Does Reflectix Double Bubble Duct insulation have a stand alone R-6 insulation value when installed with no airspace ?
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I have been reading your responses to the various situations where the bubble wrap radiant barrier product was being used by HVAC contractors as a duct insulation. I recently had to replace all the duct system in my crawl space due to Sandy flood damage on the eastern shore of Maryland and the new duct system was installed with the 1/2″ Reflectix double bubble product installed as an R-8 duct insulation. The installation neglected to include the 3/4″ spacers to create the airspace needed for the radiant barrier assembly to work as a duct system insulation assembly effectively. As a BPI Building Analyst & Envelope Professional and HERS Rater, I informed the contractor that the installation was not done correctly. The contractor contacted Reflectix and they told him that the 1/2″ double bubble product used with no air space still has an effective R-6 duct insulation value. They are basing this claim on another Test Report done by R & D on August 2, 2011 measuring Thermal Resistance Measurements according to ASTM C1668/C335 on the Reflectix Double Bubble Duct Insulation. As a building science professional and building contractor I am still somewhat skeptical on that claim being made as a result of that single test. Here is a page from the report that describes the testing that was done. I have the whole report but I am still somewhat skeptical about how accurately the results of this test equate to the claimed stand alone R value of R-6 for the Double Bubble product. I spoke to Reflectix and explained my concerns with my fairly extensive new duct system being wrapped with the product and what my options are to get the duct system insulation up to the R-8 insulation value. My HVAC contractor will do what ever is recomended to achieve the minimum R-8 value. One suggestion is to wrap over top of the Double Bubble wrap with conventional foil faced FG duct insulation. The other is remove the bubble wrap and rewrap using new Bubble wrap with the proper installation with 3/4″ air space, which would be a nightmare with the duct system already installed, or rewrap using conventional R-8 foil faced FG duct insulation. I asked Reflectix what their recommendation would be and they seemed to indicate not wrapping the Double Bubble with a layer of conventional foil faced FG insulation. I am hoping to get some feedback on the best possible practical solutions to achieve an effective R-8 duct system insulation.
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P.O. Box 2400
Cookeville, Tennessee 38502-2400
http://www.rdservices.com
Phone: 931-372-8871
Fax: 931-525-3896
Thermal Resistance of External Duct Insulation
R&D Test Number: RD112169DT Date of Test: July 20-29, 2011
Specimen Number: 1071110622-6 Manufacture Date: Unknown
Test Method: ASTM C 335, “Standard Test Method for Steady-State
Heat Transfer Properties of Horizontal Pipe Insulation”
Report Prepared for: Reflectix, Inc.
Contact Person: Monty Millspaugh
Description of Test
The resistance of externally applied air-handling duct insulation is determined using a calibrated
end apparatus operated in accordance with ASTM C 335 with analysis in accordance with Section
10.8 of ASTM C 1668-09. The calibrated end apparatus is discussed in Section 5.4 of the test
method. The test apparatus is a seven-foot long section of 8 by 12 inch rectangular steel duct.
An electrical resistance heater is mounted horizontally along the center–line of the duct. Fans at
each end of the duct provide internal air circulation. Eight Type-E thermocouples are
permanently attached to the interior surface of the duct to provide a hot-side temperature. Four
thermocouples are attached to the outside surface of installed duct insulation to provide a coldside
temperature. Thermocouples are attached to rectangular end caps of known thermal
resistance in order to determine heat loss from the ends of the apparatus. Two thermocouples are
placed four inches from the exterior side of the duct insulation to measure the temperature of the
air adjacent to the insulated duct. The entire apparatus is located in a conditional space that is
maintained at 70 +/- 2 ºF and 50 +/- 5% relative humidity. R-value for the duct insulation is
obtained from Equation (1) where the heat flow through the insulation is determined from
Equation (2). The heat flow through the end caps is calculated from Equation (3) where the Rvalue
for the end caps is obtained as a function of temperature using a heat-flow meter apparatus
operated in accordance with ASTM C 518.
Attachment Size
Reflectix_rd11418(1) R&D Test.pdf 93.31 KB
Answered by Bruce Howe
Posted Fri, 03/15/2013 – 08:47
Edited Fri, 03/15/2013 – 08:54.
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Replies
Bruce,
Like you, I am skeptical that 1/2-inch thick bubble wrap can have an R-value of R-6. Let's call that (charitably) "highly unlikely."
The document you posted is a dead link. I suspect you have to rename the document with a simple title -- perhaps a single word, like "Reflectix" -- that has no punctuation marks in it. (Titles with punctuation marks don't work as links.)
I know Dave Yarbrough at R&D Services and Monty Millspaugh at Reflectix. I have contacted both of them asking for more information.
Bruce,
I just got off the phone with David Yarbrough at R&D Services. Fortunately, the laws of physics haven't changed since I last spoke to David. Reflectix still has an R-value of R-1.
The R-6 claim is based on measurements of the R-value of an assembly, not of Reflectix. The assembly R-value included the R-value of the Reflectix, the R-value of a necessary air space between the Reflectix and the duct (maintained by a complicated and unlikely Rube Goldberg contraption of plastic spacers), and the air film on the outside of the Reflectix.
If Reflectix reps are claiming R-6 for the product alone, they are lying. They are also in violation of the federal R-value Rule.
More info here:
https://www.greenbuildingadvisor.com/community/forum/green-products-and-materials/23805/reflectix-still-claiming-r42-its-bubble-wrap-my-h
https://www.greenbuildingadvisor.com/community/forum/building-code-questions/16263/bubble-wrap-duct-insulation-energy-star-approved-and-i
https://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/bubble-wrap-duct-insulation-good-idea
If the ducts are outdoors on Mars it'll probably do even BETTER than R6!
