Originally Posted by malconium
I am completely willing to participate in whatever way makes sense to do some testing. I did however notice the following quote in the explanation of the physics of reflective foil that gives me some pause:
"In spite of the advances made by space technology in insulation systems based on understanding and modifying the effects of radiation, no universally accepted laboratory method has yet been devised to measure and report the resistance to heat flow of multi-layer foil. Until such a method that will satisfy rigorous laboratory demands is devised, we must be content to make our judgments on the basis of common sense and experience."
So the big question is how best to formulate a real world enough test within which we can properly compare my suggested two layers of foil with the other approaches that have been discussed. Over a long period of time I have tried to read up on everything that comes my way relative to the effectiveness of reflective insulation and feel like there is a lot of compelling information on the subject. Given the above quote I am not sure how the testing was done for this writeup though. The article shows some diagrams that supposedly represent a wall cavity that is only 1-1/2" thick - exactly what we have in our Airstream walls. The diagram with two layers of foil includes the following comentary:
CASE 3, TWO SHEETS OF (5% EMISSIVE) ALUMINUM FOIL divide the wall space into 3 reflective compartments. Heat loss by radiation drops 94% from Case 1. The 2 interior sheets retard convection so that its flow falls 75%. Conduction rises only 2 BTUs; from 21 BTUs to 23 BTUs. The total heat loss drops 85% from Case 1.
Case 1 has nothing but air in the wall space.
I would suggest that we collectively do some Internet surfing to see if we can find other well founded articles that talk about the relative merits of different insulation types - articles that are based on actual testing. I also suggest that we rule out very expensive types of insulation as being impractical.
I am also open to suggestions on what kind of test I could do to validate my suggestion for the two layers of foil that would adequately compare it with other types. Zep - is your test box still set up? Could I perhaps furnish panel materials for you to use with the set up? Should I consider dusting off the test panels that I used out in the sunshine and modifying them so that I can re-run some test with my IR thermometer? What do we think would be sufficiently conclusive?
Maybe some of you folks that have installed foil insulation in your Airstream could give us some feedback on how you think it is working. That would be especially useful if you can somehow give us a before and after comparison. My unit is still not road worthy yet so I don't have any good way to do report on its success. I also do not have any before information.
The following link
is to the company that probably has more knowledge in reflective surfaces in the world. They have developed glass panels up to R-20 and are responsible for Low E glass. I had a company in the 80's and we used their glass called Heat Mirror 44, 66 and 88. a 7/8" insulated glass had a R-4. with no gases added. Anytime you can create a air space as you know you get a great insulation value as long as there is no infiltration of air. A thermal break will also improve the situation.
For those that have the skin off you can put a closed cell glazing tape (I believe the thinnest thickness is 1/16" ) between the airstream frame and the skin and stop a lot of the thermal transmission, You will still have the rivets that will transfer heat or cold but you will have cut probably 75% of thermal energy movement.