By the way, do you have a vacuum thermos bottle with a reflective material deposited on the interior glass surfaces?

George, if we could build homes like vacuum thermos bottles, I'm sure reflective materials would play a part. The problem is that all these things you mention...oil fires, forest fires, high altitude test chambers, etc., are not the same as residential construction. I've never seen anyone here attack proper uses of radiant insulation and Dana1, in particular spends a lot of time carefully laying out the groundwork for explanations of where it does and doesn't work. Your rants, on the other hand, verge on religious fervor for a particular product, and count on years of carefully woven arguments to support some pretty flimsy science and engineering (in residential uses).

Is it too much to ask that you lay off the personal attacks and just stick to factual treatments of the subject, however intense you need to be?

Greetings,

Quote> George, if we could build homes like vacuum thermos bottles, I'm sure reflective materials would play a part. The problem is that all these things you mention...oil fires, forest fires, high altitude test chambers, etc., are not the same as residential construction.

Aren't they? Radiant energy is radiant energy PERIOD. The foil that reflects the energy doesn't know that.
For instance. The constant push to claim that RI is either ineffective or marginally effective in cold
conditions is a lie of major proportions and really got it's start from the mineral wool people decades ago. This lie has been perpetuated either by people wanting to push their product or by persons who do not know science basics and just spout it to build up their self importance. I notice you did not
include the arctic buildings example. Arctic buildings of the late 1800's and up to know rely on RI principles. I don't tolerate very well people that knowingly perpetuate lies.

QUOTE>Your rants, on the other hand, verge on religious fervor for a particular product, and count on years of carefully woven arguments to support some pretty flimsy science and engineering (in residential uses).

According to your opinion.
religious fervor? Religions are cults, I prefer to stick to reality.
Flimsy? According to who. People who want to push their agenda and don't want completion.

QUOTE>stick to factual treatments of the subject, however intense you need to be?

I use data from Marks mechanical engineering handbook 13th ed.

If I'm so wrong, how come ON ONE has answered my challenge to the 2btu/sf/hr I presented.
How come no one has come forward and claimed a 80-81 interior deg without ac for 6 straight days.
How come no one has come forward and said that their insul sys results in a 11 deg temp over ambient on 95+ deg day, no shade, black roof.
If they can't meet those conditions maybe they should join my church.

IF YOU REALLY WANT TO CHALLENGE MY POSITION THEN BUILD A HOUSE TO MY SPECS AND THEN DECIDE. Other wise you have nothing to compare with and have nothing to challenge me with.

How does radiant insulation deal with conduction and convective loss?

Conduction & convection never happens in rb insulated homes- all heat transfer between building material is radiated, didn't you know that? ;-)

If you air seal the rb layers they can be effective air-barriers (well, maybe not the perforated types), but convective transfer between layers still occurs in differing amounts depending on orientation of the assembly, the delta-T and to some extent distance between the layers. A horizontal warm-side up application is a lot more effective than a horizontal cold side up. Vertical orientations will always have a significant convective transfer from foil-to-foil. In any orientation as the foils get closer to each other (or to the sheathing or gypsum) convection starts to dominate the heat transfer. When the distances are large and the assembly is hot-side up the convective transfer is minimal (say from an attic floor to an attic roof on a hot summer day), and the radiated portion dominates.

But where the foil is in direct contact with structural elements the heat transfer is entirely conductive. There's no thermal break across structural timbers with rb without an air gap.

From a building code point of view, when using rb as a major insulative component,  most codes will allow you to use third party calculated "equivalent-R" thermal resistance numbers derived in the appropriate ASTM testing for the assembly type for it's performance at a delta-T of ~ 30F.  eg:

 http://www.icc-es.org/reports/pdf_files/SBC/2133A.pdf 

But note that deviation from the tested spacings will yield different results, as will different delta-Ts- it's very non-linear. Of the Fi-Foil products tested in that document, in a vertical orientation (horizonal heat transfer) none fared better than ~R7-equivalent at ~30F delta-T, and that was with 1.5" of air gap on both sides.  In the horizontal hot-side up tests their other product did a whopping R9.78 when it had a 1" trapped air spaces, rising to R11 something with 8" trapped air spaces.

This is pretty crappy performance on it's own, and wouldn't cut it from a code-compliance point of view, but it's still better than nothing.  Build in enough layers and dead-air spaces you can achieve any kind of center-cavity performance, but treating the thermal bridging is still going to be important.

Were it possible to build true high-performance building envelopes more cheaply, simply & reliably with RB than with other materials I'd be all over it, but there's no convincing existence proofs out there.  I don't find rbysis1's "2BTU per foot" mantra interpreted from the pages of Mark's engineering bible very convincing despite his being a loyal disciple for 3 decades or more.  YMMV.  I find the 100s of PassiveHaus projects with good correlation between predicted and measured energy use performance quite convincing. Again YMMV.  If & when there is similar evidence for an all-RB approach, I'll reconsider.  (SFAIK there is no RB used to achieve the performance levels in any PassiveHouse project, nor would I expect there to be.)  At insulation levels well below that of PassiveHouse structures any additional performance you'd get out of RB ceases to be relevant, but where it's essentially free (foil faced iso or EPS under rainscreened siding in a cooling dominated climate) it's worth it.

