pump selection with new solar system

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D

drwill

0
Apr 2, 2014
14
south fl
So I've read the hydraulics sticky and still have some questions.

I have a small kidney shaped pool - I've heard estimates of size ranging from 12,000 to 15,000 gallons, it's 15X30 ft, 6 ft in the deep end. The bottom drain was closed by a previous owner. There's just 1 skimmer line and 1 return, both on 1.5" piping. The pool was originally designed with the bottom drain feeding into the skimmer, so it seems to have never had more than 1, 1.5" line going back to the pump even when the bottom drain worked. The pool stays perfectly clear and seems to have decent enough circulation (it's screened in so the skimmer doesn't have much to skim).

The current pump is a hayward maxflo .75 hp, I've been told it's 10-15 years old although the model number (SP2805X7) is a current model. We thought about replacing the pump with a variable speed after all the solar installers said it wouldn't get the water up on the 1 story roof. Of course, it in fact does, the solar panels (8) are installed and the water is circulating as usual. I don't know if the flow is optimal for the solar - 4 gpm per panel (8X4=32gpm) but it is circulating and the flow doesn't feel much different than it did before the solar install. There is a suction side air leak, I think the pump may have been run dry at some point since the pool did have a severe leak when we bought the house last year (had to remodel the pool and repair the bond beam). Filter is a cartridge type, also hayward (c900). Pool pad is on opposite end of pool from where the skimmer and return are (probably 40 feet away at least).

I have no idea what the TDH is for this system and I know that no pump is going to push more than about 44 gpm with the plumbing restriction. So bigger is no better. I was thinking that a 1hp whisperflo would be good, guessing the tdh was maybe 70-80 for the system. However, looking at the performance curve for the current maxflo pump, it looks like it is incapable of pumping beyond about 55 TDH so I'm guessing the TDH for the system, even with the added piping for the solar, must be less than 55 TDH or there'd be no flow, right?

So, now I'm looking at the whisperflo specs and it looks like a full rated, energy efficient, .5hp will generate 40gpm at 60ft head. And the 1.5" plumbing won't support any more than that anyway so more pump would just be stressful on either the pump or the plumbing and my wallet, right?

I'm concerned about downsizing the pump and I want to run the system at or above 32gpm for the solar but it sure is looking like the .5hp whisperflo would work, or am I missing something?

Given the pump is so small and I would be running solar (and thus require the higher flow rate) I'm also thinking that a variable speed pump, or even a dual speed pump is not worth the cost. Electricity here in south fl is 11 cents at most anyway.

Can anyone chime in and let me know if downsizing the pump really is a good idea? Am I going to end up with a pump that can't work the solar efficiently or can't generate the pressure to overcome the static head to get the water on the roof in the first place? I feel like I know just enough to get myself into trouble but not enough to be sure at all in my decision.

Thanks!
 
:wave: Welcome to TFP!!!

I have a single 1.5" suction line and return line and a long run through 1.5" plumbing to my solar on a 1 story roof with 10 panels. My 1HP 2-speed Superflo runs the solar just fine and is a much smaller pump than the Whisperflo's you are talking about, but it is a little bigger than the Maxflo you have I think. {You have to realize that it is the wet end of the pump that affects the flow rate and not just the HP rating}

While you are correct that the solar is best while running on high speed, I take advantage of the low speed in the winter when I do not run solar and in the middle of summer when I do not need solar either. With the solar controller I have, it will automatically switch to low speed when the solar is not needed, so even in the early evening now if there are clouds or a breeze, it will switch the solar off and switch the pump to low.

With you power costs, a VS does not likely make sense, but a 2-speed could still help save yourself some money. Or just keep using what you have until it dies and then get a 2-speed.
 
Like Jason said a 2 speed may lower your electrical cost and allow you to run it on low speed when solar is not needed. As to your current flow level, you may want to invest in a flow meter to see where you are, Dave at tftestkits has a very nice flowmeter / check valve combination unit that he sells (I would have bought one if I had not already invested in a different type). Alternatively you can look at temperature rise between skimmer and return to see if you are operating at near peak solar efficiency (you can get a cheap aquarium digital thermometer that reads down to .1 degree F differences fairly cheap), in reality there is not much difference in solar panel performance from about 2 GPM per panel up to the optimal 4 or so GPM, it is important to look at the performance curve here not just optimal flow.
 
