#1  
Old 05-23-2008, 06:38 PM
Ken524's Avatar
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Default Oven Temperature Graph

After the last two firings, I used my FB Thermometer to take dome and floor readings every few hours and log them in a spreadsheet. My goal was to create some heat/energy graphs as an aid in cooking with residual heat.

I made two graphs and the results really surprised (and impressed) me! This oven REALLY retains heat.

The first graph/fire shows high temp readings, the second one emphasizes the low temp ranges. I could have done it all in one firing, but was called out of town before I could finish measuring the first fire.

I plan on doing a few more graphs at different ambient (outdoor) temperatures through the year to see if ambient makes a difference.

In both fires, temperatures were measured with an empty oven. After my next fire, I plan on throwing in a nice hunk of meat at 300F to see if I can document the energy loss.

Obviously, my charts won't do anyone else any good because all our ovens are different. But it might be a fun way for us to compare oven performance.

The software I use is OpenOffice (www.openoffice.org). It's a highly rated free, open source alternative to Microsoft Office. It does everything MS Office does. If anyone needs help generating a chart with this, I can whip up a template for easy graphing.
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Oven Temperature Graph-graph1.jpg   Oven Temperature Graph-graph2.jpg  
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  #2  
Old 05-23-2008, 10:44 PM
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Default Re: Oven Temperature Graph

Ken, cool graphs. You must have put in thermocouples, ........or was that you out there at midnight with a laser thermometer madly taking temps inside your dome?

My gut tells me that unless you actually weigh the amount of wood that you burn (assuming all one type of wood and all equally cured), and reproduce that with each test, the results will be a bit inconclusive. Heat the dome with more fuel, and the heat sinks deeper into the dome bricks, only to be later radiated back into the oven at a later/longer time.

The more fuel in, the longer the oven should stay warm. If you don't reproduce the sample size, the results will be hard to correlate. If you knew the actual weight of the wood, the results might just turn out to be proportionate though.

Kind of a cool idea to try out, if you like weighing wood.
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  #3  
Old 05-23-2008, 10:54 PM
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Default Re: Oven Temperature Graph

Very nice Ken,

It's interesting how the dome and floor seem to fall in harmony. A nice gentle fall-off, that is really useful in scheduling what you want to bake, and at what temperature.

Here is a temperature curve I did a while ago using an infrared. It shows up and down curves.
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File Type: pdf temperature_curve.pdf (188.6 KB, 519 views)
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Old 05-24-2008, 03:56 AM
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Default Re: Oven Temperature Graph

Quote:
Originally Posted by gjbingham View Post
Ken, cool graphs. You must have put in thermocouples, ........or was that you out there at midnight with a laser thermometer madly taking temps inside your dome?
George,

No thermocouples, I used my handy-dandy infrared/laser thermometer. You can see gaps in samples on the graphs. That's when I was sleeping. I considered getting up a few times during the night, but decided that would be the act of a crazy man.

Quote:
My gut tells me that unless you actually weigh the amount of wood that you burn (assuming all one type of wood and all equally cured), and reproduce that with each test, the results will be a bit inconclusive.
Yes and No.
You are right, when we use more wood, we can get the oven hotter.

When the wood is finished burning and the door is in place (at any temperature), the oven will stabilize after an hour or two. The oven bricks will become fully saturated - doesn't matter what temperature they are at.

After reading your response I got to thinking more about saturated bricks vs. unsaturated bricks. It hit me like a ton of bricks ( ) that I can see the saturation happening on my graph and can easily identify when the oven is fully saturated. See the attached picture.

Once the bricks are fully saturated, an empty oven should (in my perfect world) begin to cool down in a predictable curve. The only major variable I can imagine is ambient temp.

On my charts, I have the time labels at the bottom counting elapsed time from the oven door being shut. I see what your are saying; in order for those elapsed times to be accurate, I would need to put the exact same BTU's in the oven every time. That'll never happen.

I plan on changing the time labels to simple "ticks" at 3 hour increments. To use the chart, you take the temp of the stabilized oven at any time. Find that temperature on the curve, then you should be able to estimate how many hours it will take to get to the desired temperature.

Does that make sense or am I full of #$%@ as usual?
Attached Thumbnails
Oven Temperature Graph-graph3.jpg  
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  #5  
Old 05-24-2008, 04:04 AM
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Default Re: Oven Temperature Graph

Quote:
Originally Posted by james View Post
It's interesting how the dome and floor seem to fall in harmony. A nice gentle fall-off, that is really useful in scheduling what you want to bake, and at what temperature.

Here is a temperature curve I did a while ago using an infrared. It shows up and down curves.
James,

I was surprised at the temperature difference between the floor and dome. Once the oven was saturated, they stayed almost exactly 20 degrees apart during the entire cool down. Really fascinating.

I like your full heat-up/cool-down graph. I don't think I could do that without thermocouples. When the fire's raging, the infrared thermo is pretty useless. Everything I point at is too hot for it.
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Old 05-24-2008, 02:25 PM
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Default Re: Oven Temperature Graph

The tip of my thermocouple protrudes right into the oven by about 1/2" If I have flame directly on it, then it tends to give a false (higher) reading. Probably should have embedded it in the dome wall. Pottery kilns usually have their probes sticking right into the kiln's interior. Actually I don't even look at the thermocouple read out much anymore- just start my stopwatch when I light and we're ready to cook 2hrs later.
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