To Air is Human, To Insulate Divine

By Gary L. Orlove, P.E.
ASNT NDT / PdM Level III

Its winter again, and boy, don't we know it New England. There’s more snow on the ground than we can ever remember having!  So I thought we might take a look at some of low cost ways you can help save thermal energy in your abode.
The contributors to heat loss in a home are: conduction losses to the exterior, radiant losses from the exterior, convection from the exterior, and air infiltration/exfiltration. Here are a few examples of the efficacy of reducing conductive and air movement heat losses with simple but surprisingly effective methods.
Let's take a look at air leaks. Usually infiltration happens on the lower floors of a building and exfiltration occurs at the top floors due to the stack effect (in a heated building, the indoor air is buoyant and applies pressure to the envelope. The pressure increases with the height of the envelope). Air infiltration not only makes a building consume more energy, but it makes it "drafty and cold", especially if you are sitting next to the source of the leakage!
Take a look at the thermal imaging photos below. Here we see an unused air conditioning vent spewing out cold air on the first floor (stack effect). You can't see the air with thermal imaging camera, but you can see the cooling effect the air has on the walls and ceiling. For this retrofit I used a piece of magnetic plastic sheet. You can see in the after thermal image the dramatic reduction in airflow and the effect of adding a bit of insulation to the open areas of the vent. The delta T reduction between the vent and the ceiling was about 30%. Not bad, but I thought I could do better!
   
Before, after, and visual thermal images of an air vent with magnetic sheeting
For my next experiment, I tried using 4 mil thick plastic sheeting taped to a vent. I used a "Post It" note to provide an indication of the steady state temperature condition at the vent. Here are the results.
   
Visual, before, and after thermograms of a vent that I retrofitted with 4 mil thick plastic.
The reduction in infiltration using the taped plastic is dramatic. The delta T between the vent and the ceiling was reduced a whopping 70% and the convection pattern on the ceiling is virtually gone!
The last thing I want to mention is the use of thin plastic sheeting to cover "cold" windows. Here we have an aluminum framed window with severe weather stripping problems resulting in a very uncomfortable air infiltration problem. Covering it with the clear plastic significantly reduced the air leakage (the thermal image shows the rise in temperature along the bottom of the window area) but also reduced the conduction through the entire structure. I didn't have a Post It on this one so we can't objectively measure the improvement (remember thin plastics are transparent to thermal imaging cameras). If the window itself actually looks colder, that’s because it is.  We have successfully blocked indoor heat from reaching it as easily as before.
   
Window before and after application of plastic film (also note air leakage through the socket at right)
Try some of these fixes for the winter blues yourself, and send in some thermal imaging photos of your own solutions. We'll use them in a future newsletter.

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