IR Reflective Insulation

I used radiant barrier in my shop and really like it.


http://www.radiantguard.com/radiant-barrier-foil-insulation.aspx

I'd suggest reading either http://multifoilexperiment.blogspot.com/ or http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=125&page=1 - the consensus is it's a bit of a con, and the true R value is more like 1. Furthermore, it lools like adding more layers doesn't make any noticeable difference to the insulation value - all the benefit comes from the inner and outer skins.

Still, if the price is right it's a compact way to add a bit of insulation and an air barrier...

Simple enough to test with a sheet of the material or aluminum foil or Mylar. Build two simple rectangles from 2 x 6 lumber. Close in one end of each with XPS or polyiso. Probe thermometer in one box - sheet to be tested - 40 Watt bulb and another thermometer in the other. Turn on the bulb and record the time and both temperatures. If it gets too hot, change to a 10 Watt bulb.

Arrange it with the sheet vertical to simulate a wall or sheet horizontal to simulate a ceiling.

Q = U A ΔT You will have Q, A and ΔT You can approximate U.

From what I've seen on green building sites, forums... There's always controversy about whether radiant insulations are amazing or totally worthless. The opinion I'm forming is that there are situations where these are useful when installed correctly as BK states. They are more useful with continuous heat sources and larger temp gradients & not worth much in low gradient situations. In order to get the performance indicated in the marketin materials you'll need to replicate the conditions they were tested in ie. High temp gradients, constant heat source, no convection, no other insulation, proper air space...
On the other hand to get only r-1 you'd have to install it in a terrible bass-ackwards application since any layer of solid material will give around r-1 when you factor in air films on both sides. R-1 with the material BK linked is not possible as it's more than just a radiant barrier.

radiant barrier is not insulation ! all it does is stop heat or cold transfer to a point. works good in my shop, but may not in yours. it needs to be properly installed !

The R-1 is calculated from the cooling time for a jug of water experiment done on the first link (fourth post), where it was measured to be roughly half as effective as 50mm (2") of Celotex (polyisocyanurate foam), when compared to just a sheet of cardboard. As 2" is roughly R-2 (see http://www.planetinsulation.co.uk/ZCW3025.php), this would seem a reasonable value for the conditions quoted - heat source at ~150F inside the box, room temperature outside. If you have anything significantly hotter in the room the insulation will do better (the T^4 relationship), but this is critically dependent on distance (r^3).

I'm also curious as to how they achieve the quoted emissivity - .03 is about right for polished Aluminium when fresh, but any oxide layer will quickly degrade it to .08 or so. Presumably they have some sort of plastic layer over it, but there will be some IR losses in it. Add in a small amount of dust/ash (emissivity of ~1) and you can see how the insulating properties are liable to degrade over time.

Personally I suspect 80% of the insulation value in practice after it's been installed for a while is from the air sealing effect, with the rest being reflections from any high temperature heat sources.

Actually, re-reading BK's last post brings up something - if you're insulating in front of it you will lose most of the value of the insulation. It is claimed to work by reflecting radiation - and radiative heat transfer goes with the fourth power of temperature. Double the absolute temperature, and you get 16 times the heat transfer. If you're putting up insulation or even plasterboard, you're blocking any radiation from hot bodies - all you'll get is heat being re-radiated by the inside of the plasterboard/insulation. In those circumstances I suspect you'd see even less than the R-1 I quoted, since that was insulating a body at ~150F.

Battenkiller said:

pdf27 said:

The R-1 is calculated from the cooling time for a jug of water experiment done on the first link (fourth post), where it was measured to be roughly half as effective as 50mm (2") of Celotex (polyisocyanurate foam), when compared to just a sheet of cardboard. As 2" is roughly R-2 (see http://www.planetinsulation.co.uk/ZCW3025.php), this would seem a reasonable value for the conditions quoted - heat source at ~150F inside the box, room temperature outside.

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You make some interesting points that I'll have to think about. I do want to clarify one thing to avoid further confusion, though. The R-values you are quoting are in SI units. Over here we use R-values based on BTUs. 1" of polyisocyanurate insulation has an R-value of about 7 over here... not exactly inconsequential.

