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  1. #406
    Join Date
    Jun 2004
    Location
    Des Moines, Iowa
    Posts
    3,764

    Default Re: Does air tightness trump R value to some degree?

    Glenn
    Welcome back.
    We did have some good discussions didn't we. Things have changed a little around here and things are the same.
    Some of our good participants have made the choice to either abstain or leave altogether. We do have a few new participants that have their heads on pretty well and will get into the conversation with good questions. We don't' seem to have many of those long and twisty educational threads anymore or maybe I miss them due to my busyness.

    I remember fondly the discussion that resulted in your going to see Lisa P and all of the help we gave her here and the educational benefit for all that were involved.
    I still get a Christmas card form her every year.
    Out of those types of conversations and other events my consulting practice has grown immensely.

    Not to sidetrack the thread but good to see you here again.
    Mark Parlee
    BESI(building envelope science institute) Envelope Inspector
    EDI Certified EIFS Inspector/Moisture Analyst/Quality Control/Building Envelope II
    Level one thermagrapher (Snell Training)
    www.thebuildingconsultant.com
    www.parleebuilders.com
    You build to code, code is the minimum to pass this test. Congratulations your grade is a D-

  2. #407
    Join Date
    Aug 2013
    Location
    KS
    Posts
    323

    Default Re: Does air tightness trump R value to some degree?

    Quote Originally Posted by cdekorne View Post
    Thank you for this correction, dgbldr:

    No again. Foil is a radiant barrier and "heat barriers", whatever that may be, have nothing to do with moisture infiltration. Moisture infiltration is reduced with water barriers and/or vapor barriers.

    Cashcow, you're new here and I appreciate your contribution. But you have been posting a lot of "science" stuff that contains a fair number of gross errors. Please post less and check your facts more.
    [/QUOTE]

    4 post? are you an inbred of dgbldr he hired to make himself look smart to perhaps promote his business? I'm telling you he and you did not read the BCS report that answers this question in detail. You two could not describe that test or the results evident by your responses to it. I've read alot of dgbldr post he has no clue what he is talking about most of the time and attacks people to look smarter but he is not! The kid talks out of both sides of his mouth, needs to take his own advice do more experienced based research and stop posting so much!
    Last edited by CASHCOW; 02-28-2014 at 06:18 PM.
    Terry

  3. #408
    Join Date
    Jun 2004
    Location
    Burlington and Brooklyn
    Posts
    5

    Default Re: Does air tightness trump R value to some degree?

    Terry, it would be helpful if you stuck to the discussion rather than trying to one-up those who point out your misconceptions.
    I assume you mean BSC (not "BCS") ... as in Building Science Corp. Can you tell us what report you're talking about?
    If you're referring to the Thermal Metric Project (http://www.buildingscience.com/docum...s-r-value/view) that report demonstrates what many have said in this forum thread: air leakage certainly degrades thermal performance. But it also sheds light on the effect of thermal bridging, and demonstrates that heat flow is dependent on the temperature difference - R-value is not a constant as we tend to assume reading off the insulation product label. A good summary of the report is posted here: http://www.buildingscienceconsulting...ummary_rev.pdf
    Among it's conclusions, this is especially inteesting: "When walls are constructed with the same installed R-value in the stud space, and are air sealed both inside and outside (i.e. there is effectively zero air leakage through the assembly),they exhibit essentially the same thermal performance regardless of the type of insulation material used."
    It's worth noting that this research does not attempt to describe the thermal performance of walls in terms of "convection" or "conduction," nor does it discuss radiant barriers at all. --Clay

  4. #409
    Join Date
    Aug 2013
    Location
    KS
    Posts
    323

    Default Re: Does air tightness trump R value to some degree?

    “Terry, it would be helpful if you stuck to the discussion rather than trying to one-up those who point out your misconceptions. I assume you mean BSC (not "BCS") ... as in Building Science Corp. Can you tell us what report you're talking about? “

    Thanks for finally reading the test report’s conclusion, that was discussed long before you posted your 5th post to the site. The “Thermal Metrics for High Performance Walls - The limitations of R-Value” is the discussion, or should be, since that is the only real data posted, not what you quoted or think is my ‘misconception’ after all that was discussed and posted on the thread.

    BTW: I don’t think any of the walls tested are the "high performance" walls to date. I would have liked to see ICI, CIC. SIP other bonded monolithic sandwich construction.

    “If you're referring to the Thermal Metric Project (http://www.buildingscience.com/docum...s-r-value/view) …….”

    “Project”? Since you are correcting spelling and typos you may want to go look at the title again on the first page not the conclusion, start reading from there. If you need help understanding something which is obvious, ask questions.

    “that report demonstrates what many have said in this forum thread: air leakage certainly degrades thermal performance.”

    “ Demonstrates what people on this forum have said”????

