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Thread: which pump? 1 sp, 2 sp, variable?

  1. Back To Top    #1

    Join Date
    May 2012
    Location
    Pahoa, Hawaii (East side Big Island)
    Posts
    28

    which pump? 1 sp, 2 sp, variable?

    OK,

    I have been looking in the pump forum and also all over the internet. And I am still not sure which pump to buy.

    Our priorities and specs:

    -#1: low monthly elec. bills - would like 2-3 yrs return on investment if we buy more expensive pump.
    -a very distant second: quietness
    -1 skimmer, 1 main drain, and they are both close to the pump house, about 20 ft, nothing goes around the pool.
    -no spa, heater, etc. may get solar heater in the future, but no plans for now.
    -probably only going to use pump for filtration, circulation - we will clean manually.
    -electric rate is very high - .25-.35/kwh

    Can we get a away with a very small 1 speed to meet our needs, will amps/watts be lower with a 2 speed on low, or is the only way to get the lowest amp/ water drawn to get a variable speed, and is that worth it compared to a 2 speed on lower setting?

    I am having a hard time finding numbers to compare, and I know that that is partially because the efficiency depends on the water drawn.

    Thanks for any specific help you can give.
    18-20,000 gal?, sand filter, IG vinyl, 1 HP 2-speed pump

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: which pump? 1 sp, 2 sp, variable?

    A small single speed won't be even close to optimal. If it is large enough to prime properly and vacuum well it will be wasting electricity when circulating. The payback on a two speed pump is straightforward and large.

    With electric rates noticeably above $0.20/kwh you will have the lowest long term costs with a variable speed pump. However, if your electric rates are at the lower end of your range it will be longer than a three year payback, and there are some additional minor complications in terms of integrating it with any future equipment you might get (heater or SWG for example).

    Here are some numbers to compare:
    A variable speed pump can give you between 0.15 and 0.3 GPM/watt
    A two speed pump on low is commonly between 0.06 and 0.11 GPM/watt
    A small single speed, or two speed on high is between 0.03 and 0.066 GPM/watt.
    The units are a little strange, but you can look at the relative numbers (large is better), ignore the units, and get a basic idea of how much you can save moment to moment. Figuring payback is a bit more complicated, because it depends on the size of your pool and what flow rate your skimmers require.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. Back To Top    #3

    Join Date
    May 2012
    Location
    Pahoa, Hawaii (East side Big Island)
    Posts
    28

    Re: which pump? 1 sp, 2 sp, variable?

    Quote Originally Posted by JasonLion
    A small single speed won't be even close to optimal. If it is large enough to prime properly and vacuum well it will be wasting electricity when circulating. The payback on a two speed pump is straightforward and large.

    Here are some numbers to compare:
    A variable speed pump can give you between 0.15 and 0.3 GPM/watt
    A two speed pump on low is commonly between 0.06 and 0.11 GPM/watt
    A small single speed, or two speed on high is between 0.03 and 0.066 GPM/watt.
    .
    OK, so the small single speed I was looking at I think is what you have - a 1/2 hp whisperflo, and it sounds like that is not the way to go. I guess you can't go small enough to equal a 2 sp on low setting.

    Our rates are officially .26 kwh, going up to .32/kwh if we go above 700 kwh/month. The pump could kick us over if it uses more than 200 kwh/month, which would be about 6 kwh per day. With either a 2 sp or a variable speed, it seems like we should be under that, right?

    As for the difference between variable and 2 speed - we would need to save about $200-$250 a yr to make it worth it, I think. That would be $16-20/month or about 65-80 kwh/month or 2.3 kwh/day difference between running a 2 sp or a variable speed. That's all pretty rough, and I don't know if I did it all right, but an example would be if a 2 sp was 3.5 kwh/day to run, and a variable was 1 kwh/day to run, total (since how long it runs depends on how much it draws, I know that makes a difference, so I'll just go with totals.) Right? Does this help me at all?

    Whew.
    18-20,000 gal?, sand filter, IG vinyl, 1 HP 2-speed pump

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