Do I need/want a two speed pump?

[bobnamy]

I am looking into a 27' round AGP. At 54 inch wall height it has approximatley 17,000 gallons. I do not plan to have any additional water features other than solar panels at the ground level near the pool. Initially I will use a manual vaccum (kids) but may switch to an auto cleaner eventually (kids refuse).

I am assuming that the pool will come with 1.5" flexible piping (Do I have choice?). I plan on using a 21 or 22inch sand filter. With that equipment, it appears that the minimum gpm is 36 gpm for an 8 hour turnover. The maximum flow for the filter is about 50 gpm. The 1.5" piping has a maximum flow rate of about 42-44 gpm.

I am assuming that the head on the AGP will be around 30 feet of pressure (from what i have read), and that the solar panels will not effect the head pressure much becasue they are at the same level as the pool.

I can get a .5 hp pump that will push 33 gpm. A .75 hp pump that will push 45 gpm @30feet head, and 30 gpm @ 40 feet of head. The .5 hp seems too small. The .75 seems about right, assuming the solar panels reduce the flow/increase the head a little.

Would I benefit from a two speed pump? I can get a 1hp 2spd pump that pushes 75 gpm hi speed, and 38 gpm low speed, or a 1hp 2 spd pump that pushes 68gpm hi speed and 34 gpm low speed. My question is, what do I need the high speed for? Either pump at hi speed will exceed the max flow rate of the sand filter. Is that a problem? Will manual or auto vaccuums work at 35-38 gpm?

Would one of these 1 hp 2 speed pumps, running at low speed and pushing 35 gpm, cost less to operate than a .75hp single speed pump pushing 45 gpm or slightly less?

The pumps that I am referring to are the Hayward Powerflo II .75 hp single speed, Hayward powerflo matrix 1 hp 2 spd, and a Pentair Dynamo 1hp 2 spd.

 

[AnnaK]

We have a Pentair 1.5 hp 2-speed pump on a 12K AG pool with a 19" Hayward sand filter.

We chose the pump because we have a lot of dog hair in the pool and wanted the power to better circulate it into the skimmer. We run the pump on LO for 7 hours at night. We run it on HI to vacuum when necessary and for an hour after the dogs have been in the water. Also to backwash/rinse. We backwash when there's a 5 psi increase with the pump set on HI. Under normal usage we backwash once every 6 - 8 weeks. We use skimmer socks which cut down enormously on debris in the filter.

On the LO setting the pump runs very quietly and, at 6 hours out of 24, the increase in our electric bill during swimming season is minimal.

AnnaK

 

[mikester]

I've got mixed feelings about our 2 speed pump. On the one hand, yeah it's very quiet and cheap to run it on low speed. But it just doesn't seem to do as good a job filtering and skimming the surface on low speed.

The most annoying thing about the low speed pump is how it works with our raised spa. The spa has a single line with a check valve, which takes some circulation while the valves are set to the pool, so the spa doesn't become stagnant. On low speed, there isn't enough pressure to work the check valve correctly, so it just barely opens it, and then water backflows out of the spa into the pool.

We try to get around this by drawing from the pool and returning all the flow to the spa and let it spill over back into the pool, but then we don't get good enough circulation in the pool and stuff just falls to the bottom instead of getting pushed to the skimmer.

These could all be just related to the design of our pool - it's about 15 years old and never was designed with a 2 speed pump in mind. Anyway, I find myself adding more and more to the high speed run time and running it in low speed less and less.

 

[duraleigh]

Either pump at hi speed will exceed the max flow rate of the sand filter. Is that a problem?

Yeah, that's not too good. Overdriving a filter is just genearally a bad idea. Conversely a filter that is around 20-30 larger in GPM than the pump is a VERY good idea.....they work better together.

 

[JasonLion]

Ignoring the too large for the filter issue, a two speed pump on low can save electricity compared to a noticeably smaller pump on high.

 

[bobnamy]

So then, I really have no use for a 2 speed pump? Even the smallest 2 spd pump at high speed will exceed the max flow rating of the 22" sand filter, unless the 1.5" piping will restrict the flow to around 45gpm. But restricting the flow to less than the pump capacity is not good for the pump, right? So, what? No 2 speed pump for me? Should I just get a single speed pump at like .75 hp , or should I still get a 2 speed pump and just run at low speed only (I think that costs less to run)?

Will the slower flow rate effect vacuuming efficiency?

 

[krcossin]

I considered the 2 speed pump, I opted out due to cost and overpowered high speed, put the correct single speed pump on a good timer so it's not running 24/7. Silent at night, runs in the morning and early evening.

 

[bobnamy]

Ok, I have an additional question. I am still not sure what I would even need the hi spped for, other than possibly the 1hp 2spd pump running on low will cost less to operate than a 1sp .75hp.

If I get a large enough sand filter that could handle the 68gpm on hi speed, what would I use the hi speed for? emergency water cleanups when high circulation would be of beneift? Will the higher speed improve the manual or auto cleaners?

I am thinking that the Pentair Dynamo 1hp 2spd pump would be a good choice. Unless the 1.5" piping would not allow 68 gpm flow anyway.

So Basically, two questions: 1: What effect will the 1.5" piping have on this analysis? Will a single speed .75hp pump be sufficient vaccuming?