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Well now that makes a lot more sense, forgot about the units of (U.S) R-Value being imperial. No wonder we never have a frickin' clue what the rest of the world is talking about, nor they us...

bioman is right of course, we can't really compare radiant barriers to insulation in a 'bang for the buck' or thickness analysis since the only recognized standard measure for insulating material is R-Value & R-Value ignores the effect of the emissivity of the materials surface. So radiant barrier manufacturers (including those making insulation with r-barriers incorporated) can get away with exagerated claims (see the whole "insulating paint" fiasco). It's kinda like measuring the fuel efficiency of electric cars in MPG

Battenkiller said:

You make some interesting points that I'll have to think about. I do want to clarify one thing to avoid further confusion, though. The R-values you are quoting are in SI units. Over here we use R-values based on BTUs. 1" of polyisocyanurate insulation has an R-value of about 7 over here... not exactly inconsequential.

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Yeah, I suddenly realised that when I woke up about 3am and felt like a bit of a fool (having even less excuse than normal given that my wife is from the US!). What got me is that you guys normally use different letters to identify things and when you use the same the units usually are too (e.g. measuring electricity in kWh). We also tend to use U-values over here (U=1/R) which muddied things still further.

One other point I remembered last night - the multifoil insulation he was testing was 20mm thick (4/5"), so the performance about the same as polyisocyanurate (probably a whisker better, but it's well into the margin of error). If you can get it cheaper or install it more easily than polyisocyanurate, you're probably onto a winner.

Aaah, the radiant insulation issue. I'm gonna go with the consensus that says it can be 'useful' under your roof joists in cooling dominated climates, and to steer clear otherwise.

My question is always how bubble wrap is cheap enough to use as wrapping material and we throw it away (after popping all the bubbles, of course) and yet when I price out this stuff
it would cost like a $1000 to do my roof area. I can't believe it is that much more costly to produce. I'm suspicious that it is priced with a huge margin, to be just cheaper enough than
foam that some folks will go for it as a 'bargain'.

I am mainly worried about degradation over time as it oxidizes and gets dirty. No thanks.

I have used bubble wrap around a basement stove (With plenty of clearance of course) situated in a corner. It worked fantastic for keeping the heat from being sucked up by the block wall. One extra side wall made a 3 sided plenum with the open side facing the stair well. I think why it works is this: The reflective surface keeps any radiant heat from reaching the block wall of course. The nominal 1/2 " air space (or foam) acts as a thermal break to stall any heat seeking the colder wall by conduction. The first increment of insulation gives by far the biggest bang for the buck. Adding more R value runs up against the law of diminishing returns. There 's probably a formula for this but to throw out a number, let's say the first inch of insulation accounts for 50% of the effectiveness of an R 11 barrier. Arbitrary numbers, yes. Hopefully someone here can do the math. So with a 1/2" layer you've stopped radiant, severely cut back conduction and can direct convective heat where you want it. There's no need to do the whole basement, although you'll begin to lose some heat through the exposed portion of the wall in time, but hopefully by then you'll have moved most of the heat to the living space. Buy 20 feet of it and experiment, but be sure to support it well away from the stove, as it's flammable.

Ehouse

Ehouse said:

....Hopefully someone here can do the math....

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Say your insulation R value is R=2 per inch thickness. In a perfect world, the math sez:

1" R=2 U=0.5
2" R=4 U=0.25
3" R=6 U=0.17
4" R=8 U=0.12
5" R=10 U=0.10

So the first inch cuts your heat transfer by 50% compared to the uninsulated condition.

The last inch cuts your heat transfer by 2% compared to the uninsulated condition.

Installation costs are different for the first inch and the last inch. The first inch has the supervision, inspection, overhead, profit, labor, equipment and cost of material contributing to the total.

The last inch only adds the cost increment due to additional inch of material.

jimbom;

Looking up Dow extruded polystyrene I got this:

1/2"=R3

1"=R5

1 1/2"=R7.5

2"=R10

The doubling progression only holds after the 1" thickness is achieved, and I suspect it is an approximation for marketing convenience. I wonder what the R-value at 1/4" is. Bet it's closer to R=2 than R=1.5.

