Enough pressure to keep the vacuum valve closed

[Vandergraff]

Follow up to a conversation started in this topic. JasonLion

I just saw this post you did in January - I wonder if at 1500 RPM if I have enough pressure to keep the vacuum valve closed - how would I tell?

You can get a pump on low speed to work with solar but there are few things you need to take into consideration.

First, the solar panel efficiency is much lower when the pump is on low speed so you won't get as large a heat gain on low speed than high speed.

Second, if your panels have a vacuum release valve, it will need to be installed a few feet above the pump on the supply line. This is because low speed of a pump does not have enough pressure to keep the valve closed when it is on the roof.

Third, you will need a controller that allows the pump to prime the panels on high speed and then drop down to low speed after they are primed. This is the hard one. Most automatic controllers will force the pump to high speed when there is solar demand. You might be able to wire a mechanical timer of sorts to change speed after a certain amount of on time. Variable speed pumps/controllers do not have this problem as you can set any speed you want for any function that you want.

 

[mas985]

Re: Hydraulics 101 - Have you lost your head?

The panels that you are usinig are not conventional solar panels for pools and are typically used for hot water heating for the home. They can be used for pools and are usually better at heating in colder weather because of the glass insulation. They don't require as high a flow rate because of the insulation quality of the panels and if they are used for hot water heating, the water needs to move slower to gain temperature. Solar panels in general will have better efficiency if they are run at higher flow rates (lower exit temperatures) and I think these types of panels would benefit as well although perhaps not as much as conventional panels. You will need to watch your chem levels a little closer with these panels because of the copper. It will be vulnerable to low PH and you may find levels of copper increasing in the pool.

First ask the PB if you have a vacuum release valve (VRV). If the VRV is not closed, you probably will have no flow through the panels because the pump will be dead headed at low RPM. The Intelliflo at low RPM cannot generate enough pressure to push the water up to the panels. This probably explains why the flow meter is not registering. In order to have enough pressure to close the VRV AND to prime the panel, you will need a filter pressure of at least 10 PSI. So increase the pump RPM until you see that. Also, you may need to adjust the solar bypass because you want the pressure but you don't want too much flow rate through the panel.

 

[Vandergraff]

The panels were installed about 12 years ago so I am not sure if I can get info from the installer.

See attached picture of the panels - I assume the thing sticking up on the left is the vacuum valve. Anyway to check if it is open/closed when running? (Note the pool is behind the garage)

When I run the new Intelliflo at 2500 RPM the filter pressure is 14PSI and watts 944 - here I am certain there is good flow though the panels - at 1550RPM Filter pressure is `5 PSI (a little hard to tell) and watts 270. In both cases the flow meter in the line to the panels reads zero - I think the flow meter is dead so I have ordered a replacement.

The thing is even at 1550 RPM there seems to water flowing and I think the diverter valve is set to send most (if not all) water to the panels when the solar is on. So at 1550 RPM if water is flowing - wouldn't it be going through the panels?

One additional kink - there seems to be a small drain valve/pipe coming from the feed to the solar near the pool equipment. My understand is that it is there to drain the solar when it is not in use. The pipe goes to the inlet I use to add water to the pool. This bubbles slightly whenever the solar is running. It always has done this.

Note the Intelliflo is replacing as 1 HP single speed pump. With this set up most water was being diverted from the panels. It worked fine but at 40c per KWH in CA it was expensive. With the Intelliflo I would like to run the solar at the lowest RPM that will work hoping to save $

(I am careful with the pool chemistry. Fortunately my well water has high (not low) PH - so low PH is not a problem I see)>

 

[mas985]

It is tough to tell if the valve is closed unless you can measure the pressure at the valve which is not very easy. However, you can make a pretty good estimate by just knowing the height of the valve. That looks to be about 15'? That means if the pressure at the valve is to be +1 PSI, then at the pump, the pressure would need to be at leat 8 PSI plus the head loss in the lines to the panels. This is why I said, the filter pressure should be above 10 PSI so that you can be assured that the valve is closed. But if the filter pressure is below 8 PSI, you can assured the valve is not closed.

However, even if you get the pressure above 10 PSI, this may not be enough flow rate to purge the panels of air. A little trial and error may be in order. When you turn on the pump at 2500 RPM with the solar engaged, do you see a lot of air comming out of the returns. If not, the panels are not being purged properly even at that speed. If you do see air comiing out, then in stages drop the RPM and see if the air is still being purged. Again, there is no point in dropping the filter pressure below 10 PSI since the valve will open. You may end up at two speeds if your controller can handle it. One for the initial priming and a second for running the panels.

My guess is if you have a filter pressure of 14 PSI @ 2500 RPM, you will need to be above 2100 RPM to get above 10 PSI.

All this assumes of course that you have a VRV and it is working properly. One way to tell is that when you turn off the pump, you should be able to hear the air entering the plumbing and the panels draining.

 

[Vandergraff]

Thanks - that makes sense.

Yes at 2500RPM I could see the air purge and a bulge of hot water came though. I need to check if my Suntouch controller allows priming at start of Solar operation - it seems once primed that I can drop down to about 2000 RPM with good flow coming though. I assume I have to keep at least 10 PSI even when primed. As you say I need to experiment on what RPM is needed to prime the panels and what RPM keep the water flowing.

