Solar Vacuum Breaker Location for Best Drainage

[rogue]

[attachment=0:1sa2rnwl]Heliocol Installation Plumbing Evaluation 130715.jpg[/attachment:1sa2rnwl][attachment=1:1sa2rnwl]Final solar install configuration evaluation 130715.jpg[/attachment:1sa2rnwl]
Hi,

This post regarding my 11 panel HC-50 Heliocol solar array configuration follows my integration of a Hayward ECOSTAR SP3400VSP variable speed pump integration with my GoldLine GL-235 solar controller. The system is missing a vacuum breaker and I’d appreciate recommendations regarding proper placement for it for most effective solar array drainage when the pump is off.

My interest in the solar configuration came from a need to determine the most efficient (i.e. heat transfer) flow rate for the Heliocol HC-50 panels. The residential installation manual provides a recommended flow of 5 GPM per panel.
The solar array as shown in the attached pictures is on the far side of the roof ridgeline from the pool pump. The first HC-50 panel is fed by a 2 inch pipe approx. 46 feet long which crosses a 26 ft. high roof ridge. The 11 panels are arranged in a split series array (i.e. 6 panels feed a 2 inch line connected to the next 5 panels) as recommended in the Heliocol Residential Installation Manual which limits the maximum number of HC-50 panel in series to 8. The return pipe from the far end of the array to the pump is approximately 84 feet. The 25,000 gallon salt water pool equipment consists of a Hayward DE 7220 filter and Intermatic clocks controlling AquaRite chlorine generator, Goldline GL-235 solar controller, auto fill system, and ECOSTAR SP3400VSP pump.

A Heliocol rep replied to my request for optimum flow rate information stating “5gpm / per collector is a minimum recommended flow rate. The allowable flow rate is up to 10 gpm per panel. So your calculation of 30 gpm for the larger array of 6 if placed in series is correct.“ For my pool plumbing system with the ECOSTAR SP3400VSP installed the following data points were obtained from the ECOSTAR readout and a flow meter installed about 6 feet above the pool deck:

30 GPM at 1850 RPM/342 watts/filter 10 psi. 25,000 gal pool turnover is approx. 14 hrs
40 GPM at 2250 RPM/580 watts/ filter 14 psi. Pool turnover approx. 10.5 hrs
50 GPM at 2850 RPM/1138 watts/filter 20 psi. Pool turnover approx. 8.5 hrs
60 GPM at 3200 RPM/1600 watts/filter 24 psi.at Pool turnover approx. 7 hrs

Since I was unable to get any specific information from Heliocol regarding heat transfer variance between 5 GPM and 10 GPM through a panel I settled on 40 GPM to take into account pool turnover time.

By this time I’d read through the Heliocol installation manual several times and been on the roof to look over my solar array. I noted for my solar system configuration as shown in the attached pictures that:

1. there were no drains installed in the array as required for the 12 year Heliocol warranty for freeze damage
2. There was no check valve between the filter and the 3 way valve.
3. there was no vacuum breaker installed

Item 1 was never installed. Due to panel location on the far side of the roof ridge it looks like 3 drains will need to be installed at the low points of the arrays shown in the picture. Item 2 check valve was initially installed correctly but my pool remodeler changed the check valve location to its current location. Due to space constraints I will add a Jandy 7305 check valve with 2.5 inch connector (or possibly Jandy 7307 with 2.5/2.0 bushing) to the existing 3 way valve and a new Hayward SP0410X5025 backwash valve. Then I will remove the check valve flapper above the 3 way valve.

Which brings me to Item 3, the missing vacuum breaker. A vacuum breaker was not seen on the vertical feed pipe from pictures I took at the time the Heliocol system was installed. A vacuum breaker may have been installed on the roof originally, but when the solar array was moved from the south facing roof to the west facing roof (by the same installation company) to make room for the PV solar array it could have been removed. In any event, Heliocol instructions page 19 step 6 recommend HC-121A (now HC-121B) vacuum breaker placement “about 4 feet vertically above the filter…” Online forum discussions at http://www.troublefreepool.com/ and company web sites such as Hot Sun Industries (especially Hot Sun Industries videos/engineering descriptions at http://www.h2otsun.com/videos.html) indicate that the Heliocol vacuum breaker placement recommendation by Heliocol may not be the most effective vacuum breaker location in my case.