You have several misunderstandings when talking about TDH, though I don't think they change your final conclusions all that much. The main point is that TDH changes when the flow rate changes. Thus, even if you knew the TDH for your current setup, that wouldn't be the correct way to predict what some other pump would do, though it would be one step on the path of finding out. Another issue, the WhisperFlo is a much larger pump than you probably want, even the 1/2 HP model. HP is misleading, with other factors dominate what the "real" pump size is. WhisperFlo pumps are just about the largest pumps available at any given listed HP level.

You might be well served by a 1 HP two speed SuperFlo. The SuperFlo is fairly small for it's listed HP, enough so that a 1 HP SuperFlo is smaller than the 1/2 HP WhisperFlo. Also, as the others have mentioned, a two speed is a good idea. Even using the solar a fair bit on high, the two speed will pay back the initial investment in a reasonable amount of time.
 
I'm crunching the numbers and it still looks like the most cost effective solution is to run the .5 hp whisperflo, if it will be sufficient for my plumbing situation.

There's the 2 speed whisperflo but even the smallest one is .75hp which is probably too much and certainly draws enough current on high speed that it will be expensive to run it all day, in the summer (i.e. with the solar). Then there's the .75hp superflo dual speed (smallest size) and this draws the exact same current as the .75hp whisperflo (both 120v) but pumps less than the whisperflo .75hp 2 speed. So it's the same electrical usage but with less pumping power, so there's no point in that. Lastly, the 1 hp superflo 2 speed actually uses less electricity than the .75hp superflo (low speed uses same KW but highspeed actually uses less KW for the 1 hp pump!). So the 1 hp superflo appears to be both stronger than the .75 superflo while also using less electricity at least at high speed (this from the specs page on the pentair website).

Problem is, the 1hp superflow 2 speed still costs more to run than the .5hp whisperflo on an annual basis. I made some assumptions here, I think they're safe ones. I'm assuming a run time for the .5hp single speed of 10 hrs a day all year long. Obviously, it will be run less than that when the solar is off either right in the middle of summer if the pool is too warm or in the middle of winter when there's just no point in trying to heat the pool. The current pump (which flows less gpm) will keep the pool clear, easily, with 6-8 hours a day in the summer and as little as 4-5 in the winter. So 10 hours a day all year long is a worst case scenario, from a cost standpoint, for the single speed.

For the dual speed pumps I assumed a run time of 10 hours a day for 9 months out of the year - same as the single speed pump - and a run time of 15 hours a day for 3 months out of the year, 9 months at high speed and 3 months at low speed. Because the 1hp superflo draws 6 amps at high speed it's busy racking up the charges during the summer (10 hours a day) but is then trying to recoup that the other 3 months running 15 hours a day at low speed (2.3 amps) but the savings in the winter months aren't enough to offset the expense accrued the rest of the year. Even if I assume the low speed is used for 4 months and high speed for 8 the .5hp whisperflow still wins easily, this is also true at 6 months highspeed and 6 months low speed (assuming 4 months winter and 2 months midsummer I won't want/need the solar).

Obviously, I can mix and match the speeds during the day but then the math becomes more complex and the assumptions about my usage pattern more dubious. It's also worth noting that the 1hp superflow is capable of 35 gpm (my minimum target) at 65 TDH, the .5hp whisperflo appears to have exactly the same capability. So all I gain with the 2 speed 1hp superflo is a low speed setting, which is nice, but it won't save enough money to offset the additional cost of running the superflo at high speed. Maybe, under some circumstances, it might.. but I don't think the savings are going to be noteworthy. The Whisperflow .5hp single speed is only costing, at most, $425 a year to run (10 hours a day all day which is way more than it will be run, most likely). If I didn't plan to run the pump full speed for the solar, then yes, I would agree that a 2 speed pump would definitely save money. The .5hp single speed would cost me about $36 a month to run while the 1 hp superflo at low speed (adjusting the time up to 15 hrs a day to account for lower flow) costs about $9 less a month. That's $120 a year I would save with the dual speed if I never turned it up except for the occasional vacuuming.

So I have to return to the original question, how do I know if the .5hp whisperflow is going to be enough? Particularly to overcome the static head to get the water up on the roof in the first place? It looks like it's a stronger pump than the .75hp maxflo that's on there now, so that should be reassuring, right?

I don't particularly want to speed the money on a flow meter, especially if I'm not going with a variable speed pump. If I install some vacuum gauges in the right spots, will that tell me what I need to know?
 
