Calculating Pump Head

Engin_grad

Does anyone know how to precisely calculate the head for a centrifugal pump...especially for the piping. Is it the longest pipe run x 2 (for supply and return), or is it all of your pipe, and should you multiply that by 1.5 for valves and fitting, or getting every Cv for each valve nessesary. Please Help

Unknown

Short version

Measure the total length of the longest run, in feet, multiply by 0.06 (0.04 for the pipe, and half that again for an AVERAGE amount of fittings). If you have controls with a lot of resistance, figure those above the piping number, and add them to the total.

It'll be close, and above the actual head loss number in most cases, and will be the same pump as if you figured every single fitting and control. If you find yourself right on the edge of choosing between two different pumps, the more careful method of figuring every single fitting would break the tie for you.

Noel

hr

By precisely

I would guess you mean a number for every foot of pipe, fitting, etc. Circuit setters will have a lot more pressure drop than a basic ball valve, for example. All valves and "devices" will have a Cv number available.

Check into the B&G System Sizer available on their website, or a piping software program such as the HDS software available at www.hydronicpros.com (free demo downloadable version at that site)

Noel's formula will get you close, but maybe not close enough for an engineer

hot rod

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Brad White_2

If you are interested

I have a spreadsheet that I developed using the "Equivalent Linear Feet (ELF) method whereby a value in ELF is assigned to each fitting. Each pipe size has a Cv value (flow at 1 psig across 100 feet of pipe). You put in the flow rate for the pipe section, the number of each type of valve or fitting, the linear feet of pipe itself. Summary is on a separate referenced sheet where you put in known non-piping pressure drops such as coils, heat exchangers, etc.

The "ELF" method works out to be about 2% more conservative than dynamic fitting loss method, by the way.

I will send one to you if you indemnify me and promise not to copy it or use it for commercial purposes. Let me know!
Brad

Engin_grad

Thanks Brad,

Sure you can send me that program if you don't mind. So you're saying this is only good for residential applications?

Floyd_5

OR.....you could cheat and use ......

Siggy's HDS and just punch in the numbers....

http://www.hydronicpros.com/

Brad White_2

Spreadsheets are

on their way! I sent both as mentioned in my cover e-mail. Piping is piping (Sch. 40 steel for 2.5 inch to 12 inch and Type L copper for up to 2 inch size was my basis). John Siegenthaler's calculator is based on Type M copper and up to 3 inch size according to my version. Type M is thinner wall and allows more flow at a given pressure drop. (Or less pressure drop at a given flow if you are an optimist! :^)> )