Chicago Window Expert Nobody knows more about windows.

Mark Meshulam is an expert witness and consultant for low-e glass.
These days, everybody wants Low-E glass, but what the heck is it?

Low-E is short for low emissivity. Emissivity is a measure of radiation of absorbed energy. To fully grasp how glass with low emissivity can improve thermal performance, let’s look at the electromagnetic spectrum. A portion of that spectrum is the solar spectrum (ultraviolet, visible light and infrared). The areas of concern to us and our windows are visible light, and far infrared, otherwise known as “heat”.

Visible light and infrared radiation (heat) occupy adjacent but separate parts of the electromagnetic spectrum. These data were obtained from the NASA Langley Research Center Atmospheric Sciences Data Center

Visible light and infrared radiation (heat) occupy adjacent but separate parts of the electromagnetic spectrum. These data were obtained from the NASA Langley Research Center Atmospheric Sciences Data Center

Visible light has wavelengths within the range of 400 to 700 nanometers. Far infrared radiation, or heat, has wavelengths in the range of 25-350 microns.

For your next Trivial Pursuit game, 1 nanometer equals one millionth of a millimeter. 1 micron equals one thousandth of a millimeter.

When sunlight shines through your window, it is in those relatively short wavelengths (400-700 nm). The sunlight energy is absorbed by your floors, walls and furnishings and air. Many of these things, especially if they are dark, are high-emissivity. Remember the definition:
Emissivity is a measure of radiation of absorbed energy
Objects, especially if they are dark, absorb (rather than reflect) more of the sun’s energy, and they therefore also emit (or radiate) more of that energy. When they emit the absorbed energy, it is in the form of heat, or infrared radiation.

So your favorite black leather sofa can also be a solar heat radiator. If your house used passive solar design, it would be not only black, but green.

Your stylish black sofa is is a passive solar collector. After absorbing light energy from the sun, it releases that energy in longer wavelength infrared radiation, heating your living space.

Your stylish black sofa is is a passive solar collector. After absorbing light energy from the sun, it releases that energy in longer wavelength infrared radiation, heating your swingin' bachelor pad.


What does this all have to do with Low-E Glass?
Excellent question, imaginary respondent! As your sleek sofa radiates infrared waves, some of them (the waves, not the couch) hit your windows. If your windows are not Low-E, most of these waves will go through the glass and go on to warm your neighborhood.

Now here’s the punchline: If your glass is Low-E, due to its low emissivity, it will reflect those long wavelengths, i.e. heat, back into the room. Although Low-E glass is thought of as an insulator and is measured for insulating value, Low-E glass is not an insulator in the traditional sense of a thermally dead space. Rather it is a reflector of heat. Yet, by allowing visible light to pass through, while reflecting infrared heat, Low-E glass produces improved insulation against heat loss.
< ?php if(function_exists('announcer')) { announcer();} ?>
How much better is Low-E glass?
Another great question, my imaginary friend. Here is a chart for your edification. The U Value is the measurement of heat loss through an object (such as our glass) measured in BTU/Hour/SF/Degree F difference from one side to the other. The lower the U-Value, the greater is the insulating value.

The R-Value is the inverse of the U-Value. To convert U to R, divide 1/U. To convert from R to U, divide 1/R.

Therefore each U-Value has an equivalent R-Value, and we show these too, not just to add to the excitement, but also to unify for the consuming public the confusing rift between R Values as promoted by the wall and roof purveyors, and U value as promulgated by the window and glass folks.

Approximate Insulating Values for Various Glass Configurations
Item Glass Type Winter U Value R Value
A 1/4″ single-thickness glass 1.08 .92
B 1″ insulated glass with (2) lites clear 1/4″, 1/2″ airspace .47 2.1
C 1″ insulated glass, (2) lites clear 1/4″, 1/2″ airspace, Low-E coating on #2 surface .37 2.7
D 1″ insulated glass, (2) lites clear 1/4″, 1/2″ airspace, Low-E coating on #2 surface and argon filled air space .30 3.3
E 1″ insulated glass, (3) lites clear 1/8″, two 3/16″ airspaces, Low-E coating on #2 and #4 surfaces and two argon filled air spaces .20 5
F For perspective: 3 1/2″ batt insulation for typical wall construction – no window .09 11

Approximate U and R Values for various glass configurations. Numbers stated here are general and for comparison, and are not specific to a manufacturer.