Also, good point about the TDH being responsive to flow. So there's going to be an equilibrium between what the pump can push (flow) and the TDH that is achieved, and this is going to be a consequence of both pump power and plumbing capacity and the latter is unknown. All I care is that the pump gets to 32 gpm, more than that would be excessive on the plumbing and the wallet.
 
Don't believe all the numbers for current draw, etc that you are finding ... there are mistakes on the websites and those are max draw which is not what they actually draw. To make matters more confusing, the amp draw is a function of your head loss, which you now know is difficult to estimate.

Also, it is VERY hard to find the 3/4HP 2-speed pumps (which are 115V pumps) and if you do they cost more than the 1HP 2-speed (which are 230V pumps).

Bottom line is the more water you move, the more power it uses. The small whipserflo will move more water than the Superflo therefore it will use more power. And on low speed, you will move 1/2 the water at 1/4 the cost compared to high speed.

I appreciate your efforts to try to make sense of all this, but I think you are over thinking things ;) ... and making cost calculations with flawed data.
 
I agree I'm probably overthinking this and I see how the data are flawed, but an estimate, even a flawed one, is better than pure speculation. I'm not positive that the whisperflo will cost more to run than the superflo on high speed. The current draw says just the opposite. Even if the data are flawed such that the current draw for the whisperflo is underestimated and the draw for the superflo is overestimated, maybe the actual usage would be the same, but it's also possible that the opposite is true and the whisperflo is even more efficient that the max draw figures suggest. The pumps vary in efficiency and no doubt the whisperflo is the better model and probably enjoys better parts and a better design which might explain how it is able to move about as much water as the superflo while (possibly) using less electricity.

I'm leaning toward the better pump, rather than the two speed. I think the two speed (or variable speed) offer good savings when the single high speed is a large motor. As it is, the .5hp single speed uses very little electricity so there isn't much - less than $10 a month - to be saved by a dual speed pump set to 'low'. As we all know, the savings that come with reduced speed are diminishing. I'm going to wait a month or two and see how hot the solar gets the pool, and thus how often I'll need the higher flow. Last year my wife complained in July that the pool was too cold and it is shaded and screened so it is cool (not terribly so in my opinion, but it's hers that counts anyway).

Can we at least agree on whether or not the superflo 1hp dual speed and whisperflo .5hp single speed will be sufficient for the job? Both would be notable improvements over the .75hp hayward maxflo on there now, correct?
 
The Whisperflo is a different hydraulic design than the Superflo. It is designed to move more water (which MUST use more electricity), that does not make it a "better" design or with "better" parts. It is designed for applications where more flow is needed ... at a higher initial cost and higher running cost.

The savings at running at lower speeds are not diminishing ... it is an exponential scale so the lower the RPM, the higher the savings ... to a point. The most efficient speed is around 1000 rpm which is well below the low speed of a 2-speed motor. Of course you could buy one of the smaller VS pumps and then you could run down at the lower speeds when solar not needed.

To your question:
Looking at the performance curves, the 0.5HP Whisperflo will move slightly more water than the 1HP Superflo at the same head loss. So, both will perform similarly and be adequate.

That said, since they are moving the same amount of water, they will also thus use about the same amount of power to do so. Since the prices of the 0.5HP Whisperflo and the 1HP 2-speed Superflo are the same, and they use the same amount of power on high speed for solar ... I do not understand the logic of not enjoying the savings on low speed when solar is not needed.
 
I think you may be over focusing on cost for your expected run times, also do you have a solar controller in the system? For most people a good solar controller can greatly improve the heating efficiency of a set of solar panels, by only letting them run when heat is available, and not letting them run when they would act like heat radiators. (for my area this is important due to summer afternoon thermal thunderstorms) In the case of most locations you can realisticly expect closer to 6-8 hours of solar heating per day most days rather than the 10 hours you use for your calculations due to clouds, rain, etc. (even wind) when using a solar controller.

Ike

p.s. mine is set up to run the 2 speed pump on high when solar is operating, then switch to low otherwise.
 

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drwill said:
but an estimate, even a flawed one, is better than pure speculation
Click to expand...
True, however jblizzle is not speculating, he is working off a solid understanding of how the pumps work. Your estimates using specified peak current are way off. Real world power draw will be very different and probably not even close to proportional.