My sense is that the vacuum breaker should be placed just before the cold water feed line enters the first HC-50 panel. This would allow maximum drainage of the HC-50 panels by gravity/siphon through the solar return line when the pump is turned off.

***Would appreciate any thoughts/recommendation regarding most appropriate vacuum breaker placement for my system.

But then there is also the cold water feed line drain to consider. Its drainage is through the 3 way valve back to the pool. Some online forums recommend a 1/8 inch hole drilled into the 3 way valve face to allow for gradual draining when the pump is off.

***Thoughts/recommendations on this aspect would also be appreciated.

Finally, I read that high temperature can damage a solar system and PVC piping connecting it. On a recent 100 + deg day here in El Cajon, CA the solar system had been off for several hours with the GL-235 set to 85 deg and the aquarite water temp sensor showing 89 deg. I saw 140 deg at the temp sensor I installed on the return pipe when I put the GL-235 switch to test and engaged the solar array (note: at this high temp the Aqaurite system seems to go to Hi salt and stops providing temperature). The GL-235 manual states:

“In the “AUTO” position, the GL-235 will heat the pool or spa (rotate valve to solar loop) when the collector (solar) sensor temperature [my note…air temp sensor] is higher than the pool/spa sensor temperature [my note…feed water temp sensor] by 4ºF or more AND the pool/spa temperature is less than the high limit setting. The GL-235 will stop heating (return valve to pool loop) when the two sensor temperatures get to within 1.5ºF OR the pool/spa sensor is above the high limit setting. “

Since the pool pump in non-solar mode is operating with the 3 way valve in the solar off position I assume the solar array can’t drain past the return line check valve held closed by the pump pressure. So my impression is that the 140 deg high temp I saw was normal.

***Am I correct?

Looking forward to your comments!

 

[Isaac-1]

The placement of the vacuum breaker is a trade off, personally I think the end fitting on the low side of the panel array opposite the cold water feed makes the most sense, as it is near the apex (in theory ideal spot, but reality is many vacuum breaker valves need slight positive pressure to stay closed, which can be problematic at the apex). Mounting to too far down while allowing easy monitoring of the VCV for leaks does introduce more negative pressure to the panels while draining.

As to temperature, panels filled with water will get hotter than ones where the water is allowed to drain

On number of drains needed it is hard to say without a better understanding of your layout.

Ike.

 

[JasonLion]

I can't tell either way from the photos, but from the diagram and your description it sounds like there are low spots in the array that won't drain unless you install manual drain valves? I hope that there is some misunderstanding and that is not true. In situations like that it is impossible for the panels to fully drain, with or without a vacuum breaker

Ideally you want all of the panels to be plumbed in parallel. The 6 in parallel and then a serial connection to another 5 panels show in the diagram is less efficient. Plumbing them all in parallel does mean running the pump at a relatively high speed, but the extra heat will more than pay for the extra electricity.

Reading 140 degrees at the panels is normal. The panels are fine at that temperature if they are well supported, but if they remain full of water and the support is less than perfect the weight of the water and softening of the plastic at higher temperatures can cause them to sag and eventually damage themselves.

 

[mas985]

Vacuum release valves can be put almost anywhere in the solar plumbing. It is simply to break the vacuum so the panels will drain away from the valve. However, the closer you put the VRV to the pump, the lower you can set on the pump RPM and still keep the VRV closed. Some installers will place them a few feet above the pad so the RPM can be set really low. You might find that energy efficiency trumps heat transfer efficiency. Plus the panels will probably produce more heat than you need.

As for the 3-way valve, normally a solar valve is used for this. It has a built in check valve which allows the supply side to drain when shut off. You can also use a standard 3-way with a hole. It accomplishes the same thing which is basically a path for drainage. Another way to do this is to have supply/return bypass pipe with a valve so there is a path for drainage when the solar valve is off.

