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Old 12-10-13, 12:43 AM   #381
berniebenz
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Quote:
Originally Posted by jeff5may View Post
Yes it does!
Another unrelated "it" pronoun! Without relativity, a meaningless and unsubsatantuated statement!


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Old 12-10-13, 01:14 AM   #382
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Originally Posted by AC_Hacker View Post
.

jeff5may, I think the real crux here is that he keeps talking about "still air", and it simply does not exist... not until absolute zero.

Since his imagined model is based on still air, his imagined advantages do not exist either.

-AC
Ah, come on, AC!
The atoms may be moving within the air molecules but the air substance may be stationary, at zero velocity, for heat transfer purposes.
Natural convection is a gravitionual phenomenon that may cause motion in an otherwise still air mass at differing surface temperatures.
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Old 12-10-13, 02:11 AM   #383
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I edited my previous post with an example that i robbed from here:

http://portal.ncdenr.org/c/document_...&groupId=38322

The topic of underfloor insulation doesn't have a lot of coverage, mainly because engineers regard it the same as the boundary between the ceiling and the attic.

Another good article on air gap u-value:
http://blogs.mentor.com/robinbornoff...ation-part-iv/
If ur really interested, you can backtrack to the 3 previous posts from there

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Old 12-14-13, 04:51 PM   #384
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Quote:
Originally Posted by michael View Post
It's pretty enjoyable reading the under-floor insulation scuffle; lots of good thoughts there, and I'll take them to heart.
michael,

I think that enough time has gone by for the bloviation to fully dissipate.

I haven't forgotten that you have a nice radiant floor build going on down Mendocino way.

Hope the project is progressing as it should.

I really appreciate your photos, and look forward to more.

Best,

-AC
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Old 12-15-13, 02:06 AM   #385
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Thanks for the comment, AC. We poured the concrete floor two days ago, but because everything was coming thick and fast, I was unable to take a second to grab a camera and was caught unprepared. Now it's covered in plastic, but I'll post more photos when progress resumes. I'm going to begin working on the heat pump installation, and I'll move that conversation to another thread, probably a new one instead of adding it to the vastly long and useful thread you've got going regarding heat pumps. That way I can ask specific questions about this project and its particulars.

I'll move the heat pump discussion over to another thread (EcoRenovator>Improvements>Geothermal & Heat Pumps>Heat pump connection to radiant floor) I began some time ago in which I present a 1-ton E-tech heat pump I currently have, and it's that heat pump that I'll employ initially in this new project. Any further discussion of the heat pump and its connections will appear there.

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Old 12-15-13, 06:25 PM   #386
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Just one more thing about reflective insulation: Based on my reading of the Wikipedia article on multi-layered reflective insulation and a look at many reflective products that are for sale, it seems to me that most products would have little use because the reflective layers are pasted or attached to both sides of something relatively solid (such as foam or paper) preventing any reflection at the attachment. I've also noticed from past experience that most reflective products don't hold up well under a house at least in this region. After a few years they become oxidized and dull, and to make matters worse, banana slugs eat off the foil cover and then eat the foam or paper. I did, however, find one product sold by PEXsupply.com (concrete barrier foil) that has a reflective layer sandwiched between two layers of bubble film, so the reflective layer is protected from oxidation, and it is held apart from the warm surface by the bubble film a distance sufficient to allow radiant energy to be emitted and reflected back. It is, unfortunately, rather expensive, but to my thinking, it meets the requirements of effective reflective insulation that has a chance of surviving time, moisture and other damaging elements. It claims an R value close to 4, and I can picture using it between the sub-floor under-side and fiberglass insulation between the floor joists in order to boost the total R-value and reflect back at least a portion of the otherwise wasted radiation from the sub-floor. I'm reluctant to seal off the floor joist bottoms with a film because in this location it has been known to lead to vapor buildup within the joists, condensation and rotting. That outcome might be reduced or eliminated by the presence of a heated floor, I don't know, but I consider it too great a risk. The local building inspectors will no longer allow sealing joist spaces in a way that completely prevents the movement of air because of the fear of the entrapment of moisture. Kraft paper covered fiber glass should allow the joist spaces to "breathe" sufficiently to allow moisture to escape. Just random thoughts...not trying to upset the apple cart.

