R value of polypropelene honeycomb core with glass skins.

Well, it is really difficult. I hate to hijack Steve's thread with it.

I checked for commercial units because they would be easier, but in a tiny home or tiny boat; everything is custom.

My buddy gave me a nice plastic exchanger, but with the other issues with the Skoota, it did not get to the priority tops to build an enclosure and fan mounts. My cabin is 13x8x6'6" or a bit less, so volume is like 650 cuft. It does not need much, but gets pretty damp inside from two people overnite just sleeping.

Maybe I'll start a thread on the subject and save Steve the headache.

 

You can make a perfectly good heat exchanger from some thin metal sheet. Then it's a bit of duct work and a low flow fan. Just draw the air in one side of the heat exchanger, so your cabin very slightly over pressurises, and the air exhausts through the other side of the heat exchanger. A reverse flow heat exchanger (invented by Albert Einstein) can have extremely high efficiency, but a right angle heat exchanger can still be pretty good. I work best in metal, so that's how I'd do it, but your skill lies in other materials I think. Just make the core in metal.

Edit: sorry about the hijack. Kind of ran off at the mouth there. So to speak.

 

I would think that Fallguy was close at R=2, but on the low side. If you get foam filled panels the R value should be similar to that of the foam filling. Since the cells limit convection, the R value should increase more with thickness than double pane glass, but how much I couldn't say.

I found 2 thermal conductivity figures for polypropylene honeycomb.
Thermal Conductivity (at 10°C or 50°F) 0.102 W/mK duroplastic.com
Thermal Conductivity y Fourier Law K=.03 3M (they bought Nida-Core)
And to convert from W/mK to R: R=l/λ
l is the thickness of the material in metres and λ is the thermal conductivity in W/mK.

W/mK 0.1
l = 1 inch = 0.0254 m
R= 0.0254/0.1 = 0.254per inch

W/mK 0.03
l = 1 inch = 0.0254 m
R= 0.0254/0.03 = 0.85 per inch

Double pane glass window, air filled. R = 2

Looking at Post #6 Steve seems to be most of the way to a good answer. It looks like Duroplast gave the thermal conductivity of the plastic material only and 3M gave the value for the structure. Since a double pane glass window with air, not argon filled, has an R value of 2, I think that the conductivity values may be for unfaced honeycomb sheets and hence not much use. Given that the honeycomb would limit convection, and FRP facings would have lower conductivity than glass, the R value almost certainly would be higher than a double pane window, but Fallguy's estimate of about 2 is probably not far off.

You can get Nida-Core filled with PU foam. In the absence of any specific data, my guess based on generic insulation values would be in the range of 4-6 per inch, or roughly equivalent to the foam filling. When I say can get, I can't seem to find any source, but it can be done. I worked on military R&D so can be done is not same as can be affordable, but with an astronomical budget, we did get foam filled phenolic honeycomb. While exploring dead ends, I found Structural Core Materials https://www.gurit.com/structural-core-materials/

Good luck finding hard data.

 

When we did my fish hold bulkheads and walls we tried to get real solid numbers out of the manufacturers for r factor. Nobody would give a hard number for us they just give us a percentage they thought it would be compared to polystyrene. For coosa and divinycell it was 40-60 percent. We ended up insulating based off added insulation and just calling the core bonus.

 

I found this PP honeycomb in the UK (Sheffield). It has a PP membrane on each side and has a lambda(?) of 0.065W/mK; you'll have to find a converter to get the R value.
Insulated Boards, Sheets & Flooring Manufacturer | Panel Systems https://www.panelsystems.co.uk/product/thermhex

 

Thanks all, like i said, i did find a manufacturer of PP honeycomb panels ( Fiber Tech ) who do actually give an R value of 5.5 for a 1" panel with 17oz glass on each side. Now i have no idea how they came up with that but based on the low conductivity of the skins and the PP cell walls as well as the air being prevented from circulating from convection due to the small size of the cells i see no reason why this would not be reasonably accurate.

 

In a prior life I was a plant manager there.