Pump Efficiency

[chem geek]

I currently spend a lot on electricity for my pool circulation/filter pump (and, to a lesser extent, for my pool sweep pump). The electric rates where I live have a marginal cost of about 32 cents per kilowatt-hour which is probably higher than many other areas of the country. Though the base rate is a lot lower, the cost of the pump is incremental and I count it after everything else.

I was wondering if there are more efficient pumps than the ones that I have. My pumps are 3-1/2 years old and the main one is a Jandy HHP 1.0 HP. The reason for the "high-head pump" is that I have a solar system for heating the pool and is on the roof that is probably about 15-20 feet above the ground. All of my pipes are solid PVC 2" (inner diameter) and are Schedule 40 (i.e. standard thickness). The distance from the skimmer and floor drains to the pumps is about 70 feet (not counting turns and elbows that I'm sure are there). There are separate pipes for the skimmer and for the two floor drains. There is one pipe for the returns (at least leaving the pump area).

I do not have a pressure gauge for suction, but my pressure gauge on the filter reads 15 PSI when the solar is not on and just under 30 PSI when the solar is on. I estimated head loss on the suction side using the PVC links on this useful web page and assumed 2/3rds (or less) suction losses due to the separate piping between the skimmer and floor drains. So using the pump curves in the manual that came with my pump, it looks like I'm running at about 90 GPM (45 feet of head) with the solar off and about 65 GPM (75 feet of head) with the solar on. This results in a turnover rate in my 16,000 gallon pool of 16,000/90 = 3 hours with the solar off and 16,000/65 = 4 hours with the solar on and that's about right as I normally try to run the pump only 8 hours a day (so guaranteed two turnovers per day). Though that may be more turnovers than necessary, it looks like the 3/4 HP pumps would be unable to handle the 75 feet of head with the solar on. Also, the recommended flow through the solar panels is 4 GPM per panel (min. 3 GPM; max. 8 GPM) and I have 12 panels so should have 48 GPM optimum (36 GPM minimum; 96 GPM maximum).

So as far as I can tell by looking at various pump curves (or tables) from different manufacturers, my pump is sized about right. From what I can tell, to figure out the effective maximum pump output, one has to multiply the horsepower (HP) rating by the service factor (SF) and then one can multiply by 745.7 to get Watts of output. Alternatively, one can look at the pump chart for the largest product of Feet of Head with Gallons per Minute (GPM) and multiply by 0.188165 to get the power in watts. For my pump, this maximum appears to be about 950 Watts (which implies a service factor of 1.27) while my actual output with solar on is about 900 Watts and with solar off it's about 800 Watts. [EDIT] The electric motor manufacturer for my pump (Franklin Electric) tells me that the Service Factor for the pump is 1.65, so though it might be useful to multiply HP by SF for comparing pump motors, it really doesn't relate to actual pump output. Interestingly, 1HP * 1.65SF * 745.7 = 1230 Watts and that number doesn't seem to relate to either electrical consumption nor maximum pump output. I did note your rule of thumb that the braking HP, or 1.65 in my case, is about equal to the maximum KW, which is 1.85 as specified on the motor. [END-EDIT]

The problem is that the pump seems to use about 1720 Watts of electricity when operating with the solar off so that is an efficiency of 800/1720 = 47%. The pump is rated at 8 Amps at 230V so that would be 1840 Watts so even the maximum efficiency at maximum output would still be only 1840/950 = 52%. Is this normal? Are there pumps available with much higher efficiencies?

I looked at some pump documentation, for example the Hayward pumps, and it can be misleading as they show Kilowatts (KW) along with Horsepower (HP) in the table, but this appears to be the equivalent output (i.e. 745.7 Watts/HP) and I could not find actual power consumption for these pumps. Some give electrical requirements, but are rounded so they are 10A or 15A and therefore don't give a good estimate of what the true power consumption would be -- not even at the maximum (and most efficient) pump output.

So, bottom line, is an efficiency of around 50% normal? Are there super-efficient pumps available? Is there an easy way to look up a pump's actual electrical power consumption?

Richard

[salinda]

Richard,

I live near you and I have a larger pool, so I had a worse problem. My pressures were similar....21 psi with solar off and 29 psi with solar on. (Actually your pressure difference seems too large...maybe you should consider using a bypass to decrease head loss in solar?) I just changed pumps this summer because I was running a 2 HP Whisperflo and my rate was up to 35 cents/kwh and I was spending $$$$. I also run long run times in the summer to let the solar work well, so it was even worse.

