Low flow rate in closed loop system

[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.

[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.

[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?

[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]

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.

[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.

[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.

[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!

[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!

[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.