Physics and math

Lskul60

Well-known member
May 29, 2019
87
Long Island
Hi all,

I'm trying to figure what my electrical cost is to run my pool. I run my 1.5 HP pump for 12 hours. I also run my SWG at nominal 40% for the full 12 hours.

So that should be 946 Watts per hour x 1.5 HP x 12 hours x $0.12 per KW-hr.
My math equates that to $2.04 per day to run the pump.

For the SWG, I am running approx 20 volts and 5amps, which makes for nice simple math of 100 Watts, running for 4.8 hours per day. I do realize my SWG will increase the purity % as the water temp increases, but for the sake of this discussion we'll just leave it at a flat 40%.
So that's 0.48 KW-hrs per day, which is like $0.06 per day, which is a rediculously low number, but the math is what it is. (Unless I'm doing something wrong?).

The controller also runs for the 12 hours, but it's not doing anything other than powering the LCD and cycling the cell on/off every 15 minutes or so depending on the %.
If there's a fault, then a big bright red LED turns on, but that can't possibly use much power. Literally a fraction of pennies.

So everybody, how's my math and my logic?

Thanks in advance
 

Lskul60

Well-known member
May 29, 2019
87
Long Island
60,

Check out this link.. How Much Does My Pool Pump Cost to Run? - INYOPools.com

I get $3 buck per 12 hours of run time.. I would not even factor in the controller or the SWCG as it will not be much at all..

On reason the I have an IntelliFlo pump is so that I can run 24/7 at 1200 RPM for less than $20 bucks per month..

Thanks,

Jim R.
Thanks Jim,
I see what I did wrong with the calculation.

Regards
Larry
 

Lskul60

Well-known member
May 29, 2019
87
Long Island
Question: If the SWG can generate enough chlorine in 4.8 hours, why are you running that big pump for 12? :scratch:

Start dialing that back some. Go down to 8 for a week or two, then 6, then drop an hour at a time. When it loses some of its sparkle, go back up. Determine Pump Run Time - Trouble Free Pool
Hey Rich,

I hear ya. Loud and clear and fully agree.

I am fortunate that all my hard work goes towards lots of utilization of my pool, which includes kids and friends in and out of it all day long, so I run it 8:00-8:00. I have a slide so I need the pump on .

Also, I haven't figured out how to get them to patiently and gently walk from ladder to diving board without running thru the plants first and each of them dragging an average of 2 cu feet of mulch with them on their feet.

Has anybody invented a test kit for mulch per kid?
 

Lskul60

Well-known member
May 29, 2019
87
Long Island
Question: If the SWG can generate enough chlorine in 4.8 hours, why are you running that big pump for 12? :scratch:

Start dialing that back some. Go down to 8 for a week or two, then 6, then drop an hour at a time. When it loses some of its sparkle, go back up. Determine Pump Run Time - Trouble Free Pool
Actually, Rich, if you don't mind, I do have another question for you (or anybody else on the forum for that matter).

How do I actually calculate GPM ?

1.5 HP pump feeds DE filter, which operates at 18 PSI nominal. I doubt there's very much resistance in the multiport valve or SWG, or from any of the 90 or 45 elbows. This is all accomplished in a few feet of 2" PVC, before being split at a Hayward dial-a-flow valve that feeds 2 return lines each with 2 eyeballs. Each return line is approx 50'

On the suction side, there are 2 skimmers , one with a 10' run, the other about 15' and a main drain line about 20' in lenght

Thank you in advace
Larry
 
Last edited:

Steve_in_C

Bronze Supporter
Jul 6, 2017
333
Kinston, NC
Your original calculation is correct. Except you did not include the units 946 watt-hours/hp. That makes it work out.

I agree with the others. Crank back your run time. You likely don't need 12 hours.
 
  • Like
Reactions: Lskul60

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
13,530
Bedford, TX
Larry,

Why do you need to know GPM? I assume it is because you still believe in the old turn-over myth... Chemicals keep your pool clear, not the idea that your pool water has to go through the filter x times a day.. It just ain't so... :mrgreen:

Jim R.
 

Teald024

TFP Guide
946 Watts per hour x 1.5 HP x 12 hours x $0.12 per KW-hr.
946 watt-hours/hp.
Not to split hairs, but 1hp = 746 Watts
But your pump isn't running at the full 1.5hp and there is an electrical efficiency factor in there as well.



How do I actually calculate GPM ?
You can get it if you:
*look at the pump curve and use the approximate pump pressure differential
*know the pump power draw and the pump pressure differential.
*install a flow gauge

But to be honest, it really doesn't matter what the flow rate is. I think a lot of people struggle with this until they realize that you can just run the pump until it looks clean enough to make you happy. Flow rate isn't important.
 

Steve_in_C

Bronze Supporter
Jul 6, 2017
333
Kinston, NC
Not to split hairs, but 1hp = 746 Watts
But your pump isn't running at the full 1.5hp and there is an electrical efficiency factor in there as well.




You can get it if you:
*look at the pump curve and use the approximate pump pressure differential
*know the pump power draw and the pump pressure differential.
*install a flow gauge

But to be honest, it really doesn't matter what the flow rate is. I think a lot of people struggle with this until they realize that you can just run the pump until it looks clean enough to make you happy. Flow rate isn't important.

While correct, 746 W is the definition of 1 HP. That is theoretical. I doubt you will find many motors <=1.5 HP that are that efficient. Many smaller electric motors draw in the vicinity of 1000 watts per HP. The efficiency normally increases with the size of the motor. I just couldn't make his math work out without all the units.
 
  • Like
Reactions: Lskul60

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
10,877
Evans, Georgia
Also, I haven't figured out how to get them to patiently and gently walk from ladder to diving board without running thru the plants first and each of them dragging an average of 2 cu feet of mulch with them on their feet.

Has anybody invented a test kit for mulch per kid?
:laughblue: :laughblue: :laughblue:
 

Teald024

TFP Guide
While testing in front of my kids and their pool friends, I've used the OTO chlorine test to "test" to see how many kids pee'd in the pool. The test is color match yellow and results show up to 5 "pee's" have happened. Kids always go quiet, red faces, and eyes dart frantically at each other! :laughblue: Always a good laugh.
 

Rich D

Bronze Supporter
Aug 3, 2018
378
MA
How about something with thorns. :mad:
Thrones.... What thorns?????
If they are anything like my kids you would just end up with mulch and blood in the pool....

I am thinking more like a electric fence with a Doberman guard dog would be a good start..

Or perhaps just some nice looking river rock might be a bit more cost effective and user friendly .... :)
 

Lskul60

Well-known member
May 29, 2019
87
Long Island
Thrones.... What thorns?????
If they are anything like my kids you would just end up with mulch and blood in the pool....

I am thinking more like a electric fence with a Doberman guard dog would be a good start..

Or perhaps just some nice looking river rock might be a bit more cost effective and user friendly .... :)
Is that the river rock next to the broken glass?