Determining GPM - which is correct....

[TerryHn]

I have a Pentair IntelliFlow VSF pump connected to a Intellicenter controller and am working to properly calculate the GPM for my new pool. The contractor just cranked it up to 2000 rpm, patted the pump, and said that's good I want to understand this better.

I followed the instructions to determine the Head (at variable RPM's) by using the existing pressure gauge, and adding a vacuum gauge to the pump. Using that, and the appropriate maths, and the performance chart for the pump I got some values for GPM.

BUT, when I run the pump at those RPM's, the GPM reported from the pump and controller is 60% of my calculated values.

So, which is right? Is the GPM reported by the pump accurate ? or have I totally messed up the calculations (values below) ?

Thanks,
Terry.

pool size	17500​
factors->>	2.31​	1.13​		(another model had 1.3 for the vacuum factor)
rpm	pressure	vacuum	head
750​	0​	0​	0​
1550​	4​	0​	9.24​
2350​	11​	1​	26.54​
3150​	21​	4​	53.03​
3450​	26​	6​	66.84​

 

[Homebrewale]

Is this an academic exercise or is there a reason you want to know the GPM? I don't know the GPM on my pool and it doesn't matter. With a VSP, all I need to know is the RPMs I need to run it for all the equipment to work. The two limiting items on my pool are the SWG and gas heater.

 

[JamesW]

What numbers are you getting for flow?

What numbers is the pump reporting?

What pressure is the pump reporting?

y = 0.00465X^2, y from 0 to 70 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

 

[TerryHn]

The original goal was to calculate GPM so I could ensure the water is turned over as recommended. BUT, since I started this project I have read the articles here on TFP about why "turns" are not important. Since doing the above calculations and setting up a schedule I haven't looked at this but recently I integrated the controller into my HomeAssistant system and saw the reported GPM. So, I'm curious about the different values. Is the pump reported GPM accurate ?

Thanks for your reply,
Terry.

 

[Jimrahbe]

Terry,

I "assume" you want to know GPM because you are trying figure out your Turnover rate..

If that is true, then you are just peeing into the wind..

The idea that you have to "turnover' your pool water X times a day is just a myth..

We suggest that you run your pump at a specific speed for a reason..

In my case, I run at 1200 RPM as that is a little more than it takes to turn on my salt cell.
I also have a speed that I run so that I get a little lazy river flow when my wife and I use our floats.
I also have a speed for my waterfall...

What I don't have is mythical speed for turnovers..

Edit.. Sorry, I did not see your post above, until after I posted..

Thanks,

Jim R.

 

[TerryHn]

There are so many articles and posts about turning over your pool water that finding that article here on TFP was a surprise. It makes sense though, and I expect if I showed it to some people their reactions would be startling

Thanks for your reply Jim R.

 

[JamesW]

Turnovers are more relevant to high use commercial pools, so that is where the metric came from.

Most commercial pools have to follow state and local code for turnover rates.

Low use residential pools do not need much turnover.

In most cases, the best and most efficient way to run the pump is to run the pump 24/7 at the lowest speed that allows the SWG and skimmers to work.