Convert thermosyphon to pumped.

[r.bartlett]

https://www.dropbox.com/sh/w7lumy77hlt53x4/AAC40U_knTsnIJCvCEuvP2Bfa?dl=0

I've added a dropbox link as I am having trouble uploading pics.

the temps were taken around 11.30 today.

[r.bartlett]

Could it be that you are expecting to much from your system for this time of year?
For a better understanding of solar thermal performance for each month try downloading the free trial solar thermal assisant software from Solarpathfinder.com.
Enter a system close to the one at your site, and you can then see how performance varies for each month.
Good luck.

possibly which is why I am trying to squeeze more out of what I have

[r.bartlett]

For my part, you're most welcome. More later. This is not meant as an insult, but you seem to have a fundamental misunderstanding of how solar thermal collectors, both active and passive, as well as the subtleties of thermosihon systems work. Consult a solar energy text for more info.


I look forward to more information, including photos.

BTW, if you're not running a non freezing fluid through the collector loop (glycol/Water solution) because of non freezing conditions, the heat exchanger is not necessary, and is actually an albatross around the neck of system performance (but remember, you only need 1 cold snap and it's game over, and also keep in mind - things exposed to a clear, dry nite sky can fall way below the amb. air temp.).

If I have a misunderstanding then it would be better to correct me here rather than redirect off somehwere on a wild goose chase.What have I written that isn't correct?
I would also welcome more information regarding those subtleties thanks

as regards freezing again I reiterate there is absolutely no chance of it freezing here . My village has never recorded temps low enough. Finally, doing away with the heat exchanger is no problem but would welcome advice how I can do this on my set up?
what I have learnt is taking temperatures of what is happening is absolutely vital

[r.bartlett]

13:30

been up on the roof again. the outlet temp is 60c and return 29c tank up around 28c

[J.P.M.]

https://www.dropbox.com/sh/w7lumy77h...CEuvP2Bfa?dl=0

I've added a dropbox link as I am having trouble uploading pics.

the temps were taken around 11.30 today.

Thanx for the photos. Looks to me like the collector outlet is going directly to the tank, and the tank outlet is going to the collector inlet.

So, if I'm seeing things correctly, while you may have a HX inside that tank, the way the system is plumbed, it's not utilizing the heat exchanger.

Although your tank is not at an elevation that will prevent reverse flow entirely, that lower elevation is probably contributing some, but not too much to your flow problems. A higher tank elevation would help some, but I don't believe that's your biggest worry.

I did not see one, but in systems where the tank is not completely above the topmost collector elevation, a check valve is necessary in the collector/tank circuit to prevent reverse thermosiphoning. If there is a check valve present, three things: first, conventional check valves cannot be used - they will kill the flow because they need more pressure head to open than thermosiphon systems can possibly generate, 2d, a thermostatic check valve similar in principal to those used on liquid cooled ICE's is required. Third, check valves fail. Because it's an obstruction in the line, like any valve, it will get crudded up. That means it may get stuck partially closed(or open - same thing).

I believe your problem is a mix of air blockage(s), smaller than usual pipe diameters (for thermosiphon systems ), and any likely mineral deposits on the piping and in the valves and other line devices that reduce diameters and increase pressure drop = reduce flowrate further. That lower flowrate means a larger temp. difference between coolant inlet and outlet, and that means lower performance.

The convoluted flex joints add to the pressure drop. They're handy and useful, but need to be kept short. Short radius elbows as you have aren't helping either.

Thermosiphon systems do not easily (or at all sometimes) tolerate more than two changes in elevation: one going up and one going down. Local, that is small, changes in elevation can cause problems or at least reductions in performance. Even if that air vent at the collector is working (FWIW, I get about 2 years out of mine and it fails closed), that slight elevation drop and then rise in the line at the collector outlet can slow the flow.

Between the tank elevation, what looks like a perfect spot for an air lock in the collector outlet (if what looks to be an air vent is non operable from scaling), and what's probably some rather substantial mineral scale buildup in the system in general, the added flow resistances are decreasing the flow.

I'd get the system serviced and checked out.

Some good news: Without a HX present, you can certainly add a pump to the system, but a properly designed and reasonably maintained and cleaned thermosiphon system has substantially the same performance as a pumped system would have. Also, and hard to say without being there, but adding a pump to the existing system without addressing the other things going on may not solve too many problems.

