Reflective Foil vs fiberglass insulation 1

[PagoMitch]

Hi all,

I'm the facility engineer at a small hospital, and we have a project contractor wanting to substitue a product called "Astro-Foil" in 5/16" (R-15 according to the literature) thickness in lieu of 6" fiberglass (R19). The website here

http://www.astrofoil.net/index.html

comes across, to me at least, as something uh... less than scientific.

Assume for a moment that the R values are equal. I cannot find any articles re: UBC compliance or non-compliance for that matter regarding this "NASA developed" product. Pragmatically, while I am sure it does something, I am not convinced that it is (almost) equal to 6" of Fiberglass or about 4" of rigid Foam board.

It never gets below 80F here, so winters are not a problem. My biggest concern is compliance with IBC and IECC.

Any comments welcome.

Regards all.

Mitch

 

[AbbyNormal]

I believe the reflective bubble wrap has some merit keeping the heat out in an attic where there is normally higher levels of radiant heat transfer. I can say it will keep heat out, I cannot comment on how well it keeps heat in.

I THINK to get anywhere near the effective R-value they are claiming however, requires it to be installed with strip spacers to maintain an air space.

I know of a large project in a year round cooling environment where it was substituted without approval as a duct insulation, on ducts in an attic space. The contractor had to fly in a thermal imaging person at his expense, and his reports were giving a 3/8 type bubble wrap (foil both sides) an effectivenesses of R11 to 13.

I believe a lot of it had to do with a proper air space between the ducts and the wrap. So it was allowed to remain in lieu of the ductwrap that would have nominally been in the R6 to 8 range.

If I had to chose between the three insulations you mentioned, I would pay extra for the rigid foam. Better yet, blow in icynene foam in the attic on the underside of the roof pitch and seal the attic.








Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

The IBC probably has you designing roofs for snow loading

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[MintJulep]

Most of those miracle insulation products are snake-oil.

Beware!

 

[GMcD]

Go here:

http://www.healthyheating.com/Page 55/Page_55_o_bldg_sys.htm

and scroll down to the bottom for a number of tests and science on these products. Snake oil.

 

[willard3]

Get what you specified.......

You can get FG or rigid insulation with a reflective vapor barrier that will work the same as the substituted product.

 

[AbbyNormal]

Keeping heat in, perhaps snake oil, room temperature surfaces are not going to emit as much as the underside of roof sheathing at 160F.

It is more effective than a piece of poly and a couple air flim R values for heat flow down.

Presently going through an American Cold front, its mid 70s and low RH. Next hot sunny day I will try measuring the surface temperatures on both sides of the foil, in a place where it is the only insulation between plywood roof sheathing (below dark shingles) and a T-bar tile.

A radiant guy should recognize the merit of reflecting heat away.



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

Hottest spot of the attic is the underside of sheathing. Second hottest spot the top of the R19 above the ceiling plane, in third place the air in the attic.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

Here are sloping concrete roofs. The top side of the of the concrete is strapped with PT 2x4s on the flat to allow a means to fasten white reflective standing seam metal to the concrete.

In between the wood 'nailers' is 1.5 inches of foam. It is not as good as the Blue Dow SM or the Pink foam. Probably R4 per inch as a maximum.

The gable attic walls in the photo are insulated on the inside with 1.5 inches of the same foam. The wall paint is somewhat reflective.

The attic is not vented. This is in a year round cooling environment, latitude 19.5 degrees North.

I do not have the air conditioning started up yet, but I believe this will be more effective than R19 fiber glass at the truss chords and an attic that is a solar collector and humidifier. I am putting my money where my mouth is, these are my apartments.

Fiber glass also makes an air filter. It easily allows superheated humid air through. Difficult to have an attic vapour barrier in the tropics.

During sunny days with the ambient in the upper 80s, the under side of the sloping roof and the atttic air were both approximately 1F warmer than the ambient. I will condition the attic void with a little air, but I think I am going to monitor how the two middle units do, condition one attic and not the other.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[IRstuff]

Even the cited website indicates that a reflective barrier is to be used in conjunction with a mass barrier. Moreover, most newer fiberglass insulations come with a reflective barrier already.

At normal temperatures, the radiant emission can be at least comparable to the convective transfer, so a radiant barrier can provide a substantial reduction in heat loss.

TTFN

 

[zekeman]

I looked up that site and it looks phony to me . There is NO heat transfer data nor any crossection to look at to calculate it. Moreover the claim of .03 emissivity for that aluminum surface is false. A wrinkled surface like that would be much higher. And if they use air gap barriers, they are very tricky
since some contact between layers mus tbe present which would effectivelty reduce the effective overall R value they claim.
Nobody should consider this without evaluating technical documentation by a third party. Their socalled "technical" report is just more sales jargon.
BUYER BEWARE!

 

[MintJulep]

Well that Astrofoil site is not the sleeziest insulation site that I have seen, but it's up there.

If you read carefully, it does NOT claim that 5/16" of their stuff has an R15 or R19 rating. In fact, they don't seem to provide any conductivity or conductsnce figures at all.

BTW, playing games with the definitions of R-value, conductivity and conductance is one of the favorites of slime-bag snake-oil insulation makers.

