Low flow rate in closed loop system

[J.P.M.]

After recharging, I'm now able to see that my circulation pump is only capable of moving about 1.3 GPM through this system. However, I'm actually happy with that, as it appears I had been shooting for the wrong flow rate target. After carefully studying the manual and collector spec sheet, it appears that the recommended 1.3 GPM is for the whole array, and not per collector, as I had originally thought.

I mentioned in a prior post that, IMO, and for several reasons, the recommended flowrate is way too low and for one thing probably contributed to an increased fouling rate as f(time).

Also, since the collectors seem to be plumbed in series, not parallel, the flowrate through each collector is almost identical.

[Stringpark]

Really appreciate everyone's help on this, so just wanted to post a quick update. Filled the system completely up with distilled white vinegar the other evening and let it sit over night. Initially was circulating it through the loop, but one thing that caught me by surprise was the pressure rise (rapid too). I relieved some of the pressure and stopped circulating, which seemed to have gotten things under control, but the next morning the pressure meter was completely pegged. Nothing blew up though, so all is well. Anyway, flushed the system and got a ton a black mud out of it. At first, it seemed as though the flow rate had improved (up to 1 GPM), but over the next day it regressed back to <0.5 GPM again.

So, the next step was to get on the roof and try to identify the bottleneck. For this, I just ran city water through the system, breaking the loop in various places, and measuring the flow rate with the aid of my Flume water monitor. Jumpering around the array entirely gave me about 4 GPM and then adding one collector to the mix dropped it down to a little over 3 GPM. Adding in a second collector saw no drop in GPM, but when I added in the third collector, the flow was visibly reduced and measured at a little over 1 GPM. So, I've taken this collector out of the loop for the time being.

After recharging, I'm now able to see that my circulation pump is only capable of moving about 1.3 GPM through this system. However, I'm actually happy with that, as it appears I had been shooting for the wrong flow rate target. After carefully studying the manual and collector spec sheet, it appears that the recommended 1.3 GPM is for the whole array, and not per collector, as I had originally thought. So I think everything is on track at this point. Now to get that last collector cleaned out. Will be using the very helpful recommendations in this thread for that task. Thx again everyone!

[Stringpark]

Awesome, thx azdave and LucMan! I'll give that a go in the next day or so and then post the results. Really appreciate it!

[LucMan]

Thanks J.P.M.! That arrangement you describe does make a lot of sense. Since I've already completed all the roof work though, I think I'll see how far the current arrangement will take me for now. If these panels end up being to far gone, then I'll probably end up investing in evacuated tube (which I think would work better with my roof orientation anyway). The good news (I think) is that even with the extremely low flow (<0.5 GPM) these panels are already producing more hot water than what I know what to do with. Fingers crossed that I can get the flow rate up with some cleaning.

Thanks for the input LucMan! I think my system holds about 4-5 gallons of fluid. Walmart sells distilled white vinegar for about $2.50 a gallon, so it wouldn't cost too much to fill the whole system with it and let it circulate for a good while. I was originally thinking along the line of just filling a single collector one at a time, but the window on the flow meter in the system is pretty well glazed over with red gunk after running the system over the last several days (on water), so running through the whole system may be best to clean everything up anyway. You mentioned to try to find a plastic body pump for the process, so would it be accurate to conclude that you advise against charging the system with vinegar and then simply letting it circulate through the regular system pump?

You can try using the system pump but it may not have high enough GPM or pressure to do the job. But give it a go.
The vinegar will get weaker as it cleans the system you can use PH strips to test the strength of the vinegar and make Shure your not wasting your time circulating neutral PH . Change the vinegar solution when it gets weak . Watch your flow meter when you get 1.5-2 gpm per panel you can put it back on line and see what happens. Keep flushing with clean water after your done.

[azdave]

Sorry to keep pestering you guys, but one more quick question that kind of goes along with the pump question, is it possible to have the vinegar in the system for TOO long and/or is it a problem if it gets hot?.

Baby steps. My thoughts would be to install it in the evening and let it circulate all night and then drain it in the morning to observe what has been dissolved and check flow. If that overnight test does not seem too aggressive only then would I try a daytime event with the sun's heating as well.

[Stringpark]

Sorry to keep pestering you guys, but one more quick question that kind of goes along with the pump question, is it possible to have the vinegar in the system for TOO long and/or is it a problem if it gets hot? Basically, I'm wondering if I can just charge the system with vinegar in the evening and let it cycle through the system for all of the next day, acting as the heat transfer fluid and cleaning as it goes.

[J.P.M.]

