getting the right amount of flow to a pool heater after downgrading the impeller

[mas985]

I did get some flow, as I saw spillover from the spa to the pool. But sticking my hand in front of the return, I didn't feel any pressure. I put my finger blocking the return hole, and I felt no buildup of pressure. And it didn't seem, from watching the temperatures, that the pool was heating up with the solar on.

What size are your panels (sq-ft)?

If the water was going through the panels only, albeit very slowly, you should have felt a temperature rise because the slower the water goes through the panels, the higher the temperature rise from the panels. Did you sense the water was any warmer?

 

[haz]

What size are your panels (sq-ft)?

If the water was going through the panels only, albeit very slowly, you should have felt a temperature rise because the slower the water goes through the panels, the higher the temperature rise from the panels. Did you sense the water was any warmer?

I have 9 Heliocol HC50 solar panels on my roof, which are 50 ft2 (4' x 12.5').

I didn't feel any increased temperature coming out of the return with the 0.75 HP pump and solar on. In fact, I didn't feel any water coming out at all, although I did see spillover from the spa into the pool.

Do you think it's worth while to try getting the 1 HP or even the 1.5 HP impeller and seeing if it gets enough water to the solar panels?

 

[mas985]

For 450 sq-ft of panels, you want a minimum of 45 GPM. You said that with your current pump, you had 26 PSI with solar on. That would equate to about 53 GPM. If you downsize the impeller, you should be getting about 43 GPM on the same plumbing so not all that much different. The 3/4 HP should work fine so I really think something else is going on which is affecting the pump when downsizing the impeller. I would like to figure this out before deciding on next steps.


Is all of your plumbing 2"?

Do you have a single suction line from pool to pump or multiple lines?

What is the height of the filter gauge relative to water level?

I believe your current pump is an up rated pump but can you check the service factor?

26 and even 22 PSI without solar is a lot of pressure for that pump which indicates very high head loss plumbing so I am trying to figure out where it might be coming from. Those types of check valves tend to cause very high head loss so that is a suspect.

 

[Pool Clown]

I don't think you will get the flow you need from a 3/4 to properly run the helos. It may turn out that something in between (3/4 and 2hp) would be better.

Getting back to diffusers, impellers change in two ways when you change hp. The inlet size can change, or not, so as to be able to accommodate the diff, but the other change, that you cant get around, is the overall "thickness" of the impeller, that's where you can get into trouble with the diff. While your inlet will fit nice with the diff, once you assemble it (to the seal plate), the impeller may not be thick enough to insert completely into the diff. Thats why there is the other diff available. One that stands off lower (for the thinner impeller) than the other once attached to the seal plate.

Does that make sense?

 

[borjis]

I don't think you will get the flow you need from a 3/4 to properly run the helos.

My last pool had a 3/4 hp pump with a solar setup similar to his and it worked great. I think there's something else causing
the issue as Mark pointed out.

 

[mas985]

Getting back to diffusers, impellers change in two ways when you change hp.

Actually, three ways. Besides the inlet and vane width, in many cases, the outer diameter of the impeller changes with HP too. The outer diameter of the impeller determines the maximum head (shut off head) of the head curve so you can easily tell when a larger diameter impeller is used vs a smaller diameter impeller by just comparing head curves.

But again, Haz's plumbing has 3x the head loss as typical 2" plumbing pool does so there is clearly something wrong with the plumbing and it is probably those check valves. So no matter what impeller or pump is used, the priority should be to fix the plumbing first and foremost.

 

[haz]

Thanks for all of the help. Here's my pool equipment:


In answer to your questions:
All of the piping is 2"

In terms of the suction, there is a pool and spa suction, and the pool suction side also has a branch for the cleaner return, but that is left closed. The spa suction only opens (automatically) when the spa is turned on.

The pool level is 1.5' above ground level, with a trough of an infinity edge at ground level. The filter gauge is 45" high, so 37" above the main pool water level.

Service factor 1.10 = 2.20 total motor HP

Are the pressures in low speed (7-8 PSI) without solar too high as well? All of the water, whether solar or not, goes through that spring loaded valve. Do I need to change that check valve?