Bottom line is that yes, in the right conditions there is a value to adding a radient barrier component to an insulation SYSTEM. Foil bubble wrap by itself does not and cannot provide the same R-value as traditional insulation materials.

Oh, if anyone is interested, the all-time champion slime-bag snake-oil sleeze insulation is:

http://www.supertherm.net/home.htm

 

[AbbyNormal]

If you wanted to model or calculate it zekeman, I have half a roll of 3/8" bubble wrap

A quick descipition would be a series of air cylinders 3/8" diamter by 3/8 high" approximately 1/2" on centre. The rows are staggered.

There is a reflective foil on both sides.

It is the tail end of a cold front, I will measure some temperatures when it heats up a bit.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

Anyone ever put this on their dashboards behind the windshield when they park?

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[GMcD]

Geez AbbyNormal- you have a franchise on this stuff? I'm being humourously sarcastic, no slight intended. I agree that the foiled material WILL have a significant effect on reducing radiant heat gains into attics, etc., however the radiant heat gain is only one component of the overall heat transfer into, and through a structure. One of the issues I've seen with installations of the foiled materials is that where there is an air space above it, a significant enough amount of dust will accumulate over time (within a few years) which can seriously degrade the reflectivity/emmissivity of the foil. Guys using this stuff for staple-up underfloor hydronic heat have been going through the teething pains of this stuff- worked fine for the first year or two, but the system started losing heating capacity, and upon examination the amount of dust that collected on the foil face hung under the radiant heating pipes basically reduced the radiant function to a very slim performance factor compared to the original clean foil performance. While attic and other types of installations may have less of a dust collection issue, it's still a caution.

Using "R" values and "equivalent performance" is misleading because regular batt, or rigid foam insulation is a conductance barrier, while the foil stuff is a radiant barrier, and the way the industry standard calculates R-value, it's based on "conductance and air temperature", and it does not measure "mean radiant temperature" as one of the factors, so that's where the foil stuff provides different performance compared to the standard mass insulation materials.

 

[AbbyNormal]

No franchaise, I just rented an office with terrible insulation. If you were to pop a t-bar tile, it was a 50/50 chance of either looking through the trusses and seeing either the underside of the roof sheathing, or friction fit fibreglass between the trusses.

So as a quick fix, I bought a 500 square foot roll of bubble wrap and installed it in a manner similar to 'lining joists'in about 50% of my ceiling. Made a big difference, never calculated if it was an effective R-value equal to 'two air films with heat flow down', but next hot sunny day will take some temperatures.

In cooling the majority of heat transfer through an attic has to be radiant.

I think my apartments with reflective white roofs with R6 foam and sealed attics will be more effective than a vented attic with R19. I won't have any superheated humid air short circuitting in as infiltration either.





Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

The cold front passed and just a few minutes ago I took some readings, about 2:45 PM

Some quick readings that I have not analyzed.

Partly Sunny, in the shade outside about 82F dry bulb and 72%RH

The underside of the roof sheathing on the southern slope of the roof is about 112.5 F, used a Raytech MiniTemp

Some truss spaces only have the 3/8 buuble wrap as insulation, installed in a manner similar to line floor joists for return ducts.

Surface temperature on the underside of the 3/8 foil bubble wrap on south side of attic, again with the Raytech is 80.5 F.

Some truss spaces still have the friction fit R19, with the 'kraft paper down' rammed in betweem them, so the surface temp of the kraft paper was about 79.5F a degree cooler again measured with the RayTech. Again under south side of attic.

I stuck a thermocuple probe up in the attic above the foil and the air temperature was 91.5F. The air temperature under the ceiling tiles was about 75.8F.

It was hard to get an accurate tile temperature under just the foil or just the R19 due to placements of the diffusers.

Likewise, I can't easily get to the top of the foil in the South part of my attic, can do it in the north side, but not the same radiant heat as the sheathing is only 101 there.




Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

I will try again when the sun is overhead.

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[zekeman]

quote
"f you wanted to model or calculate it zekeman, I have half a roll of 3/8" bubble wrap

A quick descipition would be a series of air cylinders 3/8" diamter by 3/8 high" approximately 1/2" on centre. The rows are staggered."
----------------------------------------------------------
I need a detailed drawing and an analysis of the emmivity of the foil surface as a function of temperature. And then I can do it.
And, by the way if the stuff is so good, why doesn't the manufacturer get empirical data SUPPORT claims made. Maybe he can't.
However I will gladly take a stab at an analysis once you provide the data includig geometry, material, material thickness, etc if it so pleases you.

 

[AbbyNormal]

Take it easy zeke, you said you wanted to calculate it, my verbal description is sort of like a school test question.

I can take a picture and you can use some good engineering judgement. Poly air bubbles and metallized foil.

So I just posted some 'empirical temperatures'

112.5F wood is radiating at it, the air above is 91.5F and its surface temperature on the underside is 80.5F. Some R19 exposed to the same scenario is 79.5F on the underside. Am I gettin R7 plus 2 air films?

It makes a difference in my office and I have also seen ducts exposed to 80F dewpoints not sweat with it.





Take the "V" out of HVAC and you are left with a HAC(k) job.