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Old 12-15-13, 10:16 PM   #387
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The vapor barrier on under-floor insulation should always be placed close to the floor. The concrete barrier foil in the above post would work. Adding bulk insulation to the underside of the barrier foil would be a great idea.

In practice, I have seen contractors spray silver "aluminizing" paint on the kraft-paper-side of fiberglass batts before installation to help reflect radiant heat. These same guys have nicknamed the "space blanket" type insulation (ecofoil, prodex, reflectex,etc) as "bubble crap". I tend to agree, having lived through the drama of reflect-x having to revise their lofty claims after ASTM testing revealed their product to have an r-value of just about 1, counting the radiant reflectionationing, of course. The novel products' times will come as well.

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Old 12-15-13, 11:57 PM   #388
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Quote:
Originally Posted by jeff5may View Post
The vapor barrier on under-floor insulation should always be placed close to the floor. The concrete barrier foil in the above post would work. In practice, I have seen contractors spray silver "aluminizing" paint on the kraft-paper-side of fiberglass batts before installation to help reflect radiant heat. These same guys have nicknamed the "space blanket" type insulation (ecofoil, prodex, reflectex,etc) as "bubble crap". I tend to agree, having lived through the drama of reflect-x having to revise their lofty claims after ASTM testing revealed their product to have an r-value of just about 1.
I agree!
Look at the emissivity of the low temp 80 deg. subfloor radiating downward to its receptors, looking at either a properly placed and transparent bubble and aluminized reflective film or, in its absence, to a black PE sheet crawl space ground cover, neither of which are high efficiency reflectors of this long wave length radiation. This downward radiant heat loss difference among recieving surfaces is trivial, relative to the total useful upward heat loss, being radiant, conductive and convective. It exists, but is trivial! Not worth much to reduce. Do a cost / benefit analysis.
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Old 12-16-13, 12:22 AM   #389
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Before everyone jumps on the "I love it!" , "I hate it!" bandwagon that people here are so prone to I would suggest that there are uses for reflective film. The reflective bubble insulation on its face is a bit of a fraud with the claims of its insulation value of 4 or even 26 by some shysters. But just because that is a fraud many of you jump to the conclusion erroneously that reflective film is worthless.

I chalk it up to the human characteristic of people getting their hopes up with a fraudulent claim - being disappointed - then making an equal knee jerk reaction in the opposite direction. People must use some common sense. One never uses reflective foil as a substitute for insulation. For instance it will never insulate against cold. It does reflect radiation and it also does so in the infrared regime. To deny that just means whoever is saying that is being theatrical and assuming knowledge they don't have.

The best use of reflective foil is in attics where it works as claimed and spending more for reflective bubble wrap is just a waste of money there. However, I'm not completely sure foam board covered with foil wouldn't work well under a floor, as long as it is completely air sealed and has an air gap of at least an inch or so from the floor. You would then be combining regular insulation with the radiation reflective properties. I don't think it's really a big win compared to just using insulation, though.

If reflective foil did not work at least a little I wouldn't be maintaining a regular 40 degree F temperature difference in the space above the foil and the space below. Tell me again that reflective foil does not work with infrared frequencies!!

Edit:"If reflective foil did not work at least a little I wouldn't be maintaining a regular 40 degree F temperature difference in the space above the foil and the space below." I should qualify that. It happens every day for about 2 hours and then dissipates. That's because there is no real insulating value in reflective foil. It just keeps those infrared rays from warming the rest of the house during the hours of most intense sunshine.

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Old 12-16-13, 03:04 AM   #390
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I never said that radiant barrier is worthless. It does a very good job of reflecting heat and light back the way it came. It works best when you have a large amount of radiation, as in the case of suspended-tube underfloor heating, where normal feed temps exceed 130 degF. In this situation, you want a gap of 1 inch or so between the subfloor and the reflective barrier to help spread the heat through convection in the gap.

With a poured thin slab or stapled underfloor install with heat spreaders, feed temperatures are usually below 120 degF, due to the increased thermal coupling into the floor. For the same cycle time as above, there is less potential for heat loss due to the reduction in feed temp alone. The radiant barrier and airspace would still work, but would have less radiation at a lower gradient to contend with.

In both of these situations, more insulation is beneficial. Where that insulation should be put will vary. Depending on the site and design goals, extra insulation may or may not be necessary.


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