Posted By Dana1 on 01 Dec 2011 03:50 PM
Conduction & convection never happens in rb insulated homes- all heat transfer between building materirla is radiated, didn't you know that? ;-)

Trust me...I am a fan of radiant barrier.  It is the single most significant advancement in window technology, however, a home is not a window in this case.

A window is the near perfect example of how a radiant barrier should work with a trapped air space, reduced conduction, and a denser than air gas to slow convection.  None of these scenarios are true in a wall assembly.

Even that radiant barrier working well in a window only increases its efficiency by roughly 3-4X in most double pane windows.  When we look at a wall assembly in a super insulated home, we are looking at 6-10X increases in insulation value.

You got in quicker than my extensive edit, eh? ;-)

Windows are extremely low-R by themselves. Trapping a gas-space between panes gives you a decent boost, but when the panes are close together it suffers the same convective current losses of RB. A tight storm window over a tight sash-window outperforms an uncoated double-pane due to the wider spacing. But adding the low-E coatings can more than make up for that, and more trapped gas films (triple pane) takes it even further. (It's hard to hit PassiveHouse levels of performance without triple-pane low-E windows.)

Greetings,

In a multi layer (2) RI sys, say for summer.
!st reflective air space. Sheathing radiating to 1st foil + conv factor. air space temp = sheathing temp. 1st foil temp same as sheathing temp.
2nd air space about same as interior temp.
2nd foil temp same as interior temp
3rd airspace temp same as interior.
This does not account for stud/joist transfer.
Therefore RB across the stud/joists plus furring strips/drywall.
To a 75 deg floor temp.
Figuring a 110 deg foil temp, (which it will never even get close to) 2 btu /sf/hr is radiated to the dry wall or other.
There IS NOT a gradual temp diff across the foils.

Now it's kind of hard for the average person to measure the air temps between foils, but you can measure a single layer (2 air spaces) for air and material temp. Been there done that.

1st air space 100 degs.
foil, 100 deg.
2nd airspace and drywall about same as interior, 75 deg.

Considering this performance I don't get concerned about conv/cond influences. I'm looking at dry wall temps. That is what is going to determine my ac load. I wouldn't care if there was a tornado between the layers because the final foil temp is the determining factor and it is only radiating 3% of that foil temp. All other factors are for people who have nothing else to do but measure and pick, pick, pick.

The RI only knows to reflect based on delta T so it doesn't care if it's summer or winter.

Comments are made about ceiling RI not being as efficient in winter. Compared to what. That is never discussed.

In a multi layer installation the same process takes place so the top layer is going to be the same temp as the attic. The difference is the exposed joists. Since covering joists on top with a foil is going to cause condensation that is not an option, but I can put a foil across the joists, interior, plus furring and drywall, and stop the energy transfer thru the joists.

Since under the most demanding temps you can possibly get you're only radiating 2 btu/sf/hr what more could the customer want.

Posted By Dana1 on 01 Dec 2011 04:48 PM
You got in quicker than my extensive edit, eh? ;-)

Windows are extremely low-R by themselves. Trapping a gas-space between panes gives you a decent boost, but when the panes are close together it suffers the same convective current losses of RB. A tight storm window over a tight sash-window outperforms an uncoated double-pane due to the wider spacing. But adding the low-E coatings can more than make up for that, and more trapped gas films (triple pane) takes it even further. (It's hard to hit PassiveHouse levels of performance without triple-pane low-E windows.)

Yep.

Single pane with a storm combo (well sealed) will approach and R-1.8 - 2.0. 

Pretty easy to find modestly priced double pane Low-e/argon combos now that are R-4.  Non-exotic triple pane argon are R-5+ and there is a newer window coming out in a triple pane argon (krypton is 30X expensive right now) that will be R-7.  All these numbers are total unit.

2btu/hr per square foot with a delta-T of (110-75F=) 35F is 1/(2BTU/35F) = R17.5 effective whole-assembly R, which isn't exactly a high level of performance.

In winter with the cold-side up application it'll be about half that at ~30-35F outdoor temps.

There are plenty of systems that meet or beat that (low density R19 f.g.between rafters or floor joists just isn't one of them, but if that's your competition, have at it!). A typical cellulose overblow on attic floors that covers the tops of the joists by 3" or more would beat it (any joist 2x6 or bigger.)

PassiveHouse buildings neither have nor need air conditioning systems. Roofs are typically R75 or more (whole assembly, not center-cavity), walls R50-ish.

"...PassiveHouse buildings neither have nor need air conditioning systems..."

Probably a topic for a different thread, but this surely depends on climate.

Greetings,

Considering the fact that a RI INSULATED HOUSE WILL OUT PERFORM THE BULK INSULATION, TELLS US HOW INACCURATE THE "R" SYS IS.

Greetings,

Forgot.
Since the ceiling temp of FG on a 95+ deg day is 110/75 degs and emitting 37 btu/sf/hr. What is your 15" FG "R" factor?

