So, I've been doing some math (electricity usage)...

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RobbieH

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Aug 30, 2010
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Dallas, TX
... and I'm quite surprised at the results.

Yesterday I played with different GPM settings on my pump, recording how many watts are used at each step, and calculated out the power usage. Now this will vary with different pools and plumbing, but either way I'm still quite surprised to see the results.

My goal was to determine what the most efficient setting was. Running slower is not always going to result in the lowest power consumption, but in my case it did.

But what REALLY caught me off guard is how little it costs per month to run my pump. If I turn over the full 44,000 gallons once per day, at the most efficient setting, which for me turned out to be 30 GPM, my pump only adds $3.29 per month to my power bill. Yes, this includes changing run time calculation when running higher GPMs.

Before yesterday, I had the misconception that it was much higher, based on the information provided to me by a third party, which we did our best to validate through energy usage from two identical houses 6 doors apart, one (that third party's) with a pool and one without.

Now, I don't know how much of the difference has to do with the fact that they were using a very inefficient single speed pump (they buy the cheapest thing they can find), but still, I think the numbers I was given were way overstated. They sincerely believe their pump added $100 per month to their bill.
 
What do you pay for electricity?

30 GPM should be about 130 watts +- and for a full turnover, that is over 24 hrs. But assuming 24/7, that alone is 92kwh per month not counting additional usage for high speed. So are you paying less than $0.04/kwh?
 
I have a similarly sized pool but I didn't do the exhaustive testing that you probably did. To keep my water clean, comparing a 1.5HP super pump usage to the VS I have now I can confirm that I am saving a great deal more than $100/month. I replaced the pump at the pool opening last year so only compared the KWh's and $$ easily through my utility's website.
3 years of very similar costs to run the house then our 4 month summer dropped by a lot last year. one thing that also impacted me and I calculated this separately with the electrical specs of my unit is the added savings of the heat pump. I set the VS just below the acceptable flow of the heater to make sure not to have it run along there pump at all times.

G.
 
I've done my math 100 times and double checked it, and I am pretty sure I have it right, but that's one of the reasons I put this up here.

30 GPM is pulling 435 watts. Turnover is 24.44 hours, so just slightly over one day. This puts me at 10.63 kWh per day, energy cost is 1.03 per kWh, which calculates to $3.29 per 30 day month.

Here's my math, because somewhere I'm off compared to your math.
kWh per day = watts (435) x turnover hours (24.44 is a little off but close enough for this math) / 1000 which comes to 10.63.

Then of course cost per 30 days is (kWh per day (10.63) times cost (1.03)) / 100 for per day, then x30 for month's cost = $3.29

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Note - 25 gpm pulls 270, 20 pulls 225. Ramping up to 30 is a big jump.
 
I need to go back and see where I have a decimal off. I thought there was no way that pump cost $3 a month...

But still, $30 a month is a lot better!

But with the correct math, it illustrates where I could save around $10 a month or so by not turning once per day.

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GPM Watts RPM Watts/GPMx1000 Hours required to turn over pool kWh per day Cost per day Cost per 30 day month Turnovers per day
15 175 1275 85.71 48.89 4.20 0.43 $12.98 0.490909091
20 225 1400 88.89 36.67 5.40 0.56 $16.69 0.654545455
25 270 1500 92.59 29.33 6.48 0.67 $20.02 0.818181818
30 435 1840 68.97 24.44 10.63 1.10 $32.86 0.981818182
35 560 2025 62.50 20.95 11.73 1.21 $36.26 1
40 690 2180 57.97 18.33 12.65 1.30 $39.09 1
45 880 2400 51.14 16.30 14.34 1.48 $44.31 1
50 1260 2755 39.68 14.67 18.48 1.90 $57.10 1



I know that's hard to read, but it is correct now. Thanks!

That watts/GPMx1000 was just an arbitrary number I wanted to see.
 
But 435 watts for only 30 GPM is quite high. You must have very high head loss plumbing. Just saw RPM above.
 

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It's in the chart, just hard to read. At 30 GPM I am running 1840 RPM.

Keep in mind, this pool was built in 1957.

The one skimmer and one main drain are pulled by the pump into the system through 2" copper. From there, I go through the pump, filter, SWG, then there is a reducer to send the water back through 1.5" copper. There are four returns, all at the wall of the shallow end, and IIRC they are 3/4" copper, adapted to PVC during the remodel.

The returns are approximately 70' from the equipment room.

One other thing that comes to mind, there may be some restriction due to the eyeball type I have. I should probably try removing them and see what happens at 30 GPM. They only have a 3/8" opening. Should I consider changing them to 3/4" openings?

[edited]

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pabeader said:
What is the significance of turnover? I though that was something we really don't consider so I've never thought about it.
Click to expand...

I'm just using that as a constant. Note in my chart I have lower turnovers listed. And, I have a SWG, so I have to consider enough runtime and GPM for it also.
 
If you switch to larger opening returns you will get less head loss. You will also have lower pressure at the return so may effect circulation. But I think the gain in head will compensate for that. More volume moving around the pool.
 
Whoa, 3/8" really? That is like spa jet size. Definitely, you will get far more flow rate and better efficiency with larger eyeballs.
 
These are the one the PB put in when he did the replaster. I thought they looked pretty small.

All this pumping stuff is one area I get really lost in. :)

Ordering new eyeballs right now.

Before, it had little copper discs with 4 3/8" holes. No eyeballs. We are talking ancient history here. :)
 
It won't even go large enough for my pool. Besides, there are too many variables to consider. For example, how many pools have a single 1.5" run to the returns, and how many are 70' from the pump like mine?

I'm trying my best to use real world numbers on my own pool. :)

For that matter, how many 44,000 gallon pools have one skimmer?
 
mas985 said:
Pure marketing and far from reality.
Click to expand...

yes but iff you are entering your own numbers it's no different than making up a spreadsheet with the exact data the OP calculated.

RobbieH said:
It won't even go large enough for my pool. Besides, there are too many variables to consider. For example, how many pools have a single 1.5" run to the returns, and how many are 70' from the pump like mine?

For that matter, how many 44,000 gallon pools have one skimmer?
Click to expand...

I say 40k gal since the pool places around here don't calc larger but I have a similar size as yours, 1.5' return T'd off for 2, 1 ( very small) skimmer, 80ft from pad.

and marketing or not, my proof is on my elect bill. once solar heat is installed I'll be able to narrow the pump & heater's effect on costing more precisely.

G.
 
Just an interesting math note, the area of a 1.5 inch pipe is 1.77 square inches. With only (4) 3/8" eyeballs you only have 0.44 square inches of opening to you pool. With a change to (4) 3/4" eyeballs that will give you 1.76 square inches return into the pool. You said the previous set up was 4 copper plates with (4) 3/8" hole per plate. The copper plate set up is equal in square inches of opening to having (4) 3/4" eyeballs.
 

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