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Thread: Pump sizing for SWCG?

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    Pump sizing for SWCG?

    I have an approximately 16,000 gallon pool with a Pentair 2HP 1.3SF 3450RPM pump on it right now. The bearings are starting to make noise on this pump so I'm investigating my options. This led me to read this article which almost seems to be a sales pitch for VS pumps more than anything. Nevertheless, if I follow this article which otherwise makes sense, I see that I can run a VS pump at around 900 to 1,200 RPM (approximately 90GPM for my set up with the 3-2" lines to the skimmer/drain about 20feet to the skimmer and 7 feet deep to the drain or 2-2" lines to the spa and ) for 6 hours a day and get the required two turn overs a day for adequate chlorine generation.

    I've come to find out that the state of California now requires VS pumps when replacing pumps but if I R&R the bearings in the existing pump I am exempt from this requirement. My pool maintenance guy states that the repair people he works with will not install a new single speed pump but will do a rebuilt one. As far as new goes, they'll only do a VS Pump.

    The recommended VS pump from Inyo Pool will cost me $600 + whereas an exact replacement single speed is $270 and rebuilding what I have costs in the neighborhood of $200 at a local electric motor repair shop. The local utility will give me a $200 rebate on a new VS pump So after tax that brings that down to $500. Assuming I only do the rebuilt pump, that's an initial outlay of nearly $300.

    Assuming this is at my top electrical rate is $0.185 per KwH so running the pump 6 hours a day now costs me 11amps x 230V X 6hours or 15KwH/day @ $.185 or $2.80 a day.

    For the VS pump with the same run time assumptions, I'm at maybe 1000RPM or 1/2HP which is about 25% of maximum HP yielding 2.5amps x 230V x 6hours or 3.5KwH a day @ $0.185 or $0.64 a day. This is a savings of over $2.00 a day. In the course of a year it comes out to $730 which covers the initial cost of the pump.


    During the winter the run time is only 4 hours a day and the rate is at a lower tier as we're on solar and even some months we don't pay for electricity at all so this skews my numbers somewhat so maybe it is a savings of $500.

    Here's the rub.. the guy that cleans my pool is adamant about VS pumps not properly chlorinating Salt Water Pools and that it all looks good on paper but in the real world I would end up with a green pool unless I run it at full speed so I save nothing. The other consideration is that the spa cascades into the pool and with a VS pump that would slow to a mere trickle, losing the aesthetic effect of it as well as becoming a problem keeping clean. The sales rep at Inyo Pools I spoke with on the phone said this shouldn't be an issue but that seems a little hard to believe for me.

    Then there's having enough flow/pressure to run the pressure side automatic vacuum at low flow rates possibly reducing the effectiveness of keeping the pool clean and it not being able to stay stuck to the walls as it does now. Non of my analysis considers this as I'm not sure how to account for it.

    One last thing is that I wouldn't be able to control this pump with a smart phone unless dropping another $280 on a control module and it would not be incorporated into my Autelis Pool Control with my Vera Home Automation Plugin. It might be possible to incorporate it into the Jandy but I'd have to shell out a pretty good chunk of change to replace the board, which
    to my knowledge doesn't support controlling VS pumps and
    is a Jandy Model 8156 Type RS-8 Combo circa 2003.


    So all that said, what do the experts here at TFP have to say about this?

  2. Back To Top    #2
    Mod Squad pooldv's Avatar
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    Re: Pump sizing for SWCG?

    You'll use less than 1 kWh running your VS pump at 1100 rpm for 6 hours. I run my VS pump at 1100 rpm for chlorinating with SWG, it has worked great for 5 years. Even in August Texas sun at 110 degrees. No problem. Others also run 1100 to 1200 rpm with their SWG. My pump uses 150 watts are 1100 rpm and other folk's pumps use 170 watts at 1200 rpm.

    If you bought a Pentair Superflo VS pump, 342001, you could control the speed using relays in your automation panel. 1 relay for each speed you wanted to use.
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    Re: Pump sizing for SWCG?

    Thanks.. WOW! That's even less than half of what I was calculating.

    So this one?

    Any thoughts on my other concerns?

    Do you have a link to setting up the relays? TIA.

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    Re: Pump sizing for SWCG?

    I've come to find out that the state of California now requires VS pumps when replacing pumps
    Not exactly. The law applies to filter pumps only (SPA jet pumps are excluded) and it also allows for two speed pumps or single speed pumps less than 1 HP.

    Residential Pool Pump Motors. Residential pool pump motors with a
    pool pump motor capacity of 1 HP or greater which are manufactured on
    or after January 1, 2010, shall have the capability of operating at two or
    more speeds with a low speed having a rotation rate that is no more than
    one-half of the motor's maximum rotation rate. The pump motor must be
    operated with a pump control that shall have the capability of operating
    the pump at least at two speeds.
    http://www.energy.ca.gov/2017publica...0-2017-002.pdf
    Mark
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    Re: Pump sizing for SWCG?

    Yeah. You're right. I read all that. I was just simplifying things a little bit in my lengthy discussion. That said, Do I really need a 2Hp Pump? If I can get by at a pretty low speed on a VS pump, why not just downsize to a 1Hp pump and be done with it?

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    mas985's Avatar
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    Re: Pump sizing for SWCG?

    Unless you running spa jets or a high volume water feature, you can get away with a very small pump.

    If I can get by at a pretty low speed on a VS pump, why not just downsize to a 1Hp pump and be done with it?
    Because a 1 HP pump running at full speed would use a LOT more energy than the VS at lower speeds (~10x). However a 1 HP two speed running on low speed would have a slightly higher energy cost than the VS but would achieve most of the savings of a VS at close to 1/2 the upfront costs. But with the rebate, it would be hard to pass up the VS.
    Mark
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    Re: Pump sizing for SWCG?

