Bad experience with evacuated tubes.

[Chipper5783]

Repairing heat pipes - status update. The acetone recharge has been working pretty well (nearly 2 winters and 1 summer). The system performance was significantly better than it had ever been.

- Occasionally through the winter, the tubes will frost up, but then the frost melts off during the day. Sometimes, the frost will melt only on certain tubes (not a shade effect). The tubes which melt free significantly faster than the others have always had a failed heat pipe. This is my monitoring strategy for identifying failed heat pipes (not a real fast method, but so far 100% accurate).

- I only had 16 of the original tubes in service (?water? filled). Several more of those failed. I've lost track of how many originals are still in service - probably fewer than 10 out of 120 tubes.

- I had about 15 of the acetone tubes fail. When looking closely at the failures, it was generally possible to see that there was an issue with the sealing (silver solder) of the tube end.

- I recharged all the failed tubes. Needless to say, the system performance is again better than ever. Even with February sunshine (better than December sun, but still well down from summer time) - I am able to get over 10°C temperature rise from panel inlet to panel outlet. Granted it is only about a 1gpm pump - but it is the same pump for the past 5 years.

It seems using acetone is somewhat controversial. Perhaps my tubes will all quit working? All I can say is that so far I am pleased with the repair results (not happy that I needed to repair them, but that's all history now). I won't be surprised if I get a few more failures (it is hard to really get the seal perfect). My hunch is this will work out just fine.

[Chipper5783]

Repair of the heat pipes? I'm now 5+ years into this experiment of using acetone as the working fluid and recharging the heat pipes that are inside the evacuated glass tubes ("thermos bottle"). It is working very well. I still have a few original heat pipes (I didn't refurbish them if they still worked) and they seem to fail eventually. The repaired tubes (acetone charged) fail if the sealing of the end is not done very well. My technique for silver soldering the end shut has improved so I'm not having very many "do-overs". For much of the year the energy for my domestic hot water is met. The worst problem is now that I don't need so much energy during the summer and the dump load (concrete slab floor of the work shop) make the shop too warm during the summer!

[Mike90250]

......... The worst problem is now that I don't need so much energy during the summer and the dump load (concrete slab floor of the work shop) make the shop too warm during the summer!

Can you pull a couple Tubes out so there is less collection area ?

[azdave]

The worst problem is now that I don't need so much energy during the summer and the dump load (concrete slab floor of the work shop) make the shop too warm during the summer!

I used to have solar hot water collectors here in Phoenix. In the summer, the water would begin to boil in the late afternoon sun (direct water circulation system) and raised the water pressure high enough to open the pressure relief valves in the system. I solved that by placing some solar screen cloth over the face of the panels from June- August. I still had plenty of hot water but no more boiling. It was not much different than taking window screen on and off the house (other than going onto the roof).

[J.P.M.]

Can you pull a couple Tubes out so there is less collection area ?

I'd cover part of the collector.

[Chipper5783]

Can you pull a couple Tubes out so there is less collection area ?

Sure, I don't like to casually pull tubes - it is so easy to break off the vacuum seal tip, I'd rather not touch them, store them etc. unless it is necessary.

Of course covering them as JPM pointed out would work fine - but really warm for me is anything over 80°F. I just open the windows & roll up door and turn on the ceiling fans. Even in summer, we get some stretches of cloudy days and it is nice to have all the panel available (the panels provide my primary DHW heating) - and climbing on the roof to play with panel covers would get old in a hurry.

The point I was trying to make is that low tech recharging of the copper heat pipes is entirely feasible, providing reliable good performing panels in locations that have extended periods of low ambient temperatures. That sometimes I get more energy recovered than I would like is a separate topic.

[mvrielink]

Hi Chipper,

This is a pretty old thread, Its been about 5 years since the last post here, hoping you're still lurking around the forum!

I've picked up a 120 tube array, from my investigation there are 30 tubes that still work (seem to have been replaced as the bulb on top has a slightly different taper then the rest). The other 90 tubes are split from freezing at the bottom. My location is western Canada, easily gets down to -30F in the winter.