Approximate U and R Values for various glass configurations. Numbers stated here are general and for comparison, and are not specific to a manufacturer.


 
  If you are like me, after a few ganders at the chart, you will start thinking, “windows really have a long way to go before they approximate the energy performance of a wall.” The counter argument, of course, is that windows are much more desirable in living spaces than blank walls due to their ability to admit light, allow a view, and better connect us to our environment and our neighbors. Using windows in building design is all about tradeoffs…now.

We foresee a time in the future when windows and glass will make a much more positive contribution to the control of energy loss, the creation of comfortable living spaces and even the production of energy.

All summer Chicago Window Expert will focus on the latest breaking energy related and solar technologies. Subscribe now to receive notifications when new articles are posted.

Mark Meshulam, Chicago Window Expert, reflects upon Low-E glass

Mark Meshulam, Chicago Window Expert, reflects upon Low-E glass


Need to select the right glass?
Read the rest of this entry »

3 Comments

Generic selectors
Exact matches only
Search in title
Search in content
Search in posts
Search in pages
Filter by Categories
About windows & glass
Accident investigation
Aluminum windows
architecture
Bad replacement windows
Bad window installation
Bad window replacement
Best windows
Broken glass evidence
building design
Building Energy Benchmarking
Building envelope
Building science
caulking contractor
Construction defects
Curtainwall retrofit
Drafty windows
Energy Efficient Windows
Expert witness
Exterior facade consultant
falls from windows
Fiberglass windows
Glass
Glass breakage
Glass evidence
Glass Safety
Glass types
Introduction
leaks in walls
masonry
Mockup testing
mold in walls
My windows leak
Nickel sulfide inclusion
personal injury
Preconstruction mockup testing
PVC windows
Renewable Energy
Repair or replace windows?
Replace weatherstripping
Restoring windows
Safety glass
Safety glazing
Secondary glazing
Shower doors
Shower enclosure
solar energy
Solar Power
Spontaneous glass breakage
Steel windows
Testing windows and glass
The Construction Process
Types of glass
Vinyl windows
Web statistics
Window air infiltration
Window air leaks
Window condensation
Window dangers
window falls
Window gaskets
window replacement
Window retrofit
Window safety
Window test
Window testing
Window types
Window water leaks
Window weatherstrips
Windows and Energy
Windows leak
Wood windows
Wynn Hotel
Contact

No matter where you are,
Chicago Window Expert can help you
Mark Meshulam
Email me               CV-Resume'
Brochure      Testing Credentials
Follow us on Facebook or Twitter
for updates you won't see here
View Mark Meshulam's profile on LinkedIn

Caulking, Waterproofing                Window Warmers
Now offering caulking, tuckpointing and waterproofing services in selected areas. We also have a system to warm window surfaces to reduce or eliminate condensation. Contact mark@chicagowindowexpert.com
for details

Photo of the day

d4-composite-panel-seam.jpg
Top view of the top of a composite panel seam. The edges of each panel are folded back to create the appearance of depth at the seams. The panels are fitted with aluminum extrusions that allow the panels to be hung onto a receiver system. The receiver system has a slot for the insertion of a vertical strip of panel. This strip is seen when looking into the panel seam, giving a finished appearance.

Locations

Alabama, Alberta, Arizona, Arkansas, British Columbia, California, Colorado, Connecticut, Florida, Georgia, Hawaii, Illinois, Indiana, Iowa, Japan, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, New Jersey, New York, North Carolina, Nova Scotia, Ohio, Oklahoma, Ontario, Oregon, Pennsylvania, Russia, Singapore, Tennessee, Texas, Utah, Virginia, Washington State, Washington DC and Wisconsin

Coming soon to you