Need help with GPM Estimate Spreadsheet

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phalcon51

phalcon51

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Oct 5, 2010
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So. California
I'm hoping someone can help me with a problem I'm having using Mark's GPM Estimate v3 spreadsheet. The problem is entirely with me I'm sure, not with the spreadsheet, as I really don't know what I'm doing in Excel.

I recently installed a Hayward EcoStar SP3400 VSP and I'm trying to get an accurate estimate of the gpm so I can program the pump appropriately to get the right turnover rate.

Using the pump's on-board menu I got the wattage at 1000 rpm intervals from 1100 to 3400 rpm and also noted the filter pressure at each speed. I was hoping to enter the information into the spreadsheet and have it propagate the gpm and other info for the various speeds.

Starting with the Watts2GPM tab I entered the pump model into columns B thru X and then put in the RPM and the input power in the next 2 rows all the way across. The original spreadsheet was only populated with data out to column M, so I copied and pasted the individual cells in the yellow section to populate columns N thru X. I then did the same thing in the PSI2GPM tab. I was hoping that the spreadsheet would then calculate the data for the various rpm ranges, but it doesn't. I'm sure I'm doing something wrong and I was hoping someone could point me in the right direction.

Thanks for any help,

Gary
 
First, if you have watts, then use only the watts2gpm sheet. The PSI2GPM sheet is meant only for those who do not have access to the power input to the pump aand gives them another method of determining GPM.

If you need more columns, select the right most column N plus the additional columns to the right that you need and then do a fill right (ctrl-R or Edit - Fill - Right). There are hidden cells and if you don't do a fill right, you might miss coping the logic over.

If you changed any of the logic (non yellow cells), you might be better off downloading the sheet again and starting over.
 
Thanks Bama and Mark, it worked great. One question, though. There's an anomaly at the lower pump speeds where it shows the gpm decreases for the first five cells (from 1100 to 1500 rpm) and then picks up and increases from there on. Is there something I can do to correct this?

GPMSpreadsheet.jpg


Gary
 
There could be several things going. The model fits the 6 points from the CEC data to a polynomial. The fit is pretty good for the EcoStar and since they have 3 points at 1000 RPM I would expect the results to be fairly good there but the equations are sensitive to changes in the Watt input. You can see how well the model fits the data on the CECCal tab. The CEC data relies upon actual measured input power and not the EcoStar display. I would expect the EcoStar to display the same power but I cannot confirm that so it is uncertain if they actually match. If the EcoStar is not displaying the correct input power, then that could explain the descrepancy. I would hope the CEC data is correct but you never know.

In plumbing without check valves or a heater, you will normally see the plumbing curve remain fairly constant vs RPM. With a check valve or heater, you would normally see the plumbing curve increase more at lower RPM. But in your case, the plumbing curve is lower at lower RPM which would mean that the plumbing is improving with lower flow rates. I am not sure what would cause that so I am not sure if it is real.

At this point it is hard to say if what you are seeing is real or a result of error somewhere. A few questions:

Did you allow the pump to settle when changing RPM? Sometimes, the wattage will not stabilize right away.

Did you see any variation in the wattage readout with constant RPM? What was the variation?

Could you please describe your plumbing. Based upon the plumbing curves, it looks to be 1.5" diameter but how long are the runs from pool to pad. Also, do you have any special equipment not listed in your sig? What is the model# for the DE filter?

Do you feel any flow rate difference out of the returns between 1100 RPM and 1500 RPM?

One simple solution is to calibrate the plumbing at a high RPM and then just scale the flow rate by RPM. For example:

GPM = 48 * RPM/2100

This of course assumes that your plumbing is not changing with flow rate which could be incorrect.

[EDIT] - Just found something interesting. The pressure loss curve for the Pro-Grid DE filter is shown here on page 8. It is as if it has no head loss up to 40 GPM, then it starts to experience head loss. It is a very unusual head loss curve and could explain some of what you are seeing.
 
mas985 said:
At this point it is hard to say if what you are seeing is real or a result of error somewhere. A few questions:

Did you allow the pump to settle when changing RPM? Sometimes, the wattage will not stabilize right away.
Yes, I waited until the wattage stabilized as much as it would. I took all the readings with the pump drawing only from the skimmer. Main drain and vacuum lines were closed.

Did you see any variation in the wattage readout with constant RPM? What was the variation?
Yes, it varied about 6w at the lower speeds, about 10-15w in the middle range and about 12 - 18w in the the upper range

Could you please describe your plumbing. Based upon the plumbing curves, it looks to be 1.5" diameter but how long are the runs from pool to pad. Also, do you have any special equipment not listed in your sig? What is the model# for the DE filter?
From the main drains to the skimmer is about 10' lateral and 7' vertical. From the skimmer to the pad is 44' plus 1' down from skimmer to the horizontal pipe and about 2' up from horizontal pipe to pump. It appears to be 2" pipe from the mains and skimmer till just before the Jandy valve where for some reason they reduced it to 1.5". The line from the vacuum port to the pump is 1.5" all the way. The return lines are 1.5" from the filter into the ground and then they expanded it to 2" till the 1st return, 1.5" till the 2nd return and finally 1" to the 3rd return. If you need the length of the return lines, from the filter it's 24' to the first return (2"), 27' to the 2nd return (1.5") and 69' to the 3rd return (1").

No special equipment.

The filter is a Hayward DE 4820. The design flow rate is 96 gpm.

Do you feel any flow rate difference out of the returns between 1100 RPM and 1500 RPM?
Yes, there is a very noticeable increase in flow from 1100 to 1500 rpm.

