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.