Thanks J.P.M.! That arrangement you describe does make a lot of sense. Since I've already completed all the roof work though, I think I'll see how far the current arrangement will take me for now. If these panels end up being to far gone, then I'll probably end up investing in evacuated tube (which I think would work better with my roof orientation anyway). The good news (I think) is that even with the extremely low flow (<0.5 GPM) these panels are already producing more hot water than what I know what to do with. Fingers crossed that I can get the flow rate up with some cleaning.

Thanks for the input LucMan! I think my system holds about 4-5 gallons of fluid. Walmart sells distilled white vinegar for about $2.50 a gallon, so it wouldn't cost too much to fill the whole system with it and let it circulate for a good while. I was originally thinking along the line of just filling a single collector one at a time, but the window on the flow meter in the system is pretty well glazed over with red gunk after running the system over the last several days (on water), so running through the whole system may be best to clean everything up anyway. You mentioned to try to find a plastic body pump for the process, so would it be accurate to conclude that you advise against charging the system with vinegar and then simply letting it circulate through the regular system pump?

If the vinegar doesn't produce sufficient results, you can always step up to hydrochloric acid. Basically, that's pool acid, often called muriatic acid you get at pool supply places, and according to the MSDS, pretty much the active ingredient in Rydlyme. Cut it about 10:1 and see what happens. Just wear gloves, add the acid to water - not he other way around and stay upwind of the fumes.

[Stringpark]

Thanks J.P.M.! That arrangement you describe does make a lot of sense. Since I've already completed all the roof work though, I think I'll see how far the current arrangement will take me for now. If these panels end up being to far gone, then I'll probably end up investing in evacuated tube (which I think would work better with my roof orientation anyway). The good news (I think) is that even with the extremely low flow (<0.5 GPM) these panels are already producing more hot water than what I know what to do with. Fingers crossed that I can get the flow rate up with some cleaning.

Thanks for the input LucMan! I think my system holds about 4-5 gallons of fluid. Walmart sells distilled white vinegar for about $2.50 a gallon, so it wouldn't cost too much to fill the whole system with it and let it circulate for a good while. I was originally thinking along the line of just filling a single collector one at a time, but the window on the flow meter in the system is pretty well glazed over with red gunk after running the system over the last several days (on water), so running through the whole system may be best to clean everything up anyway. You mentioned to try to find a plastic body pump for the process, so would it be accurate to conclude that you advise against charging the system with vinegar and then simply letting it circulate through the regular system pump?

[LucMan]

Connect a high pressure purge pump to the system and circulate vinegar until flow is restored. If vinegar fails to clean try Rydlyme. If all else fails use commercial coil cleaner(sulphuric acid, or hydrochloric acid) as a last resort.
Use this setup http://mistersustainable.blogspot.co...rs-for-my.html
Try to find a plastic body pump.
The expansion tank needs to be a SOLAR rated expansion tank, a hydronic expansion tank is not suitable and will come with the bladder charged to 12PSI.

[J.P.M.]

One ongoing but unseen or ignored problem with residential solar thermal systems has always been that owners treated them like the conventional water heater in the basement, that is, they ignored routine maintenance. That probably happened with this system. The glycol change outs, if done at all, probably where infrequent. As things got more fouled, the glycol flowrates which probably never were that high, slowed more. That raised the collector temps. more and contributed to the glycol breakdown and further fouling, and so it went.

I suspect the collectors may be fouled to the point that they may not be able to collect much useful energy.

If the internal flow arrangement of the collectors is what I think it is, such a configuration should be plumbed from the bottom at each side and not the top as it is for this application. What it looks like you have are 3 sumps with no way to drain them and a header arrangement that guarantees maldistribution of flow, particularly at the low flow rates suggested by the assembly and operating manuals. A better arrangement would be to stack the collectors in landscape orientation with flow in the bottom and out the top. At least that way you'd be able to drain them and also have the advantage of some thermosiphon movement to aid flow, particularly in case of a power failure.

Although the flow maldistribution would still exist due to the internal's arrangement, that maldistribution tends to be corrected to some degree by the enabled thermosiphon action.

[Stringpark]

White vinegar you buy at the store is diluted acetic acid. It's a 4% concentration. Use it as it comes out of the jug. You can buy what's called glacial acetic acid, but you don't want to get involved with that unless you REALLY know what your doing.

How long has the system been in existence and, a separate question, how long has it been in use ?

Awesome, thx J.P.M.! From what I understand, the system was installed new in 2008. The previous owners let me have the system for the effort of de-installation, which I did earlier this year. The loop was completely dry when I de-installed it (pump was destroyed with cooked glycol in it, etc.), and if I recall correctly, the previous owners said it was not working when they bought the house a few years ago. So age of the system is 13 years, but I'd have to guess on the in use time and say maybe 10 years or so.

