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AAc blocks instead of Vermiculite insulation under slab - Forno Bravo Forum: The Wood-Fired Oven Community

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  • #46
    Re: AAc blocks instead of Vermiculite insulation under slab

    Here we go - more data to add. This was a longer fire over 4h, with a fairly varied rate of burning (also known as a tea break). I've added the graphs again below if anyone's interested - one degrees C, one in degrees F, depending on your preference... W - I'll PM you this lot in spreadsheet format in a couple of minutes - if you've got time to do your clever stuff with the numbers, I'm all ears. Still no door on this oven as it cools - hoping to make one next couple of days.

    I stopped adding wood after 1 1/4 hours (tea break) then added more wood until 4 hours, after which I left the whole thing to cool down. Interesting to see how variable the surface temperature of the dome is, and how it drops very quickly once the fire goes out. You can really see how all the heat is locked up in the core of the dome - the 2" deep probe remained hottest all the way through the cool down.
    http://fornoeconomico.blogspot.com/

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    • #47
      Re: AAc blocks instead of Vermiculite insulation under slab

      That's a great dataset - I can't run the model right now (it is 11 p.m. here - way past my bedtime), but I'll do it tomorrow.

      Many thanks,
      W.
      "Carpe diem." - Fish of the Day (The Uxbridge English Dictionary)

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      • #48
        Re: AAc blocks instead of Vermiculite insulation under slab

        Originally posted by Carl View Post
        Here we go - more data to add.
        And the model fit is quite good, explaining pretty much all the data variation (99.9% of the variance). See the first snapshot.

        And because this is a nice and complete run I am much more confident about the result, which puts the losses at a more realistic 16% with pretty good accuracy (see the second snapshot, which gives a 95% confidence interval of between 15.3% to 16.9% losses).

        Does 84% insulation efficiency sound sensible to you?

        Best wishes,
        W.
        "Carpe diem." - Fish of the Day (The Uxbridge English Dictionary)

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        • #49
          Re: AAc blocks instead of Vermiculite insulation under slab

          Fascinating. That's a really good fit to the model. Can you explain to me what the 16% loss means - does this mean that 16% of the heat is lost per time period (hour) - or am I barking up the wrong tree? 84% efficiency feels quite good to me, especially with no door on - a gaping great hole to lose heat through... I'll get more data once I've got the door.

          You're appealing to my inner-geek here. Hope we can do this again with the door fitted - that'll be the information that's most of interest. Thanks for taking the time to play with the numbers.
          http://fornoeconomico.blogspot.com/

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          • #50
            Re: AAc blocks instead of Vermiculite insulation under slab

            I was impressed with the data quality. Did you use a logger or just wrote them down?

            How to interpret the 84%? The model assumes that heat flows from the internal to the external surface of the oven at the rate proportional to temperature difference. The door is not really involved in these losses, as throughout most of the data I used, the temperature of the internal surface is higher than that of external. If the insulation on the outside of the dome was perfect, then the two curves would get to the same level eventually, but from the plot it is evident they will not - the inner temperature peaks, the outer temperature peaks with a lag, but at a lower level.

            As the construction dries out I am sure the losses of this kind will diminish.

            16% is per hour (I kept your time-scale), and if you look at the rate at which the temperature goes down - this rate looks about right.

            Best wishes,
            W.
            "Carpe diem." - Fish of the Day (The Uxbridge English Dictionary)

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            • #51
              Re: AAc blocks instead of Vermiculite insulation under slab

              Thanks W - think I understand that now. My method's simple - biro and back of envelope. At reasonably regular intervals - about every 15 minutes in the end. Was using the 'nail four boards on then get another reading' method.

              More data once I have a door...

              Cheers, carl
              http://fornoeconomico.blogspot.com/

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              • #52
                Re: AAc blocks instead of Vermiculite insulation under slab

                ... and as promised, here's the data with a door. I won't be using this particular door again because it, erm, burnt a lot. I've now re-thought my door design I'll try and post about this later if I get time to get back on the computer.

                I was pleased with the performance with the door - hearth gets up to 400C after a 3.5 hour fire, then is still at 200C 12 hours later. I'm happy with this - only a 4" thick AAC block below this firebrick hearth, with about 1" of sand to level the firebricks on. With the door on the temperatures soon even out, and it takes a good 24h from the end of the fire to get down to 100C. This oven's still drying out too - still steam from the insulating vermiculite...

                W - if you fancy a look at the real numbers, let me know, and I'll PM you the data.
                http://fornoeconomico.blogspot.com/

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                • #53
                  Re: AAc blocks instead of Vermiculite insulation under slab

                  We've talked a lot about AAC, but I'd never actually seen it up close. Here's a new hotel under construction on the bay in Traverse City Michigan, which appears to be made of the stuff.





                  Note that the interior of the stairwell is made from conventional blocks, perhaps for code reasons.



                  A chip off the old block.



                  Notice that the window and door openings are framed out in pressure treated lumber. They are using engineered wood joists between floors.

                  In any event, thought you insulation fiends would like to see the stuff in use.
                  My geodesic oven project: part 1, part 2

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                  • #54
                    Re: AAc blocks instead of Vermiculite insulation under slab

                    Those appear very much like Insulated concrete forms to me. I used a similar product to build my last home. They are EPS foam blocks into which you place Re-bar and pour concrete. I really like them

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                    • #55
                      Re: AAc blocks instead of Vermiculite insulation under slab

                      The people up the street are using those styrofoam forms to build their new detached garage. They had a pump truck up there yesterday filling the cores in- I had to find several reasons to walk past and spectate.

                      I still can't figure out why they're insulating the crap out of their garage when they live in a house built before 1900.. I've lived in one of those, and geez, even with blown in insulation, they're drafty. Maybe they wanna live in the garage and park in the house???
                      Elizabeth

                      http://www.fornobravo.com/forum/f8/e...html#post41545

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                      • #56
                        Re: AAc blocks instead of Vermiculite insulation under slab

                        Thanks for the clarification: I misunderstood what I was looking at.
                        My geodesic oven project: part 1, part 2

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