Head Loss and Elevation

[Mid Michigan]

I am in design stage of new system. I am actually going to break out the calculator on this one and do a little learning and understanding of all the why's.

I am using this formula for figuring head loss: HL = K * C *L * (f1.175)
I run my AHU circuit through the above formula and get 4' of Head Loss at 7 GPM.

My question is would you not also have to figure in the elevation change also?

For example: I have to pump water up to AHU in the Shop. The AHU is 12' above floor.
I install a cir. pump figuring 4' of head will it lift water to 12'?

Or is it once the air is out of the system you have as much water pulling down the return as you have pushing up the supply and its almost a wash?

 

[Mid Michigan]

More questions: If I have 3 parallel circuits and the head loss on them are 4', 10', and 15'. Do you just use the largest one for the total?
Yet if they were all open at the same time it would seem you would have to overcome all 29' of head???

 

[emesine]

It might be a good idea to post a diagram. Going uphill does not change head loss if you are pumping in a circuit. The pump will see more pressure both on the inlet and on the outlet, which is a wash. All you have to worry about is friction through the pipes.

If you have parallel circuits, the head loss will be the same across all of them at any one point in time. If one circuit has a 4 feet of loss at 7 gpm, and the other has 10 feet of head loss at 7 gpm, then more water will flow through the low head loss circuit until the pressures equalize out. The low head circuit will get most of the flow, and the high head will get very little.

Andrew

 

[Mid Michigan]

That helps!
Elevation is a wash---Good
I want to use 1 secondary pump that is variable speed. Zone valves on all equipment. The head loss is going to very from zone to zone. So I I am thinking right, Figure out which one has the highest head loss and use circuit setters to increase head loss on other zones to mach and they should be getting the right GPM they were designed at. As zones shut pump will slow down on GPM.
Things that make you go Hmmmm.

I have drawing on Post https://www.hearth.com/econtent/index.php?ACT=24&fid=21&aid=26406_S7s2Uni30g7yTGqMeqCz&board_id=1