Pool Clown, I understand what you say about the inlet size and thickness affecting its fit into the diffuser. Currently I have the diffusers for both the smaller and larger impellers.

It seems the consensus that the plumbing is at least part of the problem. Currently I have the bypass valve from the pump directly to the SWG and return turned off, so all of the water goes through that cheap spring valve, up to the solar panels if on, to the gas heater, then finally past the bypass to the SWG and return. I opened that valve completely to see the pressures with a bypass option around the spring valve, and (with 2 HP impeller) the pressures went (without solar) from:
high speed: 22 -> 18
low speed: 7 -> 6

I think all of the valves in my system are the good Jandy flap ones that minimize head loss. There is this in the pool return line:


and I'm not sure if that could be a valve of some sort, but the guys who did the pool are very well respected, do lots of residential and commercial pool, whereas the guys who put the solar panel (and maybe that spring valve) weren't good.

What do you guys think?

And do you agree that if I find the minimal HP impeller that I need, and I just use the pump in high speed for solar on and low speed otherwise, that my 2-speed pump is efficient enough, and that a variable-speed pump isn't necessary?

 

[mas985]

Are the pressures in low speed (7-8 PSI) without solar too high as well? All of the water, whether solar or not, goes through that spring loaded valve. Do I need to change that check valve?

Yes. My pump has a similar head curve as yours but my filter pressure is half of that.

The picture above is another check valve but not the Jandy type. Probably another spring loaded check valve which has a lot of head loss.

Also, I really can't tell what is going on with that plumbing layout from the picture. Do you have a schematic of the plumbing?

 

[haz]

So it seems that the pressure is too high even when able to bypass that spring valve before the solar outflow, so it's not that valve alone causing the head loss.

Here's the schematic of my pool's plumbing:


which says 27.99 total dynamic head. Don't know how that translates into an acceptable filter pressure.

In regards to that ?check valve on the pool return pictured in my last email, the pool builder used Jandy valves everywhere else in their piping. Would it make sense that they'd use good valves everywhere else then put an inefficient valve where all of the water returns? I could ask them.

Now it seems like I ought to at least change the spring check valve before the solar (if not this other valve before the pool return). I have a FlowVis check valve/flow meter. I was previously told the optimal place to put a flow meter, if I wanted to use one to assure the optimal flow to the solar panels, is on the solar outflow. If I replace the check valve before the solar valve, that would give me solar inflow flow rates. To me, unless there's a leak, it seems these numbers should be the same, and I'd hate to add another element of head loss w/ one check valve on the inflow and another on the outflow. Should I just replace the spring check valve before the solar valve with the FlowVis on the solar inflow, or do I need a flow meter on the solar outflow?

 

[haz]

Looking at the schematic, it shows a check valve on the spa return line, but that check valve I photographed above is actually on the pool return line after going through the SWG, and the spa return line has no flow valve. Don't know if that was intentional or not.

This is the adjustable spring check valve photographed above that is on the pool return line:
http://www.ndspro.com/water-flow-management/flo-control/spring-and-swing-check-valves

and its manual:
http://www.ndspro.com/images/stories/pdfs/flo-control/flo-control-technical-data-and-installation.pdf

Here's a photo of the outflow pipes to the pool, spa, and trough return. Note there's a second pump that pumps the waterfall/infinity edge:

 

[mas985]

If the spa is raised above the pool, then normally, you would want a check valve on the spa return line so when the valves are set for spillover, the spa won't drain when the pump is shut off. The only thing it could prevent is the pool draining into the infinity spillover but you would need a check valve on the bubbler too or is the bubbler in the spillway? If that is the case and the spa is lower than the pool level as well, the check valve location makes sense.


Originally, you said all of the piping is 2" but the schematic says different. Which is correct?

If the schematic is correct, then you should have fairly low head loss. 22 PSI without solar indicates a return head loss (without suction head loss) of about 52' of head which is twice what the PB calculated. So I suspect that the solar check valve is adding the extra head loss and that should probably be replaced. Once you see what the pressure and flow rate is afterwards, you can then decide on replacing the impeller or pump.

However, pools with an infinity edge typically have large pumps to provide enough flow rate for the spillover effect so I am not sure you want to reduce flow rate with a smaller pump or even lower speeds. If the flow rate is too slow, the debris will get stuck on the edge of the pool and the water will just dribble over the edge. Does that happen now with the 2 HP at full speed or low speed?

