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Old 04-13-09, 11:33 PM   #19
AC_Hacker
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Default AC_Hacker does a heat transfer test (part 2)...

So here's my test data & analysis...

Time Temp
____________
0.00<tab>54
0.133<tab>57
0.167<tab>57
0.50<tab>60
1.733<tab>70
4.00<tab>79
6.25<tab>83
7.50<tab>85
8.433<tab>86.5
14.833<tab>92
15.25<tab>92
15.517<tab>92.5
19.883<tab>96
21.00<tab>96
22.083<tab>97
24.03<tab>100
25.82<tab>100
27.65<tab>99
31.67<tab>99
40.317<tab>99
44.23<tab>101
49.60<tab>102
63.65<tab>102
68.93<tab>103
89.55<tab>106
102<tab>107
113<tab>107
123<tab>108
143<tab>109

(I had to use the "<tab>" thingies, because the real tab didn't appear correctly in this blog)

Since I don't have an automatic data logger (yet) I logged all the data by hand. The time intervals were irregular but I think that it doesn't matter so much.

The first thing I did was to put the data into a curve analysis program. The program I found is a really great shareware program called CurveExpert for Windows available here: CurveExpert 1.3: Download

I've used this program for lots of things. There are even tutorial pages available, if you need.

At any rate, it was very useful to get well done graphs as the test progressed. The program does automatic curve fits and it was interesting to see that the program selected various curves before finally settling on an MMF type curve.


heat transfer curve

From CurveFit, it's even possible to get the equation of the curve that is the best fit and to project the curve forward in time. I was interesting to predict what the temperature would be at a particular time and to check the results as they came in.

But this wasn't really getting me what I needed, which was a quantified characteristic of the earth formation in my yard. This is where the document mentioned in the previous post: TCTestingSum.pdf, came to the rescue.

I tried to follow the proceedure but wasn't able to get the same results as the author had. Either I was making a mistake, or I was using a version of Excel that was older and didn't have the exact feature he was using. But I devised a work-around and got reasonable results.

Here was my proceedure:

1) Start Excel
2) Open the data from a tab-delimited text file. This just means that the data is written in a test file and you hit the 'tab' key after the Time data, but before the Temp data. If the tab could print like this: <tab>, your data would look like this:

...
0.00<tab>54
0.133<tab>57
0.167<tab>57
...

Anyway this is a standard text format that Excel understands.

...of course you could just enter the data straight away into Excel and I could save myself some time & typing.

If you graph the data I have included, it would look like this:

See picture

Looks similar to the graph from CurveExpert.

At this point, the author of TCTestingSum.pdf was able to do a right-click on the graph curve that Excel made. Then he was able to choose "Add Trendline" and then a Logarythmic trendline, and the result, as illustrated, was a linear graph. I was not able to get these results, certainly not the graph as illustrated. So my modification to the process was to return to the spreadsheet, 'Insert' a column between the Time data and the Temp data. Then I wrote a simple formula (=ln(A1)) that took the natural log of the data in the time cell. I copied this formula down to the rest of the data cells. Then I made another graph of these data columns, "ln(Time)" and "Temp". At this point, I got a graph that resembled the illustrated results.


line slope graph

I then did the right-click and 'add trendline' this time I chose "Linear", since the natural log function had essentially linearized the graph. This did give me a formula with slope. Then I was able to use the rest of the proceedure as described. This all gave me a "k" value of 0.569464441. I was in turn able to use this value to calculate the total length of borehole, which would yield 12,000 BTU/hr. This calculated borehole length came to 214.23 feet. Which is reasonable, as I hear from local installers that they estimate that 12,000 BTU/hr (AKA: one Ton) borehole length to be in the range of 175 to 225 feet.

I have attached my spreadsheet for your consideration.

Some improvements:
* Get a real data logger
* Use the actual type and configuration of Polyethylene pipe I plan to use in the actual installation.
* Use a borehole that is closer to the actual location of the installation (the test borehole was within three feet of my basement, so error is to be expected)
* use the type of grout I plan to use. I'm currently planning to use "mix-111", more information available here:
Information Bridge: DOE Scientific and Technical Information - Sponsored by OSTI

I welcome your comments.

Best Regards,

-AC_Hacker

P.S.: For those who want to know more about the topic of borehole testing, I have located what might be the definitive paper on the subject:

http://epubl.luth.se/1402-1544/2002/...DT-0239-SE.pdf

P.P.S.: Here is a link to a report from a professionally done borehole test. Note the unusually high results and the speculation as to why such unusual results were obtained.:
http://www.tva.gov/commercial/TCStud...iles/Se-02.pdf

...and another done in Alabama in 2000. These are more typical results.
http://www.tva.gov/commercial/TCStud...iles/Jo-18.pdf

...and yet another done in Illinois in 2008.
http://www.midwestsustainable.com/Co...%20Example.pdf

>>>>>>>>>>>>>>>>>>>>>
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Attached Files
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Last edited by AC_Hacker; 05-27-09 at 02:14 PM.. Reason: Links to misc. borehole tests
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