As for your last point, yes the check valve will be held closed when solar is shut off so normally the panels will remain filled to a height indicated by the filter pressure. If the WATER (not Sun) temperature is at 140 F, then this could be a problem for the PVC pipe as it will soften some at that temperature. If the VRV is plumbed too low, when the pump does shut off there can be a high vacuum at the hot PVC pipe and the pipe could deform. So in this case, you are better off plumbing the VRV close to the input to the panels so the vacuum cannot get too high.

However, another way to manage this is to step down the pump RPM when solar is disengaged so that the panels will drain at least part way down so there is no water in the panels or pipes on the roof.

 

[Isaac-1]

One more note, from the photos it does not look like these panels were installed with any upward slope (the top edge looks to be parallel with the peak of the roof), this may cause a problem with air getting trapped in the panels and blocking flow, there is a an animation of this problem about half way down the page at:

http://www.h2otsun.com/PG5ht.html

Ike

p.s. there is also an animation of a 2 bank parallel fed system, that you may want to look at, if you converted yours to this layout (minimal plumbing change) it would reduce the number of manual drains you would need..

 

[rogue]

Hello,

Many thanks for your thoughtful comments!

To be clear re geometry, solar feed water climbs 20 ft the to the roof, then 14 feet to the 26 ft high ridge line then down 12 feet to the bottom of panel #1. The panels are all mounted parallel with the roof line with no slope (unfortunately!) My sense is that because the array is on the far side of the roof ridge, unless complete drainage can be effected by siphoning, water will be trapped. Recognizing this fact and to prevent winter freezing damage, drains would need to be placed at the capped ends of panels 6 and 11. Because of the hip roof separating panels 2 and 3 a drain at the beginning of panel 1 would also be needed to ensure complete system drainage for winter.

All that said:

Issaic 1: when you say "end fitting on the low side of the panel array opposite the cold water feed " do you mean the capped end of panel 11? I understand your comment re re-plumbing, but at this point I will need to maximize capability of my current configuration.

JasonLion: Understand about incomplete draining due to panel locations, but perhaps the question is where should the vacuum breaker be placed for THE MOST drainage occur in the current configuration?

Mas985:
-I set the solar at 2250 rpm (filter at 14 PSI) and for non solar 1400 RPM (4 PSI). I recall a factor of 1 PSI = 2.31 ft head. If true then for solar the psi 14 PSI would equate to about 32 feet...6 feet higher than the roof peak. Getting water to the 26 foot roof peak would require 26/2.31 = 11.25 psi. So the 14-11.25 = 2.75 psi differential would be available to keep the vacuum breaker closed. Enough? Close?
-I'll open the 3 way valve and see if it has a bypass feature.
-Yes the 140 deg was WATER temperature measured by the thermometer placed in the solar return line as shown in the picture

Looking forward to hearing from you!

 

[mas985]

-I set the solar at 2250 rpm (filter at 14 PSI) and for non solar 1400 RPM (4 PSI).

The the panels/pipe should drain to about 9' above the filter gauge when switching off solar. But given this, I don't understand why you would have gotten the high water temperature. When you saw 140F, had the pump stepped down to the lower speed first before it was shut off?

 

[JasonLion]

There are two potential spots for a vacuum breaker to promote drainage. The simpler approach is to put the vacuum breaker valve anywhere on the pipe that supplies cold water to the panels, before the panels. The alternative is to put the breaker at a high point of the pipe between the two banks of panels. That has the disadvantage of putting the breaker at the top of the system, requiring a slightly higher pump speed during operation, but would just slightly improve the drainage as each bank could syphon independently of each other.

However, nothing is going to allow those panels to fully drain without plumbing changes. When the plumbing travels up and down and up and down like that there will always be a significant amount of water left in the panels. A properly installed panel array will have water traveling uniformly up until it reaches the top and then down from there back to the pool. That gives a clear drainage path, without requiring a syphon. Any setup that requires a syphon will drain somewhat, but the syphon will always be broken before the panels have fully drained, leaving water in the panels.

