Bad experience with evacuated tubes.

[MikeSolar]

I've been playing with tubes for about 25 years. First the Philips tubes (Corning, originally), then Thermomax and Viessmann all of which are single wall vacuum and all of which have the same problem over time.....the seals at the ends of the tubes veerrrryyy slowly have air diffuse through.

I have seen some of the Philips tubes that were tried in the arctic by the Canadian military. Some were still good and I made a few panels out of a total of 200 tubes, but most had lost their seals. This was almost 20 years after they were made.

I cannot say whether I have seen any reports from Australia about tube longevity as most of it was noted at conferences in Germany or here. According to a couple of Chinese manufacturers I have talked to over the years, it is taken for granted that the tubes will occasionally fail which is why they are easily bought singly for $1 or 2 in China. They don't consider it a big issue.

[Peter69_56]

Tube Failures

I've been playing with tubes for about 25 years. First the Philips tubes (Corning, originally), then Thermomax and Viessmann all of which are single wall vacuum and all of which have the same problem over time.....the seals at the ends of the tubes veerrrryyy slowly have air diffuse through.

I have seen some of the Philips tubes that were tried in the arctic by the Canadian military. Some were still good and I made a few panels out of a total of 200 tubes, but most had lost their seals. This was almost 20 years after they were made.

I cannot say whether I have seen any reports from Australia about tube longevity as most of it was noted at conferences in Germany or here. According to a couple of Chinese manufacturers I have talked to over the years, it is taken for granted that the tubes will occasionally fail which is why they are easily bought singly for $1 or 2 in China. They don't consider it a big issue.

My tubes are Linuo Paradigma solar collectors CPC-1506 C-1-0/06-47/1500/1-5so

[Peter69_56]

My tubes are Linuo Paradigma solar collectors CPC-1506 C-1-0/06-47/1500/1-5so

Is it obvious if they have lost vacuum? Apart from lost heat ability do they discolour or frost over or anything?

[MikeSolar]

Is it obvious if they have lost vacuum? Apart from lost heat ability do they discolour or frost over or anything?

Yes, every tube (Sydney tube or single wall) has a "getter" which is a small ring at the bottom of the tube and is designed to absorb any gasses. When the tube looses its vacuum, the getter basically evaporates and makes the tube cloudy at the bottom, the silver is gone and it is a stark difference from the silvered tip.

Schott got out of the residential thermal collector market a few years ago. Their tubes were too efficient and the glycol couldn't handle it (there were other issues too) and I had to look at all the projects we did and they paid to replace the collectors with one of my choosing. I chose the the Paradigma CPC panels with the SS U-tubes. These ones are 1.8m long and 2.4m wide (almost 5m2 panel!!!) These were the highest quality ones available IMHO. Even with these, there has been a couple of lost tubes in the past few years on an apartment building that I look after.

The problem is that most people would never know if the tube was compromised other than very carefully looking at the utility bill in the summer but most people just carry on with their lives and don't normally go up on a roof to check these things.

[Peter69_56]

Lost Tubes

Yes, every tube (Sydney tube or single wall) has a "getter" which is a small ring at the bottom of the tube and is designed to absorb any gasses. When the tube looses its vacuum, the getter basically evaporates and makes the tube cloudy at the bottom, the silver is gone and it is a stark difference from the silvered tip.

Schott got out of the residential thermal collector market a few years ago. Their tubes were too efficient and the glycol couldn't handle it (there were other issues too) and I had to look at all the projects we did and they paid to replace the collectors with one of my choosing. I chose the the Paradigma CPC panels with the SS U-tubes. These ones are 1.8m long and 2.4m wide (almost 5m2 panel!!!) These were the highest quality ones available IMHO. Even with these, there has been a couple of lost tubes in the past few years on an apartment building that I look after.

The problem is that most people would never know if the tube was compromised other than very carefully looking at the utility bill in the summer but most people just carry on with their lives and don't normally go up on a roof to check these things.

Mike thanks for the update, I will keep an eye on mine and see how they go. I regularly get up on my roof and check out how everything is going, wash off all the bird crap and so on. Will let everyone know if I have failures. Mine are U tube style.

[Tony2046]

Thanks Mkel

I've been experimenting with evac tubes for a few years now. Have 80 tubes on the roof and last year I started to have heat tube failures. I want to add some comments about my experiences and maybe they will help someone else.... some of these comments are my opinions with no scientific tests.
Please don't rip me if I miss-spell something --

1. I read where a infra-red heat detecter could be used on the glass tubes to determine if a heat tube had failed inside. I did a reading on all 80 tubes and wrote down each reading. there were a number of tubes that read 4+ degrees higher than others (supposedly indicating the heat tube is bad). When I pulled the tubes I found no correlation based on this method.

