Low loss header - boiler side - pump away? (or to the boiler?)

Chuck_17 · June 2016

Typically for a primary secondary boiler connection, the boiler (secondary) pump would pump "to" the boiler.
But what about if you are using a packaged low loss header?
The Lochinvar boiler install manual shows the boiler pump pumping "to" the boiler.
The B&G low loss header shows the boiler pump pumping "away" from the boiler (to the header). (Actually it shows the boiler pump pumping away for the example secondary loop also.)

The system pump would pump "away" either way (not in question).
I'm inclined to go with the boiler detail. What do you think?

Paul S_3 · June 2016

the lochnivar boilers do not have a substantial pressure drop across there heat exchangers... i believe the wh and khns are very low .....the reason most modcon boilers show the boiler pump on the return is because of that substantial pressure drop on that specific boiler ..... best way is pump away from "the point of no pressure change" using a low loss header i would pump toward the boiler on the the boiler side of the header....( LLH is the point of no pressure change for the boiler pump) install the system pump on the supply of the LLH , pumping away from the expansion tank....Caleffi idronics has nice diagrams for this.

hot_rod · June 2016

A properly proportioned separator presents very little pressure drop in the system. Ideally a 3-1 ratio, pipe size to barrel dimension.

As such, expansion tank connection near any of the 4 ports establishes the PONPC through the vessel.

On caution is to avoid the expansion directly below the sep to prevent any dirt removed from settling on the diaphragm in the expansion tank. If you use the bottom connection install a tee and pipe the expansion tank off the branch.

SWEI · June 2016

Which Lochinvar boiler specifically? Some of their older designs use high head loss heat exchangers and those are quite different with respect to pumping requirements.

Firecontrol933 · June 2016

Just thinking out loud, but on the low mass mod cons, if you pump towards the boiler you keep the water at the HE at the highest pressure in the loop/system. This "might" help in certain conditions where the fluid against the outer wall of the HE might want to flash.

It's more of a worse case scenario thought, but even the best system design and installation someday will suffer from some form of issue and why not give it the best chance of the least amount of trouble when that time comes.

SWEI · June 2016

Higher pressure in the boiler can work against you in a tall building.

Pumping on the return does lower operating temps for the circulator.

hot_rod · June 2016

Firecontrol933 said:
Just thinking out loud, but on the low mass mod cons, if you pump towards the boiler you keep the water at the HE at the highest pressure in the loop/system. This "might" help in certain conditions where the fluid against the outer wall of the HE might want to flash.

It's more of a worse case scenario thought, but even the best system design and installation someday will suffer from some form of issue and why not give it the best chance of the least amount of trouble when that time comes.

More so high pressure drop type boiler HXers. Copper tube boilers are considered low mass, low water content, but have large short tubes, not as much pressure drop as some coil type mod cons.

There are some brands of mod cons that have pressure switches on the boiler for low water conditions, you defiantly want to pump into those.

Really no harm in pumping into any boiler, as long as the expansion tank is located upstream of the circ pump.

Low loss header - boiler side - pump away? (or to the boiler?)

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