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]

Actually what I have is 5/16"

It is can see the staggered bubble pattern, approximately 3/8" diameter, about 1/2" on centre and staggered rows.

it would appear to be air pockets in between the cylinders.

however these cyclinders are better described as disks, there are two disks then about 5/32" in height in series, not the 3/8" tall cylinders like I was guessing at before.

Metalized film is on the two sides, most likely aluminum

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

 

[AbbyNormal]

Based on the temperatures on the underside of the insulations compared to the air temperature at the ceiling below the tiles, the foil coated bubble wrap looks about 78% as effective as the friction fit R19. So that sounds too good to be true.

79.5-75.8=3.7

80.5-75.8 = 4.7

3.7/4.7=0.787

Could be some air short circuitting from the attic and throwing readings off. The underside surface temperatures was taken by an infrared, the air by a thermocouple. I will see what happens on a hotter day with the sun directly overhead. Too bad this thread did not start a couple months earlier. Will also see if that raytech gives readings besides 'point 0' or 'point 5' as well.

But, I have seen it be effective at keeping heat out, just not so sure at keeping heat in. The highest R-value they show on the Astrofoil site is for "heat flow down" implying an attic almost triple what they claim for heat flow up, implying an attic in winter. They also seem to be relying on air flilms in those values. So would I use it in lieu of Dow Sm under the pex tubing in a slab, No.

Some houses here use it in their attics on the under side of the roof pitch,in lieu of fibre glass at the truss chords. The temperatures are bearable in those attics around 100F, while those temperatures with the insulation at the truss chords could kill you. That 130F attic air is the third hottest thing in an attic and it loves to short circuit the fibre glass. At 100 or 130, that air here still has an 80 dewpoint. So ducts less likely to sweat when exposed to 130.

Before my office, I have only used it myself as a return duct insulation where I was tight for space going through trusses.

But I have seen supply ducts not sweat when it was used, I have seen it applied to horizontal runs of large condensate drains as well, and I read a thermal imager's report on it some years back.

Maybe a couple inches of foil backed fibre glass can be more effective than thicker layer without foil in a hot attic.

Anyways, if you spent some time on attic patrol in the summer, maybe you would not be so gung ho to get on the complete 'snake oil' band wagon. I am in a year round cooling environment and the OP sounds like he is in Samoa.

A northern climate, it is easy to have a sealed vapour barrier at the ceiling plane, it is difficult in the tropics to do this. You would have to apply poly to under side of trusses, then insulate beneath the poly, then drop a ceiling below, to get the vapour barrier on the warm side of the insulation.With insulation at the truss chords you cannot get a sealed vapour barrier above it. So the function of the vapour barrier is to keep moisture from diffusing into a colder builing cavity, but it also stops humid air from passing through. Stack effect pushes up on the ceiling plane in the winter, but pressure differentials or even inverted stackes will pull attic air down in the summer.

You could take what seems the best approach for hot humid climates and not vent the attics, seal them, and insulate them at the pitch of the roof. The concept of attic venting was to eliminate ice dams, however in a hot climate it is veiwed as flushing out the heat.

If you can do it on the exterior of the sheathing, you are better off than doing it on the underside of the sheathing. It eliminates having a solar collector on the top of your structure.




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

 

[zekeman]

Quote "Based on the temperatures on the underside of the insulations compared to the air temperature at the ceiling below the tiles, the foil coated bubble wrap looks about 78% as effective as the friction fit R19. So that sounds too good to be true.

79.5-75.8=3.7

80.5-75.8 = 4.7

3.7/4.7=0.787"
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I applaud you for doing this and respectfully submit that your numbers on R16 look off to me. Even if the temperature on the upper surface of the R16 were 110, the total drop to 75.8 would be about 35 deg. Since R16 is about 16 times the resistance of the air film which is 1 at most, I would have to say that at most the inside surface temp difference to the inside temp is about 1/16 of 35 deg which is about 2 degrees vs your 3.7. Also, this method of comparison depends on small differences and so needs very accurate data which cannot be obtained with IR readings. maybe TC readings on the surfaces would be more accurate.
May be that the IR readings (which depend on assumed emmisivity) are not right. Please correct me if you think otherwise. By the way, why don't you take upper surface temp readings to make the findings more meaningful.

 

[AbbyNormal]

Easier said than done getting at the top side in the south part of the attic.