But I'm assuming you live in a warmer place with a thicker atmosphere, and even if your ducts are in the crawlspace, rather than the exterior of your habitat/pod/house whatever, it's unlikely that you're going to see the large temperature differences between the duct & Reflectix and the Reflectix and crawlspace temps that would actually give it decent performance. (In an unconditioned crawlspace anywhere on Mars would deliver good performance though, but you'd probably need/want a lot better, even there.)
Hey, thank you all for the quick feedback. I am renaming the saved test file and reattaching the test report that was sent to me by Reflectix that supposedly represents the Double Bubble 1/2" Duct insulation tested according to ASTM C1668/C335 where the Double Bubble insulation that was tested was wrapped in direct contact with the metal duct with no air space. This I was told is proof positive that Reflectix can now make the claim that the Double Bubble wrapped tight to my metal duct system, located in an unconditioned crawl, without the spacers and 3/4" air space between the radiant barrier and the metal duct, the bubble wrap will still have an insulative value of R-6. I was told this was a different test then the assembly test. I have been talking with my HVAC guys and they were thinking that the most practical fix might be to just wrap another layer of conventional foil faced R-8 FG insulation over the bubble wrap to attain an R-8 insulation value on the duct system. I am not convinced that this is the best way to go considering the logistics of limited maneuvering space in the crawl and the possible lost efficiency of the Double Bubble/Foil Faced FG sandwitch with conductive heat loss. I think it may be best to remove all the bubble wrap and reinstall conventional time tested tried and true Foil Faced R-8 FG duct insulation. At least then you know what you got!!
Bruce,
The test report is for an assembly, not a product. The description of the assembly is somewhat unclear:
"A layer of double-bubble duct insulation with nominal thickness 3/4 in. and an interior layer of low-emittance material was installed around the test duct without spacers. The insulation was identified with the notation BB060410V2. Both sides of the double bubble reflective insulation were faced with low-emittance material. Approximately 72 inches of material was installed around the test section of the duct to provide two layers of insulation on the top of the duct and two layers of insulation on one-half of the surface on the vertical sides."
Here's my interpretation:
- There are "two layers of insulation" in the assembly.
- Each layer is "insulation with nominal thickness 3/4 in." I'm not sure what the product is, but each layer is evidently 3/4 inch thick. Two layers of this product would presumably have a thickness of 1 1/2 inch.
- It seems as if each layer of this product was modified before the insulation sandwich was assembled. Here is the description: "Both sides of the double bubble reflective insulation were faced with low-emittance material." I'm not sure what that means. Did the "double bubble reflective insulation" come from the factory that way? Or did the workers in the test lab make a custom sandwich, with each layer consisting of low-emittance material, followed by double bubble reflective insulation, followed by another layer of low-emittance material? (Presumably, if the latter approach is the one they took, they made two such sandwiches and stacked them on top of each other.)
Regardless of how these ambiguities are resolved, it's clear that this report is not talking about a 1/2-inch-thick product.
Hi Martin, I totally agree with your assessment of that test. I was wondering the same thing when I read the description of the test specimen which seemed to indicate a test on several layers of material and a very vague description explaining exactly what was tested. I am somewhat surprised that Reflectix would tell me that this was a test done on a single layer of the the double bubble product installed on metal duct with no air space that verified the Reflectix representative's claim of the stand alone insulative R-6 value of the product. I think there must be quite a number of HVAC contractors and suppliers out there that have bought into the Reflectix claim and are using this product as a duct insulation as a better insulation to use especially in areas like crawl spaces with potential moisture issues. That combined with the fact that many of these HVAC suppliers and contactors that are using this product are not familiar with the proper installation of radiant material as a duct insulation makes this a pretty big problem. I hope there is some believable independant testing done to definitively verify any attributes and efficiency values of the duct insulation application of this radiant barrier material to cut through the Reflectix hype.
If you look at the conditions in the report, and the trend lines- the stuff goes DOWN in R-value with increasing delta-T (which isn't what happens with the purely radiated fraction- the direct contact and convection within the bubbles are screwing it up.)
But they're also maintaining the crawlspace at 70F which is exactly the temp in your crawlspace, right? (I thought so! ;-) )
When the duct temp is 138F (a delta-T of about 68F) it's performance is about R4 surface to surface, R5 surface to air, within measurement error limits. (The implied accuracy of 3 significant digits is silly, but necessary in the report.)
A double wrap would not double it's effective R at any delta-T, since it's the low-emissivity of the exterior layer that's giving it any performance boost at all. It might add R1-R2, not more. It needs the air gaps to have any appreciable improvement in average performance.
So...
In an unconditioned vented crawlspace that runs 35-40F during mid-winter coolth, and a hot air furnaces delivering 125F air, you're looking at an even greater delta-T than tested, but an interpolated extension of the trend lines would put you at about R 3.5 surface to surface, R4.5 surface to air.
It's performance with 125F ducts when it's 70F in the crawlspace is immaterial, since that's only happening on the hottest day of July, eh?
From their tables, the air-to-air calculated R only hit's 6 when the ducts are 95F, a fairly low 25F delta-T. That would be valid for tepid-air geothermal heating ducts routed completely inside of 70F conditioned space, but a far cry from an attic or crawlspace duct condition, and again, it would be sub-R5 wherever it is in contact with building materials.
Expect no better than R3-3.5 for an average performance on warmer heating duct in a crawlspace.
Better than nothing, but not worth much, and probably not worth what you'd pay to install it. A 1" shot of closed cell foam to insulate the ducts, followed by a sprayed on intumescent paint might be better overall value.
While it's possible to hit any arbitrary performance level by successive layering with air spaces, getting there with low-E coatings on thin materials just isn't worth it for Earth-bound systems, the lone exception being enhancing the thermal performance of windows.