QUOTE> There are plenty of systems that meet or beat that (low density R19 f.g.between rafters or floor joists just isn't one of them, but if that's your competition, have at it!). A typical cellulose overblow on attic floors that covers the tops of the joists by 3" or more would beat it (any joist 2x6 or bigger.

You wish. You really need to get out in the real world and see how these sys perform under "real" conditions.

In the early 70's OC was pushing the Arkansas model. It was a 6" wall structure and they were claiming these great savings. OOPs. Come to find out it was a computer model and they got their actual reductions by reducing glazing area.

6" ceiling cellulose? I'm sorry to bust your bubble, but, it won't in the real world.

Posted By Jelly on 03 Dec 2011 10:00 AM
"...PassiveHouse buildings neither have nor need air conditioning systems..."

Probably a topic for a different thread, but this surely depends on climate.

The Lafayette LA PassiveHouse has a 1-ton mini-split that provides all heating & cooling.  The air conditioning loads are primarily latent loads from both interior sources and ventilation air- the sensible loads are miniscule. A window-shaker could handle it, but a mini-split is both quieter and more efficient.

So I suppose if you include tiniest-in-class mini-splits & dehumidifiers under the heading "air conditioning systems", sure, even a PassiveHouse needs such a "system" in cooling dominated high-humidity climates.

rbsys1: A 2x6 joist with 3" of cellulose above the joists has 8.5" of cellulose center-cavity, not 6", which will have a center-cavity R north of 25, (it's R30, and meets code-min by some vendors' tests, but I'd derate it a bit.) At the joists it's R15+, with a whole-assembly R over R20. It's such cheap stuff that going R10 or even R15 over code-min isn't a deal-breaker if you have the space, and it'll perform well.

Blowing cellulose dead-even, without overtopping the joists, with 5.5" of cavity fill there's no thermal break over the framing, and it comes in at ~R14 for a whole-assembly number.

I never recommend using low density fiberglass anywhere, least all in attics due to it's IR translucency in summer, and convection losses in winter. Sure it's crap, and just about everybody knows that it's crap. Dragging out that straw man for a thrashing every time somebody points out the limitations of radiant barrier doesn't make your case, or refute anything.

I make a living designing & measuring stuff, verifying that performance meets design spec. I have professional bias toward accepting the results of those who do the same, in a meticulous repeatable-verifiable manner, such as the folks at the Nat'l Labs who test entire assemblies in climate simulators, and who develop energy use models for houses based on their construction, the VERIFY the model by building actual houses and monitoring performance. The PassiveHouse model was developed in academia, but has undergone rigorous verification & correction since it's initial version, and it works. DOE2 is pretty good, as it Hot2000 both fully verified models, with real-world data behind them. The real world isn't such a strange and alien place to me. YMMV ;-)

I'm a bit less sanguine about performance claims based on random unverified-by-third-party measurements and a reference page to an engineering handbook. Again, YMMV.

I am going skiing this winter and based on rbisys1's recommendations, I have thrown out my thermals and jacket in lieu of this.  What do you think?



Should keep the satellites from reading my thoughts.

Greetings,

Unfortunately you picked a cheap knock off brand.
Crappy seam sealing.
Can't you young whipper snappers do anything right?
And what length staples did you use to hold it on your body? You need at lest a 1 1/2" length.
Damn, do I have to tell you how to do every thing?

I notice you did not include the arctic buildings example

What is the arctic buildings example?

Greetings,

QUOTE> What is the arctic buildings example?

In 1964+- the Navy CBs replaced the wall FG in their Arctic buildings with a 3 layer RI product that was mnfgrd by ALfoil. The navy issued a manufacturing spec HH-I-1252 specifically for this project.*

The reason for the upgrade was due to the fact that the FG kept turning into ice cubes within a few days of replacement, which, according to a member of the CBs, that I met, was a continual process. In fact I ran across two individuals who where involved.

The result was no more replacement and a heating oil savings of about 30%.

One of the individuals was a chance encounter and the other I sold RI material to for several months before he moved to another state. He built about a dozen homes before moving with the RI.

* What is even more significant about this spec is that it broke the back of a federal law that was passed about 1959-60 banning the use of RI in government jobs. The law was initiated by a Colorado US Senator who was responding to a Rockwool Industries urging. If RI are so useless why did the government do this along with at least two other actions by the Senate and one by the US AG at the urging of the mineral wool companies.
Hint, it's green and flexible. At least one RI company went out of business because of this law and the industry, as a whole, was severely crippled from which it has never fully recovered.

If it had not been for these illegal Gov. actions we wouldn't be talking today about FG and most likely cellulose.

God Bless the USA, INC.

Buildings in the arctic are completely different animals from residential construction here in the lower 48. The panels needed a vapor barrier. The fact that the SeaBees experimented with a product whose spec was cancelled back in the 1980's doesn't do much to support your contentions.

If it had not been for these illegal Gov. actions we wouldn't be talking today about FG and most likely cellulose.

I see. And what happened when the "illegal Gov. actions" went to court? More conspiracy theory, right?