But the underside of R19 in one truss space and the bubble wrap in the next truss space were taken with the same thermometer, one degree difference against the same heat.

Below these two different insulations was an air space of a couple inches then a T-Bar tile.

Maybe the numbers appear off because you are only thinking conduction and convection, a typical heat loss appraoch when sizing a furnace. I would expect the top side of the R19 to be warmer than the air above it. A thermocouple measured the air at 91.5F. Was easy to stick a bead up to get that measurement.

Based on the underside insulation temperatures, the foil seems to be 78% as effective as the R19 friction fit. An error of a 1/2degree could be quite significant. Is the R19 truly R19 as installed who knows.

When I get some overhead sun, I will try again. But preliminary measurements are suggesting it is not snake oil when the goal is to keep heat out.



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

 

[AbbyNormal]

you want me to put black tape on the underside of both?


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

 

[zekeman]

quote"Maybe the numbers appear off because you are only thinking conduction and convection, a typical heat loss appraoch when sizing a furnace. I would expect the top side of the R19 to be warmer than the air above it. A thermocouple measured the air at 91.5F. Was easy to stick a bead up to get that measurement."
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First off , I am fully aware of radiation and its effect on the total thermal process. In this case, the effect of the radiative component from the wood to the upper surface acts like it has an h= about 1 for the 110 degree temp and since the film between the 91.5 and the upper surface has an h about = 1. You had better rethink your statement about the upper surface being higher than the air above it. If that were true, you would have 91.5 degree air between two surfaces, each higher than 91.5, an impossibility for thermal equilibrium.
Accordingly, the simple one dimensional thermal model for the R16 case is a source(point 1) at 110 deg connected by a resistance of 1 (equiv radiation resistance for a black body) to the upper surface (point 3) and another source at 91.5 (point 2) connected by another (film) resistance, coincidentally also about =1, Now taking the upper sirface as a node point(3) you get another resistance = 16 for the R16 insulation to the lower surface node point 4 ; from node point 4 to the room ambient air = 78 (point 5) we have another film R=1, which completes the simple model.
From this, I get an upper surface temp of about 101 and a lower surface of about 79.3. Your measurements don't come close to this and I am wondering why.

 

[zekeman]

It looks like I made your case for the temps on both sides of the upper air being higher; but this violates thermal equilibrium and suggests that the 91.5 deg air is still being heated and doesn't represent an equilibrium state.
What do you think?

 

[AbbyNormal]

Where is the "16" coming from, the frcition fit fibre glass insulation is marketted as 19 and the bubble is getting marketted as 15. Did you calculate the bubblewrap as 16 finally

But 'whatever' the R-value is, you could focus on the underside temperature.

I don't know the trade name of the bubble wrap I have left over so I can't say if it is Astrofoil or Reflectix etc.

The attic air temperature was taken perhaps "inches" above the top of the insulations, and the underside of the wood sheathing is "feet" above the insulation. The roof pitch is not high like in a Paston Effect, more like a 4:12, but air could stratify a bit none the less.

With sun over head, it is not unreasonable for the roof sheathing to be the hottest temperature in the attic, the top of the insulation being the second hottest part of an attic and then the attic air temperature in third place.

http://edis.ifas.ufl.edu/EDISImageP...&dlNumber=EH245&tag=IMAGE EH:EH245F3&credits=

Room air was measured as 75.8 up just below the tiles.

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

 

[AbbyNormal]

Cloud goes by less sun hitting roof, cloud passes more sun,thermostat cylces on off air temp below fluctuates, wind blows a little harder on Gable wall vents. Is it ever an equilibrium?

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

 

[AbbyNormal]

To be clear again, there is an ar space between the under side of the insulation and then a t-bar tile.

I measured the surface temperatures the under sides of the insulation, and then the air temperature (75.8) under the ciling tile, pehaps an inch below.

There was more on an air gap below the bubble wrap as it was arced up into the truss space where as the kraft paper of the R19 was more or less flush with the truss chords.

In another part of the attic just minutes ago,roughly a noon EST, top side of bubble wrap 98.5 , underside of bubble wrap 80.5, again with the raytech, air above the bubble wrap 86.7 with thermocouple.

Raytech seems to only give either 'point zero' or 'point 5' readings. Tired it on walls , books , myself. Always ".0" or ".5"

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

 

[stanlsimon]

If there are no ratings for flame spread and developed smoke (UL 181) then and inspector probably shouldn't allow it to be exposed in a building.