you're right, the 007, and 007e are fundamentally variable flow, net flow is dictated by the system resistance. first step in sizing the pump, is knowing the amount of BTU's that have to get delivered to load. Next the piping has to be sized adequately to accommodate the flow rate required based on Load. quick rule of thumb for a 20 degree delta T, is approximately 1 GPM per 10,000 BTUs. the resistance through the selected length of pipe and diameter will give you the two variables necessary (Flow & Head), to size a pump. Here's where your analysis compares, the flow rate through 250 lineal feet of 1/2" pipe is the pressure drop the pump is pumping against and dictates where the pump operates on it's curve. This is true with both types as Jamie Hall so eloquently explains in this tread. There's a great video on tacocomfort.com called understanding ECM circulators. For your convenience, I provided a link.http://www.tacocomfort.com/products/variable_speed_products/007e/index.html
great way to understand why electronically commputated motors, ECM are more efficient, in comparison to PSC type AC motors.
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