 

[Isaac-1]

To answer your question, yes, my suggestion was the capped end of #11, as it is an easy place to tapped into. Again with this layout there is no ideal answer. I am not sure what you mean by needing to maximize capability though with your current layout, as the series layout probably insures a more even flow, but I am not sure if it maximizes heat transfer, parallel operation may have slight imbalance of the panel flow, but you would likely have less thermal gradient between the two banks.

Ike

 

[rogue]

[attachment=0:2mz8luc2]Solar Re-design concept.jpg[/attachment:2mz8luc2]
Hi,

A lot of moving parts here! I'll put the vacuum breaker at the entry point of the feed line to panel #1. I can always cap it off and move to one of the other recommended position if that doesn't work out.

Mark: The solar water temp of sustained 140 deg was seen after the pool pump had been on low (1400 rpm) for several hours mid-day with solar off. This would have prevented much draining from the system. I'll leave the pump off 'till 2pm one day then start up with solar off initially, followed by solar on. If the temp gauge shows only momentary 140 deg temp then perhaps that shows some panel drainage had occurred

Ike: I looked over the Hot Sun Industries animations, videos and printed material again and came up with the attached re-design concept. Is this what you had in mind? For array tilt, section one (panels 1-6) is about 30 ft long and section two (panels 7-11) 20 feet. I didn't see a factor (ie inches drop per 10 ft run) for tilt of the sections. If small enough perhaps I can accommodate with existing hardware. Considering that section 2 has one panel less than section 1 should the feed pipe be reduced in this re-configuration to 1.5 inch to help balance the flow between the array sections?

Regards,

Chris

 

[Ken Hot Sun]

Chris, You asked me all this by e-mail and I suggested posting to a forum and it looks like you've received a lot of help already. Sometimes after reading www.h2otsun.com people come away thinking solar is a lot more complicated than it needs to be. There are some shortcuts that might help everyone. One is that good collector efficiency is a function of two things and two things alone. It has to be a black thing in the sun that is cold. Temperature and color. That's it. So simply feel the solar collectors when they are operating in Hot Sun. My dealers use infrared thermometers. You can cheap out sometimes and balance flow with valves. If there is an issue with tilting of the collectors (sloping the headers so the air will rise up and out) then the temperature check will tell you. Above someone asks about the specifics of that recommended slope from my web site. There is no specification because as long as the header is horizontal the air can release as long as its not a really long header. Again the temperature check will tell you if all is well. If there is a temperature gradient it may be easier to vent the air to release the air blockage than tilt the collector bank. Now that you have checked temperatures on a sunny day and everything black is the same temperature its time to check pressure. Pressure is the enemy. It will cause premature collector failure and it loads the pump. To keep life simple we just supply pressure gages with every Hot Sun Powerstrip system and tell people to check the pressure at the vacuum breaker location. The vacuum breaker location you say? Yes. What I have concluded in my 27 years experience doing this about 5000 times is that you want the vacuum breaker to have pressure on it when solar is on. That way it doesn't chatter and introduce air constantly. The proper vacuum breaker location is teed off the pipe entering the solar panels. If there are multiple banks at multiple heights put the vb on the inlet pipe to the highest bank of collectors. Its high up that way but not at the top and there is restriction downstream to keep it closed. Don't oversize your return piping and don't run a 2 pipe straight down 2 stories. That air column can cause a pressure pulse upon start up that can be damaging to hot collectors. There's a bit of an art to some of this. I like to treat it artfully and not put steadfast rules on every issue. To satisfy rigorous engineers you'd have to plumb entire pools in cpvc if they are solar connected. Solar can hit 180F easily on a hot day with the pool up to temp. Engineers short cut on pvc plumbing design is to say maximum 140F The more detailed engineer will look at pressure vs temperature but at 180F we can't really use pvc pipe. So where do we draw that line? We use some art in specifying solar designs to minimize the pressure. We do try to make sure the piping especially the piping located above the solar panels height empties when solar is off. That's just to take the weight off the pipes when they get hot. There are some real subdelties being discussed in these forums and I'm honored that my web site animations and explanations are referenced so much. I'll try to come back often if nobody get flamey.

