Low flow pumps - Is Air in Solar system ok?

[mas985]

Re: Low flow pumps - Is Air in Solar system ok?

I have a controller which ramps up the speed to prime the panels, then sets the speed to a lower RPM after priming. But my panels are about 2M off the ground so I can run them on the same low speed with or without solar anyway.

But how long does solar usually run anyway? Maybe that is all you need in terms of run time? Most pools can get away with less than 2 hrs of run time.

what I could do is swap the solar pump for another eco pump, and adjust it. That might save some wattage vs the basic solar pump.

Might be cheaper to find a VS that has relay control inputs (e.g. Pentair SuperFlo VS, Hayward MaxFlo VS) and sell the Davey.

 

[Dirk]

Re: Low flow pumps - Is Air in Solar system ok?

If you can adjust the speeds to anything you want, then you definitely don't need the solar pump and without the solar pump the Davey eco is going to be much more efficient by itself and will be able to match the same flow rate as the combo.

Shoot, now I'm lost again. I thought the idea of the solar pump was so a controller could turn it on and off, based on air/water temp, and so save electricity when the pool gets to temp, independent of what the filter pump needs to do to keep the water clear. How would eliminating the solar pump and adjusting the RPMs of the remaining pump be more efficient? The controller would then run that? Can the controller select the pump's speed?

But... being able to adjust the RPMs does greatly reduce the need for a variable speed pump, because if you can dial in the RPMs to optimize flow, then you're golden. Especially if both pumps can do that. Optimize solar flow. Optimize filter flow. You're done! (Then, if you can take out that U and the valve and see if the bubbles are still gone, you'll have a perfectly tuned system without additional expense or equipment!)

 

[tomfrh]

Re: Low flow pumps - Is Air in Solar system ok?

Dirk, yes that’s what I’m thinking. The impracticality of single speed pump in my setup, and the possibility of tuned filter and solar pumps.

 

[Dirk]

Re: Low flow pumps - Is Air in Solar system ok?

I think we're all getting collectively closer, especially if you can tune your RPMs. Some of this is above my pay grade, but if you can tune both pumps, then you can just tweak each until: the panels get the flow they want (by adjusting the solar pump), and the solar pump gets the water it wants (by adjusting the filter pump). I bet by the time you get both dialed in, the bubbles would go away to boot (without that U and extra valve).

What I can't help with is how you know either is achieved. As I said, I use a flow meter (no math, no guessing, no mystery). I don't know how else to do it, and especially not how to use math to do it. But someone here will...

 

[tomfrh]

Re: Low flow pumps - Is Air in Solar system ok?

I am going to try tweaking the low flow when I get home, to see how it affects water in the trap. I suspect a small increaae will raise the water high enough that the trap isn’t required for the solar off case.

the question is would it also work in solar on case without the trap/valve? Probably, since the solar-on was on the verge of being bubble free anyway.


i can measure the solar flow via the clear sections, by observing the speed of the bubbles as it’s purging the air.

 

[mas985]

Re: Low flow pumps - Is Air in Solar system ok?

Water seeks its own level so i still dont see the point of the trap. Other than the extra head loss, it shouldnt make any difference st all.

 

[needsajet]

Re: Low flow pumps - Is Air in Solar system ok?

I'll just stay focused on what you can do for now. In the meantime, I would increase your low speed so the booster pump is not pulling water through the main pump and filter. Total guesstimate*, but I'd say 2 steps (1500 RPM)

In the longer term, and dollars permitting, you can think about and shop for a controller that can change the speed on the VS pump when solar is called for, along with an actuated (electric) valve, then decide if the dollars make sense. Your pump motor and onboard controller appear to be the exact same as mine, and I haven't found a way to signal the pump controller externally.

The valve is probably a waste vs. tweaking up the VS pump, but from what I'm hearing, your U is stopping suction of air bubbles by venturi when the solar is empty.

*guesstimate mentioned above

Please confirm if this is your VS pump: https://davey.com.au/media/custom/upload/401925-8_PowerMaster_ECO.pdf
If so, it's the same motor as mine with a slightly different impeller. Yours has a wee bit more head and a tad less flow.

I set mine on recirculate to bracket your low head condition when the booster is pulling water
These are my numbers:
1450 RPM, 170 LPM (45 GPM), ~0 PSI
2400 RPM, 250 LPM (66 GPM), tad under 5 PSI
2800 RPM, 290 LPM (76 GPM), 7 PSI
Then when filtering (perfectly dirty filter for my taste, around 1 or 2 PSI above clean pressure)
1450 RPM, 120 LPM (32 GPM), ~3.5 PSI
2400 RPM, 160 LPM (42 GPM), 9 PSI
2800 RPM, 180 LPM (48 GPM), 13 PSI
So to get the 40 GPM recommended earlier, I'm guessing 1500 RPM on your VS pump in this outside-the-square situation.

FWIW, my solar pump flows 150 LPM (40 GPM) when all is right with the solar. I only have 16 sq m of panels, so my flow rate is well above spec (although pressure at the top is ideal, so I'm fine with that). Mine is single story, and the pump is just a typical low head 1/2 HP pool pump.