I'd get the system serviced, meaning cleaned, checked for equipment operating normally, and maybe clean up the piping layout (shorten and straighten the runs and get rid of that at least partial air lock at the top), and then see what happens before I added a pump.

Some other things:

Looks like plastic tubing on the tank out to the house. Bad idea, particularly if/when the system starts producing really hot water.

I didn't notice any safety relief valves in the system. That's a big deal. Seriously. Are there municipal building/plumbing codes in force ?

The closed cell foam insulation such as you have in place is good stuff, but it needs to be protected from sunlight. Your stuff is deteriorating. I've found aluminum duct sealing tape (NOT cloth duct tape) lasts ~ 5 - 7 years outside under direct sun and does a good job of protecting the Armaflex type insulation. Your insulation is also shrinking. Insulation gaps will cause a larger decrease in overall insulation effectiveness than apparences may make you believe - a 5% area uncoverge will probably decrease overall insulation performance by a lot more than 5%. 20+ % or so is more likely.

[LucMan]

possibly which is why I am trying to squeeze more out of what I have

Do you have flow restrictors on all of your faucets and shower heads? You want to keep your terminal flow rates below 1.5 gpm if possible, especially with a horizontal storage tank. With high flow rates it becomes and issue with the entering cold water mixing with the hot water effectively reducing the amount of HW available. Vertical tanks are are less prone to this issue because of the additional distance between the cold water inlet & HW outlet.
Looking at your pictures the collector looks to be approximately 30 degrees a good compromise for year round use. Increasing the angle to 50+ degrees would optimize the collector for winter operation with out losing to much for the summer season.

[J.P.M.]

Looking at your pictures the collector looks to be approximately 30 degrees a good compromise for year round use. Increasing the angle to 50+ degrees would optimize the collector for winter operation with out losing to much for the summer season.

Once upon a time, some horizontal tanks came with cold feed line inlets and collector returns that ran the length of the tank with holes along the length to help avoid destroying the thermal stratification. Others techniques such as diffusers of various designs were sometimes tried. I toyed with a few such designs, but came to the conclusion it wasn't worth the time/hassle/effort in most cases, and that reducing the draw was a good solution for preventing most thermocline disturbance by the makeup water, in conjunction with perhaps a larger collector return preserved most of the thermal stratification.

I thought about suggesting a higher slope of, say, 50 deg. or so for the reasons you cite as well as a bit more head for driving density differences, but at 28 deg. N. latitude, and the goldilocks ambient seasonal temps., the high year round clearness index, and with everything else the system needs, I figured there was already enough going on. FWIW, I agree in principle with a higher tilt.

[r.bartlett]

Thanx for the photos. Looks to me like the collector outlet is going directly to the tank, and the tank outlet is going to the collector inlet.

So, if I'm seeing things correctly, while you may have a HX inside that tank, the way the system is plumbed, it's not utilizing the heat exchanger.

chromagen diag.JPGchrmoagen.JPG

it's plumbed in as per the above (espanol)
Not sure what you mean exactly though tbh.

Although your tank is not at an elevation that will prevent reverse flow entirely, that lower elevation is probably contributing some, but not too much to your flow problems. A higher tank elevation would help some, but I don't believe that's your biggest worry.

I did not see one, but in systems where the tank is not completely above the topmost collector elevation, a check valve is necessary in the collector/tank circuit to prevent reverse thermosiphoning. If there is a check valve present, three things: first, conventional check valves cannot be used - they will kill the flow because they need more pressure head to open than thermosiphon systems can possibly generate, 2d, a thermostatic check valve similar in principal to those used on liquid cooled ICE's is required. Third, check valves fail. Because it's an obstruction in the line, like any valve, it will get crudded up. That means it may get stuck partially closed(or open - same thing).

there was a check valve on the bottom of the tank return to the collector. I removed the inners to ensure no restriction

I believe your problem is a mix of air blockage(s), smaller than usual pipe diameters (for thermosiphon systems ), and any likely mineral deposits on the piping and in the valves and other line devices that reduce diameters and increase pressure drop = reduce flowrate further. That lower flowrate means a larger temp. difference between coolant inlet and outlet, and that means lower performance.

The convoluted flex joints add to the pressure drop. They're handy and useful, but need to be kept short. Short radius elbows as you have aren't helping either.

I can re-pipe it

Thermosiphon systems do not easily (or at all sometimes) tolerate more than two changes in elevation: one going up and one going down. Local, that is small, changes in elevation can cause problems or at least reductions in performance. Even if that air vent at the collector is working (FWIW, I get about 2 years out of mine and it fails closed), that slight elevation drop and then rise in the line at the collector outlet can slow the flow.