    I see. Thanks.

    What about the spill over cascading waterfall from the spa into the pool? Will I need to crank it up to run that properly? I have three pumps. One for the pool and waterfall cascading from the spa, and another for the spa booster pump. The other one either does the spa or shear descents. I suppose I need to take a closer look at the valve positions when in each mode so I know what pump serves what as I low speed pump may not work too well if it is pushing water to the spa and or descents by valving changes when triggered by the controller.

    Hmm.. I didn't really think of this in my initial inquiry here but now I have a little bit more investigating to do..

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    Re: Pump sizing for SWCG?

    One other thought comes to mind.. Time to heat the pool at low speeds.. I figure that goes up, or does the slower speed allow the water to enter the pool at a higher temperature so it heats in the same amount of time? The reason I ask this is because we do heat the pool in the spring and late fall when the weekends are going to be warm and the pool is a little bit cool/cold to swim. As an example, I heated our pool this past weekend because it was in the mid 60's but the air was hitting 90 and I hate to look at a cold pool on a warm day when I can be in it!

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    Mod Squad pooldv's Avatar
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    Re: Pump sizing for SWCG?

    Yes, that is the one. The relay set up is covered pretty well in the manual available here, http://www.pentairpool.com/products/...d-pump-464.htm

    Yes, it is very cheap to operate. Less than 12 bucks a month for me t run 24x7 at 10.25c/kWh.

    I use my pump to run solar, heat pump and/or waterfall. My pump is 3hp, but I run it at 1950 rpm for solar, it uses 550 watts. I also run my heat pump at that speed because solar is usually running when the heat pump is on anyway. My heat pump has a recommended entering and leaving water temp differential, I think it is 2C. You can tweak the run speed to achieve that. My pump provides plenty of water flow to the waterfall at 1950 rpm with only partial water flow diverted to the water fall, less than half, the rest goes to the returns.
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    Re: Pump sizing for SWCG?

    Cool. Thanks! Are you generating chlorine too with it? I'm pretty sure the algae influx in DFW is every bit if not more of an issue than here in SoCal.

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    Mod Squad pooldv's Avatar
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    Re: Pump sizing for SWCG?

    Yes, I have an IC40 SWG. No issue generating chlorine even in 110 degree August Texas sun. I even mostly maintained 28ppm SLAM level FC with my SWG when I was SLAMing a few years ago.
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    Re: Pump sizing for SWCG?

    AUX Inputs.jpg
    As can be seen here, I have a few AUX inputs unused. I need to physically check the availability of Relays I think to control the pump. From what I am gathering, and I just started to read the manual for the pump, is that I merely need to have these relays tell the pump what speed to run.

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    Re: Pump sizing for SWCG?

    Relays.jpg
    I'm pretty sure I can put one or more Z-Wave 24V relays in here to do exactly what I want. I use my VeraPlus Home Automation with the Autelis/Jandy plug in to control the pool now except for standard run and filtration times anyhow. The one linked is for one control but they have them with multiple controls too. I use this one for triggering my garage door.

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    Mod Squad pooldv's Avatar
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    Re: Pump sizing for SWCG?

    Yes, one relay for each speed you want to be able to select. I have speed 1 at 1100 rpm, speed 2 at 1950 rpm and speed 3 at 2500. Speed 1 is for filtering, SWG and solar standby, speed 2 is solar on and now also for my heat pump. Speed 3 is almost never used unless I want a lot of skimming action or something. But, you could just as easily select that manually at the pump if you are messing around with the pool.
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    Re: Pump sizing for SWCG?

    So depending on whether mine uses the same pump for the descents as for the filtration, I may want to have it so that when the descents come on which is not all the time, I can have it go to the next speed. Ingenious! I am getting less and less upset about having to put out more cash for the pump all the time. Invest some now and get savings on my power bill month after month for the life of the pump which I would think is 10 years or more..

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    Re: Pump sizing for SWCG?

    So maybe I don't need anywhere near 2 Hp for anything at all? The pump you recommended is 1 1/2 Hp and does what seems to be more than I need to do. Hmm.. Interesting. My thoughts is that the pool builder put in an oversized pump to limit call backs without regard to the repeating energy cost to the end user and by extension, society as a whole.

    - - - Updated - - -

    I just keep thinking about this..

    Could I maybe just get a larger VS pump and use just it instead of multiple pumps? Of course some re-plumbing would be in order to accomplish this.

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    Re: Pump sizing for SWCG?

    Is it safe to say that my pool guy is out to lunch when saying that running a VS pump on low speed will not properly chlorinate my pool?

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    Re: Pump sizing for SWCG?

    Quote Originally Posted by Sammy2 View Post
    Is it safe to say that my pool guy is out to lunch when saying that running a VS pump on low speed will not properly chlorinate my pool?
    First a pump doesn't chlorinate a pool. It does however, distribute it. And yes he is out to lunch.
    Mark
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    Re: Pump sizing for SWCG?

    Quote Originally Posted by mas985 View Post
    First a pump doesn't chlorinate a pool. It does however, distribute it. And yes he is out to lunch.
    I'm sorry. I didn't properly phrase that but I think you understood what I meant which is .. running a VS pump on low speed will not move enough volume of water across the catalyst to properly chlorinate..

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    mas985's Avatar
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    Re: Pump sizing for SWCG?

    Every SWG does have a lower limit for flow rate but most are pretty low, ~20-30 GPM. They all have an alarm when flow rate gets too low so you know right away.
    Mark
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