Low flow pumps - Is Air in Solar system ok?

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

Dirk said:
Had I put it at the very highest point in my system, would it have been quieter? I couldn't find a consensus about the optimum placement for a VRV when I was designing my system. Highest point of panels? Lowest point of panels? Just below the roof? A few feet above the equipment pad? Etc.
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Possibly. The panels drain away from the VRV in both directions so the noise is probably the water falling back down to the VRV from the panels higher up.


Dirk said:
And if that's the case, isn't that making his system even less efficient, by compromising the flow even more?
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Yes. The heat transfer from the panels decreases with flow rate so to get to the same temperature, run time will need to be longer.
 
Re: Low flow pumps - Is Air in Solar system ok?

Mas985,

yeah the u bend and valve would be providing a more resistance.

The u bend is primarily for the solar-off case. At low flow theres not enough pressurise to push any water up the solar return pipe, so I put the U bend below the main return to isolate the solar return air.
 
Re: Low flow pumps - Is Air in Solar system ok?

I didn't read the question as looking to have efficiency optimised, but rather wanting to stop the bubbling, and wanting to know if air in the system is troubling. Thanks for adding the clear pipe so we could learn more! While not needed, I think that was a cool idea for adding to the information here at TFP. We learned that the turbulence and/or venturi effect at the T has about 200 mm (8") of suction at the solar return line.

Getting the air out of the system is a significant efficiency gain, because it removed the head loss from constantly lifting water to the highest point in the system. Tweaking beyond that is also a worthy consideration, but is unlikely to provide an efficiency gain large enough to justify adding automation to ramp the VS pump, and an actuated valve.

Efficiency, in terms of heating the pool, is high in a solar heating system. Mine has a separate pump and a CoP of around 30 (heat kWh divided by pump kWh). A heat pump has a CoP of around 5, if you don't include the water circulation cost. A separate solar pump is simple, and when the solar pump wears out in 5 or 10 years, it costs $260 to swap it out. It can also circulate the water in the pool if the circ pump goes on a holiday. At the correct pressure for the panels, I'm able to push around double the spec flow with my 1/2 HP solar pump, so I'm happy with my system. I agree that ramping the VS circ pump could be more efficient, but I doubt by very much. The lion's share of the work, pushing the water to and through the collectors, has to be done either way.

The difference arises in full life cycle cost, including the cost of automating the solar heating system. The solar controller and pump he's using costs a lot less than an automation system capable of ramping the VS pump, and a valve actuator. For the single pump option, that cost difference would need to be recovered.

My solar system costs about $120 per year in electricity. If I could save 10% by going with a single pump, I would save ~$12 per year. An automation system and valve actuator would have cost me around $1000 more than a dedicated solar controller and pump, so the payback was not compelling. In tomfrh's case, he would be adding the pump automation and actuator, but also unable to avoid the cost of the existing solar controller and pump he already owns, so the payback would be even longer.

There is a style difference here, which affects the value of pool automation. The most common setup here is a salt water chlorinator with onboard timers and diagnostics, and a 8A to 10A (240V) outlet for the plug on the pump. Benefits include that the SWG can only run when the pump is on, and if the SWG detects low flow, it shuts off both the SWG and the pump to preserve both. So automation is harder to justify here in dollar terms other than for a very complex pool. Automation would certainly be a fun addition, but since we're talking efficiency, I think it's a worthwhile distinction to explain.
 
Re: Low flow pumps - Is Air in Solar system ok?

needsajet said:
I didn't read the question as looking to have efficiency optimised, but rather wanting to stop the bubbling, and wanting to know if air in the system is troubling. Thanks for adding the clear pipe so we could learn more! While not needed, I think that was a cool idea for adding to the information here at TFP. We learned that the turbulence and/or venturi effect at the T has about 200 mm (8") of suction at the solar return line.
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yes the question was about stopping air bubbles, rather than improving efficiency. I think my system is reasonably efficient as it is, and the cost of actuators and controllers simply so I can use a single pump doesn't sound compelling.

Regarding the 200mm "suction", I should clarify that my pumps and filter are above the pool. The water level in the trap is actually about 600mm above the pool water level. If the pump and filter were below ground then none of it would be an issue.
 
Re: Low flow pumps - Is Air in Solar system ok?

Oh OK, I misunderstood. I thought the water was settling in U of the solar return side 200mm below the bottom of your main return pipe on the other end of the U.
 
Re: Low flow pumps - Is Air in Solar system ok?

needsajet said:
I didn't read the question as looking to have efficiency optimized...
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This is an excellent point, of course (regarding the actual cost benefits). But replacing two pumps with one VS pump would add efficiencies and cost savings beyond just the solar component. So to do the math correctly, he'd have to also consider how the VS pump's efficiency would affect cost for all his cycles, not just his solar cycle: filter, vacuum, features, spa, whatever. I'm not saying a VS is going to save him money, just saying it could, overall.

