Primary/secondary and GPM on a circuit

TomTA

I was reading “Pumping away” (very interesting book) but one of the many things that still confuses me is the GPM flow over a circuit. The example in the book that prompted this question had a primary/secondary setup. The primary flows 14 gpm, and there are 3 secondary circuits which demand 3, 3, and 8 gpm each, for a total of 14. The GPM flow of each secondary circuit is calculated based on the emitter size and temperature drop (I assume). What I don’t understand is how do you LIMIT that circuit to 3 gpm (or do you?). Do you add enough restrictions to the circuit so that the pump curve puts flow at 3 gpm? I can’t imagine intentionally setting up an energy waste like that. Or is the 3 GPM the “effective flow” in terms of heat loss; that instead of flowing 3 GPM with a 20 degree heat drop, it might be flowing 6 gpm with a 10 degree heat drop. You just let the pump push through whatever it wants/can, and the emitter size will strip off the appropriate level of BTUs?

Zman

I think you do understand it. The output of the radiator will not be exactly linear with the flow but, close enough.