P/S loop sizing

GW

Brad, you made me read that twice... how techie of you :)

My simple answer is "YES", if it's your typical delta T drops. Many times in the P/S world the delta Ts get stretched out way beyond the average 20 degrees that we've all grown up with, so as your delta t goes up, your flow rates can go down, and therefore you pipes can get smaller. It's all math... more delta T and less flow is the SAME btu delivery as less delta t and more flow.

Gary



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mtfallsmikey

Here's today's dumb question

Do the "rules of thumb" regarding pipe sizing of both primary and secondary loops, as well as circ. pump head change if used for a non-pressurized system (OWB in this case)?

Brad White_184

The differences

are in any "lift" that might be imposed. In other words, in an open system the "ferris wheel effect" or continuous siphon effect of a closed loop might be lost.

Picture if a system at rest settles at a level below the top of the system. On start-up, that lift to the spill point has to be added to the system head. (Cooling tower systems are one example of this as you know.)

Add to this any oxidation of the piping interior which will detract from the performance over time.

Grundfos for one offers curves for the same pumps for both open and closed systems to give you a graphic example. I will add to this that open systems will require bronze circulators for this reason.

Directly to your question though, the pipe sizes will be the same for all intents and purposes. If you think the piping sizes are "close", go up a size if in doubt.

mtfallsmikey

You ALWAYS have to read Brad's posts twice!

But, it's not a bad thing!...Actually Brad, you hit the nail on the head as to the original goal behind my question. In this case with an OWB in an open system, the water level in the boiler will be at around the same level as the HWBB in the house, and the supply lines to and from the boiler to the house plus the load were at the border between 1 1/4" and 1 1/2", factoring in the amount of head. If I remember correctly (??)from my youth,(long ago!) didn't the term "feet of head" originate because all early hydronic systems were non-pressurized, with expansion / storage tanks mounted in the attic? I've seen more than a few of these in the past.

Weezbo

i think\" Feet of Head\"

was more of a social comment in the 60's...