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Old 09-22-11, 11:31 AM   #1
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Default Air: R (RSI) vs Pressure

I have been looking a bit on the internet and cannot find a graph for the relationship R vs Pressure of air. I am renovating my very old house and was pondering putting a vacuum layer, almost against the exterior finish. I understand a perfect vacuum would have an infinite R Value, and I read that closed air at 14.5 PSIA (1atm) has about R-1 / Inch. If I can only get my retrofit vacuum panels to 7.25 PSIA would I be looking at R-2/inch, R-10/inch, ...?
Anyone have some interesting thoughts?

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Old 09-22-11, 03:25 PM   #2
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I've seen a DIYer on Youthube that installed copper pipes to his heat exchanger
with large PVC pipes over them as insulation. He vacuumed the air out of the PVC
and got a real low rate of loss..

If you vacuumed a flat panel you would need to have support inside, to prevent collapse.
That support would have to be something with low heat transfer..

And, nature abhors a vacuum.. You would have to worry about leaking panels..
Rubbery paint on the outside of all seams might help..?.

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Old 09-23-11, 10:26 AM   #3
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Quote:
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And, nature abhors a vacuum..
Yeah, I was thinking an 'active' system. With a connection to a vacuum pump so that the imperfect vacuum could be drawn back down each (hour, day, month, year) depending on the magnitude of imperfection in the system.
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Old 09-23-11, 10:43 AM   #4
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Default vacuum loss prevention valve

So, you would need a good check-valve on each panel.
Once your vacuum pump came on and got the pump lines down to a low pressure,
the check-valves on panels that had leaked down a bit,
would open due to less pressure in the pump line.
Once the pump turned off, the 14 PSI would hold the check-valves closed.

Check Ebay for "vacuum check valve", maybe an automotive type would work?


Hey, one could set up an un-used HVAC vac pump, on a timer?
Let it run for 10 minutes a day?

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Old 09-23-11, 12:05 PM   #5
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Oh, that style pump would work great. I was thinking I would put a regular
valve (like the image attached) on each panel to isolate panels as they fail, and one check valve and vacuum gauge (or switch) on a manifold....
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Old 09-23-11, 12:23 PM   #6
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Default VacWall

The problem with that type of valve is the stem, I have a similar valve on my R410A manifold.
Turn a valve and watch the vacuum pressure come up.. They leak!!



I hate leaks!!

Maybe they were designed to hold pressure inside, and not work the other way.?.

With a vac check valve, you could have them installed right on the panel's port, in areas that weren't normally accessible.
Just suck the air out of the attached hose, and the rest is automatic.
If the check valves were cheap, you could stick some in the lines going to the
VacWall's-manifold(?), so if there was valve leakage, the feed line would already be at a low pressure,
and slow the leakage down.




Have you ever seen these things?? Very few of them hold low pressure very long..

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Old 09-24-11, 01:34 AM   #7
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Quote:
Originally Posted by pinhead View Post
I understand a perfect vacuum would have an infinite R Value
This might be true for heat transmitted by conduction, but radiant heat would not be stopped by a vacuum... at least that is what the Sun thinks.

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Old 09-26-11, 07:10 AM   #8
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Very good point... I think I will be scrapping this crazy idea in favor of conventional insulation... or ridged extruded poly throughout.
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Old 09-26-11, 08:34 AM   #9
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Yeah, it might not be safe anyway. A big leak during the night could turn on the pump
and you could end up with really low pressure indoors..



Of course, your house would have to be pretty tight..

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