 

[Ken Hot Sun]

Looking closer at the above...I'd have plumbed the solar panels in parallel not series. We see this all the time with Heliocol systems. Like my last post though. As long as you can move enough water thru them without causing too much pressure drop (load on pump) then its fine. I'd guess that this isn't fine. Heliocol panels are very restrictive (small flow passages). Just check the collector temp with water flowing on a hot sunny day and see. A simple way is to look at the total temp rise thru the system. You want a low temp rise and a high flow because its all about temperature and color. That's all there is to efficiency of solar panels.

As for the check valve location. Its just to prevent backwash of the filter when the pump is shut off. Is that a problem? Maybe its a non issue in this case. If it is then you're right you have a major replumb to do. That check valve can go between pump and filter by the way.

The big question I have is where is the dealer that installed this and guaranteed it for 20 years as per Heliocol ads? What does he say about all of this. If he's not challenged then he keeps doing this over and over. I see this kind of thing all the time. Its as if Heliocol is training its dealers to do this. It still works. Its not that bad. People who pay attention want things done to a higher standard. I've always treated solar as a technology game but to larger businesses than mine who have to answer to their shareholders and advisors tend to take a sales based approach. Solar pool heating really is a technology with a lot of finicky little issues that need to be done right. It takes a full understanding of what is happening mechanically. That';s why i don't like to say this is wrong and this is right. I like to say check the collector temperature and pressure and if its OK, its OK. Just make sure you don't leave any water in a polypropylene panel over the winter .

 

[jblizzle]

Just wanted to post say: Welcome to TFP, Ken!!!

 

[Isaac-1]

Ken, welcome, you have some of the best information on the web on your site, I used it extensively in my solar panel replacement / upgrade earlier this year.

Ike

 

[rogue]

Hi Ken,

Thanks for engaging and providing detailed perspective and tips!

My take away for my current configuration:

1. Vacuum breaker and a pressure gauge on the feed line as it enters the 1st panel are acceptable locations
2. 2 inch return pipe dropping two stories is problematic
3. Horizontal solar headers of short length are acceptable, though not preferred. Hopefully the 30 ft section #1 and 20 ft section #2 are considered "short"
4. The check valve can go between the filter and pump as opposed to between the 3 way valve and filter...this helps a lot considering restrictive space constraints of the filter location!
5. Drains at panel #1, #6 and #11 are needed to remove trapped water during winter
6. I'll add a 2nd isolation valve on the return line

So two questions remain

1. What vacuum breaker does your company use during installations?
2. Does the diagram in my last post, with changes noted, result in a "parallel" system? It seems to match the elements of your animated diagram but thought I'd ask

Regards,

Chris

 

[rogue]

Hi,

While waiting for my Heliocol contractor to respond regarding installation of a Vacuum breaker and drains to complete my configuration in accordance with the Heliocol Residential installation manual I added a Jandy 4716 shut off valve to my return line, a Jandy 7305 check valve between pool filter and pump, and removed the Jandy 7305 flapper valve improperly located on the feed line above the shut off valve (see attached). This will allow me to isolate the solar system and reconfigure it without shutting down the pool pump, as well as preventing any DE flowing back into the pool. Thanks, Ken, for your suggestion to place the Jandy check valve between the filter and the pump!

Two questions from installing the valves:

1. An odd item while installing the Jandy 4716 shut off valve to my return line. It is located below the Jandy 7305 return line check valve (i.e. allows downward flow). When I cut the return line I noticed that water was trapped behind the check valve. Removing the check valve face allowed a lot of water to exit the pipe. My thought was that there should have been enough pressure from 34 feet of water in the 2 inch pipe leading to the 26 ft high roof ridge to open the check valve in its normal direction of flow, but that ***[attachment=0:2wydpanf]Alternate Parallel Configurations.pdf[/attachment:2wydpanf]lack of a vacuum breaker prevented this from happening. Am I correct? The check valve operates normally with solar flow on.

