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Originally Posted by Les
The formula
(metric) P = Q*H*s/366
is the formula for "Pump output power (P w )" in Watts
where:
Q = flow lph
H = Head in meters
s = specific gravity.
The source makes the, perhaps, misleading statement that "Pump output power (P w )" is "also called water horsepower." They also use "Q = rate of flow, m 3 /h" for another formula on the same page.
These two facts could lead to your interpretation of the equation.
However the correct interpretation is as shown.
Here lolito_fr gives a derivation of (Pw) in Watts:
"Derived formula: P=0.16Q.H
P in Watts
Q in lpm
H in m"
These are (allowing for approximations) the same formula.
My usual statement of the formula is "Watts ~ m(H2O)*LPM/6". The " ~" used to imply an approximation.
My non-rigorous derivation for "Pump output power (P w )" gives:
Power(Horsepower) = 0.00365 x Head(mH2O) x Flow(m^3/h)
I stand by this as being numerically correct. |
Thank you. Now I know for certain.
I'll fix my graphs accordingly in short time.
Quote:
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Originally Posted by Reaper_Unreal
Alright, well I've re-done the calculations as suggested, and I've even written a program to find all of the stats for me (I'll post it later if needed). This time, I took loads of points off of the P-Q graphs of each pump, and found the power at each point. I took the average of the powers I had found (not including 0 head and 0 flow). I then took the average of all of the heads, and the average of all of the flows, then found the power that way. I then took the average (not geometric mean) of the two power values I had found to give me my value for power. That's about as accurate as it'll get. I've got here the results for the 5 pumps I did. The program I wrote will be posted later if requested when I can find somewhere to host it.
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I really don't want to begin to touch this with a ten foot pole.
IMO a single point value assinged to a pump is, for all intensive purposes, useless. The properties of a pump cannot be boiled down to such simple terms.
If you insist on pursuing a single point "efficiency", at least base it of of pump input power/pump output power and not electrical input power/pump output power. Pump input power is the power imparted to the pump shaft by the pump motor. leave the motor inefficiencies that never make it to the water out of it.