PB: These panels have a funky internal arrangement. Think of a U-tube shell and tube heat exchanger in a vertical orientation with the U bends at the bottom.

For this collector system looking at the collectors without the glazing on them, you'll see 1 half length (or width for the portrait orientation) header. From there, the risers drop, make a "U" turn and head back up to the outlet (half) header which is at the same elevation (for the portrait orientation) and regardless of orientation, colinear with the inlet header. As plumbed for this application, the collector system can't be drained which, if the system stood unused for any length of time, may have contributed to any fouling that may exist in the collectors.

That makes sense for how I imagined the header to be configured as well. These are the Sol 25 Plus collectors (Stiebel Eltron's first gen collectors, as I understand it). I've had the collectors apart, and what I remember is that the bottom 3 quarters (in portrait) looked like the below, with a common footer pipe. The "half" header you described is the only thing that made sense to me, although I never looked at header when I had the collectors apart (I was focused on fixing pinhole leaks on the footer).
Collector configuration.png

[J.P.M.]

I am confused. It looks like If I was I standing on the bottom drip edge of the roof looking up that the flow goes into the upper left hand corner and then flows through the three collectors in series before exiting out the upper right hand corner? That is unusual. I do not pretend to know what the internals look like but most collectors would be oriented 90 degrees so they are vertical with a common bottom and upper header connected to all the panels so the flow is in parallel. Normally inside of the panel is just multiple smaller vertical tubes with fins hooked to common header. Hooking them in series means all the flow has to run through the three panels so friction in piping could be an issue and is not typical for SHW collectors. I have seen versions that were fed from the bottom with horizontal internal tubes but they were hooked in series and really didnt work well. Panels can only absorb 80 deg F over ambient and that best done with vertical internal tubes in parallel. The tubes may be small so there are lot of them and that means low velocity in each tube.

The trick with pressure gauges is realize you are measuring two different pressures, static and dynamic. If there is no flow in the line then all you are measuring is how high the gauge is relative to the source of pressure. Assuming you have steady water pressure in the street then three pressure gauges would be handy. Mount one on the line coming in from the city, one on the vent on the roof and one at the discharge where you are dumping the water. Now with no flow write down all three readings, this is static pressure. The difference in pressure between the roof and the supply gauge should be the elevation difference divided by 2.31 which will convert to PSI. If its not, one of your gauges is not calibrated. You can also just use one gauge and run up and down a ladder ideally with a temporary valve to hook up to at each point. Now start the flow through the system and read all three gauges, this is the dynamic pressure. Now subtract the static from the dynamic and then subtract the pressure from the gauge up on the roof with the one on the inlet and compare it to the difference between the gauge on the roof and outlet. My guess is you will see a much bigger value between the inlet and the vent on the roof. That means that it either piped incorrectly or you got a plug. To go farther than that would require more pressure taps on the inlet and outlet of each collector. They should be equal dynamic pressure drop (subtract the outlet from the inlet when flowing, if one is much higher than another you got a plug. If they are equal than its probably incorrect piping.

FYI , your piping piping looks small but hard to judge in photo. Measure the piping going in an out. 1/2" copper tubing is only good for around 3.5 psi with big pump, 3/4" Tubing is good for 7 GPM

PB: These panels have a funky internal arrangement. Think of a U-tube shell and tube heat exchanger in a vertical orientation with the U bends at the bottom.

For this collector system looking at the collectors without the glazing on them, you'll see 1 half length (or width for the portrait orientation) header. From there, the risers drop, make a "U" turn and head back up to the outlet (half) header which is at the same elevation (for the portrait orientation) and regardless of orientation, colinear with the inlet header. As plumbed for this application, the collector system can't be drained which, if the system stood unused for any length of time, may have contributed to any fouling that may exist in the collectors.

[J.P.M.]

Thx guys, so with the vinegar, is that straight, or a certain percentage of water mixed in, or what do you recommend?

White vinegar you buy at the store is diluted acetic acid. It's a 4% concentration. Use it as it comes out of the jug. You can buy what's called glacial acetic acid, but you don't want to get involved with that unless you REALLY know what your doing.

How long has the system been in existence and, a separate question, how long has it been in use ?

[Stringpark]

Thx guys, so with the vinegar, is that straight, or a certain percentage of water mixed in, or what do you recommend?

[peakbagger]

FYI, if the coils are corroded from the inside due to acidic stagnant antifreeze cleaning may cause a leak. If there was weak spot better to know it now than later. In some cases leaks can be patched while in others its not worth it as the panel are just plain shot.