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U-Factors for Plexiglas® Sheet
The amount of heat conducted through Plexiglas® glazing is slightly lower than for glass of the same thickness. The values tabulated below are U-factors for vertical (windows) and horizontal (skylights) Plexiglas® glazing. R-values = 1/U-value. U-values are largely unaffected by the color of Plexiglas® sheet.
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Table 12: U-Factor for Vertical Windows (BTU/hr./sq.ft./°F) |
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Construction |
Winter Heat Loss*
Sheet Thickness (in) |
Summer Heat Gain**
Sheet Thickness (in) |
|
.118 |
.177 |
.236 |
.354 |
.472 |
.118 |
.177 |
.236 |
.354 |
.944 |
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Single-Glazed |
1.06 |
1.01 |
0.96 |
0.88 |
0.81 |
0.98 |
0.93 |
0.89 |
0.82 |
0.76 |
|
Double-Glazed 1/4" air space |
0.55 |
0.52 |
0.49 |
- |
- |
0.56 |
0.53 |
0.50 |
- |
- |
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Double-Glazed 1/2" air space |
0.47 |
0.45 |
0.43 |
- |
- |
0.50 |
0.48 |
0.45 |
- |
- | *15mph wind velocity.
**7.5 mph wind verlocity
Table 13: U-Factor for Horizontal Panels
(BTU/hr/sq ft/°F) |
Description
Plastic Bubbles |
Winter* |
Summer** |
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Single-Walled |
1.15 |
0.80 |
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Double-Walled |
0.70 |
0.46 | *Values from ASHRAE Handbook of Fundamentals. Thickness not listed; assume 3/16".
**Based on area of opening, not total surface area.
Total Energy Transfer Through Skylights
Computer programs are available to calculate the complicated balance of energies due to solar heat gain, heat transfer, daylight and electrical lighting.
Many of the national skylight firms offer this calculation service. In addition, a Skylight Energy Handbook or an IBM computer disc is available by writing: AAMA,1827 Walden Office Square, Suite 104, Schaumburg, IL 60173; or by calling (847) 303-5664
INTERIOR INSULATING WINDOWS
Interior insulating windows are a relatively new idea. Unlike exterior storm windows, interior insulating windows glazed with Plexiglas® acrylic sheet can be virtually airtight. The Plexiglas® sheet sets up a thermal cavity between the single-glazed window and the inside of a building.
This arrangement cuts energy losses at every window while creating a more comfortable, draft-free interior. And the idea works year-round, preventing winter heat from getting out, and summer heat from getting in. Interior insulating windows also reduce troublesome noise transmissions through single-glass glazing by approximately 10 decibels over the entire sound spectrum.
Plexiglas® glazing may only be used for interior insulating windows under building codes that permit combustable interior windows in the same manner as combustable primary windows. (See building codes for more information)
Plexiglas® sheet in 0.80" and greater thicknesses meets the requirements of the ANSI Z97.1 standard for safety glazing materials (see "Building Codes" for more information).
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