AAc blocks instead of Vermiculite insulation under slab Pompeii Oven Construction Discuss AAc blocks instead of Vermiculite insulation under slab in the Pizza Oven Design and Installation forums; I am also a geek by trade, and have been speaking to geek friends about this. I had thought to ...

[Ed_]

I am also a geek by trade, and have been speaking to geek friends about this. I had thought to embed rather more thermocouples than necessary (probably something like Carl did) and I'm toying with the notion of automated data logging. As many have pointed out, this is entirely unnecessary for successful baking, but when you're a geek it's hard to resist the temptation.

So I think it's neat! And if it actually helps quantify the benefits of this or that insulation, that's good too.

Ed

[Wlodek]

Absolutely! Geek by trade is the best description

Automated logging (and a dedicated laptop running Labview or Matlab with things) is probably an overkill indeed, but putting in too many sensors did cross my mind ...

Like Carl I have a little unwanted PID (aaawww...!) hanging around in the drawer (they tend to do that, don't they?) and I'll probably give it the job of displaying the temperature. I don't have an unwanted temperature logger, but with sampling every 3 minutes or so, as Carl worked out, it will be fine.

I think such comparisons will be useful, otherwise discussing advantages of one version over another becomes somewhat academic

Thanks for your support

Best wishes from sunny (!) Lake District

W.

[Frances]

Well, you'll have to make sure you build your ovens with different materials then, red bricks vs. firebricks , vermiculite vs. insulation blanket etc.

Else you'll have a load of data which is all the same....

[Wlodek]

Yes and no. The comparative analysis I suggested will only work for very similar oven cores and different insulation versions.

I hope the data won't be the same, this would mean that it does not really matter how we insulate ...

W.

[Frances]

I dunno, I think that would also be a very interesting result. Seems unlikely though.

[Carl]

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.

[Wlodek]

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.

[Wlodek]

Originally Posted by Carl

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.

[Carl]

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.

[Wlodek]

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.