I looked at that as well. However, 4 x 1" lines have an acceptable pressure drop for 13.5 gpm , and are "ok" balanced as described. Just to be clear, all the boreholes for each loop are in series, correct? You should be able to have enough velocity in the loops to purge all the air out, with a normal purge cart (1.5-2.0 HP). Do you have a reducing header? Other question is what the length of the header pipe from the house to the loop field, and what is the diaper of the pipe going out to the loop field?