Modeling soil temperature at a depth of 5ft

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Discussion Overview

The discussion centers on estimating soil temperature at a depth of 5 feet in Saskatchewan, Canada, considering seasonal temperature variations and the insulating effects of snow. Participants explore modeling approaches and the parameters involved in the calculations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks guidance on estimating underground temperatures using a specific model, noting significant discrepancies in their results.
  • Another participant suggests a potential error in the exponential function used in the model, indicating a possible sign issue.
  • A different participant questions the definition of "A" in the model, proposing it should represent the amplitude rather than the total temperature difference, and provides alternative temperature estimates based on this adjustment.
  • Some participants discuss the impact of snow coverage on soil temperature, with one noting that snow is an excellent insulator, while another mentions that the model does not account for this factor.
  • One participant references a specific table from the model's source, suggesting that the insulating effect of snow is acknowledged in the documentation.

Areas of Agreement / Disagreement

Participants express differing views on the correct interpretation of model parameters and the impact of snow insulation, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Participants highlight potential issues with the model's assumptions and parameters, such as the definition of "A" and the effects of snow insulation, but do not resolve these uncertainties.

Jyan
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Hello everyone,

This isn't really my area of expertise, so I am looking for a bit of guidance. I wish to estimate the temperature underground at a depth of 5ft. The climate is Saskatchewan (Canada) so it is covered with snow in the winter, and fairly hot in the summer. There is no tree coverage, only grass. The widest average temperature swings are from about -28C to +32C.

Currently, I'm attempting to apply the model described here: http://archive.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-180.html#archived

My results however are pretty questionable. I am using an average yearly temperature of 2.6C, and a thermal diffusivity of between .8 and .15. I've calculated that the temperature swings from -35C in the winter, to +42C in the summer, obviously this doesn't make a lot of sense. Can anyone point me in the right direction for estimating underground temperatures? The model doesn't need to be accurate either, +/- 10 degrees is pretty acceptable.

Thank you,
 
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I've calculated that the temperature swings from -35C in the winter, to +42C in the summer, obviously this doesn't make a lot of sense.
Looks like a wrong sign in the exponential function.
 
I think the problem is with the value "A". " A is the difference between the maximum and minimum temperatures for the period", shouldn't it be the difference between the max/min temp and the average (The amplitude)? I used 60 for A, but I think it should be 30 instead. 2.6C average, with a 32.6C max and 27.4C min. This gives me a temperature swing 5ft below ground of about +23C and -17C. Do these values seem reasonable? What about the snow coverage? Snow is an excellent insulator.
 
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Jyan said:
I think the problem is with the value "A". " A is the difference between the maximum and minimum temperatures for the period", shouldn't it be the difference between the max/min temp and the average (The amplitude)?
I agree with you. The web page description is wrong.

Do these values seem reasonable?

Check that you can reproduce the numbers in Table 1.

What about the snow coverage? Snow is an excellent insulator.

So is earth. Since the web page doesn't mention snow, maybe it doesn't make much difference. But I'm not an expert on soil mechanics or civil engineering.
 
Insulating snow is mentioned directly under Table I, and the effect upon the average soil temperature being elevated from that of a surface with no surface snow.