Trying to figure energy usage

[Maestro]

Lots of changes around here this year – replaced my single-speed pump with a dual-speed, installed a SWG, and had solar panels put on my house (for electricity, not pool heating). Now I'm trying to educate myself about how much power it's taking to run my pool, but I'n a newbie at all things electrical. I'm hoping one of you experts can check my math.

Here's what I've got so far. The label on my new pump says it runs on 230 volts using 9.1 amps on high speed and 3.4 amps on low. I generally run it 6 hours a day on low speed, only using high occasionally like when I'm adding chemicals. So I multiply 230 volts x 3.4 amps x 6 hours and get 4.7 kWh per day.

Now this next part confuses me. When I push the "diagnostics" button on my SWG panel it says it's running on 25.4 volts and using 6.18 amps. Are those the numbers I should use to figure the usage? I'm running it at 30%, so when I multiply 25.4 x 6.18 x 6 hours x 30% I get .28 kWh per day.

That seems very low. Should I be using a different number for the voltage? Is the 24.5 reading DC volts instead of AC, and what difference would that make? (The SWG is plugged into a dedicated outlet which is connected directly to the same timer that is running the pump and the heater, so maybe they're all running on 230 volts.)

And one one more thing: there's a label on the SWG that says "24 VDC, 5A MAX." What does that mean and is it anything to worry about since I seem to be over both of those levels?

 

[pooldv]

24vdc is what goes to the cell, not the power connected to the power supply. Yes, 0.28 kWh is about what an SWG uses, they don't use much juice at all.

Your math is good, 2 speed pumps are pretty energy efficient. That's why we keep recommending them.
230x3.4=782 amp hours x 6hours = 4692/1000 = 4.7 kWh x 30 days = 141 kWh per month x $0.1025/kWh = $14.43 per month

 

[mas985]

Here's what I've got so far. The label on my new pump says it runs on 230 volts using 9.1 amps on high speed and 3.4 amps on low. I generally run it 6 hours a day on low speed, only using high occasionally like when I'm adding chemicals. So I multiply 230 volts x 3.4 amps x 6 hours and get 4.7 kWh per day.

Those are label ratings, not what the motor will actually draw although for high speed it could be close. But based upon the label ratings, I assume you have a Super II SP3015X202AZ or equivalent which is an uprated 2 HP. That would use about 2kw on high speed and 400 watts on low speed.

Now this next part confuses me. When I push the "diagnostics" button on my SWG panel it says it's running on 25.4 volts and using 6.18 amps. Are those the numbers I should use to figure the usage? I'm running it at 30%, so when I multiply 25.4 x 6.18 x 6 hours x 30% I get .28 kWh per day.

That is the DC power deliverd to the cell and yes that is correct. However, you are not accounting for the transformer and rectifier efficiency which is probably around 80%. So on average, the SWG probably uses around 200 watts while energized. But it also continues to use a small amount of power while the SWG is off for the control functions.

And one one more thing: there's a label on the SWG that says "24 VDC, 5A MAX." What does that mean and is it anything to worry about since I seem to be over both of those levels?

Those are nominal numbers. There are allowable tolerances around those numbers. The readings you have are fine. If you have an Hayward SWG, then 8 amps is the maximum before the unit will shut off.

 

[Maestro]

Thanks for for the responses, guys. Now I see the balance between pump time and SWG percentage. The SWG uses a lot less power per hour. Upping the percentage and shortening the run time will cost less per day but will shorten the life of the cell. Has anyone ever figured out where the sweet spot is? I'm pretty happy with six hours of run time costing me about $1 per day (my summer electric rates are more like $.19/kWh) with the SWG running for 30% of that time. Maybe I could figure how many years it would take until it'll be time to replace the cell and factor that into the equation, but right now I'd rather go in for a swim!

But based upon the label ratings, I assume you have a Super II SP3015X202AZ or equivalent which is an uprated 2 HP. That would use about 2kw on high speed and 400 watts on low speed.

That's the exact model number - do you read minds for a living?

 

[mas985]

Shortening run time and upping percentage does not reduce cell life. Cell life is measured in amp-hours so it doesn't matter. The cell is on for the same amount of time.

Set cell to 100% and adjust pump run time for correct fc.

 

[Maestro]

Yes, I realized that while swimming laps (always the best time to think). I could cut my run time by 2/3 to 2 hours and triple the SWG percentage to 90%, generate the same amount of chlorine, and save a lot of energy. So from an energy conservation perspective, it's always better to run the SWG at close to 100% and adjust the run time down as necessary.

But I do enjoy running the pump at low speed during the prime afternoon swimming hours because it's nice to have that little bit of flow and skimming action. So I'll make some adjustment, but not all the way to 100%. Thanks for helping me think it through!

Now can someone tell me if there's a formula to figure how many gallons of propane it will take a 40,000 BTU heater to increase a 22,000 gallon pool temperature 1°?