Pump Efficiency, Head, Flow, and related technical info

[chem geek]

Mark,

I know I'm being a mensch about this, but are you looking at this PDF file on page 47 with the graph "IntelliFlo Flow and Power vs Flow Pump Curve" and then starting with 80 feet on the left and moving across that horizontal line until it intersects the black line "Head @ 3450 RPM"? It not only visually looks almost exactly halfway between the 80 and 100 vertical lines for GPM, but it measures that way also -- possibly at 91. I zoomed in a whole lot just to make sure. If I look at this PDF file which is in the 4x160 manual on page 25, then I can get something more like 92 which is getting closer to your number. Note that there are 4 vertical lines between 80 and 100 so that is 5 sections so each vertical line represents 20/5 = 4 GPM and the intersection is at the 3rd vertical line (after the 80 vertical line) so that is 12 GPM more than 80 or 92 GPM. I suspect that you counted each vertical line as being 5 GPM instead of 4. I discovered this unusual vertical line spacing (i.e. 4 lines instead of 3) because I used a ruler to measure between the two marked vertical lines (80 and 100) and didn't worry about those intermediate lines.

If you look at the first of the two links above showing the full IntelliFlo manual, then that graph does show the power (electrical) consumption curves for three RPM settings. That's how I got that data for my table.

So I looked at the documents you linked to and they are absolutely fantastic. Thank you so very much! When I referred to "leakage" it's really just a recirculation that is occurring (at a net 0 GPM and maximum head). There is no output work being done. I now see that this isn't a chamber or piston kind of pump effect, but a centrifugal impeller and vane technique so if the centrifugal added velocity goes against a pressure that brings the velocity back to zero, then there will be no net flow (but because this isn't the BEP point, there will be recirculation flows and uneven pressures in between the vanes and this can damage the pump).

The first document link you gave contained a very useful formula that helps figure out equivalent power efficiencies and identification of the most efficient point at each RPM. That is the definition of specific speed:

Ns = n * sqrt(Q) / H^(3/4)
or Specific Speed = RPM * sqrt(GPM) / (Head in Feet)^(3/4)

If I add this as a column to my spreadsheet, I find that though the specific speed varies with GPM and Head, the peak (electrical input to pump output) efficiency point at each RPM corresponds to roughly the same specific speed of around 1320. So that gives me additional useful information so that I will know if I am operating near the BEP point with both solar on and off (when I get my IntelliFlo pump).

I've made a detailed piping diagram for my system and the reason that my solar system has such high resistance is that it isn't on a single flat roof, but is on a roof with several hips so that the piping has a lot of 90 degree elbows and extra distance -- it's not at all a straight shot. There are 2 panels on one hip, 7 on another (5 higher and above 2 that are lower), 2 on another, and 1 on another. I did find a possible problem with the piping of the solar that could cause uneven flows (they didn't make the total path lengths the same throughout and instead did some Ts to return too soon so I essentially have two sets of solar panels with different path lengths). So my last 3 panels probably have lower flow than all the rest -- now I can understand why I actually saw a decrease instead of the expected increase in heat output when they added the most recent panel. They only worsened the already unbalanced situation. I'll calculate the expected flow rate difference and if it's significant, then I'll have them fix that as it should have been done correctly initially. Should be easy to fix by just breaking at the T and adding extra pipe.

Richard