predicting surface temperatures and condensation through a wall section at various indoor and outdoor temperatures. huh?



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    Jonathan Chertok

    some typos i see:
    “dee point” is dew point.
    “trust this walk seftikn” = test this wall section
    “on the wall de ruin” = on the wall section

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    Mark Baker


    In order to help answer your questions on this forum - it would be more helpful if you used capital letters and complete sentences and divide your questions into separate thoughts.  It's really hard to follow your train of thought in this post.

    Calculating temperature change through a wall section is an easy enough process.  It just takes work.  You are given the temperature.  Its a matter of thickness of the material, R-Value of the material, and the difference in temperature.  I can't seem to find a good explanation of this currently, but I will try for you.

    Dew point, you would have to have another chart that shows relative humidity by temperature, and then follow the temperature through the wall to know where the RH hits 100% (aka the dew point).  I doubt that these two would show up in one question.  Perhaps they may be on a case study as two separate questions.

    In a cold climate - you want the vaor barrier on the inside so that the water does not get INSIDE the wall to condense.  You leave the exterior without vapor barrier, so the wall if it would get wet can dry outwardly.

    You contradict yourself with the "inside temperature" - also - the interior temperature would be 68dF the exterior would be 32 dF.  If your interior temperature is 32 and your exterior is 68, then you are inside a faulty freezer, or an overactive refrigerator.  Which, for your reference, they sandwich metal panel on insulation.  The metal panel acts as vapor and water barrier, and no water gets through the wall to create dew. 

    Indoor air is conditioned - which includes removing excess humidity.  If its warm inside, the air is LESS HUMID then it is OUTSIDE. If the air is cooled inside, then it less humid than warm outside air by way of the air conditioner.  You always leave the LESS HUMID side open, and the MORE HUMID side PROTECTED AGAINST WATER VAPOR.

    hows that?

    Mark, Archizam



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    Jonathan Chertok

    ok. thanks for the bump mark. and also the help here. yeah thanks for catching the temp switcheroo. i find it slightly aggravating to have to recreate a whole question here to try to ask a question.
    is it now the case i can’t post photos? we used to be able to do this.
    can we take a step back and just discuss big picture what is happening here?
    the materials have an R value that reflects their ability to - well their ability to - to resist the transmission of heat? so this R value gives us some abstract measurement of how well it resists the transmission of heat?

    is this ability to resist heat a single value independent of how hot it is? i mean if the temp goes up it doesn’t resist more or resist less it will simply resist the heat by this abstract - of i guess it is actually a concrete amount in that it does in fact have units? i find the concept confusing for some reason.
    i mean i guess there is some law of thermodynamics that says energy will be conserved.
    so if it is 32 outside and 68 inside i can have a wall section of some kind in between and it will resist the transmission of heat from inside to outside?
    and in any specific instance i will be able to draw this sort of - well it is sort of a not to scale graph with nothing except inside and outside on the x axis and - well and a some scale less representation of temperature in the y axis?
    i mean i don’t get this concept.
    if it was 0 degrees fahrenheit outside and 68 inside what would happen? presumably the R values would remain the same and the graph would change along with the surface values in the wall section?
    i mean there is some kind of weird assumption or tautology happening with this example.
    i mean if it was 68 inside and 32 outside and i changes the materials to a ham sandwich presumably there would be no significant resistance in the wall section and you couldn’t maintain the 68 deg indoor temp.
    do you know what i mean? i mean somehow the wall section has done minimum amount of R value to resist the heat being transferred so the interior temp stays at 68. i guess there is a kind of logical step i am missing on this one.

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