Ehouse said:

jimbom;

Looking up Dow extruded polystyrene I got this:

1/2"=R3

1"=R5

1 1/2"=R7.5

2"=R10

The doubling progression only holds after the 1" thickness is achieved, and I suspect it is an approximation for marketing convenience. I wonder what the R-value at 1/4" is. Bet it's closer to R=2 than R=1.5.

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An air barrier with no insulating value, i.e. a single pane of glass or foil would be R-1. What I love is that they DO include that in the stated R-value of the material.

Ehouse said:

jimbom;

Looking up Dow extruded polystyrene I got this:

1/2"=R3

1"=R5

1 1/2"=R7.5

2"=R10

The doubling progression only holds after the 1" thickness is achieved, and I suspect it is an approximation for marketing convenience. I wonder what the R-value at 1/4" is. Bet it's closer to R=2 than R=1.5.

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Woodgeek is correct. They may be including air film.

Conductances for air film are quantified for still and moving air. For still air they are further subdivided by heat flow direction and the slope of the insulation surface. They are different for different depths of the still air cavity and mean temperature. Different for the surface emittance.

Different values are published for moving air above 7.5 mph for summer and above 15 mph for winter.

So it is hard to tell what value they may have used.

1981 ASHRAE fundamentals has published an increase in R value of about 1 going from surface emittance of 0.9 to 0.05. So a highly reflective surface gets you 1 Btu/h*ft2*F increase if the air space is deeper than 0.5 inches.

Heck, I guess I'm going to bow out at this point. I'm not prepared to discuss the differences between a thermal break, air barrier, and air film. Interesting subject though.

Ehouse

Battenkiller said:

pdf27 said:

Yeah, I suddenly realised that when I woke up about 3am and felt like a bit of a fool (having even less excuse than normal given that my wife is from the US!). What got me is that you guys normally use different letters to identify things and when you use the same the units usually are too (e.g. measuring electricity in kWh).

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...we're the fools for failing to embrace SI units. ...)

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+ 1

Battenkiller said:

Maybe this has been mentioned before, but...


While I was searching for options to finish my basement, I had a contractor stop by to talk about IR reflective insulation. It turns out it's not the best option for what I want to do (mostly because he only sells his stuff installed... $$$), but here is a similar product that might be just the ticket for basement burners who don't care to finish their basement but want to keep the heat in.

It is a low emissivity (only .03 compared to .95 for most common materials) thin roll product that works by reflecting the radiant heat back into the room. Kinda like two giant space blankets with large-cell foam sandwiched in between the layers. Provides heat loss reduction that is equivalent to R-15 (R-7 in horizontal applications) and comes in 175' rolls x 4' wide (700 sq.ft.) for $225 (.32/sq.ft.)


http://www.insulation4less.com/Insulation4lessProduct-1-Prodex-Total-48-Inch.aspx#fragment2

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That product of rigid foam and foil and plastic only has an R7 value and what does it cost?

For my 2x4 shed walls I am using John Mansfield R15 Fiberglass and R3.9 Reflectix foil that I can buy cheap at Lowes

So for 2x4 walls they will be R18.9 all together plus the R2 backer board under the grooved cedar shingles that makes R20.9

Then slap on some paneling to make it look good!

See pics

woodgeek said:

Aaah, the radiant insulation issue. I'm gonna go with the consensus that says it can be 'useful' under your roof joists in cooling dominated climates, and to steer clear otherwise.

My question is always how bubble wrap is cheap enough to use as wrapping material and we throw it away (after popping all the bubbles, of course) and yet when I price out this stuff
it would cost like a $1000 to do my roof area. I can't believe it is that much more costly to produce. I'm suspicious that it is priced with a huge margin, to be just cheaper enough than
foam that some folks will go for it as a 'bargain'.

I am mainly worried about degradation over time as it oxidizes and gets dirty. No thanks.

Click to expand...

Whoa there. You saying bubble wrap in place of the reflective radiant foil type stuff people use in their attics?

Ok. Bubble wrap does not equal reflectix. I just think reflectix must be overpriced for what it is, and the performance/application is pretty limited.