The VRV seems to working - everything drains when the pump is off.

 

[mas985]

I assume I have to keep at least 10 PSI even when primed.

Yes, you should try to be above 10 PSI. If you drop below that, the VRV might open and you may start to see air coming out of the returns and/or flow rate dropping very quickly.

 

[Vandergraff]

This is not good.

Brand new flow meter and still reading zero flow through the panels even at 2500RPM 14 PSI. I can hear water going through the panels - but I also see some bubbles coming out of the return.

That said there is definitely a good flow of water going somewhere at 2500 RPM - the skimmer is drawing well and I can feel a strong flow from the outlets into the pool. The diverter valve seems to set to send all water to the panels when in solar mode - so something a little strange is going on. Where is the water flowing if not though the panels. The flow meter is between the pump and the panels. I suspect the valve at the top of the panels must be opening and closing - but there still seems a discrepancy in the flow.

Now if I go to 2700 RPM the water bubbles go away in the outlet and the flow meter now acknowledges there is flow at about 12 - 14 GPM. Something is still strange because I would have though the flow would be much higher at 2700 RPM , filter PSI at 18 and with the pump at about 1100W. Again - were is the water going?

Also at 2700 RPM 1100W I am really not getting that much saving over the old 1HP which seemed to be taking 1500W (by reading the meter).

Ideas? Suggestions?

 

[JasonLion]

I would check into the solar diverter valve. My guess is that it never goes into the 100% solar position. With the valve part way open the flow on low speed would not be sufficient to prime the panels. It might have been configured with a stop to prevent it from going into that position because of an older single speed pump.

Also, keep in mind that the savings with a variable speed pump are never as larger when you are running solar as they would be without solar.

 

[Vandergraff]

Whay is this?

I am wondering what this is - is it another valve? It is in the line going from the pump to the panels (after the valve for turning the solar on/off).

Could this be my problem?

If it is another valve - do I need both valves (the one above the panels and this one)?

The small line going out to the left goes to my inlet that I use to add water to the pool. This inlet bubbles when the solar is running - always has even with the old 1HP pump and when I run the new pump at 2700 RPM and above. (Per my post above I am also getting bubbles on the return at below ~2700RPM when they go away).

Jason - I will also check the diverter valve. I have the installers of the Intelliflo coming Wednesday morning and I want to get as much information by then.

 

[JamesW]

The line is probably a drain line to allow the panels to drain. It will cause you to lose a lot of flow to the panels.

If you need to have a drain, it should be very small. If you have a 3-way valve, you can drill a small hole (1/8th inch) in the gate to allow it to leak down when the solar is off. They used a 3/4 inch PVC line as a drain, which is a bad design. The 3/4 inch PVC will allow too much water to be lost.

It was probably sized for the single speed pump to limit the amount of water going to the panels. With the new IntelliFlo, you don't need this line and it can be capped off

Can you provide a more comprehensive picture of everything?

 

[Vandergraff]

The line is probably a drain line to allow the panels to drain. It will cause you to lose a lot of flow to the panels.

Can you provide a more comprehensive picture of everything?

This picture was taken a few years ago before the Intelliflo and a new Polaris Booster pump. The plumbing however is still pretty much the same. I'll take a new picture tomorrow. See first post in the thread for a picture of the panels. The pool and equipment is behind the garage.

 

[JamesW]

You are also losing pressure to your Polaris booster pump, especially when the Polaris is on.

The Polaris suction is in the wrong place, it should be after the solar return. Also, the Polaris should not run while the solar is on. The Polaris should be on a timer and run for about 1 hour per day.

 

[Vandergraff]

Thanks the intelliflo is set to run at a higher speed when the Polaris is on on. I actually find that 30 minutes a day is fine.

Which is a bigger issue the drain line or the polaris location?

I am still wondering if the drain line valve and the VRV at the top of the panels are both needed - or if one can come out?

Trying to see if I can get good flow rate through the panels at lower RPM....

 

[JamesW]

The drain line can be removed and the Polaris suction should be moved. You can put a small hole in the diverter valve gate to allow the panels to leak down when the system is off.

 

[Vandergraff]

Some photos and observations.

Attached is an updated photo showing new pumps and current plumbing.

1. I note the flow from the Polaris specific line is negligible at low RPM (testing by feeling flow at the outlet by hand) - but at high RPM it definitely is taking flow from the panels. At 2700 RPM the Polaris is moving round the pool and probably cleaning pretty well without a booster pump!

2. It looks like I have a second drain line - see photo? It looks like this one either drains into the solar return into the pool - or through the faucet if open (I recall this was to ensure it was fully drained for the winter when the solar was off). It seems I shouldn't need two drain lines - in fact JamesW is suggesting I can remove the one by the pumps - what about this one? JamesW I am also unclear what you mean by 'You can put a small hole in the diverter valve gate to allow the panels to leak down when the system is off.'

