Jax, you still don't understand the principle that it is better to keep your
mouth shut and have people think you are stupid than opening it and
confirming the fact.

Most vacuum panels are filled with Instil, an inert open celled silica based
foam board from Dow. It has a crush strength of about 50 PSI, well above
the 14.7 atmospheric pressure, and an R value at standard pressure of about
5. At 1 milibar vacuum the R value is about 25 and at .1 milibar it is
about 30. Glacier Bay uses a special reinforced aerogel material called
Nanogel made by Cabot (the Cabosil people) with an R value at standard
pressure of about 15. While the bare material is extremely delicate its
latticework structure makes it very strong under even compression. At 10
milibar the R value is about 30 and at .1 milibar it is about 50. The curve
of vacuum to R value is flatter with Nanogel than with Instil. The obvious
advantage is that as the panel loose vacuum the Nanogel will maintain more
insulation value. The disadvantage is that Nanogel is much more expensive
and harder to work with.

The problem with all vacuum insulation is that it is impossible to
maintained a high vacuum with a low conductivity flexible membrane. Air
molecules will slowly find a way in. Back in the 80s
a vacuum panel made of a stainless envelope packed with precipitated silica
was popular in refrigerated containers and some high end European
refrigerators. It was only effective in large sizes because the steel
conducted a lot of heat around the edges. In the mid 90s Toyo and Dupont
developed films consisting of several layers of various UHMW plastics coated
with a very thin layer of aluminum that made smaller panels practical and
easier to fabricate. Those films have been greatly improved over the last 5
years. Around the same time SAES introduced a room temperature getter
material to absorb stray gas molecules and packages it in small inexpensive
pucks to be inserted in the panels.

The net result is that you can reasonably expect 10 to 15 years of R values
better than 25 per inch from almost any well constructed vacuum insulation
panel. The Glacier Bay Panels will last about 30% longer and have the
distinct advangate of maintaining a reasonable level of insulation even with
no vacuum. The down side is that they are about twice as expensive.
Regardless, marine refrigerators made with vacuum insulation should be built
with the need to eventually replace the panels in mind. I am counting on 8
to 10 years and will probably replace them even if they are still reasonably
effective. At the present rate of improvement by then the technology will
be far better and the prices significantly lower.

BTW, you should NOT use two part pour in place foam to fill gaps between
vacuum panels. Two part foams produce a lot of heat as they cure. The
vacuum panels are so effective that they will trap the heat and possibly
damage the plastic film. Moisture curing spray foam like Great Stuff is a
lot safer.


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"JAXAshby" wrote in message
...
Rusty, you take measurements for a living, but are not a design eng. a
couple
of things to make note of:

1.) "shiney" is shiney from both sides, as far as radiation is concerned.
shiney out or shiney in, same same.

2.) shiney on the outside does NOT make for greater (or lesser)
conductivity
or convectivity. shiney on the outside makes for reflection of the
radiant
heat **from the outside** (where heat is in a reefer system). shiney on
the
inside means some of the radiant heat is absorbed on the way through the
insulation (makes for warmer insulation) and then is reflected back into
the
insulation where some of it is also absorbed (making for even warmer
insulation).

3. You, Rusty, sound like a shill for N. Bruce Nelsen of Glacier Bay, a
man who
over the years has made one hell of a lot of claims that don't stand close
examination.

4.) "vacuum" panels are not vacuum at all, but rather are panels with a
plastic
latice inside (to hold the sides of the panel apart) with much, but by no
means all, of the air removed. (air pressure is 14.7 pounds PER SQUARE
INCH,
so a 1 square foot panel encasing a true vacuum would have over 2,000
pounds
pressure trying to collapse the sides.