Pump speed for solar heating

[brimorga]

You just NAILED why the industry 'turnover' myth is *exactly* that.

One neighbor has a bunch of water features and a heater. One neighbor has a plain Jane pool. A 3rd neighbor had something in between and heavy trees that clog their small filter often. Yet all 3 need 3 turnovers a day, thay they have zero chanve of calculating without a flow meter. Now Multiply those variables across the land and how is anybody supposed to actually know when they hit their 3 turnovers.

Now, the truth is that each pool needs the skimming and filtering that it needs. Some need 2 hours, others 4 or 9. Heck, even the same pool will need wildly different schedules to clear the various crud levels throughout the season. Yet if they make everybody run for 16 (?) hours, they are RIGHT !!!!

If shooting for 1 or 2 or 3 turnovers makes you sleep better, then by ALL means do it for you. If you want to figure out what you truly need, try a runtime for a week. If the water is stupid clear? Try less next week. If the water isn't quite right, add some runtime. Reasses whenever necessary like in the early spring when you get overrun with pollen. I had to run 24/7 then to keep up with 80 Oaks. Shortly thereafter I barely needed to run at all for a couple of months if we weren't throwing a bunch of parties. Towards the end of the season I needed to ramp it up again.

I didn't care to ever care so I just ran 24/7 at low RPMs for peanuts. But I knew I was doing it for me and not some one size fits all reccomendation.

Also, absolutely LOVE the data if you are so kind to experiment and do the appropriate math. It will be a GREAT resource to point to for real world results as to why all 50 RPMs are not created equal, for flow or cost.

It’s really strange how the GPM works but I guess in addition to having much more resistance pushing water up to the solar panels, it really seems to matter how many returns I have going. The most efficient setup in terms of RPM to GPM is to run the pump while filtering both pool and spa. If I just do pool only, efficiency drops about 5 GPM. If I just do spa only, it drops about 10 GPM.

Like you said, I’m just doing a swag on runtime, trying to get a decent amount of total turnover at the cheapest possible cost. Since I have an autocover, I don’t really even need much in the way of skimming. Fortunately I have my pool in a spot where there are no major trees, just some bushes so there isn’t too much that ends up in the pool. It kinda of feels wrong to not run the pump at all, especially in winter when I don’t need to generate much chlorine, but based upon what you are saying I’m not exactly sure what the point of running the pump is if I have clean chlorinated water and use the autocover.

 

[Dirk]

@Newdude explains the "turnover myth" perfectly. In most cases, just a few things determine your runtime (I may be leaving out some?). Enough to:
- distribute chlorine
- satisfy an SWG's runtime
- heat the pool to the desired temperature
- clean the bottom
- skim the surface
- clear the water (filter)

Usually, one of those things determines the minimum runtime and RPM, the others are taken care of during the same run. So, for example, if you have to run your pump at 2400 RPM for 8 hours to get it warm enough to your liking, chances are good that'll also be enough runtime for your SWG, the water will look clear, and no leaves will be floating on the surface.

But say at the end of eight hours, your water still looks a little cloudy. Then you up the runtime, and/or the RPM, for as long as it takes to clear the water. Maybe that's 10 hours. But within that 10 hours, your pool got plenty warm, so that means that filtering becomes the determining factor for runtime.

None of which has anything to do with "turnover." And as newdude points out, the governing factor that determines minimum runtime can, will, vary from season to season. It's trial and error, throughout the year, that will eventually reveal your runtime(s).

My pool needs 8 hours for my SWG. That determines my runtime nine months of the year. Everything else happens within that time frame (heating, cleaning, filtering, skimming, etc). When solar is called for, my system ramps up my RPM to get the flow my panels need, the rest of the time I'm at 1500 RPM (my SWG's minimum). That's all there is to figuring out my scheduling and pump speed. I don't even know how many "turnovers" that is, and it doesn't matter. My pool is warm and clean and sanitized... done deal. The other three months I don't use SWG or solar, so I run about 3 hours a day at 1500 RPM, plus another hour at night for the vacuum. I could probably do with less, but I like the surface nice and clean.