I'm likely going to start repairing the broken heat tubes with acetone per your guidelines, just thought I would try you to see how your experience with the re-charged tubes has been to date.

[lonfu]

yes, I too am dealing with my old ground mount system installed in 2010. I replaced that unit in 2015. a 30 tube, with cooper heat pipe inserts, 300L/80gallon main tank with a "assist tank". I use the unit as a pre-heater (winter) for my in house 40 gallon electric water heater part of the year and 5 months (summer) provides all hot water needed... one of my 3/4" soldered cooper fittings failed. had to shut off the water for a while until I could get to the repair. One of the tubes had failed internally about 6 years ago and I just left it. system still heated my water just fine. This time, when I was filling the tank, a different one of the vac tubes exploded??? yikes??? suspect the cold water I was filling with had somehow gotten down into the tube past the heat pipe top grommet... when I replaced the glass tube with some I had left over from previous unit, all matched up except that the aluminum fin had desolved into the bottom of vac tube. I've tried to order some "fins" for the heat pipe but the company that makes them only sells in lots of 1000. hmmmm.. so, I installed them with nothing around the heat pipe in 2 of the vac tubes. found one youtube vid where the fella used steel wool around the heat pipe to center it which is what I was worried about??? So, not sure if it is worth draining the water and installing the steel wool? I tried a couple of "pill" bottles as they were the perfect size to fit into vac tube but they just melted. both of the 2 tubes I removed had water in them, mine is un-pressurized tank. I'm in the mohave desert in Arizona so water is precious and I hate to waste 300L. then exterior of the assist tank is rusting out so I found a new one on Alliexpress but suspect the plumbing connection size or gender is wrong. Won't know until I get it. I was surprised to see the silicon seal mounted in the main tank that seals up the vac tube were working and in good condition. found some replacements on Ebay but don't seem to need them. I removed both, cleaned them and was able to re-install with no problems. they were a little discolored but seem to seal up with no leaks. I decided to use plumbers grease to lube the ends of the vac tubes when re-installing. So, sounds like the heat pipes are split, not the vac tubes, correct? youtube had some videos about making them..... My original unit didn't have the copper heat pipes and it worked well. when I replaced them with the heat pipe models in 2015 the system seemed to improve and get hotter faster. this system saves me (2026) about $50 per month in electricity for heating water for my house. what are you using to replace the aluminum fins???100_9896.jpg 100_9905.jpg 100_9900.jpg 100_9897.jpg

[Liam]

Man, I’ve seen this happen more times than it should… those heat pipes just don’t hold up well once freezing gets involved.

A friend of mine had almost the same issue — a bunch of tubes failed after one winter, and when we checked them, the fluid inside was all over the place. Some barely had anything, some looked contaminated. Quality control seems really inconsistent on some of these. I still like the idea of evacuated tubes, they can perform great when everything works… but reliability is a bit of a gamble depending on where you are. If you’re in a colder climate, I’d definitely be cautious. Curious if anyone here has actually found a brand that holds up long-term?

[lonfu]

Man, I’ve seen this happen more times than it should… those heat pipes just don’t hold up well once freezing gets involved.

A friend of mine had almost the same issue — a bunch of tubes failed after one winter, and when we checked them, the fluid inside was all over the place. Some barely had anything, some looked contaminated. Quality control seems really inconsistent on some of these. I still like the idea of evacuated tubes, they can perform great when everything works… but reliability is a bit of a gamble depending on where you are. If you’re in a colder climate, I’d definitely be cautious. Curious if anyone here has actually found a brand that holds up long-term?

