Guido48

Does anyone know the heat transfer from 5/8" pex to concrete for different delta T's between glycol and concrete?

beenthere

Varies with how much glycol(10, 20, 30, 40, or 50%).
What your center is.
And what you GPM is.

EG:
30% glycol/water solution at 120°F entering temp, and 110°F leaving temp(10° delta).

50 BTUs per sq ft, 12" OC equals .01056GPM per foot of tubing.
So 200' of tubing would have a flow rate of 2.112GPM.
20 BTUs per sq ft, 12" OC equals .00422GPM per foot of tubing.
So 200' of tubing would have a flow rate of .844GPM.

Both of the above BTU examples are at 10° delta.

You need to know more then just delta to calculate BTUs.