More energy efficient to run a pool filter @ 220 than 110V?

[ScottI2R]

HI Everyone,
I received a phone call from my Boss last night and he needed the formula for power. OK, easy enough. However, he told me of how he had his pool filter motor changed over ($190.00) to 220V instead of 110V he was using. My math says the power consumption is ALMOST the same. EG) 110V @ 12.7 amps as opposed to 220V @ 6.3amps. 100mA less than half on the higher voltage. His father, a retired linesman, believes 220V will save money due to reduced power consumption. I have also heard that running at the higher voltages (if the motor is capable) is more cost efficient. Is any of this true? And where is the mathematical equation I should be using to determine this if it is true?

Or is it going to take 179 years to break even on the original cost of the change? If so, I will post his email address and you can tell him

Thanks,
Scott

In a hundred years, it isn't going to matter anyway.

 

[itsmoked]

No! It will take 1986273452093784 years to break even on this boondoggle.

[flush]

1.5hp = 1.5hp!

 

[IRstuff]

How was it "changed over?" Was it rewound or replaced?

TTFN

 

[itsmoked]

Basically the savings is in smaller wire. If the system is already installed you aren't going to save in that area at all.

For say a 120V verse 240V motor on a drill press the the drill press might have a little more umph with a 240V motor but otherwise the difference is nill. The energy consumption is the same.

Now if you were talking a 500hp motor a higher voltage would allow smaller wiring, breakers, etc., etc., that might add up to quite a savings.

 

[ScottI2R]

IRstuff,
It was a dual voltage motor 110/220 and the $$ was spent on the electrician that wirred it and installed the new recepticle.

Itsmoked, did you sit and do the math saved by 100mA? LOL! I didnt think that part was worth the effort!!! Thanks

Scott


In a hundred years, it isn't going to matter anyway.

 

[IRstuff]

In that case, I'd be dubious that there was even a 100mA difference; that might just be round-off error.

I assume that the only way that this would work in practice is that the identical current is flowing in a given wire in both cases; it's just an external wiring difference.

TTFN

 

[davidbeach]

The savings realized will be in the reduction of I^2R losses in the conductors feeding the pump. Without doing any calculations, itsmoked's calculation appears highly optimistic. ;-)

 

[jraef]

Another "old electrician's tale" debunked. The other one I like is the old chestnut that it is cheaper to leave something on, like lights, than to turn them off and back on.

Back to the OP, the reason I think this fairy tale persists is because there is some mony savings if you have a ratcheting instantaeous peak demand charge from your utility, which some industrial and commercial users do. Starting current on a 220V motor would be lower than at 110V, but in either case, it will not really make a difference and most demand meters are time-integrated now anyway. On top of that, I know of no residential service areas where they tag on demand charges!

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[itsmoked]

My calculator didn't have an infinity sign on the display and since I have to decipher a single blinking LED it has for a display(to save energy) I just stopped interpreting.

 

[electricpete]

Since power factor is not stated we can't draw any conclusions about motor efficiency based on volts and amps alone.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[ScottI2R]

Thanks all,
I think I'll just forward this to him anonymously! Once again, the math is right and the numbers dont lie. BTW, if it IS an actual 100mA reduction, that uses 11 watts less and at .09/KwH, well that is .00099 savings /hr. This assumes PF=1 since I do not have that info.

Thanks again all,
Scott

(we can see I have little to do today)

In a hundred years, it isn't going to matter anyway.

 

[bacon4life]

jraef

Perhaps the electrician was thinking of how much he got paid for the second it would take to reach over to turn off the light. At $36/hr, that’s a penny a second! He could leave a 100W bulb on for an hour and still save money!

I had actually started looking up the lost of life to fluorescent bulbs due to starting, and the resulting labor and materials cost to replace bulbs. If you regularly cycle instant start types, replacement could cost more than energy. I have created an example to explain this based on the equations given in "Economics of Switching Fluorescent Lamps".
Cost of bulb: $10
Cost of labor: $10

STEADY BURNING
Number of hours on per day: 10
Total cost per year: $19.82
Energy cost per year at $0.05/kW*h (94 watt bulb): $17.16
Replacement costs per year: $2.67
Duty cycle: 10 hours

CYCLED
Number of hours on per day: 5
Total cost per year:$30.80
Energy cost per year at $0.05/kW*h (94 watt bulb): $8.58
Replacement costs per year: $22.22
Duty cycle: 0.01 hours

 

[jraef]

Interesting. Where did you come up with your info on loss of lamp life from cycling? I heard that doubling the duty cycle on fluorescents reduces the lamp life by only about 15%. This site tends to back that up, and beleive it or not, someone at Lawrence Berkeley Lab apparently did a study on this! Lamp life link

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[bacon4life]

I used the equations listed on that site. There were several web references to the paper, but I don’t have a copy of it. I had started off trying to find out how much lifespan each start cost, but didn't have good luck finding that information so I made some assumptions about duty cycles.

It would depend what you mean by double the duty cycle. If that means you have the lights on for the same amount of time each day, the lamp life loss would be in the range of 15 to 25% based on the equations in the site. However if instead the lamp is on for half the time also, you would actually extend the number of years the lamps last, which is in part why my duty cycle was ridiculously fast to find the economic crossover point.

There we not very many applications I could think of that would regularly have short 50% duty cycles. Most lights would typically be on for long periods then off for long periods, unless someone has just left or reentered the room.

There would also be the human factor of having to guess how long a room will be empty when you leave. It just seems easier to train everyone to always turn off lights. There are also motion sensor applications, but those calculations would also have to include lost productivity of standing up and waving at the sensors, or being in a restroom stall when the light goes out.