Rebuilding a pool-pump for a 5K Pond...

[taekwondodo]

So, my WAVE II pump's motor is going out (Baldor 1/2 HP) and I will need to find a solution for the pond this coming summer.
I'm estimating ~15'-20' of head (based on filter PSI) and ~600W. 600W is quite a bit that needs to run in the summer 24x7 (at CA electrical rates), running me ~$150 month in the summer (PG&E's top tier electrical rate is around $0.40/KWh).

Here is a copy of the pump's curve:

And, I am highly skeptical on the curve vs. actual performance, as I had a 1HP Whisperflow powering the pond at one point with much more flow.

I can just replace the motor, however I would like to find a way to cut the power in half (~300W) and still get reasonable flow. I also have access to several wet-ends (Whisperflo, Northstar, Max-E-Flow) that need new motors, so "designing a pump" with a low-power motor might be a route as well.

Just looking for ideas here on ways to get the power down without affecting the flow too much.

 

[JasonLion]

What matters most is the impeller, not the motor. A 1/2 HP impeller will draw less power that a 1 HP impeller even with both of them hooked up to a fairly large motor. The main issue with using a very small impeller is that the pump might not be able to prime correctly. If the pump is below water level, this may not be an issue, but if the pump is above water level it needs a certain amount of power to prime.

 

[mas985]

Just to add to what Jason mentioned, if your current pump was at 20' of head, the flow rate would be 55 GPM according to the head curve. Assuming the same plumbing curve, the Whisperflo 1 HP (full rated) would have produced around 88 GPM at 50' of head so no surprise that the Whisperflo puts out more.

But the interesting thing is the efficiency. Your current pump would produce 55 GPM @ 600 watts or 5.5 gallons/watt-hr vs the Whisperflo which is around 2.75 gallons/watt-hr or about half the efficiency. This is not too surprising since the 2.5 HP uprated Whisperflo at half speed has about the same efficiency at the same flow rate (48 GPM @ 510 watts or 5.7 gallons/watt-hr). Flow rate has the largest impact on efficiency.

Also, the head curve of your current pump indicates a design with a small diameter impeller with wider vanes which results in a low head pump at a higher specific speed (i.e. higher flow rates at lower head). But the best thing about low head pumps is that they are more efficient than a high head pumps which is why AG pumps usually have better efficiency than IG pumps.

So the bottom line is that you probably can't get more efficient than the pump you have and may be better off just replacing the motor. If you are willing to sacrifice flow rate, you could trim the impeller by 20% which will reduce the flow rate by 20% and save close to 50% in energy.