Hot Water Primary Pumping - best option??

[BronYrAur]

Any recommendations on the best approach for primary pumping? I will be replacing boilers/pumps on a primary/secondary system. Right now everything is constant volume.

I will definitely be changing the secondary pumps to variable flow based on a DP out in the system. My question concerns the best approach for primary pumping. I will be installing 3 boilers.

I could put in a constant volume primary pump and also have individual boiler pumps to "inject" water into the primary loop. (figure 14 attached).

I could eliminate the primary pump and let each boiler be its own primary pump as shown in figure 15. But couldn't my secondary flow exceed my primary if only one boiler is runing? If so, maybe that's OK since the primary loop would be acting as more or less an injection into the secondary.

I have the freedom to do what I want, but I'm not sure what is best.

 

[ChasBean1]

Is Figure 15 the same as 14? Regardless, the primary pumping loop is a good design. Keep the primary boiler pumps and run your secondary pumps on a VFD to maintain DP.