Regarding your solar heating... I use the Heliocol minimum, too: 5GPM. The physics involved says the higher the RPM, the more your panels will heat your pool (though it is a diminishing return). There are two limiting factors: the stress on the panels and plumbing, and the energy costs. Obviously, you don't want to blow up your panels, so you stay away from the high end RPM/flow limit. So then it just becomes a matter of how much do you want to spend in electricity to get your pool warm enough. At 5GPM, my pool gets to 80-85° at about 2:00. Warmer or cooler, sooner or later, depending on the month and the air temps. That works for me. You'll know soon enough what works for you and what it's going to cost. Is one more degree worth $10 more a month? Two degrees, $40? Etc. (Or whatever your scenario will be, it'll be exponential.) Once you figure that out, you'll use the Vis to monitor your system, making sure that its maintaining the magic RPM number throughout the swim season.

Or do what I did: bolt enough PV solar on your roof and stop worrying about electricity costs altogether. I think I'm right around the date where my PV has paid for itself. I haven't paid anything to PG&E since they were installed. Not a dime (in fact, they write me a check for about 20 bucks once a year). I like my "free" electricity, so I still run my pool and air conditioning efficiently so that I don't go over. If/when I have to start sending PG&E a check, I'll bolt on another PV panel...

 

[Newdude]

I’m not exactly sure what the point of running the pump is if I have clean chlorinated water and use the autocover.

Exactly. You need to accomplish only what you need to accomplish. The cover stops most of the debris and FC loss. If you need to heat for 8 hours, then you need to heat for 8 hours. And so on. The needs/wants can change greatly during the season and you adapt to them.

A set turnover reccomendation for every pool in the land is nothing but hoping they made them all run long enough so that they are correct in a way.

 

[Newdude]

*25 page helpful post

 

[Dirk]

I was never here...

 

[riny]

On the topic of turnovers... that's also the same way I thought about it when I first came to TFP. After getting a good smackdown, I went deep into the rabbit hole, trying to understand the science behind measuring turnovers. If you're interested, here are some relevant studies:

1. https://consensus.fsu.edu/FBC/Pool-...4_study-efficiency_of_circulation_systems.pdf
2. A quantitative analysis of swimming pool recirculation system efficiency | Journal of Water and Health | IWA Publishing
3. Revisiting the Gage–Bidwell Law of Dilution in Relation to the Effectiveness of Swimming Pool Filtration and the Risk to Swimming Pool Users from Cryptosporidium

Some possible conclusions are: (a) you only need 30 minutes of pump runtime to keep your chlorine distributed for effective sanitization, and (b) the efficiency of your filtering medium is far more important than the daily turnover count.

For further reading, look up the "Gage-Bidwell Law of Dilution." The whole notion of turnovers came from a short section of this 1926 paper:

The American Journal of Public Health (AJPH) from the American Public Health Association (APHA) publications

American Journal of Public Health (AJPH) from the American Public Health Association (APHA)

ajph.aphapublications.org

This discussion of turnovers was presented without data or evidence and has been the basis for public pool recommendations for the past 100 years, even though we now know substantially more about how pool chemistry works. A google search will show you that there's a ton of controversy around this model today. It was originally designed to address "dirt" in the water and while these turnover rates may address specific concerns (e.g. removal of fecal matter from public pools), the model is incomplete and is largely inapplicable to residential pools.

At this point, I feel like counting turnovers is just something people recommend because they heard it from someone or that's how they've always done it, without any basis for using that approach.

 

[Newdude]

Another thing that had my wheels turning this afternoon is pool size VS gallons. A 20k gallon sport / shallow pool would have a larger surface area to suck up crud, compared to an 8 ft deep pool that was also 20k gallons. A 20k above ground pool (with its own surface area) would only be subject to airborne crud and not whatever blows across the lawn/patio also. But all 3 need 60k gallons of filtered water per day for their magical 3 turnovers ? Sight unseen and not factoring in the huge Maple above the sport pool ? And none of them have flow meters to actually measure anything ? They are using a manufacturers chart ? Like window sticker MPG verses real world MPG ? Yeah.

 

[Dirk]

Just to help @Newdude make his point: here are two examples of turnovers. Both utilize two turnovers, but notice how all the variables are totally different. I think this puts the turnover myth to bed, once and for all.

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