2. My ratio of failed heat tubes was about 40%. They had split and I do agree with statements in this forum that this was a product of freezing.

3. Found a number of tubes that had NOT split yet were expanded at the bottom.

4. My supplier offered to replace all my heat tubes however I declined because I have no faith that the new tubes will have anything different in them and would just become a future failure. I have repaired all 80 tubes by soldering a refrigerant access valve on the bottom of the tube. Pulling the schrader valve out I can charge the tube with fluid and then replace the valve. Heating the tube I depress the valve until I feel a bit of moisture from the fluid. At that point I close the valve and replace the valve cap.
These tubes work great and because of the valve I was able to experiment with different mixtures and quantities to find the best ratio for my tubes.

5. In this process I cut all the tubes that had not burst. I found that every tube contained a different amount of fluid with a variance of as much as 8cc. Some tubes had almost nothing.. maybe 2cc. The fluid appeared to be dirty water and I suspect the copper dust is not a product of engineering but residue from poor manufacturing of deburing or pipe prep. The amounts of residue went from a trace to quite a bit and some had none.

6. SUMMARY -- I believe the tubes that split had much more fluid (water) in them than the ones that didn't split. the pipes that were expanded had more fluid in them than the ones that looked normal.
It appears the manufacturing process is sloppy at best. The random liquid levels in the heat tubes may explain why the infra-red heat reading didn't work. In experimenting with different amounts of fluid in the tubes I found a wide swing of temperatures depending on the amount. I lined up 8 tubes with different amounts of fluid from 2cc to 14cc. This provided interesting results and I found 7cc to be the perfect amount for my pipes. Less than 7cc worked well in direct sun but at 7cc I got some heat even when it was cloudy... only dropping off when clouds were very thick. Solution of choice turned out to be acetone. Nothing else I tried provided as good of results... and it won't freeze. There is ZERO chance of a failed acetone heat tube contaminating the water circulating in a evacuated tube system. Also for those who are paranoid of explosion... I put one of these acetone heat tubes in my burn barrel and cooked the crap out of it with no explosion.. solder did melt and acetone escaped with no event noted.

Hope some of this info helps others. It is a shame the manufacturing of these tubes has left the customers with this problem. Worst part for me was the huge number of trips up and down from the roof removing and replacing the tubes.
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mkel

Have been researching tube failure and efficiency etc... This was an excellent post. Thanks for the information. Very helpful.

[mkel]

Have been researching tube failure and efficiency etc... This was an excellent post. Thanks for the information. Very helpful.

THANKS FOR THE COMMENT... I'm glad you found this helpful.

I haven't been to this forum in a few years but after I got the e-mail of your post I went and did a short edit at the bottom of the original post I made.
Basically repairs to heat tubes ... failures of repairs etc.

http://www.solarpaneltalk.com/showthread.php?4096-Bad-experience-with-evacuated-tubes/page4

I still love the system I built but these heat tube failures have been a giant pain in the butt.
mike

[eddy6053]

tube failure

I have two 20 tube banks of evacuated tubes put in 09 [sunmaxx} and after the terrible winter we had in MN this year my output has really dropped. Up on the roof I went....was a cloudy day, as I felt the glass tubes with bare hand some were cool and some were warm.... 9 warm in one bank and 13 in the other. Pulling the glass off one tube the copper bottom was enlarged or swelled but not split. Copper was black..from high heat I presume. I haven't really noticed any foggy bottom of glass tubes like the vacuum had been comprised. Comments?? any ideas?

[mkel]

I have two 20 tube banks of evacuated tubes put in 09 [sunmaxx} and after the terrible winter we had in MN this year my output has really dropped. Up on the roof I went....was a cloudy day, as I felt the glass tubes with bare hand some were cool and some were warm.... 9 warm in one bank and 13 in the other. Pulling the glass off one tube the copper bottom was enlarged or swelled but not split. Copper was black..from high heat I presume. I haven't really noticed any foggy bottom of glass tubes like the vacuum had been comprised. Comments?? any ideas?

