Greg .. please tell me someone is joking!
I'm not sure there are any single phase motors left that you would be allowed to use - and to what end? And what is this 'default speed' gibberish? Looks plain to me they're trying to mandate 3-phase motors on a 1:3 phase VFD.
As you point out, the solar collectors would be served with a slower, rather than higher, flow rate. Perhaps whoever wrote that was looking at a 1750 rpm centrifugal pump curve, and assuming collectors atop a two-story house!
This reads more like a 'product specification' written by a salesman to eliminate the competition from the bidding.
While I'm all in favor of good design, I'm all against litigating it into our lives.
