Has considerable impact on glass thermal
stress because it causes uneven heating. Shadowing in the morning hours will
raise stress the most. Meaning any variations illustrated below:
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Straight Shadow |
"L" Shaped Shadow |
"T" or "V" Shaped
Shadow |
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Frame Condition
Will affect how much restriction there is to
glass expansion. Usually rigid frames or deteriorated gaskets will increase the chances of
a cracked pane. Direct metal to glass contact, where no gaskets or sealant are present at
all, add considerable stress to a glass pane as it expands.
Glass Condition
Is the most critical factor affecting a pane's
tendency to crack. Chipped edges severely weaken the strength of glass, and unfortunately,
these are almost impossible to detect without removing the pane. Windows that break
despite application of conservative films are usually due to chipped edges. Remember,
curved edge panes are nearly always chipped or roughly cut therefore, are considerably
weaker than straight edge panes.
Altitude Above Sea Level
Is a temperature related influence. At
higher altitudes, nights are cooler and morning sunlight is stronger. This means in the
morning the glass quickly changes from cold to warm and a wide temperature difference
forms between shadowed and sunlit areas. Wide temperature differences from one spot to
another equals extra thermal stress.
Pane Size
As the pane size
increases so does
chances of mechanical stress from the weight of the glass. Film
application to a windows over 100 square feet (10m2)
is not recommended UNLESS the window is single-pane, heat-strengthened,
or tempered glass.
Calculating square feet by
feet measurements is done like this:
Multiply (feet width) X (feet height) = total square feet
example: 3' X 4' = 12 sq ft.
Calculating square feet by inch measurements is done like this:
Multiply (inch
width divided by 12) X (inch height divided by 12) = total square feet
example:
36"
÷
12 = 3' and 48"
÷
12 = 4'
thus 3' X 4' = 12 sq ft.
Attachments
Tends to thermally insulate a window and slow the
dissipation of heat gained by solar absorption. Closer, darker, interior drapes and blinds
means a higher glass temperature.
Close fitting curtains or blinds within 4 inches
(10cm) of window
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