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Thread: VS pump .. calc minimum RPM using filter psi?

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    VS pump .. calc minimum RPM using filter psi?

    Split from vs-pump-calc-minimum-rpm-using-filter-psi-t40667.html Butterfly


    Hi,

    I just installed an IntelliPro (not the IntelliFlo) pump for my 15,000 gallon pool in Florida, and I have the same questions as the original poster. I was hoping someone could look at my information and recommend pump speeds/times for my situation.

    I have two, 2" suction lines that run through a spacesaver Jandy valve (set so both lines are fully open)and then into the pump. One line is for skimmer which is about 55' away. The other line is for the drain which is about 60'. The filter feeds into a 48 cubic foot Hayward DE filter (DE-4800) with a Selecta-Flo valve (SP-740-DE) with 2" piping. Unfortunately the pool builder downsized the piping out of the filter to 1 1/2" (which pisses me off) going into and out of a Hayward chlorinator. This is split with another spacesaver Jandy valve into two 1.5" return lines (only one of which is usually selected). One return line goes to the four nossels in the pool - the first of which is about 40' away. The second return line goes to a couple water feature fan-out sprayers than make an arched, fanned out sort of fountain back into the pool. I ususally leave those off so that the pressure is fully used to keep the water circulating, but maybe I should turn them on to increase the pump's flow rate?

    I took some pressure readings last night. The pressure guage on the top of the pump is about 46" above the water level. Here is what I got:

    750 rpm: the scale does not move so I will guess 1 psi
    1000 rpm: 2 psi
    1500 rpm: 3 psi
    2000 rpm: 5-6 psi
    2500 rpm: 10 psi
    2600 rpm: 12 psi (I set this as the max rpm since the rep. told me this was equivalent to the old 1.5 hp pump I had)

    I do not have any solar or other heater setup and I no longer use a suction pool cleaner.

    The pool stores seem to recommend two turnovers per day, but other places say you only need one. I am thinking one in the winter is probably ok, but maybe 1.5 or 2 would be better the rest of the time (really we only have an 8 month summer and a sort of 4 month fall/spring here in Florida). If anyone has input on this I would appreciate it. I used to run my old 1.5 hp pump for 6 hours in the winter and 8 hours in the summer.

    I am wondering if it is better to run the pump longer at a lower speed to keep the algae away, or if a low rate (like the 750 setting) is too low to circulate the water well enough. At the 750 setting barely any water comes out of the 3rd and 4th return points. Maybe, it is better to use two or three speeds? Of course, since I bought one of these expensive, multi-speed pumps, I want to use the most energy efficient rpm/time setting(s) to save on my energy bill - while keeping my pool properly filtered and circulated.

    So, I wondering what flow rates I should be getting at a given rpm with my pool, and how I should configure the pump to run.

    Sorry for the long post, but I wanted to give as much information as I could.

    Thanks,
    Andy

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    mas985's Avatar
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    Re: VS pump .. calc minimum RPM using filter psi?

    Here are my estimates:

    Flow Rate (GPM) = RPM / 39

    Head Loss (ft) = 0.0103 * GPM^2

    Note that if you have a check valve in your plumbing, then the error at lower RPM will tend to grow and the actual flow rate will be less but the model seems to match fairly well down to 1500 RPM.

    As for turnover, I go to a half turnover per day in the winter and usually no more than one turn per day in the summer. Turnover is mainly just for asthetics to remove the debris from the water and as long as you run long enough for circulation and chlorination, you can reduce runtime as much as you want to depending on your tolerance for debris.

    Also, you generally don't want to go below 900 RPM as that is where the Intelliflo starts to get inefficient again.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: VS pump .. calc minimum RPM using filter psi?

    Quote Originally Posted by mas985
    Here are my estimates:

    Flow Rate (GPM) = RPM / 39

    Head Loss (ft) = 0.0103 * GPM^2

    Note that if you have a check valve in your plumbing, then the error at lower RPM will tend to grow and the actual flow rate will be less but the model seems to match fairly well down to 1500 RPM.

    As for turnover, I go to a half turnover per day in the winter and usually no more than one turn per day in the summer. Turnover is mainly just for asthetics to remove the debris from the water and as long as you run long enough for circulation and chlorination, you can reduce runtime as much as you want to depending on your tolerance for debris.

    Also, you generally don't want to go below 900 RPM as that is where the Intelliflo starts to get inefficient again.

    Thanks for the great info and quick reply Mark.

    I do not have a check valve so hopefully those values will hold reasonably true at lower RPMs.

