Pump efficiency and capacity

[RJM]

Hi,
I am interested in getting a new pool pump to save on electricity. I have found very little real information on how to choose a pump, except for Mark's excellent posts and spreadsheets. I'm learning some from them, but I have a couple of questions at this point. I am trying to figure out which pumps are adequate for my pool and most efficient. The pool pump tools spreadsheet calculates my return head at 27.5' which is similar to other ways I calculated it. My plumbing corresponds to curve C. To look at efficiency and lifetime cost, I am using the Energy Cost sheet. I entered a target turnover of 1/day. I entered the same RPM values for all the pumps I am trying to compare (3450 high and 1725 low). Is this a fair comparison?

With these settings, The TriStar VS 1.85 URHP, MaxFlo 0.75 URHP, and MaxFlo VS 1.5 URHP pumps are the least expensive (monthly and lifetime) pumps that I have investigated for our pool. I am just not sure if my comparison method is correct; I think it might be underestimating the efficiency of VS pumps. Also, I am wondering if there's a way to calculate my present pump's efficiency on the spreadsheet. I was going to try to enter its data on the pump data sheet and add the links, but I don't have much of the data.

As a side note, I have also looked at the CA energy commission's energy factors for pumps, which are a standardized measure of W/gallon moved. However, the flow rate in the ratings varies tremendously, and it ranges from 13-16 GPM for the 7 most efficiently rated pumps. Since this flow rate is way too low for my pool, I am not sure if these ratings mean anything for my application.

 

[JasonLion]

Welcome to TFP!

That isn't really the correct way to compare things. If you really want to do the whole, rather complex, calculation you need to find the most efficient speed for each pump and compare gallons per watt at that speed. One turnover per day is not important, or relevant, for a residential pool. Ideal speeds are typically somewhere around 1,000 RPM. And so on. Or, if you have some specific GPM requirement, for example from a heater, you need to compare the various pumps all running at that specific GPM rate. But really there is not a lot of point in doing all that yourself unless you just enjoy that kind of thing.

At the high electrical rates common in California the best choice is normally either a MaxFlo VS, or if higher maximum flow rates are required an EcoStar. The MaxFlo VS isn't quite as energy efficient, but it's lower up front costs more than make up for it's only very slightly higher electrical costs. However it peaks out well below the flow rates that can be achieved with the EcoStar, which might be required for a spa or larger waterfall. In rare cases, when very high flow rates are required nearly the entire time, the IntelliFlo has a very slight advantage, but that situation is not very common.

Finally, at the most typical very low flow rates normally used for simple circulation, the energy efficiency differences between several of these pumps often get drowned out by other factors, like up front costs and automation options, as the cost savings differences may amount to only a couple of dollars over the life of the pump.

 

[RJM]

Welcome to TFP!

That isn't really the correct way to compare things. If you really want to do the whole, rather complex, calculation you need to find the most efficient speed for each pump and compare gallons per watt at that speed. One turnover per day is not important, or relevant, for a residential pool. Ideal speeds are typically somewhere around 1,000 RPM. And so on. Or, if you have some specific GPM requirement, for example from a heater, you need to compare the various pumps all running at that specific GPM rate. But really there is not a lot of point in doing all that yourself unless you just enjoy that kind of thing.

At the high electrical rates common in California the best choice is normally either a MaxFlo VS, or if higher maximum flow rates are required an EcoStar. The MaxFlo VS isn't quite as energy efficient, but it's lower up front costs more than make up for it's only very slightly higher electrical costs. However it peaks out well below the flow rates that can be achieved with the EcoStar, which might be required for a spa or larger waterfall. In rare cases, when very high flow rates are required nearly the entire time, the IntelliFlo has a very slight advantage, but that situation is not very common.

Finally, at the most typical very low flow rates normally used for simple circulation, the energy efficiency differences between several of these pumps often get drowned out by other factors, like up front costs and automation options, as the cost savings differences may amount to only a couple of dollars over the life of the pump.

Thanks! I appreciate the recommendation. I think that the Energy Factors are the complicated calculation that have already been done for me by the CA Energy Commission. The most efficient pump they rank is the ECO H2O-VS-100003-BK at a stunning energy factor of 40, flow rate 16 GPM for curve C. I entered 1 turnover per day just to homogenize things. I realize I might not need that much, but ultimately the pump's purpose is to run the water through the filter, so there must be some minimum turnover goal no? At its most efficient setting the Eco would put all the water through the filter in about 28 hours, not that bad I guess. I realize that this is a pretty complicated calculation involving several variables including how long the pump is run.

 

[JasonLion]

No, turnovers are not important at all. That is an old rule of thumb from commercial pools that simply doesn't apply to residential pools. For a residential pool, surface debris clearing is normally the limiting factor, with basic filtration finishing in much shorter times than debris clearing.

The CA energy commission results don't tell you the ideal RPM to get the lowest possible gallons per watt. They tend to pick fairly arbitrary RPMs to test at, which are are almost never directly comparable between pumps. You really need to compare the pumps either at their ideal speed or at a speed that provides your specific GPM requirement, neither of which are likely to appear in their charts. Those numbers can be derived by fitting a pump energy curve to the points they provide and extrapolating the pump efficiency at other RPM settings, but can not be read directly from their table.

Because energy efficiency is primarily a function of motor speed, with lower speeds being more efficient, the pumps that got tested at lower speed appear to be superior. But as it turns out it is often some other pump, which was not tested as speeds that low, which is actually better. There are some additional considerations that can affect the rankings in non-intuitive ways, but that is by far the single largest factor preventing direct comparisons using their data.

And finally, as I mentioned before, for the super efficient pumps when run at lower speeds the differences between the pumps tend to be drowned out by other considerations. The lifetime energy costs get so low that even apparently significant advantages in energy efficiency can work out to less than the up front cost differences when totaled over the full lifetime of the pump.

 

[RJM]

Thanks - I have been thinking that about the CA rankings. And point taken about the upfront costs and the small differences in energy use.

I guess I see your point on the turnovers if you're comparing pumps with roughly similar capacities. But surface debris cleaning isn't something I can calculate, which would seem to leave one in the realm of relying solely on expert opinion for selecting a pump. Unless you have a heater like you say (which I do, but it's broken and we haven't used it so we should take it out I guess...).