I went with a variable speed pump and my electric bill definitely dropped significantly. I'll private message you the information on the contractor I worked with but there are definitely caveats. Not cheap, but quick payback. Also, they made significant mistakes that I had to stay on top of. Good thing I know my pool....

I have also heard good things about the new Intelliflow pumps. I wish I looked into them more. You set your required flow rate and the pump motor adjusts to get you there, so you will see a difference with solar on/off.

As far as your original question, I don't know the answer except that motors don't run at full-efficency new and get less efficient with age. You can feel your pump running warm right? That is heat loss. I don't know what the standard efficiencies are.

[mas985]

Richard,

I live in CA as well and pay the same rates as you so I feel your pain. There is more pain to come as California is going to time of day charging so for those of us that have solar and would like to run during the day, our rates will stay high or may even increase.

Over the past couple of years, I have done a lot of research on pumps, hydraulics and energy usage. I cannot speak for all pumps, but I have done quite a bit of analysis on the Hayward Northstars since this is what I have.

First, it is difficult to know the exact efficiency of the pump since you would need the actual power efficiency curve which is difficult to come by. I have not found anyone at Hayward willing to give it to me. Power draw varies with head load so unless you create your own curve using a power meter or power company meter, you are stuck using the maximum draw. Also, current meters are inaccurate since they do not give you the phase between the voltage and current (i.e. power factor). Without a watt meter, the most accurate method is to use your power company's electric meter. Actually, this may be more accurate than a power meter since this is how they charge you so it includes any errors. I have counted the spins per minute with pump on and off and got a pretty accurate usage. You have to find the gearing ratio for your meter to convert to kwh.

Second, the kw rating for Hayward pumps are in euro-units for HP. You are correct that this does not include the pump efficiency and is the output power of the pump.

So using the maixmum current load for the pump and the formula:

Efficiency = (Head * GPM) / (3960/.746 * Max Input KW),

I estimated that my 1 HP Norhstar peaks at about 54% efficiency for 60 feet of head (86 GPM) which is pretty good. It is actually probably a bit better than that since the current draw will probably be less than the max.

I have not done this analysis for too many pumps but I know that the Northstar is one of the most efficient pumps out there.

Also, I have solar on a second story house but did not need to go with a high head pump since most high efficiency pumps are fairly high head to begin with. Anyway it probably does not mater since most pumps deal quite well with static head on the pressure side. During startup, head loss is basically the static lift since water flow is low until prime is complete which for a two story house is usually less than 30 feet. Nearly every pump should handle this quite well for the panel priming. After that, negative static compensates for the positive static so you left with only the dynamic friction loss in the panels themselves.

You seem to have quite a bit of friction loss if your solar system and may benefit somewhat with a solar bypass. A 15 PSI increase is not typical for a solar system which is usully between 4-8 psi. It could be due to your pump or probably the solar system. You don't need much flow through the panels to get good heat exchange so if you bypass some of the water, your friction loss will drop and flow rates will increase. This way you don't need to worry so much about high head pumps or extra strain on the solar panels.

A couple of useful formulas:

For Pumps

http://www.mcnallyinstitute.com/02-html/2-01.html

Note that when you lower the braking HP of the pump, the flow rates will be lower and thus the head loss will decrease. However, if you go with a 3/4 HP Northstar, for example, the braking HP is acutally 1.23 which is not much different than what you have but I suspect the power draw will be much less. So you should see a drop in energy use without increasing your turnover rate.

For the plumbing system, you can use Darcy-Weisbach equation which seems to be a bit more accurate than Hazen-Williams for swimming pool plumbing:

http://www.engineeringtoolbox.com/da...ion-d_646.html

Head loss ~ GPM ^2 / D ^5 (D = Pipe Diameter, ~ proportional)

This allows you see what effects there are from changing either flow rates or pipe diameter on head loss. The operating point for the plumbing system and the pump is where the head curve crosses the plumbing curve.

For even more energy savings, you might want to consider a 2 speed pump. Energy rate drops by 2/3 and flow rates drop by only 1/2 so for the same turnover, your energy use should drop by a 1/3 or 33% savings.

Poolplaza.com gives all of the pump head curves and some of the current draws for the pumps. For Northstars, I asked Hayward for the current draws but they would only give me the maximums for each. Here are the current draws for the full rated pumps.

