The physics behind Insulating Curtains and Thermal Window Treatments
Window Quilts® Outperform Insulating Curtains and Other Thermal Window Treatments. The Result is Exceptional Comfort and Savings
Anyone who has tried alternative products like insulated curtains, thermal drapes or cellular shades knows that Window Quilt® shades work far better. Why is that, when the R-value stated for these products is often similar to what we state for Window Quilts®?
Published R-values of insulating material, including thermal curtains, are meaningless unless tested on a window
In fact, some common approaches, such as insulating curtains with a fairly good R-value can actually make a room colder and far less comfortable than with the windows uncovered.
If the insulation does not seal on the window, as is the case with insulating curtains and thermal drapes, the effective R-value will be much less than that of the insulating material (fabric). Competitive manufacturers typically publish R-values for the fabric. Window Quilt® publishes the R-value and Air Infiltration values of our shades as installed on a test window as determined by an independent laboratory using standardized test methods.
R-value, when tested properly (on a test window) does relate directly to heat lost by conduction out the window, but that represents only one part of the story. There are several other factors that are equally important to occupant comfort and reducing the heat requirement.
Cold drafts due to leaky windows and convection currents from cold windows affect comfort and heat load. Dramatically!
Makers of competitive products, such as insulated curtains and drapes, thermal curtains, and typical cellular shades, won’t talk about this, because their products don’t really help the situation. In fact insulated curtains and drapes can actually setup convection current drafts which can be very uncomfortable. For a technical treatment of how insulated curtains and drapes actually can diminish occupant comfort see this article from the University of Texas.
Window Quilt® shades employ an air tight vapor barrier to block both air infiltration and convection currents. We publish our air infiltration results, which have been determined by an independent laboratory in accordance with American Society for Testing Materials methods. What other manufacturer of insulating window treatments does that?
Take the "Cold Feet" Test!
On a cold day, close your drapes. Remove your shoes and socks and stand next to the window. Feel the chill? It’s the cold air falling off your window. It’s known as the “reverse chimney effect”. All unsealed window treatments actually work as an air baffle that promotes the movement of cold air downward across your cold window glass by streamlining the airflow while drawing in heated air from above. That draft is robbing your house of the warmth and “coziness” you want!
Cold windows draw heat away from the occupant’s bodies. That’s why it’s so uncomfortable to sit near non-insulated windows or to be in a room with a number of them on a cold day.
The technical term is that that the windows lower the mean radiant temperature of the room. That effect can be countered by wearing winter garb in the home or by addressing the problem at the source – the windows. The effect of mean radiant temperature on occupant comfort has been studied for years; one brief treatment can be found here:
Wikipedia: Mean radiant temperature
For a more thorough and really interesting discussion, read Assessment of man's thermal comfort in practice.