Between the tank elevation, what looks like a perfect spot for an air lock in the collector outlet (if what looks to be an air vent is non operable from scaling), and what's probably some rather substantial mineral scale buildup in the system in general, the added flow resistances are decreasing the flow.

I'd get the system serviced and checked out.

the AAV is working correctly. I will look at repiping with better smoother lines and no undue rise/falls

Some good news: Without a HX present, you can certainly add a pump to the system, but a properly designed and reasonably maintained and cleaned thermosiphon system has substantially the same performance as a pumped system would have. Also, and hard to say without being there, but adding a pump to the existing system without addressing the other things going on may not solve too many problems.

I'd get the system serviced, meaning cleaned, checked for equipment operating normally, and maybe clean up the piping layout (shorten and straighten the runs and get rid of that at least partial air lock at the top), and then see what happens before I added a pump.

I will repipe.

Some other things:

Looks like plastic tubing on the tank out to the house. Bad idea, particularly if/when the system starts producing really hot water.

I didn't notice any safety relief valves in the system. That's a big deal. Seriously. Are there municipal building/plumbing codes in force ?

yes there is a PRV on the cold inlet. no PRV on the solar loop. Plastic is used here all over the island. It's rated above 100c.

The closed cell foam insulation such as you have in place is good stuff, but it needs to be protected from sunlight. Your stuff is deteriorating. I've found aluminum duct sealing tape (NOT cloth duct tape) lasts ~ 5 - 7 years outside under direct sun and does a good job of protecting the Armaflex type insulation. Your insulation is also shrinking. Insulation gaps will cause a larger decrease in overall insulation effectiveness than apparences may make you believe - a 5% area uncoverge will probably decrease overall insulation performance by a lot more than 5%. 20+ % or so is more likely.

upgrading the insulation can be done at the same time as the repiping.

big thanks.

[r.bartlett]

Once upon a time, some horizontal tanks came with cold feed line inlets and collector returns that ran the length of the tank with holes along the length to help avoid destroying the thermal stratification. Others techniques such as diffusers of various designs were sometimes tried. I toyed with a few such designs, but came to the conclusion it wasn't worth the time/hassle/effort in most cases, and that reducing the draw was a good solution for preventing most thermocline disturbance by the makeup water, in conjunction with perhaps a larger collector return preserved most of the thermal stratification.

I thought about suggesting a higher slope of, say, 50 deg. or so for the reasons you cite as well as a bit more head for driving density differences, but at 28 deg. N. latitude, and the goldilocks ambient seasonal temps., the high year round clearness index, and with everything else the system needs, I figured there was already enough going on. FWIW, I agree in principle with a higher tilt.

When I repipe I will reduce the outlet pipe diameter . I am starting to think I need a second system. One of the problems you mention is high draw there is a long distance between the solar tank and the main house. the solar is sited on a small second house to feed two dwellings.
tenerifehouse plan.JPG
the tank is sited on the grey roof and feeds the small finca and under the path to the main house ....note solar located finca roof is now red so not to confuse you!

[J.P.M.]

Couple things:

1.) When/if you add a check valve back into the system: DO NOT use a spring loaded check valve as is commonly available. As I wrote, common spring loaded valves need more velocity head against them to open (commonly called "cracking pressure") than any thermosiphon system can generate. A spring loaded check valve may well stop operating flow altogether. Swing type or gravity check valves are better, but will still reduce flow to what's probably/likely an unacceptable degree, with little in the way to tell if/how much it reduces flow. If you do use a swing check valve, get one that's a pipe size larger than the line it's in and use 2 pipe reducers, one on either side of the valve to fit the line.

2.) The big deal/reason for using a check valve is to prevent reverse flow that can reduce tank temps as much as or more than they increase during the previous day. A check valve is necessary in thermosiphon systems when the tank is not completely above the collector as is your situation. One sure fire way to get around a check valve altogether is to elevate the tank so that it is completely above the collector (I know, a real PITA and a whole lot easier to say than do solution). But, in doing so you will eliminate the need for a check valve altogether. The way it is now, and after it gets serviced, you'll lose some collected heat at night. So, you'll need a check valve or a tank raising. Between those two options, finding a suitable thermostatic check valve with low pressure drop may not be possible. That leaves raising the tank, or taking a chance on a swing or gravity check valve having low opening/operating pressure drop characteristics. I'd raise the tank.

