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Thank you frankchong. I will reserve my opinion about the efficiency of submersible pumps until I have real data.
In most catalogs and brochures for fractional horsepower pumps they provide a curve with Q plotted against H. They could easily plot amps on a third axis within the same graph, but they do not. The only time you also get the power consumption curve is when shopping for large capacity pumps of many horsepower.
Intuition would lead a person to believe that the "sweet spot" (maximum efficiency) is neither at the point of maximum H where Q approaches zero nor the point of maximum Q where H approaches zero, but somewhere in between. However, buying and installing several different pumps only to check the amp draw and select the most efficient one is not an option for most of us. In the absence of real data, are there any general guidelines for making an educated guess about the point of maximum efficiency? Is it likely to be near the center of the Q/H curve?
Also, the plot of amp draw superimposed on a Q/H graph would make a fairly normal inverted bell curve. Correct? There must be practical design limits to the range of the amp draw curve. For example, if the point of maximum efficiency is 1 amp, the maximum possible amp draw will not be 10 amps but something much less. The smaller the range, the broader will be the bottom of that inverted bell curve (area of lowest amp draw). Thus, the amp draw will initially increase very gradually as you move away from the sweet spot. The net effect should be that the annual electrical cost does not change much as long as you are in the vaciity of that sweet spot. Does that make sense.... and is it correct?
-steve hop
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