HP SF BHP Kw
3/4 1.85 1.3875 1.265
1 1.85 1.85 1.794
1 1/2 1.6 2.4 2.346
2 1.35 2.7 2.714
2 1/2 1.35 3.375 3.3925

Note that a good approximation is that BHP = KW. So if you don't know the current draw, you can estimate it from BHP.

So from the head curves, here are the efficiencies:

Energy Efficiency

HP/Head 40 50 60 70 80 90
3/4 49% 54% 54% 44%
1 48% 53% 54% 51% 42%
1 1/2 43% 50% 52% 51% 45% 29%
2 44% 50% 52% 51% 47% 34%
2 1/2 40% 45% 49% 50% 48% 42%

(oops wrong table replaced with the correct one)

Good luck in your quest for energy reduction.

[chem geek]

Thanks for all of the useful info. The formula you had for calculating output power turns out to be the same as I had (except yours is simpler and more direct). I now see that the main flaw in my solar panel argument was thinking that the head loss for each panel would be cumulative while, because they are hooked up in parallel, the loss should actually be the same as a single panel -- on the order of 2-4 feet of head (1-2 PSI). I have the FAFCO Revolution which has specs at this link where they have a chart for the head loss for each panel. So most of the head loss is probably in the piping to and from the panels and these are indeed long runs since to equalize pressure, the distances going to and from each panel are made approximately equal so that it looks like the flow goes through the full length of the roof twice (since that's what the furthest panel has to do), so that's probably about 80*2 = 160 feet. Then there's the path to and from the roof to the pool house which is another 50*2 = 100 feet. I understand I can ignore the height difference (except for priming) since the pressure loss going up is cancelled by the pressure gain coming back down, but I still need to count the height length of 15*2 = 30 feet. So the loss is 290 feet of 2" (inner diameter) pipe at the 65 GPM should be about 6.8ft/100ft so about 19.7 feet of head (8.6 PSI) so the total expected loss should only be about 10-13 PSI or thereabouts (not counting the 90 degree elbows). When I said I am seeing 15 PSI, that is probably exaggerated and the actual amount may be around 13-14 PSI so it seems to be in the ballpark.

I think it's the size of my property, the layout of where the pump house is relative to the pool and the house, and having a long and narrow (as opposed to square) house has led to long runs and large friction losses. The pool builder should probably have used 2.5" pipe for the long runs -- I'm assuming that the pipe in the ground is the same as the pipes "entering into" the ground at the pool pump (and verified that the pipes going to/from the roof are also 2" internal diameter). If 2.5" pipe were used, then the friction losses would be less than half of what I am currently seeing. Too bad for me -- I wish I had known all of this when the pool was installed (not that I could have convinced a builder otherwise -- I suppose he wouldn't care so long as I paid for the difference in pipe cost). And the solar panel people should have also used the larger pipe as well (at least for the long return runs, if not the panels themselves which can't be changed).

I suppose there is a lesson for others in all of this. If you have long runs of pipe, be it to your pool or for a solar installation or both, then encourage your pool builder to use the largest pipe (especially for the solar) to minimize friction losses. This will likely let you use a smaller pump motor and save on energy costs. Does that sound about right?

As for my situation, a replumbing to the solar (and maybe of part of the solar) may not be out of the question since the pipes don't go under any sort of hardscape -- they run under dirt near the property line. Changing the lines to the pool is out of the question, but that's not where a large pump is needed anyway. I'll see about getting an estimate and see if something can be done that would save enough money to pay for itself in a reasonable period of time. Cutting down to a 3/4-HP unit would probably save me about 30% of pump costs or about $350 per year. I suspect the new pump plus labor is going to make the payback time a bit long, but we'll see.

I'll also look at pump-replacement-only options such as a variable speed pump since that will help in the hotter part of the summer when the solar turns off because the pool is warm enough. That's probably a more economical option (more expensive pump, but maybe a lot less labor).

Thanks again, salinda and Mark (mas985) for your helpful advice.

Richard

[mas985]

I suppose there is a lesson for others in all of this. If you have long runs of pipe, be it to your pool or for a solar installation or both, then encourage your pool builder to use the largest pipe (especially for the solar) to minimize friction losses. This will likely let you use a smaller pump motor and save on energy costs. Does that sound about right?