3.) Thermosiphon systems require VERY low system operating pressure drop. That means large(r) pipe diameters than for pumped systems, as few bends/elbows as possible with all those bends/elbows of a wide radius type, and as I wrote, only two changes in elevation for the whole system, one up, and one down.

4.) You mentioned something about reducing a pipe diameter - Don't do it - Make it bigger. Looks to me like your system was put together by someone who was trying to save money on piping at the expense of system performance, or ignorance of the importance of keeping thermosiphon system pressure drop low, or both. The piping on the collector loop is simple and pretty straightforward. I'd raise the tank about 60 or 75 cm. or so, plumb the collector loop with 3/4", or better, 1" copper - No plastic crap - and use reducers at the tank and collector connections. I'd then reinsulate with 1" or greater thickness closed cell foam, either jacketed or (as I did) wrapped with aluminum duct sealing tape (NOT cloth type "duct tape"). Do it right and you might get away with as few as 4 to 6 long radius elbows if you play heads' up ball with the tank elevation.

5.) While you're at it, check and service the expansion tank. They can fill up with water after a few years as the bladder's usually will leak after a period of time.

[r.bartlett]

I am off to buy a new NRV (I have a 1 hr drive) and an electric heater kit I think the nrv is a major factor on why I don't have enough hot water esp in the morning.

The rest of the upgrading as per your post will be done over Christmas.

[J.P.M.]

I am off to buy a new NRV (I have a 1 hr drive) and an electric heater kit I think the nrv is a major factor on why I don't have enough hot water esp in the morning.

The rest of the upgrading as per your post will be done over Christmas.

I'd respectfully suggest you consider learning why any suggested improvements, including mine, be helpful before you do the upgrade. You have the advantage over everyone here in that you are on site and can see all that is going on better than anyone. More education will lift the scales from your eyes.

Also, and to reiterate, increasing the tank elevation is a better solution to the problem of reverse thermosiphon flow than a check valve. The check valve is a necessary evil brought on by the low tank elevation.

Good luck.

[r.bartlett]

I have concerns regarding check valves as it seems pointless smoothing out the water paths and having a naturally highly restrictive component in the circuit

as part of my daily advancement:
Can you educate me as why a tank at panel height can reverse TS but a tank higher can't
thanks

[J.P.M.]

I have concerns regarding check valves as it seems pointless smoothing out the water paths and having a naturally highly restrictive component in the circuit

as part of my daily advancement:
Can you educate me as why a tank at panel height can reverse TS but a tank higher can't
thanks

I'll help folks some - as I believe I have on this thread, and as I see part of the mandate of my former profession (engineering), but in general, and not directed at you personnaly, I consider spoonfeeding folks things they can readily find and learn by their own efforts to be no more than enabling behavior on my part - a behavior I do not engage in too much , too often or too deeply, and which does no one any good.

But, you can easily teach yourself which is what I've been suggesting all along in this thread.

I won't feed you, and I won't teach you to fish, but I will point in the direction where you can take control of your situation, be self actualizing and learn to fish on your own.

I'll get you started: www.appropedia.org/Thermosiphon will explain a lot of the basics. Otherwise , google "Why do thermosiphon systems work ?", learn the basics, and then use your critical thinking skills and logic to figure out why more height will lead to higher flowrates in thermosiphon systems, and for your situation and question, why the minimum necessary height of storage to completely prevent reverse thermosiphoning is above the highest heating (or - hint - cooling) surface elevation ( the collector).

My prior posts to this thread also contain some nuggets. Reread them after knowledge quest about the basics. You may gain some further insights.

[r.bartlett]

just to say I got the heater kit installed and had a good feel around inside the tank. there was no evidence of any scale build up . all seemed clean as a whistle. still looking at upgrading to larger loop pipe and cleaner flow lines.with large radi elbows etc.

n the meantime i dropped the return pipe so it sags below the level of the bottom of the panel. I read this means this return pipe is the bottom of the cold loop and the panel is all in the upflow..if that makes sense)

. I set the stat at 50c for the electric heater. However the water seems very hot . but we do have a clear bright sunshine days atm.

I know and understand the principles of TS. It's not rocket science. There still is no clear explanation of why a tank situated higher wont reverse . apart from 'because' which isn't really an answer

If the TS effect increases with tank height due to I presume 'head' why the reverse effect isn't made stronger too...