[EDIT] - Just found something interesting. The pressure loss curve for the Pro-Grid DE filter is shown here on page 8. It is as if it has no head loss up to 40 GPM, then it starts to experience head loss. It is a very unusual head loss curve and could explain some of what you are seeing.

Do you think that's real or a mistake?
Click to expand...

Here's a few pictures of the plumbing:

Main Drains
DSC01167.jpg


Suction and Return Lines
FromPooltoPad.jpg


Suction Lines to Pump
PadPiping.jpg


Thanks again for all your help

Gary
 
Thanks, the pictures help quite a bit. Your plumbing should be fairly low head loss but the RPM/Watts value indicates high head loss so I am starting to think it might be the filter. Can you give me the filter pressure and input watts at full speed?
 
I'm not sure if it makes any real difference but I just found that someone installed what looks like a vacuum adapter in the skimmer line to the pump. Might've been my son who was taking care of the pool while we were on vacation last summer, so it's been in there pretty much the whole time.

DSC01799.jpg


DSC01800.jpg


DSC01801.jpg


I pulled it out and I'll check a few of the speed vs. watts vs. filter psi readings just to make sure it didn't have any significant effect.
 

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Sorry, I tought you were going to post back new results without the plug. That could have some effect but I wouldn't expect too much. Again, my first inclination is that the published filter PSI loss is quite high for the given GPM so that in of itself would reduce the flow rate considerably. Also some of the PSI loss is not reflected in the filter PSI because of the backwash valve. But if I use my hydraulics model, I can get your measurement numbers if I assume that the filter has very high losses (~8x normal).
 
Oh, sorry Mark, you're right. I got sidetracked by a bunch of other stuff and had to put this aside for a little bit. I'll try to get those new readings later today or tomorrow and post them here.

Does that type of backwash valve add a considerable amount of flow restriction for the pump to overcome? Is there a better alternative to that type of valve?

What causes the 8x normal filter losses, and what does that mean exactly? (8 times what?) Is it just poor design of the filter?

Also, I don't understand your statement "that the published filter PSI loss is quite high for the given GPM so that in of itself would reduce the flow rate considerably." What is meant by "the filter PSI loss" ? Looking at the chart on pg. 8 in the PDF manual from Hayward's webpage for the DE4820 filter are you referring to the PSI numbers on the left vs. the GPM numbers on the bottom, i.e. 14 PSI @ 100 GPM? What could I compare this to to get a better sense of what a more reasonable number is? (Sorry, I'm not very technically oriented when it comes to hydraulics)

Thanks again for all your help, I really do appreciate it.

Gary
 
My Hayward cartridge filter has about 3.5 PSI loss at 100 GPM where as the manual for your filter shows about 13.5 PSI but that is with a multiport valve and not a slider valve like you have. From the manual, your filter is about 4x the head loss of a cartridge but I had to double that again to get the numbers to match what your seeing. So the extra head loss could be due to the backwash valve or something else in the plumbing. You might double check the SWG to make sure there is nothing stuck in there. Other than that, the only thing I can think of is that the filter is causing the extra head loss.
 
mas985 said:
My Hayward cartridge filter has about 3.5 PSI loss at 100 GPM
Click to expand...

Wow, that's a lot lower than mine. Is that because of the difference in the surface area of the filters (425 sq. ft. cartridge vs. 48 sq. ft. DE grids) ? Is my filter appropriately sized for my pool size (25,000 gal)?
 
Actually, I think that most of the difference comes from the backwash valve at least that is what I surmise from the slim published data that both Hayward, Pentair and Jandy have on their web sites. One of the best backwash valves that I have seen is the Jandy Neverlube which supposedly has 0.8 PSI loss @ 80 GPM. Most valves run between 5-15 PSI @ 100 GPM.
 
Unfortunately, the Jandy backwash valve has the pipes mounted on 8" centers where my filter is on 5" centers. I didn't see anything different than what I've already got on either the Hayward or Pentair sites so I guess I'll have to live with that for the time being. Oh well.
 
Well, I checked my speed vs. watts vs. psi numbers again without the vacuum adapter in the skimmer hole and there's virtually no change at all. So, using the figures in picture below I figured that to move 25,100 gallons in a day for one turnover I can run the pump / Pool Cleaner for 2 hours at 2200 rpm (570w / 49.59 gpm) and then 9 hours for the pump only at 1500 rpm (216w / 37.2 gpm) for a total of 26,039 gal. per day. Do those sound like reasonable numbers? I'm not really sure what to do with those gpm numbers from 1100 rpm through 1500 rpm (38.19, 36.41, 34.16, 33.62 and 37.20 respectively) as they don't really make sense. I'm just choosing the 1500 rpm number because it seems reasonable.

I've got the pump programmed for a minimum of 1100 rpm and a max of 2600 rpm.

SP3400VSPGPM.jpg
 
Do you happen to have a way to measure the pressure at the pump outlet drain plug? That might give you some additional information as to how much head loss is in the filter.

But as I just posted in another thread, knowledge of the actual flow rate is interesting and somewhat helpful but it is not totally necessary either. There are no hard rules as to the number of turnovers a pool needs so some trial and error would necessary either way. But if you really want to know the flow rate, you might consider a flow meter.
 
I don't have a pressure gauge but I could certainly get one. Do you know if the outlet drain plug typically has a standard type thread that a pressure gauge would fit, or am I likely to have to get some sort of adapter?

It would be interesting to know the actual flow. Any good sources for a flow meter that you're aware of?
 
I think that they are normal 1/4", the same size as the filter. In fact, if you have a 1/4" plug, you can use the filter gauge.

Blue-White are pretty good meters but if you don't install them correctly, the accuracy is not so great.
 

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