 

[mas985]

Re: Low flow pumps - Is Air in Solar system ok?

Given the panel size and one story install, shouldnt need more than 120 lpm.

Also if you are interested in the actual flow rate, you can estimate from a pressure measurement on the solar pump return drain plug and a suction measurement on the eco suction drain plug.

 

[tomfrh]

Re: Low flow pumps - Is Air in Solar system ok?

Needs a jet, Yes that’s my pump.

and yes when solar is off the U trap is preventing air sucking when in low flow mode. If the equipment was mounted under the pool this wouldn’t be an issue.

increasing to medium flow when solar is off adds over a meter of water to the solar return column, thus it wouldn’t take much flow increase to eliminate the need for the trap.

 

[mas985]

Re: Low flow pumps - Is Air in Solar system ok?

I dont think the trap is doing anthing for sucking air. Why would it? It adds no restance to air and water seeks its own level so why would it matter all? Water will fill the solar return pipe to a level dictated by the water pressire at that point with or without the trap.

 

[needsajet]

Re: Low flow pumps - Is Air in Solar system ok?

Yep for sure. As it turned out, I could have gone maybe 0.4 or 1/3rd HP. But as it is now, I tune it with the bypass which is also the drain path. If I send less up to the roof, I would burn a few more watts, so I just send it up through the collectors. My top pressure is on spec, so I think it's OK. The panel manufacturer recommends popping the top off the VRV, and tuning a vertical stream of about 0.5 m high, which was good enough for me, but I don't know the pressure in PSI. I also wanted headroom to add more panels if it didn't pan out the way the manufacturer said it would, but I have to give them kudos cause it seems dead on with their calculator.

My solar runs all day (when sunny) for about a month to get the pool up to temp in spring before swimming season, then after that it's usually on at 9am and off by 11am during good weather. On "sunny with cloudy periods" like the last few days, it's up and down like a... ummm... yoyo. I'm actually starting to think part of my pH drift is related to all that aeration

 

[needsajet]

Re: Low flow pumps - Is Air in Solar system ok?

I'm probably imagining the trap incorrectly, but I thought it extended below the pool water level, and then connects back into the return line which is above pool water level. And if not, that the pressure coming from the main VS pump (on low) was not quite enough to push a bit of water up the solar return line. tomfrh said there was a few bubbles coming from the solar return with solar off and VS pump at low speed, but that this stopped with the trap, so I was just imagining how that might happen.

 

[tomfrh]

Re: Low flow pumps - Is Air in Solar system ok?

Mark,

the U is preventing air in the solar return from getting into the main line. The water level in the solar return side of the U sits about 200mm below the T. The air which previously fed straight into the T from above cannot get down around the U.

needs a jet,
youre imaging it almost correct, except the U doesn’t go below pool water level (our slab is same as water level, so that would be difficult!). Because the pump is running the water level doesn't fall as far as pool water level.

 

[mas985]

Re: Low flow pumps - Is Air in Solar system ok?

Mark,

the U is preventing air in the solar return from getting into the main line. The water level in the solar return side of the U sits about 200mm below the T. The air which previously fed straight into the T from above cannot get down around the U.

I know what you think it is doing. But i am telling you that it isnt doing that. In pressurized systems, traps dont do anything. Air will not enter the main line without the trap unless the pressure is less than atmospheric which it is not.

Did you ever get air in the returns with solar off?

 

[needsajet]

Re: Low flow pumps - Is Air in Solar system ok?

By the way, Dirk, I'm not ignoring your question. I'm intrigued by tomfrh's situation, both hydraulically and with respect to payback. I just now went back and requested that your question be moved to a new thread titled "optimizing flow rates". Sorry my old brain struggles with multiple pools in the same thread, especially this one

I can give one quick answer, Mark is the man for head calcs, pump curves, flow rates, hydraulics and many other things. My experience comes from farming with medium scale irrigation (max 50 HP, most 10ish), boilers and other heating, refridgeration, building, landscaping and the like. More recently a keen interest in pools, but still limited to around a dozen pool-years on four pools.

 

[tomfrh]

Re: Low flow pumps - Is Air in Solar system ok?

Mark,

Yes, air with solar off, coming from the solar return tube.

 

[mas985]

Re: Low flow pumps - Is Air in Solar system ok?

Are you sure it is coming from solar?

And the air was.not just temporary?

 

[needsajet]

Re: Low flow pumps - Is Air in Solar system ok?

I had this medium-sized huntsman helping me when I got those flow rates.

 

[tomfrh]

Re: Low flow pumps - Is Air in Solar system ok?

Mark,

yes it was coming from the solar return tube and persisted indefinitely.

 

[mas985]

Re: Low flow pumps - Is Air in Solar system ok?

Ok, i think I might know what is going on. Most solar installs, at least here in the US, use solar valves and without one, the solar plumbing is pressurized to the pressure of the pipe entering the solar pump. This is probably higher than that of the water at the solar return, due to dynamic head loss, so air enters the return.

However, this should stop at some point because the air in the solar plumbing would eventually all escape and no more air should enter the solar plumbing. However, eventually it should stop but it might take a while. How.long did you wait for the air to stop?