[quote=“ayev8tor”]The science behind Thermal Control Membrane is similar to Low e glass, it performs by providing not one but several low e surfaces. It’s a common misnomer to attach “air spaces” to a low e surface since that’s what gives insulation the R factor: trapped air spaces.
Further, the distance between reflective surfaces is not critical to performance as is insulation products that do not have low e surfaces.
Your comment about “trapped air spaces” in the foil covered bubble wrap (brand name “Reflectix”), starts out with four reflective surfaces but loses 50% of the performance due to being laminated to the plastic bubble wrap which immediately allows heat to transfer through conduction.
The Thermal Control Membrane product is actually one of the best thermal inhibiting products available and the web site that sells it has 3rd party validation from a university showing a .02 emissivity which is the lowest I’ve seen from any reflective insulation product. savenrg.com is the web site I saw it on.
You are confusing “air space” with insulation and not taking in to account how a low e surface works. This method is used in spacecraft which is where I first became aware of multi-layered thermal products in my aircraft business.
In fact, for a metal standing seam metal roof, or any metal roof for that matter, this TCM stuff would be the ultimate roofing membrane since it’s not bitumen based, would never dry out over time from infrared heat (like all shingles and tar paper underlayment does), and since it’s multiple layers, would never be affected by dust.[/quote]
Thanks for responding. However I can’t say as the response makes much sense to me.
There are three ways to move heat: convection, conduction, and radiation. Moving air currents move heat by convection. Solid materials conduct heat through the material (copper conducts quite well, for example.) Concentrated mass (plasma, hot gas, liquid or solid) will radiate heat into the open space (vacuum or air gap) next to them.
Low emissivity materials coated on the inside of a window pane will keep that pane from radiating heat into the interior. The glass may still be hot from the sun shining on it, but only the air currents, via convection, will pick up that heat by direct contact. Adding a second pane of glass keeps nearly still air trapped in the space between the two panes, reducing the convection heat coming off the outer, low-e, pane even more. However even still air conducts heat (the third way) a little, so a little heat will move from the outer pane to the inner one.
Low emissivity materials such as attic radiant barriers and aluminum sheeting products on the interior of unfinished metal roofs on sheds and barns are working into large air space (the attic or building interior.) Like the low-e glass, they help by not radiating heat inward, though they still can feel quite hot to the touch, and some heat, quite a bit less, will still move by the convection of circulating interior air touching the hot surface and then moving to occupied portions of the interior.
Spacecraft are working in a far larger vacuum, and for them low-e surface materials, --because-- such materials are always at the same time low absorbers of radiated energy, are an essential cooling mechanism. The heat bounces off back into space before heating anything.
The TCM material didn’t have a gap. It was mostly zero gap. The two or three foil layers are directly touching each other more often than not, except where the sparse shim (fiber netting with 1/2" holes) slightly separates the foil layers. If such material is sandwiched between other solid roofing materials, such as when used in place of the usual tar paper underlayment, then this is little better than sticking a few layers of tin foil between the roof coating (metal, say) and the roof deck. Heat directly --conducts-- between the various layers that are in direct contact. It doesn’t matter if the material is some perfect zero emissivity product. It’s not the --radiation-- of heat into an open space that matters when there is almost no open space and instead much direct contact. And where there is not direct contact between the foil layers of TCM, due to the shim netting, there is a very thin layer of air, which will conduct heat fairly well. Most any material short of an absolute vacuum will conduct heat to some degree, depending on how thin the material layer is.
Putting tin foil (or expensive equivalents) between my roof layers sounds like a waste of money to me. Low-e surfaces work when there is a gap into which they don’t radiate.