I found this formular:
-0,96λ²+13λ+29,6 = spezific heat extraction capacity/ spez. Entzugsleistung (W/m)
λ = thermal conductivity
If I use it with data from Thermal Response Tests, the results seem valid and are close to my estimations.
Now I am interested in finding a source that explains this formular and if it can be used for quick checks and first estimation of borehole heat exchangers?
Does anyone can give me a hint where to look?
Thanks for helping!
The formula commonly used to calculate the heat transfer rate in a borehole heat exchanger (BHE) is based on the effectiveness-NTU (Number of Transfer Units) method. For a BHE, the heat transfer rate Q can be expressed as:
Q = U . A .Delta T{lm}
where:
Q is the heat transfer rate,
U is the overall heat transfer coefficient,
A is the effective heat transfer area,
Delta T{lm} is the log mean temperature difference.
The log mean temperature difference Delta T{lm} is calculated as:
Delta T{lm} =(Delta T1 - Delta T2)/[lm . (Delta T1/Delta T2)]
where:
Delta T1 is the temperature difference between the hot fluid entering and leaving the BHE.
Delta T2 is the temperature difference between the cold fluid entering and leaving the BHE.
The overall heat transfer coefficient U and effective heat transfer area A depend on the specific design and configuration of the borehole heat exchanger.
Greeting ...
Dear Mr. Sascha Speil
you can flow this link below
With regards
https://www.sciencedirect.com/topics/engineering/borehole-heat-exchanger
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