I think you could save a bunch with your existing plumbing. Small pipes are better suited to smaller pumps than large pumps. Unfortunately, you already have a small pump. To get smaller, you have to go with a 2 speed and run on low speed most of the time. Think Pentair has a 1/2 HP 2 speed which might work.

As for my situation, a replumbing to the solar (and maybe of part of the solar) may not be out of the question since the pipes don't go under any sort of hardscape -- they run under dirt near the property line. Changing the lines to the pool is out of the question, but that's not where a large pump is needed anyway. I'll see about getting an estimate and see if something can be done that would save enough money to pay for itself in a reasonable period of time. Cutting down to a 3/4-HP unit would probably save me about 30% of pump costs or about $350 per year. I suspect the new pump plus labor is going to make the payback time a bit long, but we'll see.

Agian, a large pump is not really required for your solar even with 2" pipes. I think it would be more cost effective to just reduce your flow rates with a 2 speed pump and save energy. Remeber that at low speed, the head loss (PSI) gets reduced by a factor of 4 so with solar you will have about 7 PSI and without solar about 4 PSI.

I'll also look at pump-replacement-only options such as a variable speed pump since that will help in the hotter part of the summer when the solar turns off because the pool is warm enough. That's probably a more economical option (more expensive pump, but maybe a lot less labor).

You can run at lower speed with solar (after priming) or without solar and save money.

Thanks again, salinda and Mark (mas985) for your helpful advice.

Richard

See comments above.

[chem geek]

Mark,

OK, I think I'm beginning to understand this. So at lower flow rates there is less frictional loss. OK, so let me work backwards from the optimal flow rate for the solar panels which is 4 GPM per panel and I have 12 panels so that means 48 GPM. The minimum recommended per panel is 3 GPM because efficiency drops, but that gives a minimum of 36 GPM.

So, at 48 GPM (instead of 65 GPM) the frictional loss in a 2" (inner diameter) pipe is 3.9 feet of head per 100 feet (instead of 6.8 feet of head per 100 feet -- that's a heck of a difference!). With my 290 feet of total round-trip run length, this is a loss of 11 feet of head (instead of 20) and I add 0.87 PSI or 2 feet (it's lower than before due to the lower flow rate) for a total loss for the solar panels of 13 feet of head which is about 6 PSI. That's a whole lot better than I have currently (with my current pump, the solar difference is 13 PSI or a head of 30 feet) and is closer to what you say is normal.

So now I can look at (full-rated) 3/4 HP pump curves to see if they can handle the base 15 PSI (yes, I know this will be less as well) plus this 7 PSI increment or 22 PSI total which is about 50 feet of head (instead of about 65 feet of head I had before). It looks like most 3/4 HP pumps will readily handle the 50 feet of head and even if priming needed another 15-20 feet, they could handle that as well (though at a slower GPM, which is fine for priming). After priming, the pump at 50 feet of head delivers 66 GPM which ironically is where I'm at today. So in practice what will happen is that the higher flow creates more friction and as you pointed out it's where the two curves intersect that will be what happens and this will clearly be somewhere between 50 and 60 feet of head, which is 66 to 51 GPM. The turnover will be slightly longer at around 5 hours instead of 4 (with the solar on), but that's fine.

Now, with the solar off, the pump will output less than before (it's a smaller pump, after all) so the GPM will be less than the previous 90 GPM and the feet of head will be less than the previous 45, but there is no question that whatever it settles down to, the pump will be fine. The bottom line is that a 3/4 HP pump should work fine for my pool system with the existing plumbing.

Gee, this is fun. Just goes to show how truly geeky I am. Did I roughly do the above correctly and would you say that I probably could get away with a 3/4 HP pump to replace my current 1 HP pump? If so, then it looks like I will save at least 500 Watts which translates to over $300 per year in savings. Looks like that would pay for even a high-quality expensive pump (e.g. the Hayward Northstar) in just a little over a year for the pump cost plus more years of operation to pay for the labor (which I have a feeling might add up to quite a bit, but even so this seems worth it).

Richard

P.S.