3. Also attached is a picture of the diverter valve when the solar is on. It seems to me that it is NOT fully set to send all water to the solar but some is probably going back to the pool without going through the panels.

Some measurements today.

At 1500 RPM with Solar On the pipe INTO the solar is warm? It was consuming about 280W with zero flow registering on the flow meter into the panels
At 2200 RPM with Solar On the (metal) pipe from the solar isvery hot! Zero flow registering on the flow meter into the panels
Ar 2500 RPM with Solar On PSI is 15, 936W - if I step down from higher RPM the flow meter shows 15.5 GPM - however if I start at this RPM the flow meter shows zero
At 2600 RPM with Solar On PSI is 16.5, 1035W and flow meter to the panels reads 16 GPM (from the spreadsheet PSI/GPM and Watts/GPM both indicate a total flow of 52 GPM - so 36 GPM going somewhere else)
At 2700 RPM with Solar On PSI is 18, 1139W and flow meter to the panels reads 17 GPM (from the spreadsheet PSI/GPM and Watts/GPM indicate a total flow of 53 - 56 GPM - so 37 - 40 GPM going somewhere else)

I assume the somewhere else is the polaris line and through the diverter back to the pool.

This seems very inefficient. I need about 2600 - 2700 RPM to get good flow through the panels - but at these RPM only about 30% of the water is going through the panels.

I have the pump installer coming out Wednesday AM. He didn't do the original plumbing however he did install the pumps and after a long time setting the up left the non-solar RPM at 1000RPM, solar at 1500RPM, at when polaris is on at 1700RPM. Clearly the solar RPM is low and probably the non-solar RPM as well.

It seems the best options are.

- Remove one or two of the drain lines
- Switch the diverter to send all water to solar when in solar mode (assuming I am correct that it isn't doing this already)
- Move the polaris feed to after the panels.

Now I just spent quite a bit on the pumps - so I would like to minimize cost on any rework to the plumbing. Is there a suggested priority for trying the three solutions - or do I need to do all three to get reasonable flow through the panels at lower RPM. I am not looking for the ultimate solution - but the best bang for the buck in any plumbing rework. At 40c per KWH I would like to minimize the cost of running pump - but also don't want to spend a lot on new plumbing for now.

One final question - that may or may not be related. If the solar is on it seems I get reverse flow through the filter as the panels drain - sending DE back in to the pool. Obviously this shouldn't happen - isn't that a valve in the line out of the pump to prevent that from happening? If so does the valve need replacing?

 

[JamesW]

JamesW I am also unclear what you mean by 'You can put a small hole in the diverter valve gate to allow the panels to leak down when the system is off.'

The 3-way diverter valve will block flow going to the solar when the solar is off. This will also block the flow of water coming from the panels, which will prevent the panels from draining. If you open the diverter valve, you will see the gate that blocks the flow of water. If you drill a small hole in the gate (about 1/8th inch diameter), that will allow the panels to drain when they are off.

Here is a good site for solar information which contains the following image:

You should change the location of the Polaris suction to after the solar return. You should remove any open drain lines. The diverter should be set to close all of the way during solar operation. If it is not closed all of the way, then it will cause flow to the panels to be lost.

There is a check valve showing in the pictures. It should be preventing backflow from the draining panels. It might need to be replaced.

At 1500 RPM with Solar On the pipe INTO the solar is warm? It was consuming about 280W with zero flow registering on the flow meter into the panels
At 2200 RPM with Solar On the (metal) pipe from the solar is very hot! Zero flow registering on the flow meter into the panels

This is probably because there is enough pressure to partially fill the panels without allowing flow. This will cause the supply pipes to get hot. I don't know what the copper pipes are.

 

[Vandergraff]

OK - an update after a couple of months. Two changes were made.

- Switched the diverter to send all water to solar when in solar mode
- Moved the polaris feed to after the panels.

The drain lines are still there and the plumbing still has two many angles - at least in my opinion - but things are working better.

Ar 2100 RPM (500W) I am sending 14 GPM to the panels - so about 2GPM per panel. I have run the pump for 7 hours a day for couple of months with this configuration. Water looks perfect and solar heating at least as good as before with the old 1.5 HP pump. I can get gains of up 7 degrees per day in my ~16000 gallon pool.

However there are still air bubbles coming out of the returns indicating that the valve is still not fully closed. I talked to the person who originally installed the panels (different to the IntelliFlo installer which was Leslie's). He is a very experienced solar pool and hot water heating guy. Given that I know 14 GPM minutes are going to the panels (I have a flow meter in the line to the panels) - I must also have 14 GPM coming out of the top of the panels. The air would seem to be coming into the line after the panels. In discussion with the solar installer we could couldn't see a problem in running in this configuration.

As I say I am happy. The pump is running at 500W for 7 hours vs the old pump at 1500W for 6 hours, The water condition is great and pool heating is great. I did wonder if the bubbles might be similar to airation and cause the PH to rise - but no problems yet. I know I could probably make it more efficient by removing one of the drains and simplifying the piping - but for now it seems to be working well. I can also run the pump faster maybe 2600 RPM and eliminate the air bubbles in the return. However this would cause much higher power usage and seems to offer no other benefit for now.