ft of head loss

Paul S_3

Hey wallies How do you guys get an exact head loss of a radiant , snowmelt and other hot water systems.....i know the rule of thumb is loop length X 1.5 (fittings and valves) X.04 (4 feet of head loss per 100 ft)....how accurate is that? I have the b&g system syzer app on my android but there is nothing for pex on there and is the "total pressure drop" in the "System Syzer" the amount of head loss in feet of that particular circuit that i would use to size a circulator .....i also have downloads of UPONOR radiant and snowmelt manuals they have charts for this....should i use these charts for pex and system syzer for the copper from the boiler room to a remote manifold if its a radiant job thank you any input greatly appreciated Paul S

hot_rod

The pex tube is a smaller id, compared to copper or steel pipe. So if you are after the most accurate #, then use the tables in the upon manual for the pex.

Depending on how long you loops are, there may not be a huge difference. Try it both way to see, with the Syzer, then the Uponor table.

Paul S_3

Thank you for the response. ... this is my first time using system syzer i want to verify if the "total pressure drop" after i enter my pipe length and my friction loss in ft per 100 ft of pipe is the amount of head loss for the whole piping circuit in that zone that im sizing.....which i would use to size a circulator pump thanks Paul S

hot_rod

Here is a graphic I use to demonstrate head in a system. Circulators add it, all the piping components remove it.

This link has some excellent reading on circ pump sizing and selection. It demonstrates how to determine the head, but also develop a system curve to see where the circ actually ends up running.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

Tinman

Along the same lines as what Hot Rod shared, if you know the inlet and outlet pressure of the pump, the density of the fluid based on its temperature and its corresponding value, you would be able figure Head fairly precisely.

H = 144(delta P across pump) / D

Tinman

Problem is your not apt to see pressure ports until you start getting into the larger pumps. I'd like to see one on every pump flange.

Paul S_3

What does D mean? Density of fluid of a given temp? Paul S

Tinman

Yes. Do you have Siggy's Modern Hydronic Heating book? He lists some common densities like 60* F water, 180* F water, and a glycol mix...also goes into much greater detail of course.

Paul S_3

No i do not i will get it.....i have all the idronics editions....i dont know if your familiar with the B&G system syzer, but i wanted to know if that program gives you total head loss with the fittings and valves or i would have to add them to the total loop length?im trying to find an easier and faster way to calculate head of a loop to size my pump that i would be building without counting all fittings and valves or there is no way around it thanks Paul S

Tinman

I use the System Syzer wheel and I find that to be as accurate as I need . I have the app but haven't used it yet. The wheel is awesome!

Just last night, I was intent on getting a precise measurement of Head rather than the rules of thumb that are used, particularly for existing buildings where there are too many unknowns. I, too, looked in Caleffi idronics and Siggy's books. I took that equation right from the book. I may not have taken it far enough though? Can someone confirm that?