More thoughts...
I think that any increase in heat transfer due to turbulent will only be from the water to the plastic pipe shell. From there is has to flow into earth which will be massively slower (an assumption & I know different locations are better/worse), so your overall loop field heat transfer is likely to not change any measurable amount. I think of it like a 1 ohm resistor in series with a 100k ohm resistor....you still got a big *** resistor. Resistor = R value in this analogy. I do need to check what an average R value is for dirt vs for plastic pipe.
Now if you are in a pump and dump, or pond, or any HX where the secondary medium is great heat conductor such as water vs the earth, then I think that there are some overall gains to be had.
Len
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