If I can find a 2-speed pump that was 3/4 HP and 1/2 HP or a variable speed pump (expensive! about $1000) that I could set and if it could be triggered by the same switch that the solar valve triggers on, then I could be even more optimal and save even more money when the solar was off. Any suggestions? I looked up the Pentair (that you mentioned) WhisperFlo that is 3/4 HP (full-rated) and it looks like the high-speed will work perfectly with the solar system, but the low-speed curves may not be good enough for the solar off situation, mostly due to the longer lines to the pool, though as you say at low GPM this should not be a problem. The pump curves are at this link. I noticed in these specs that the efficiency at the high-speed is not good (2-speed 3/4 HP full-rated is 14.6A * 115V = 1.68 KW which is almost as bad as what I have now; only the low speed 4.7A * 115V = 540 W would save money). I need at least 33 GPM flow rates to have an 8-hour turnover and that implies no more than about 12 feet of head (about 5 PSI). I'm not sure that will be attainable -- the pipe head might only be 3 feet of head or less (at 33 GPM), but I have no idea what the filter head will be at that GPM (actually, I just looked up some typical charts and the filter head is minimal -- even at 90 GPM it's 3 PSI and at normal lower GPM it's less than 1 PSI). If I just figure 1/3rd the amount of head (based on head loss tables of 50 GPM vs. 90 GPM) then I should be at around 5 PSI (12 feet of head). Maybe this will work out OK after all though it seems right on the edge and has longer turnover (8 hours vs. 5 hours) when the solar is off.

OK, now this is probably insane, but the Pentair IntelliFlow at this link automatically adjusts the speed to maintain a constant settable flow rate. It's an expensive pump (about $1500 online) but it does look like it could save a substantial amount of money. I could optimize for the 4 GPM per solar panel so 48 GPM with the solar on and it would automatically slow down to maintain that same rate with the solar off. It looks like it could save at least half or more of my main pump costs and that would be at least $500 per year. My main concern is how reliable this is since it's an expensive "toy" to break! I'd love a long warranty with this guy, but only comes with a 1-year warranty. I thought about using this single pump for the pool sweep as well (which would turn on with a valve), but I think the flow/pressure requirements for the pool sweep are quite high (which is why it has a dedicated 3/4 HP booster pump) so would be incompatible with the much lower flow rates in the rest of the system. Oh well...

The last radical thought I had was going down to a 1/2 HP pump since most have pump curves that can output 50 GPM at feet of head of 22 (Hayward Maxflo), 30 (Pentair SuperFlow, Hayward SuperPump), 40 (Pentair Challenger), 45 (Hayward Tristar), 50 (Pentair WhisperFlow). At the lower flow rate, the total head with the solar on will likely be less than 30 feet. Anything from the Pentair Challenger up should work out just fine, even with an extra 15-20 feet at lower GPM to prime the solar. I just have to be careful since some 1/2 HP pumps don't seem to use any less electrical power than 3/4 HP pumps though most do use less.

[Big_D]

Richard,
I went with and Intelliflo in June of last year when I built my pool. I also went with the Intellitouch system because of the Intelliflo. I move 40 GPM at under 600 watts. When I run my Cleaner it goes up to 70 gpm. When I want to make the spillway really move it goes to 100 gpm. When in the spa mode it is set for 100 GPM for spa or with the blower it is at 120 GPM. I stubbed for a solar but have not installed one yet, but when I do I will also program flow for that. What is great is the ability to tweak flow rates any time I want to. Power cost went through the roof this past year so I programmed for most efficient flow rates. I was shocked when I used a clamp on amp meter on my neighbors pump and saw how much power his was using compared to mine. I was less than 50% of the power for similar flow rates. I hesitate to quote the actual delta because pipes and plumbing are not the same. I feel very safe saying my power consumption is 50% lower than his for similar size pools. Get a clamp on amp meter and see what kind of current you are using now. When you slow down the flow rate the system is extremely efficient both in filtering quality and power consumption.

Back last Summer the 4x160 could be had for about 900.00. If you do not have the Intellitouch system the 4x160 is probably a better option as you loose most of the functionality of the full intelliflo without the intellitouch. I think the 4x160 does 4 settings vs intelliflo which has many. To be honest I could have used only 4 and been just fine.

I was recently asked if I had it to do all over again would I spend so much on the pump? Absolutely, I will recover my additional cost for the pump in a year with the power savings, so why not. The additional cost for the intellitouch system in 2 years. My pump has a 3 year warranty, maybe because I have all Pentair equipment but not sure. I thought the standard came with a 2 yr, but I am not 100% on that either. If you have any more Questions please PM me as I do not come here very often but would be happy to help.