    You may want to read it again it makes no reference to this forum, or cares what people “have said”. The test however DID quantify what was NOT KNOWN! And applies a new metric “thermal performance” to wall cavities vs “R-Value”

    “But it also sheds light on the effect of thermal bridging, and demonstrates that heat flow is dependent on the temperature difference - - R-value is not a constant as we tend to assume reading off the insulation product label. A good summary of the report is posted here:http://www.buildingscienceconsulting...ummary_rev.pdf

    Assuming you gathered this from the conclusion, the report goes far, far, beyond “thermal bridging” from delta Ts. It sheds NO light on the well known fact that wood and metal studs thermally bridge. Further, heat flow or transfer is dependent on more than delta Ts.

    Use this equation as a guide:

    q = (specific heat) x m x Δt
    where q is heat flow, m is mass in grams, and Δt is the temperature change...

    Take particular note of mass, specific heat, and I’ll add density and thickness when determining thermal effect or performance. This test as stated did not account for material properties, nor measurements of R-value as temperature dependent, however it did make some assumptions.

    The report also looked at pressure deltas, interaction between heat flow and air flow. It failed to look at moisture and endurance, vibration, icing, impulse, waterproofness, sand & dust, fungus, hail strike, quality of field construction, shock, to name a few.

    “Among it's conclusions, this is especially inteesting: "When walls are constructed with the same installed R-value in the stud space, and are air sealed both inside and outside (i.e. there is effectively zero air leakage through the assembly),they exhibit essentially the same thermal performance regardless of the type of insulation material used."

    “Inteesting” ? Interesting? Yes indeed! “zero” leakage how often do you find that in wall cavities and how is it measured? It is a "well known" loss hence the test, if we had walls with no air movement there would be no need to be concerned about r-value nor an expensive test with big industry players wasting time. You misunderstood this, see below…..

    From report: “All wall assemblies experience a loss in thermal performance due to air movement through the assembly. This is true for all of the assemblies tested regardless of the type of insulation material used (e.g. cellulose, fiber glass, ocSPF, ccSPF, XPS). “

    The specifics are in tabular form in the report for each wall.

    “It's worth noting that this research does not attempt to describe the thermal performance of walls in terms of "convection" or "conduction," nor does it discuss radiant barriers at all. –Clay”

    I’m not quite sure how a test that tested “combined heat and air flow in wall assemblies” did not test for convection, conduction, or material specific radiation barriers”? If you want a better of understanding of the reports measures of convection, conduction, and radiation, it is noted throughout the report starting at the beginning.

    From report: “Conductive heat flow is the basis for most of the heat flow calculation methods used in the building industry. One-dimensional steady state conductive heat flow through a homogenous material can be described by Fourier’s law:”

    From report: “In this study temperature dependency of insulation R-value was accounted for by material-specific thermal conductivity measurements (made at the hot-box test temperatures). “

    Note “One dimension steady state” is NOT the case. Conductivity and convective loops occur often in wall cavities in reality, that are difficult to sustain by use of select materials, sill seals, calking, mastic, etc, s/b of particular concern not steady state r-value, as seen in the testing, that play a MAJOR role in sustained r-values or ‘thermal performance’ a better dynamic. ORNL is now using a DBMS value, not R.

    From report: “Over recent decades a much broader range of insulation types, and application methods of insulation have been developed and deployed than were available when the R-value was conceived. As the building industry strives to reduce energy consumption for environmental and economic reasons, building enclosures with high thermal performance, reliably and affordably installed in the field are demanded. The R-value of the insulation products in many of the new building enclosure systems is increasingly unable to measure their actual thermal performance because system effects, sensitivity to construction defects, and airflow can play such a significant role in overall performance.”

    Exactly! The energy impact of air and moisture, gas flows depends on the flow path, the interaction between the air and the solid conductive materials in the assembly, and the installed “R-value” of the assembly.

    You might want to reconsider your interpretation of convection, conduction, and radiation, their thermodynamic, aerodynamic and fluid dynamic relationship to one another, and being a teacher of this subject by just limited experience and a misunderstanding of a limited test report conclusion. By induction of air and other variables, the limited results showed what happens to r-value by convective loops measured in 1-3 dimensions, conduction losses, and radiation. In actuality, 1d, 2d or 3d models do not fully describe this complex convective dynamics, and without some conduction there is no transfer of heat through materials or resistance (wouldn’t that be nice in some cases) . Radiation was also tested of course, it is integral to heat flow Q through any material. Radiation varies with absolute temperatures, convection delta T, orientation, and air permeability. Hence, “R_Value” is only valid under specific conditions and is a poor indicator of performance if those conditions vary, which in all reality is the case.

    I could go on and on but I am interested in other things right now like designing out of the variations…..I’m out! Test like this are a good guide and can cause confusion obviously. For better info develop it yourself with a good test plan and Engineer.
    Last edited by CASHCOW; 03-19-2014 at 02:12 PM. Reason: spelling
    Terry

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