I do like the notion of having a separate, dedicated system that could double as a main system backup, that's cool...

Can I say, regardless of what he does, what a great discussion! I'm guessing well over half of what I added to my pool's equipment, since I bought the house, I did so trusting in my pool guy to pick and choose and recommend. Being the novice I was, I just went with what he wanted to install. Derr! I definitely have the wrong controller, and arguably the wrong SWG and vacuum system. He sold me the wrong drain covers and pool light, too. Had I been involved with TFP sooner, I would have a much better system, for sure, just by coming here and asking first...
 
Re: Low flow pumps - Is Air in Solar system ok?

Dirk, I have a variable speed main pump (3 speed, not fully variable).

i run it on the slowest speed. This saves a lot of power. It draws under 200W

to drive the solar with that pump I’d need to run it on medium speed at least, however running at medium speed uses slightly more power (~700W) than low speed plus the solar pump (~600W together)

If someone can show us a single pump would provide further meaningful efficiency gains I’d be interested to hear it, as I’ll have this pool for a while (touch wood)....
 
Re: Low flow pumps - Is Air in Solar system ok?

The point of two pumps are:

To add ft/head, as in your regular pool pump is good for volume but not for pressure.

To add volume, but this has a lot of caveats, it's not like you can just add in a pump.

In this case I think the op would be hard pressed to find a single pump to do the job at less wattage, there is one but it would not be cost effective to change it out since he has a vsp already.
 
Re: Low flow pumps - Is Air in Solar system ok?

tomfrh said:
to drive the solar with that pump I’d need to run it on medium speed at least, however running at medium speed uses slightly more power (~700W) than low speed plus the solar pump (~600W together)
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Medium speed on your 3 spreed will produce higher flow rates than low speed with the solar pump. Depending on the current flow rate and the size of your panels, the higher flow rate will improve the solar panel heat transfer efficiency. This could be enough to offset the difference in energy use with a shorter run time. But it depends on the current operating point.

As you can see from the following chart, the efficiency of a single panel drops off fairly quickly at lower flower rates:

Solar-Pool-Heating-Panels-Best-Flow-Rate-Efficiency1.png
 
Re: Low flow pumps - Is Air in Solar system ok?

tomfrh said:
Dirk, I have a variable speed main pump (3 speed, not fully variable).

i run it on the slowest speed. This saves a lot of power. It draws under 200W

to drive the solar with that pump I’d need to run it on medium speed at least, however running at medium speed uses slightly more power (~700W) than low speed plus the solar pump (~600W together)

If someone can show us a single pump would provide further meaningful efficiency gains I’d be interested to hear it, as I’ll have this pool for a while (touch wood)....
Click to expand...

Sorry to belabor this, but in reading your latest post, it seems you still don't quite understand what a couple of us are getting at. How much electricity (cost) your saving is not just about reducing the RPM setting of either of your pumps. RMP is one factor, yes, but so too is run time: how many hours your pump(s) run in order to heat the pool to your desired temperature. So your conclusion "i run it on the slowest speed. This saves a lot of power." may not be true.

By running the pump(s) at the slowest speed, you reduce the amount of water that flows through the solar panels. This can reduce the efficiency and heat output of the panels. So you might have to run the pump(s) longer than you would using the higher RPM settings, which could use more total electricity, and end up costing more. There are relatively simple ways to determine which pump settings will actually cost less, you just have to do the tests and the math. (Which we explain how to do in previous posts.)

Now that the bubbles are "fixed," if you're happy with your current set up, and what it costs you to run, and how it heats your pool, then you're done. (And we're done.) But if you're seeking the least expensive way to heat your pool, then you still have a ways to go to determine that.

IMO, using the right kind of controller and a variable speed pump (not just a three-speed pump) with an actuator could reduce your overall energy use the most (not just during solar cycles). But the savings would be offset by the cost of replacing equipment, as needsajet points out. Would the energy savings that new components might provide ever "pay for themselves?" At least before they'd wear out and need to be replaced? The wild card is that I don't know how you'd determine before installing a VS pump what RPM would optimize the panel output, so you'd be missing that figure in order to do the math correctly before you buy a new pump. A catch 22.

Alternately, one of the RPM settings of your existing pump(s) might be providing just the RPM you need to run your panels most efficiently, and therefore most cost effectively. And you can determine that. That would give you the best bang-for-your-buck, as you'd optimize your solar heating system without any additional expense. We're just saying that using the lowest speed setting might not be saving you the most money. And adding the trap and valve might have actually made your heating cost increase, even it if did solve the air problem.

But again, if it ain't broke, don't fix it. Bubbles are gone, if your system is doing what you want now, then just go swimmin' and enjoy!
 

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

Dirk, yes i understand that it’s more thermally efficient to have higher flow rate thru the panels. But higher flow rate equals more power. It’s a trade off.

