The claim lately on VIP r value seems to be 50 or 60 for a 1 inch thick vacuum panel.
If you have an inch of
rock wool in the panel, it is R4 at best. So if and when you loose your vacuum you are dropping at least TEN fold in R value.
For this reason, I would not even consider doing this without a vacuum system attached to the panels. Plumbing for both pressure and vacuum, is already being done. In this case the vacuum required is not much. Negative is negative, and means there is no air present. If the panels are plumbed in parallel you can quickly locate a leak. It is possible with a ballast tank, to have perpetual leaks.
It's a low vacuum and would draw down very quickly. In theory you R value would go from 4 to 40 in seconds. With a durable bladder (vacuum bag), the vacuum pump might kick on once a month.
Foil bags are used to control radiant heat. You have two spaced radiant foils that probably brings that R4 (rockwool) to R10 ( dependant on application)
Why has this not been a major going concern before now?
Have you seen the price of insulation lately ! And, the new code requirements for insulation !
Vacuum pumps and hose are cheap.
Even a central vac pulls a negative 3 or 4 psi. Every time you turn it on.
OK, I just heard a bunch of mad inventers scrambling for the man cave.
A central vac-wall panel maintainer.
Terry eh