Variable speed pump efficiency

[HeavyD328]

I just wanted to provide an update as to what's been happening. Pentair earlier this week placed a flow meter on the plumbing and it does seem as if there is a rather large amount of error in the flows being calculated by the VSF pump particularly at higher speeds. At 3450 RPM, the flow meter was reading flows near 100 GPM vs the display of 50 GPM from the pump.

They are perplexed as to why the pump has such a large magnitude of error (they switched out to a brand new pump with same results) so at this point have ordered a full study of our pool system including measuring vacuum and return pressures under different operating conditions. I'll post the spreadsheet results here when I get them.

Makes me feel a little better at least knowing our flows are better than what the pump is showing!

 

[mas985]

Thanks for the update. It will be interesting to see the results.

 

[JamesW]

I think that it would be better if the pump actually measured the suction and pressure instead of calculating them from the power usage.

Maybe it's accurate sometimes, but I suspect that it's probably not super accurate in many cases.

Of course, the cost would be extra, but I think worthwhile.

 

[mas985]

That would significantly complicate the design of the pump and inflate the cost. Plus, it would still require an accurate measurement of the head curve to get back to flow rate so it might still suffer from errors.

If flow rate is truly required, which in most cases it is not, then a flow meter is probably the better solution and it would be far cheaper if kept separate from the pump as off the shelf sensors could be used. However, it could still be integrated with the pump controller or separate controller via a sensor wire connection.

Something like this could be used but the controller would need to be compatible: https://www.amazon.com/DIGITEN-Sensor-Flowmeter-Control-10-200L/dp/B00VKAT30C