2. When I opened the misplaced feed line Jandy 7305 check valve to remove the flapper valve a lot of water flowed out. My guess is at least the 34 ft water column to the 26 ft high ridge line. Right below this check valve is the 3 way valve, but the remaining water in the pipe above the valve did not drain out after 10 minutes. ***Is this a case where a hole needs to be drilled into the 3 way valve face to allow draining?

An added benefit of the contractor delay was time to think through the possible parallel configurations to replace the series array currently configured (i.e. 6 panel HC-50 array #1 feeding into 5 panel HC-50 array #2 as discussed earlier in this thread). In a post on 12 Nov 2007 Jason Lion stated “You want the water entering the panel to be as cold as possible, the larger the temperature difference the more heat is transferred. If the water has already gone through one panel it will be warmer, and thus the second panel in a series hookup will be less efficient. To avoid that you want to have water directly from the pool feed to each panel. “

With this in mind the attached diagrams show two parallel configurations, parallel configuration #1 and configuration #2. Based on what I’ve been reading on the forum it ***looks like the configuration #2 is the best choice. Correct? Would appreciate your thoughts on which configuration would be best to maximize heat transfer from the two arrays to the pool. Either configuration change from my current series configuration is relatively minor in scope.

***And of course is the location of the vacuum breaker as shown still a good choice for the parallel configurations shown?

Regards,

Chris

 

[mas985]

1. Correct, a partial siphon is set up so it can prevent the water from draining. The supply side of the plumbing is now longer and is creating a slight suction on the check valve so it remains closed.

2. Now, you have allowed air to enter the other side of the check valve, and it will travel up the pipe displacing the water. However, it won't drain the entire solar plumbing but will stop once it reaches the top. And if you had a hole drilled in the solar valve, eventually, the supply side would drain as well. If the supply side was allow to freely drain without restriction as we;;, the return side would have had much less water coming out of the pipe. Most of the water would have traveled up the pipe and out of the supply side. But because the valve was closed, this could not happen.

As to the configuration, can you bridge the panels together? So the space/gap between the panels has a pipe connecting them and then you can treat both panels as a single panel fed from the bottom left and returned on the top right. They are still fed in parallel. You can put the VRV on the bottom right.

 

[rogue]

Hi Mark,

Appreciate the prompt and detailed response!

All 11 Heliocol HC-50 panels were originally in one array as you suggest. However the Heliocol installation manual and engineers confirm that 8 HC-50 panels are the maximum in series. Some lee way was apparently given up to 10 panels but at 11 panels I understand one would loose ability to have adequate flow throughout the array and one would have less than 11 effective panels.

The original installation contractor corrected this single 11 panel configuration and made two arrays of 6 panels and 5 panels then put them in series. From forum discussions it appears these two arrays should be in parallel.

My sense is that my configuration #2 shown with the T feeding both arrays at the same time would help with the flow balance issue.

Regards,

Chris

 

[mas985]

I think I understand what they are saying but I doubt it would be a problem. The header head loss is not much different than an equally sized pipe so the end panel should get the same flow rate as the first the panel if the supply and return are on opposite corners. The system is symmetrical so each panel should get close to the same flow rate and all panels are still in parallel so efficiency should not be reduced.

Anyway, if you feel more comfortable going with configuration #2, that should work as well.

 

[rogue]

Hi,

Thanks again for all the ideas and support!

I have all the parts now to add the vacuum breaker, drains and re-configure to a parallel setup as shown in the attached.

A quick question: would a WYE fitting at the upper left hand corner of the attachment circled in green be a better choice then a T fitting where the return lines from both parallel arrays join? Perhaps better flow, less pressure?

Regards,

Chris[attachment=0:1yacys28]Rondestvedt Solar Parallel Configuration B.pdf[/attachment:1yacys28]