Head Pressure & GPM calc...

e070924

I wanted to do a deep-dive and really calculate my GPM and head-pressure; something I don't think was done in 1999 when my current 126,000 BTUh SlantFin boiler was installed. —Taco 007 was installed with it. Before then it was the in-line Taco 110. I'm in a 2-story home, with some long pipe runs, and one of my zones has eighteen 90degree elbows.

One zone comes up to 6.8GPM at 22feet of Head, and the other comes up to 5.7 GPM at 18feet of head. so…… If both zones call at once, I need a pump that moves about ~12GPM at 22feet of head. Remember that this house used to have an in-line Taco 110 connected.

Taco007 won't handle this. I can provide a summary of my data & calculations if anyone wants to help determine if I'm way out in left field on this. Thanks!

hot_rod

It is a bit complicated but there is really no such thing as head pressure. Head is the energy contained in the hydronic system, measured in feet of fluid. Pressure is a measurement of force, typically psi is used in hydronic systems.

A deep dive here.

https://www.pmmag.com/articles/101174-siegenthaler-theres-no-such-thing-as-head-pressure

Or a snapshot here

Circulators add "head" energy to a closed hydronic system. All the piping, components in the circuit use up or consume that head added. Pressure is used to determine the amount of head added to a circuit.

The simplest way to know or measure energy being added by the circulator is check pressure on inlet and discharge side when it is running. Fig. 5-8 has some examples of how to use a gauge to do that. I prefer a single gauge so you do not have error between the two gauges. A small circ is not adding that much pressure, so you want an accurate number from the same gauge.

Idronics 16 takes you through the steps to determine with this pressure measurement, how many GPM the system is moving using the pump curve from the brand and model of pump you have, Fig. 5-7.

If your system is a typical 3/4" fin tube circuit, generally in the 60- 80' length, 22' head would be an unusually high number.

Use the steps in Idronics 16 to see if you can get more accurate numbers

HydronicMike

Are you sure about those 'head' numbers? They seem really high. You should show the math.
Are these zones separated by zone valves and one circulator?
If you're math is somehow correct, you would only need a 7gpm circulator @ 22' of head. But let's go over the math.

GGross

https://forum.heatinghelp.com/discussion/comment/1890648#Comment_1890648

if the math is correct then OP would need to add both zones flowrates together which comes out to about 12GPM. flowrate doesn't work like pressure drop where you just take the highest number. either way the head calculation feels really high, and the flowrate calculations may be a little off. almost like just trying to figure out how to move the total boiler capacity at a 20 degree delta rather than a known load and calculating flowrates based on emitter requirements to heat the space. we get way too stuck on the 20 degree delta T, more important to mind recommended velocity restrictions to avoid noisy systems imo.

EdTheHeaterMan

@e070924 said: "I can provide a summary of my data & calculations if anyone wants to help determine if I'm way out in left field on this."

I would like to see the numbers.

Often pump head and static head get intermixed when they are two separate measurements. I used to think of head as pressure until I read that book by Siegenthaler. It makes sense to me now after years of not understanding this stuff (only a few years though—I’ve been infallible ever since the 1994 publish date).