yep those tubes froze. The glass tubes are fine but with the expansion of the bottom of the copper heat tubes somehow the fluid has leaked out. if it was still in there they would make some heat at the top even on a light cloudy day. The chinese are selling heat tubes on ebay now... but they ask a lot for them. I would contact sunmaxx and see if they will replace them for you.
Over the last few years of frigid winters I don't have any working original tubes left in mine. It sucks but we've been screwed. If you read this entire thread you will find where I've been fixing them... (with some failures) .... I still haven't nailed down a perfect amount of fluid... 7cc seems to be the winner .. and they must be brazed with 15% silver or they will fail again if the system stagnates. Good luck with this.
mk

[eddy6053]

Any ideas why some tubes feel warm and others cool to the touch? I pulled the glass off one of the warm ones and the bottom, looked swelled but was to hot to handle. I wonder if the copper is getting hot but not transferring heat to manifold and just sits there and get warm....where the cool tubes are still transferring heat to manifold. any ideas? I have contacted Sunmaxx and there going to get back to me.

[mkel]

Any ideas why some tubes feel warm and others cool to the touch? I pulled the glass off one of the warm ones and the bottom, looked swelled but was to hot to handle. I wonder if the copper is getting hot but not transferring heat to manifold and just sits there and get warm....where the cool tubes are still transferring heat to manifold. any ideas? I have contacted Sunmaxx and there going to get back to me.

BINGO ! .... that is exactly what is going on ... when the heat tube fails the copper gets super hot but because there is no fluid it can't transfer the heat to the manifold.
The copper may be black in color if it's been failed for a while.
Sometimes you can tell by putting your hand on the glass tube like you talked about.... cool = probably working warm = most likely failed.
I have found that using this method seems to work better on a mild sunny day and it is more difficult to tell on a super warm sunny day.... why? don't know... might be radiant heat off roof.

BTW .... out of my 80 tubes I have had freeze failures in all of them over the last 5 years ...
However I have had only one glass tube failure .... maybe I've been lucky but the vacuum glass tubes seem to hold up fine even when super hot.
mike

[eddy6053]

Mikel, I am replacing my bad tubes....Sunmaxxsolar has told me there going to ship new tubes to replace my bad ones under warranty. Unfortunately there on a slow boat from China. I don't think I want to put the new tubes in service if they are still using water as their gas medium. Anyway, as I pull them down and cut the swollen end off I plan on putting 7cc of acetone and braising with silver solder. I wanted to ask you about the felt? wool? gasket? they use for insulating up by the end of tube that goes into the manifold. Mine are falling apart as I take apart the tubes. Did you experience that and what did you use if anything. Also did you use any of the silver paste that they sent to use coating the bulb end that goes into the manifold?

[MikeSolar]

Eddy, have you been able to pull out the tube from the header yet? Some times it nearly welded into it. Very difficult to get out.

The upshot of all this is that, with the exception of a couple of controller failures, all my flat collector systems are in great shape. This kind of experience is why I seldom put in tubes any more.

[eddy6053]

Yes I have been able to get the tubes out.....I take the glass off, then slide the aluminum collector off the copper tube, then put a c-clamp on the end of copper pipe and tap on the c-clamp and drive out the stuck ones. There not all that hard to do and you have better luck when everything is cool.

[mkel]

Mikel, I am replacing my bad tubes....Sunmaxxsolar has told me there going to ship new tubes to replace my bad ones under warranty. Unfortunately there on a slow boat from China. I don't think I want to put the new tubes in service if they are still using water as their gas medium. Anyway, as I pull them down and cut the swollen end off I plan on putting 7cc of acetone and braising with silver solder. I wanted to ask you about the felt? wool? gasket? they use for insulating up by the end of tube that goes into the manifold. Mine are falling apart as I take apart the tubes. Did you experience that and what did you use if anything. Also did you use any of the silver paste that they sent to use coating the bulb end that goes into the manifold?

The tubes I repaired I brazed with silver but I am not satisfied that I can get a good enough vacuum inside them as it takes longer to braze them shut and I think I loose a lot over that time.. they do not seem to work as well as my original repairs .. however the original didn't hold up over time.
As far as the felt ... I don't have that on mine ( must be a sunmaxx thing... and I am not using any paste on my bulbs.

I recently contacted my supplier and he knew I had past issues so he sent me 60 new heat tubes and 20 complete glass tubes with heat tubes.
Damn this is a great guy ... didn't charge me a thing...
I haven't installed them yet but this will give me a bunch of old tubes to do some serious experimenting with over the next year.
I am like you as I wonder if the medium is the same and I will have a repeat of this problem after the next polar vortex.
I think I am going to take a heat tube to work and put it in the kitchen freezer which runs at -10 degrees. That should answer that question.

These things are awesome when they work but I am starting to think "flat panel" if I do a future system.
mike