If you want real world numbers, the California Energy Commission measures the energy efficiency of the various pumps. Using their curve-C results, the 1/2 HP WhisperFlo has an energy factor of 3.4, the 1 HP SuperFlo on high speed has an energy factor of 2.9, while on low speed it is 6.9. Energy factor is essentially GPH/watts, or gallons moved per watt hour. They also show that the 1 HP SuperFlo (SF-N2-1A) is an ever so slightly larger pump than the 1/2 HP WhiperFlo (WFE-2). These numbers vary somewhat with details of the plumbing system, but they remain essentially proportional within the range we are dealing with.

So the WhisperFlo is a "better" pump in some sense, moving more water per watt when both pumps are on full speed. But the SuperFlo more than doubles the performance of the WhisperFlo when running on low speed.
 
drwill,

I think you would be better off with another MaxFlo. The pump you have now is actually a smaller pump than the Whisperflo WFE-2. For typical 1.5" plumbing, here are some numbers to consider:

APSP Curve-A Plumbing

MaxFlo: 46 GPM @ 941 watts = 2.93 Gallons/watt-hr
WFE-2: 55 GPM @ 1230 watts = 2.68 Gallons/watt-hr

Your current pump is actually more efficient than the Whisperflo. Now you may want to replace it and that's fine but another MaxFlo wouldn't be a bad choice. Assuming that was working for you to begin with.

I have both pumps in a spreadsheet database if you like to fool around with spreadsheets. It is in the Pool Tools link in my sig.
 
These CEC ratings are really helpful. Wish I had seen these earlier. I know the 'c' ratings aren't right, but should I be looking at the 'a' or 'b' ratings? I have 1, 1.5" line coming from and going to the pool, plus solar on my 1 story roof (8 panels). There's 1 return eye. The maxflo on there now seems to work so-so but I would expect there to be not much skimming action with much less flow. That and the marginal cost savings from a 2 speed pump (vs. a very small single speed pump) make me inclined toward an energy efficient single speed in the .5hp range.

I was originally thinking pentair for the variable speed but I'm going to go dual speed or single speed, is there a better brand? Hayward's top of the line "tristar" in .5hp has a energy factor (curve a) of 3.23 which looks really good. Plus, the flow on curve b, which would be worst case scenario, is right at 33 gpm which would be the sweet spot for my solar system.

Any other pump suggestions besides the maxflo, superflo 2 speed, whisperflo single speed, and maybe this tristar? Is jandy worth looking into?

My pump now is a maxflo but the model number isn't in the CEC or APSP sheets, it's SP2805X7. Maybe it is outdated. There is a brochure from Hayward, though, where it is listed. http://www.hayward-pool.com/pdf/literature/Max-Flo_sellsheet.pdf

Edit: I read somewhere that 1.5" piping simply will not flow more than 44 gpm, any truth to this? If so, seeing as how many pumps, even small ones, are well into the 50 gpm range on curve A, does this suggest I should look at curve b ratings instead? For curve b, they're pretty much all under 45 gpm, which if the 1.5" rule of thumb is correct then perhaps curve b is calculated with the same conditions as what I have in my pool.
 
the 44 GPM number is based on an outdated engineering design number that was concerned with extremely long term friction wear in pipe joints, from back when not much was really known about PVC pipe. And was based on wear characteristics of metal pipe.
 
Curve-A is typical of 1.5" plumbing which is why I posted those numbers. But if you want something that is closer to your own situation, you can use the Pump Pump Tools spreadsheet.

My pump now is a maxflo but the model number isn't in the CEC or APSP sheets, it's SP2805X7. Maybe it is outdated.
Click to expand...
The Pool Pump Tools workbook contains data from both the CEC & APSP data sets but it also has a few extra pumps including yours.

And as others have pointed out, so called flow limits in pipes are not flow limits at all and are just recommendations to limit head loss and water hammer. There is no physical limit to flow in pipes assuming you can get a pump big enough to deliver that flow. However, pumps do have flow limits as well as pressure/head limits.
 
ok, I may be sold. This pump, as it is, is working the solar well enough. We had a pool party today and the water was perfect. When the pump goes (hopefully) soon, I'm going to upgrade to something a bit better, probably a 2 speed. I really appreciate everyone's input, this has been insightful.

To answer some earlier questions, I do have a solar controller (aquastar II) which diverts flow to the pool when the solar is not hot enough. And in South FL I think on a good day, mid summer, it'd be easy to get 10 straight hours of sun, maybe even more. Being so close to the equator, the days are about 12 hours long at midsummer.
 
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