    Since you mention the Intelliflo gets inefficient blow 900 RPM, then I was thinking I could just set it at 1000 rpm for 10 hours - which (using your rpm/39 specifier) looks like it would turn over just over 1x. I take it this would pretty much be the most efficient way to run the pump. Do you think that would be enough velocity to effectively circulate the water throughout the whole pool (no dead spots)? I didn't know if it would be better (circulation wise) to run at a higher rate for some period and then go down to the lower rate - or just run at a little bit higher rate the whole time (1500 for 6 1/2 hours maybe). But, if it doesn't really matter, then I guess I would be better off running slower and longer to keep the water moving over a greater time period and reduce energy consumption.

    Is the intellipro pretty much equivalent to the intelliflo in terms of flow rates and efficiency? I believe the only real difference is the design of the wet end. I went with the "pro" over the "flo" on the recommendation of three different pump installers. They seemed to like the design of the wet end better and thought it would hold up longer under the Florida heat/humidity/UV conditions.

    Lastly, I notice at the lower speeds that a little bit of air accumulates in the basket area over time when the pump is running at lower speeds. I called a rep and asked about it and he said that was normal. If it is a leak in the suction line then it would have to be a very small one. I used a 10" long 2" wide PVC pipe to connect from the Jandy valve to the input of the pump - as recommended to avoid cavitation, but I wondered if that could have anything to do with it. I do notice at lower speeds the pump makes just a little bit of sound like there might be something moving around it it. I do not notice the sound at higher rpms though. I have read that if it sounds like there is gravel in the pump then that is a sign of cavitation. I wondered if you had any thoughts on this.

    Thanks again for the great information.

    Much appreciated.

    Andy

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    mas985's Avatar
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    Re: VS pump .. calc minimum RPM using filter psi?

    Quote Originally Posted by dat
    Since you mention the Intelliflo gets inefficient blow 900 RPM, then I was thinking I could just set it at 1000 rpm for 10 hours - which (using your rpm/39 specifier) looks like it would turn over just over 1x. I take it this would pretty much be the most efficient way to run the pump.
    Yes


    Quote Originally Posted by dat
    Do you think that would be enough velocity to effectively circulate the water throughout the whole pool (no dead spots)? I didn't know if it would be better (circulation wise) to run at a higher rate for some period and then go down to the lower rate - or just run at a little bit higher rate the whole time (1500 for 6 1/2 hours maybe). But, if it doesn't really matter, then I guess I would be better off running slower and longer to keep the water moving over a greater time period and reduce energy consumption.
    Hard to say. Every pool is different so some trial and error is probably the best way to figure it out. I find that my skimmers work a lot better at high speed.



    Quote Originally Posted by dat
    Is the intellipro pretty much equivalent to the intelliflo in terms of flow rates and efficiency? I believe the only real difference is the design of the wet end. I went with the "pro" over the "flo" on the recommendation of three different pump installers. They seemed to like the design of the wet end better and thought it would hold up longer under the Florida heat/humidity/UV conditions.
    My mistake on the that one but their performance is pretty much the same although the Intellipro does seem to have a little bit better energy factor on lower speeds.



    Quote Originally Posted by dat
    Lastly, I notice at the lower speeds that a little bit of air accumulates in the basket area over time when the pump is running at lower speeds. I called a rep and asked about it and he said that was normal.
    That seems to be the norm for both VS and two speed pumps on low. If it is only a little bit of air, it is most likely outgassing of dissolved air in the water but it could also be a very small leak. The pump basket lids seal better under higher suction.



    Quote Originally Posted by dat
    I do notice at lower speeds the pump makes just a little bit of sound like there might be something moving around it it. I do not notice the sound at higher rpms though. I have read that if it sounds like there is gravel in the pump then that is a sign of cavitation. I wondered if you had any thoughts on this.
    It is nearly impossible to get get cavitation at low speeds (not low enough pressure) but much more likely to get it at higher speeds. It could just be something is loose in or around the pump.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: VS pump .. calc minimum RPM using filter psi?

    Thanks again Mark. You have been really helpful.

    The skimmer for my pool has never really done much of anything in terms of removing gnats, pollen, and dirt/dust floating on the surface. The pool is screened in so that is about all I get in it - which I end up mostly cleaning out myself. That being the case, I guess I will start out with the 1000 rpm setting for 10 hours and see how that works out initially.

    I appreciate the info about the outgassing and cavitation as well. I'm glad to hear that it is most likely not a cavitation issue.

    Thanks,
    Andy

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