Needless to say, it doesn't get that cold here. worst I've seen it is 16 degree's that lasted about 10 days a couple of years ago. normally rarely gets below 28F in the coldest winter months for just couple of weeks. You mention -30F... reminds me of when I was a kid in Wisconsin where I saw 5 to 10F....brrrrrrrr.... I use a hot water recirculating pump to keep the water moving through the entire length of the house which is about 60 feet from the electric water heater and 100 feet from the solar unit. Before I first installed it I could hear the water in the solar tank "boiling" I could see steam coming out the vent in 90F ambient temp. In the summer the pump keeps the water from boiling in the solar tank as the hot water gets trapped indoor electric tank. During most winter months the the solar acts as a preheater for the water before it goes into the inside electric water heater, ground temp of water is typical 60F. So input water is raised to 90 degrees or so before going into the inside electric water heater which reduces power costs but does not eliminate the, during the winter. I start the recirc pump about 7am winter and 5am summer, I turn it off about an hour after sunset.... In the summer I turn off the inside electric water heater and we use only solar heated water for about 5 months, It normally comes out of faucet about 120 degrees. In the winter I have the electric inside water heater timer set to run at 9am to 11am then again at 4 to 7pm. Yes, wife complains about running out of hot water late evening or early morning showers.... the recic pump uses very little power, less than $5 per month but provides instant hot water at faucets 100 feet away from the solar water heater...... So, if I were designing your system, I would plan on installing a recirc pump and running all night long to keep the evac tubes from freezing. I'd set my timer in cold months to run 24 hours. I would then reduce the hours to daylight hours when temps get above 40F. I would have to test to see if one could turn off the electric in the summer time, I would suspect that you could. I'm sure your summers there are not as long as ours and are a lot cooler. We often see 115F in june july and august but only 100 in may and sept. What I look for is when I get up, if the temp ambient is at 40 degrees then I turn on the electric inside water heater timer. My first unit didn't have heat pipes at all. functioned just like the one with heat pipes but tended to not get as hot early in the mornings or stay hot late at night. In 2010, recirc pumps were not popular with these units but I went ahead and installed one anyways. it was a smart move. the recirc pump uses a bypass valve that has to mounted at the furtherest point from the recirc pump, they last about 3 years or so. my water heater timer is an old style with out wifi controls. when the next one fails I may install a wifi unit. https://www.amazon.com/Water-Recirculating-Pump-Tank-Heaters/dp/B0FP5C2B9T/ref=sr_1_5_sspa?dib=eyJ2IjoiMSJ9.usYoWtQYQsh1hE3c0 2CE2WV_LnSUyOxHLipYKT520sHDHdrAk5WbxhGaC-0V81ZkbkZArID7H6oOA41WDj8NO27A7_idseOrEGV-hOoU02ECggdzq0xf-F2A_GXS94rAkzPMGrhY4t9zDAnJe-y6LfXLvSoOI3Hf_nCZFMGA5TiXLfk4Ag8UGmwjmgVuDM29LUup 2hkjU-wdAd4V8xZWd9vR6orAKfAUqfkGksFRGjAMqGRNgGeIaz7TLkhv oEwgALqTEF-_CsXXyO9PnWfizZqX0sj7WBt77GfZeGLI-8E.TLjDDOVikwigBV6DVGPRdeTkuuprHDBH2Fgo3SyUKE0&dib _tag=se&keywords=hot%2Bwater%2Brecirculating%2Bpum p&qid=1776351037&sr=8-5-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1

[lonfu]

I'm guessing, but sounds like last installation didn't include a recirc pump or bypass valve. I've replaced the bypass valve about 4 times over the last 16 years. I keep several spares. Like you I don't mind used equipment, so I search craigslist and FB market for spare parts and such.

[lonfu]

Man, I’ve seen this happen more times than it should… those heat pipes just don’t hold up well once freezing gets involved.

A friend of mine had almost the same issue — a bunch of tubes failed after one winter, and when we checked them, the fluid inside was all over the place. Some barely had anything, some looked contaminated. Quality control seems really inconsistent on some of these. I still like the idea of evacuated tubes, they can perform great when everything works… but reliability is a bit of a gamble depending on where you are. If you’re in a colder climate, I’d definitely be cautious. Curious if anyone here has actually found a brand that holds up long-term?

Lastly, the newest material to put into a heat pipe is now acetone. it freezes at -139F. there are several Youtube vids about how make one using acetone. for a while I discovered that they were using water inside the heat pipes instead of acetone. Might explain the frozen units.... any pix??