Thanks

 

[bobnamy]

Ok, I think I can maybe answer my own question. The only sand filters I can find that will handle a 68 gpm flow are huge, way bigger than a 22 or 24 inch. So I think I am going to give up on the 2 spd pump, as I see no need for the hi speed on my system.

So, one final(?) question. on a 27' round with appr. 17,000 gallons, with a minimum flow rate of 29 gpm for a 10 hour turnover, and 36 gpm for an 8 hour turnover, is a 1/2 hp pump (Hayward Powerflo II) that pushes 33 gpm @ 30 feet of head a good choice?

Maybe the same pump in a 3/4 hp version (45 gpm @30 feet, 30 gpm @ 40 feet) would be better?

I will have three 2x20 solar panels at ground level, but no other water features.

 

[b2001]

I will use a manual vaccum (kids) but may switch to an auto cleaner eventually (kids refuse).

Go ahead and start saving up for that auto cleaner ... :-D

is a 1/2 hp pump (Hayward Powerflo II) that pushes 33 gpm @ 30 feet of head a good choice?

The uncertainty that I have about your situation is the effect the solar panels will have on your pressure. I'm assuming that with 3 panels, you're adding a lot of additional footage to your setup due to the internal plumbing of the panels. I would be nervous if a 1/2 hp could handle it. I'm no expert though - but it's a question that I would want answered if I were having your setup built. My calculations seemd to support a 1/2 hp for my pool, but several industry sources, including Pentair told me that I might be disapointed.

I would wonder if low speed would be effective enough with the panels - meaing that a 2 speed might not work, or rather an inability to take advantage of the low speed.

 

[bobnamy]

b2001, here is another take on the concerns you raise. On a diferent post I have going here, someone posted that their flow rate decreased substantially, and psi increased substantially after adding the ssolar panels. Others confirmed that is normal and to be expected. Well then, from what I understand about pump/pipe dynamics (virtually nothing), it would seem that a 1/2 hp pump would be better than a 3/4. as I believe there is little to be gained from a stronger pump pushing harder for deminimus increase in flow.

If that is true. then perhaps that opens up a new possibilty. I had actually ruled out a 3/4 hp 2 speed pump because the 25 gpm on low speed seemed too low. But maybe the lower gpm would be better with the solar panels. I would need a longer run time (11 hours to turn over pool) but at least I would have the high speed available to increase flow when bypassing the solar panels and vaccumimg, etc.

What do you think about the 2speed pump idea?

 

[b2001]

Personally, I just like it. I've had mine for about three weeks and I like the flexibility of either running on high or low speed. Of course high speed is needed for vacuuming; but if I get an algae bloom, I could run on high speed to get quicker results. Currently I run on low speed most of the time. Low speed is very, very quiet.

I have a sock in the skimmer basket, and with my pool being under 5 oak trees, I get a lot of junk in the sock and have to clean it out twice a day. I think the lower pressure of low speed helps in the skimmer basket not being clogged as easily.

My main motivation was cost savings of running the pump at low speed. I don't have bills to look at for results yet. However, 3 amps at low speed for my new pump vs. 9 amps at high speed, or 16 amps for the old 1 1/2 hp pump should yield results.

I don't recall seeing any 1/2 hp 2 speed pumps; I believe that I did see some 3/4 hp 2 speed pumps. There were not many of the Pentair Dynamo 2 speed pumps available - limited number of dealers carrying it on the internet. Buying local was out of the question - prices too high and it had to be ordered anyway. I paid about $280 for my 1 hp 2 speed. The Hayward's might be more plentiful. Also, not many of the 2 speed pumps that I looked at had an electrical cord; you'll have to get that separately and wire it yourself, which is not too difficult - one screw holding the back of the motor housing, and wires with connectors. I'm guessing You should be able to find one from a place that sells motors. You have to get a cord that attaches to the motor housing with a water-proof attachment. Sorry, if you already know all this - I didn't until I got into it. It was easy for me to do because I just pulled the cord off of the old motor.

I hope this helps you some. Good luck with your decision. It would seem, based on what you've said, that a 3/4 hp 2 speed would work for you.

 

[bobnamy]

B2001, I have not seen any 1/2 hp 2 speed pumps. The smallest I have seen is a Pentair Dynamo 3/4 hp 2 speed, which is what I think I will get. Since there does not appear to be a black and white absolute correect choice, I will go this route. I too am primarily interested in low operating costs, and I thnk the 2 spd operating on low, even for a longer time, will cost less than the others.

Thanks for mentioning the cord issue, I was going to ask that next!. I was assuming that the cordless pumps just get hard wired without a plug. I think I would prefer that if possible.

 

[b2001]

I was assuming that the cordless pumps just get hard wired without a plug. I think I would prefer that if possible.

I'm thinking a cord might be better. That way when the pump/motor goes bad - you unplug it and replace it without any wiring changes except for the pump/motor itself. Also, I winterize my pool, and store the filter assembly, and pump/motor in my shed out of the weather elements.

I do have a spa with a 220 volt pump/motor - I don't know if that is hard wired in or not; but it is protected from the weather elements by the spa frame.

I had a single outlet installed 5 feet or so from the pool, whatever the code calls for, for the pump, and a second outlet installed about 10 feet or so from the pool, again whatever the code calls for, for a 12 volt light system (Note: if you haven't thought about it; installing one or two lights in the side of the AGP below the water line makes the pool look great at night and is a safety feature for swimming after dark).

Anyway, just things to consider ...