 

[haz]

Yes, the spa level is a few inches above the pool, and the main water return is to the spa, which spills over into the pool. There is a separate 3 HP pump (looks like it's listed as a 1.5 HP pump in the schematic, but it's 3 HP) that pumps the water feature, which is the waterfall. That water return, which doesn't go through the water filter, is seen coming from the left in the middle of the photo above (3rd pipe from the bottom coming from out of view). It branches off, with a manual valve shifting most of the return to the low branch labeled "pool waterfall return" in the photo, and some return to the other branch "pool fountain", which sends some water to the bubblers in the trough / infinity spillover.

So just to be clear, the 2 HP pump with the impeller I tried to change is for the water filtration and solar. There's a separate 3 HP pump for the infinity edge that would remain as is.

IN terms of pipe diameter, I thought you were asking if they were at least 2", and that they are, but it looks like some are bigger. Unfortunately I won't be able to measure them for a few days, but from the photo, for instance the pipe 2nd from bottom coming from out of view on the left looks 1" larger than the other pipes. that one is labeled "waterfall suction" and must come from the infinity spillover to the 3 HP pump. Just to be clear, I'm not looking to change the impeller on that 3 HP pump that only pumps the infinity edge water feature.

I think we all agree that the spring check valve before the solar valve creates unnecessary head loss and should be replaced. Does the check valve on the pool return line:
http://www.ndspro.com/water-flow-management/flo-control/spring-and-swing-check-valves

have the same type of head loss, and it should definitely be replaced too? If the issue is just the solar check valve, I would have predicted the pressure to go down to what you'd expect (which you're saying should be around 10-15 with solar on and pump in high speed) when I opened the bypass from 100% closed to open, but it didn't. So you'd suspect the check valve on the pool return must be the issue too, correct?

 

[mas985]

The bypass only bypasses the heater correct? Neither check valve is bypassed is it?

For the second check valve, when turning the return valve valve from pool to spa, does the filter pressure change by a lot? If not, the check valve is probably ok.

 

[haz]

The bypass only bypasses the heater correct? Neither check valve is bypassed is it?

The bypass valve bypasses, in order, the
1) check valve
2) solar panels (when on)
3) gas heater

That flow then joins the water going thru the bypass valve, and that goes into the SWG. If the spa is off, the pipes split, with an open valve allowing water return into the pool, thru this check valve:
http://www.ndspro.com/water-flow-management/flo-control/spring-and-swing-check-valves


and also directly into the spa, without any check valve.

If the spa is on, the automatic valve after the SWG then directs all of the water into the spa thru its jets, without any check valve.

For the second check valve, when turning the return valve valve from pool to spa, does the filter pressure change by a lot? If not, the check valve is probably ok.

The filter pressure went up from around 22 to 28 (solar off, high speed) when I switched from pool to spa. I tried opening the bypass completely, which allows flow around the check valve before the solar, and that just brought the pressure with the spa on down from 28 to 27.

It seems to me that if the check valve before the solar were the only issue, then by opening up the bypass valve completely and allowing bypassing of that check valve, the pressure would drop to what you would consider normal levels, but that doesn't happen.

I wonder if anyone knows someone in the Palm Beach / Broward County area in South Florida who knows about these things. My pool builder is good with getting the pool to function, but they haven't noticed this.

 

[mas985]

Sorry, I lost track of this one.

Something in the setup is causing a large amount of head loss. Plumbing with that size pipe and a cartridge filter should not be causing that much pressure.

But I did notice that you only have floor returns for the pool. How many and what size are they? They aren't in-floor cleaner returns are they?

Can you post a picture of where the bypass is plumbed into and out of the plumbing?

 

[haz]

Hi, just wanted to see if anyone had any more thoughts on this. Much appreciated!

