A potential error for the thermal resistance calculation for 1U pipe
Description
Thanks to Jakob for pointing this out. In the HeatTransportBHE process, the thermal resistance of the pipe need to be calculated.
For 1U pipe, the calculation can be found in BHE_1U.cpp, line 186:
double const R_con_a = std::log(_pipes.outlet.diameter / _pipes.inlet.diameter) / (2.0 * pi * lambda_p);
The same calculation in 2U type is however different (BHE_2U.cpp, line 206):
double const R_con_a = std::log(_pipes.inlet.outsideDiameter() / _pipes.inlet.diameter) / (2.0 * pi * lambda_p);
By looking at it, it seems that the 2U calculation is correct, while the 1U calculation is wrong.
Influence
If one use the same diameter values for the inlet (downward) and outlet (upward) pipe, the 1U calculation will give zero from the log function. However, the R_con_a values should be some positive value.
What needs to be done?
This wrong calculation will lead to different calculation results in BHE applications. Hence it needs to be checked and corrected.