My solar pump does 40gpm (150lpm) at 5m head (top of panels).

if instead I ran the solar with my variable speed on medium speed I would roughly double the flow rate, and increase thermal efficiency by say 10%, however that’s negated by the increased wattage of the higher flow pump.

hence my question of what variable speed single pump could provide real overall efficiency gains.
 
Re: Low flow pumps - Is Air in Solar system ok?

tomfrh said:
Dirk, yes i understand that it’s more thermally efficient to have higher flow rate thru the panels. But higher flow rate equals more power. It’s a trade off.

My solar pump does 40gpm (150lpm) at 5m head (top of panels).

if instead I ran the solar with my variable speed on medium speed I would roughly double the flow rate, and increase thermal efficiency by say 10%, however that’s negated by the increased wattage of the higher flow pump.

hence my question of what variable speed single pump could provide real overall efficiency gains.
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OK, sounds like you have a handle on the flow issue, and 40 is nothing to sneeze at, that's about what I need to run for my Heliocols. Sounds like you're good-to-go.

It was relatively easy for me to justify my VS, over the two-speed it replaced. Low-speed was not keeping the pool clean enough, and high-speed made for crazy PG&E bills. Plus, I knew I was going to automate, so having a VS made sense for me beyond just energy efficiency. I saw immediate savings with the VS. But then negated some of those savings when I added solar, because I had to goose the RPMs to get the flow I needed. I'm pretty sure the VS was still cheaper to run than the old two-speed would have been on high speed. Where it really pays off is in the winter, when I can dial everything down, and do so through software, inside. Switching the two-speed back and forth was something we tried for a while, to keep the pool clean enough, but that was a hassle and didn't really work that well. The other issue was the tech: the new VS pump, even if I matched the RPMs of the old two-speed, was far more energy efficient.

So there's the math component in swapping out pumps, but also the convenience factor, too (at least that's how I justified the VS expense).

I don't know how best to address your question about overall efficiency, since I don't know how you determine what a VS will provide in that regard until you actually have one installed in your system and optimize the RPMs! There's the catch. Maybe a Pentair tech guy would know how to figure out the math on that.

And as I mentioned, this is all moot to me for my system because I'm now running PV solar. So in six years all my pool energy will be free... If I was going to put money anywhere to lower my electricity cost, it would first be into PV solar. That definitely pays for itself in short order. Then you can run your pool systems flat out if you want to!
 
Re: Low flow pumps - Is Air in Solar system ok?

PV cells, there’s a whole new angle! One day maybe.

Not sure if you’re answered this already - but does your variable speed pump adjust flow depending on whether solar is running? What speeds does it run in the various modes?
 
Re: Low flow pumps - Is Air in Solar system ok?

tomfrh said:
My solar pump does 40gpm (150lpm) at 5m head (top of panels).
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That's just the static head and only relevant during priming. Dynamic head is likely to be much more than that and is more important for operation.

BTW, the W500 is 150 lpm at 3M of head.
 
Re: Low flow pumps - Is Air in Solar system ok?

Just to clarify, the solar booster pump is single speed, I believe 1/2 HP.

Could you tell us the brand and model of both pumps? You probably need to set your low speed a wee bit higher. (most 3-speed VS pumps can have the default RPMs changed, that's why I need to know the model). Right now, I think there's a good chance the solar pump is pulling more water than you're pumping on low speed through your circ pump. The reason I think that is because you had the air bubble problem in the original state, and your solar pump should have been able to pump enough to prevent that.

Are you able to measure the temperature difference between pool water and heated water coming back from the panels? Also, I can't find the height of your panels... is it single story or a double, and how much is the equipment pad and the house above/below the pool water level, roughly?

And finally, what type of collectors? (panels/tubing) And how many square metres?

By the way, it would be really helpful if you could add a signature with your pool details, and also your city or State. There's instructions in a link in my signature called 'read before posting'
 
Re: Low flow pumps - Is Air in Solar system ok?

Main pump is Davey powermaster eco.

solar pump is Davey whisper 500

solar is black tubing (4 tubes per strip). The sheets lay in the tile grooves. The Total area is 50-60m2, so approximately 25M2 of black strips. That’s a rough estate. I’ll measure it properly, and will measure the temperature gain.

Single storey. Bottom of solar tubes about 3m above pool surface. Top of solar tubes about 5m above. VRV at bottom of tubes.

filter and pump are above the water. The equipment pad is approximately level with the water surface, ie filter and plumbing above the pool.

Thanks for the tip on adjusting the flow rate of the 3 speed. I looked up how to do that. I’ll try bumping up the low flow a touch. In retrospect this could potentially have solved all problems on its own without the need for trap etc. Another 50 or 100rpm might have done it.
 
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.
 
Re: Low flow pumps - Is Air in Solar system ok?

Mas. does your pump change speed depending on whether solar is on?

I don’t think this Davey one can do that. If the pump doesn’t go back to low flow when solar is off then and efficiency gains would be eliminated.


besides, this system is setup as two pump. No actuators/controllers etc.


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.
 

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