 

[mas985]

Ok so I just wanted to summarize what you are seeing with regards to pressure. Let me know if I am not getting something right:

1) Bypass valve next to filter set to bypass all solar plumbing including the solar valve and check valve: 18 PSI

2) Bypass valve set to flow through solar valve and check valve but solar valve in bypass: 22 PSI

3) Solar valve turned on: 26 PSI

Condition #1 is about what I would expect with two returns and the rest of the plumbing and I estimate about 82 GPM in flow rate. However, your schematic says that the pipe diameter going to the pool returns is 3" but from the pictures, it look's to be 2". Do you know what kind of returns you have? Exit diameter?

Condition #2, indicates an additional 9.24' of head loss through the solar check valve and valve so that tells me there is a lot of head loss right there and it is probably the check valve. So I would consider changing that. Flow rate will drop to about 68 GPM.

Condition #3 has the highest head loss 18.5' above that of #1 with a flow rate of 55 GPM. So the panels are adding quite a bit of head loss too. 4 PSI rise is a little high for panels plumbed in parallel. What size pipe goes up to the panels and are all the panels plumbed in parallel?

 

[haz]

1) Bypass valve next to filter set to bypass all solar plumbing including the solar valve and check valve: 18 PSI

correct. Pressures in high speed 18. This is bypassing all of solar plumbing, but the water can either go through the solar valve and check valve or around it, whichever path has the least resistance.

2) Bypass valve set to flow through solar valve and check valve but solar valve in bypass: 22 PSI

correct (in high speed)

3) Solar valve turned on: 26 PSI

correct (in high speed)

your schematic says that the pipe diameter going to the pool returns is 3" but from the pictures, it look's to be 2". Do you know what kind of returns you have? Exit diameter?

The pool return pipe is 3". Two 2" pipes (the pool return from the filter to SWG as we're been discussing, and the infinity edge pump's return) combine into a 3" pipe, as seen here:


The exit diameter of the pool - I figure this is the diameter of the holes of the returns, and it's about 3".

Condition #2, indicates an additional 9.24' of head loss through the solar check valve and valve so that tells me there is a lot of head loss right there and it is probably the check valve. So I would consider changing that. Flow rate will drop to about 68 GPM.

Will do that, thanks.

What size pipe goes up to the panels and are all the panels plumbed in parallel?

They are 2" pipes. All of them are in parallel. Given that the roof starts around 26', and the bottom of the panels are above that, wouldn't that contribute to a good amount of head loss, or you think less than what we're getting? Here's a photo:

 

[mas985]

They are 2" pipes. All of them are in parallel. Given that the roof starts around 26', and the bottom of the panels are above that, wouldn't that contribute to a good amount of head loss, or you think less than what we're getting?

As long as the panels are fully primed, static head gets canceled out because the water goes both up (pressure loss) and down (pressure gain). However, if the VRV does not close because the pressure is too low at the VRV, then yes, that would cause extra head loss. Where is the VRV located. Upper right corner? How much higher is that?

30' of panel rise, requires a minimum of 13 PSI at the pump. However, that is without dynamic head loss. So if the panels cause 4 PSI rise and the check valve causes another 4 PSI rise, then the pump/filter PSI must be at least 21 PSI. With 26 PSI, you have some margin. But with a 3/4 HP pump, that margin would disappear and it is no wonder that it didn't work. Too much head loss in the plumbing.

 

[haz]

The guys who installed the solar panels didn't know the nuances of solar installation, and they didn't install a VRV... that's on my list of what needs to be done. Was going to install that either below the gutter or on the horizontal part of the roof.

30' of panel rise, requires a minimum of 13 PSI at the pump. However, that is without dynamic head loss. So if the panels cause 4 PSI rise and the check valve causes another 4 PSI rise, then the pump/filter PSI must be at least 21 PSI. With 26 PSI, you have some margin. But with a 3/4 HP pump, that margin would disappear and it is no wonder that it didn't work. Too much head loss in the plumbing.

Are you saying the pressure should be closer to 21 PSI, and mine at 26 is too high for some reason? Besides needing to change the spring check valve for a Jandy-type check valve, o you think there something wrong with the plumbing that, once fixed, might allow me to install a 3/4 HP (or a 1 or 1.5 HP pump) and get enough flow to prime and circulate enough water flow through the solar panels?

Also, I was recommended to install a check valve on the solar return before where the water bypasses with solar off. I was planning on installing the FloVis flow meter as that check valve. Does this add too much extra head loss?