Bad experience with evacuated tubes.

[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.

[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.

[J.P.M.]

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

I'd cover part of the collector.

[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).

[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 ?

[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!

[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]

Repairing heat pipes - the saga continues

David,

Who is your supplier and will they sell heat tubes to others who may need replacements? Since this seems to be such a problem I would think someone would be able to supply them as long as they are better than the originals. Thanks.

My appologies RJM - I have not checked this thread in a while. My supplier has vanished! Their web site is still up, but many phone calls and e-mails later - no reply. So I repaired 88 tubes (adding to the ~15 good originals) and I operated through the summer. My performance was much better. I finally got some more of my system connected, so now I can also pre-heat my domestic hot water (as well as the underslab in my work shop). In the past week I got back to the task, as of today I finally have my full compliment of 120 tubes (104 with acetone). Likely there are still a few that are failed, so I am waiting for a frost event (see my earlier description) and hope to be able to identify any additional failed heat pipes.

Regards, David

[LucMan]

Search Resol solar controllers

[RJM]

Thank you for that information, had heard about them but not seen any as of yet. I tried to find a capable installer to no avail in Ulster County NY. The system is up and running already and generating heat, this is the first winter installed in the Fall. My problem has been with the burst heat pipes, found remedies for that but looking for replacements which would be preferable. I felt the basic piping design had room for improvement and it is working as I planned using a manual 3 way valve. Would like to see the capabilities of the differential controller you speak of can you give me more info on who makes it? Thanks.

What you are looking for is s differential controller with multiple sensors that can control a 3 way valve to change the water flow circuiting ($200) to the heat exchanger.
Vs a pump pack $600 plus. These controllers are readily available. I have one one in stock.
You must be a newby to solar. I suggest you start doing some extensive research before continuing your project as you will be wasting lots of money and effort.

[RJM]

Russ, I didn't make this up myself:

From Bob Nape: http://blog.heatspring.com/which-is-...be-collectors/

"Flat plate collectors can only heat water up to 170-180 degrees Fahrenheit, which means there is very little risk of overheating. Evacuated tubes, on the other hand, can heat water to well over 250 degrees. For this reason, they are much more likely to overheat than flat plates, and you need to be more concise with your design. If you’re using evacuated tubes, it’s always better to oversize your storage tank rather than under-size it for this reason. Evacuated tubes are also used more in colder climates because they are more efficient than flat plates in extremely cold temperatures. In extremely warm climates, evacuated tubes have a very high chance of overheating, so be careful if you’re in the southern states."

Before you point out his side by side comparison remember the systems are not of equal surface area as he mentions.

From Solar Panels Plus which sells both flat plate & evac tubes: http://www.solarpanelsplus.com/evacu...be-collectors/

"While evacuated tube technology clearly surpasses flat panels for nearly all water heating applications, the advantages are truly dramatic when used for solar air conditioning, heating or commercial process.

That’s because evacuated tube heat pipe collectors can more easily attain the higher temperatures needed, they can collect and retain heat even when it is very cold outside, and due to their superior Incidence Angle Modifier they collect solar energy more evenly throughout the day resulting in a lower buffer or thermal storage requirement. There are many other advantages as well."

I did a great deal of research a number of years ago and purchased a system but was only able to install it recently. I thought I would share my thoughts with others on how we ALL can improve on the systems and hear from others on how to improve mine....didn't mean to ruffle feathers but, I will stand up for myself when dismissed.

RJM - This is an old, old topic that has been gone over many times. New to you as we can see by your comments.

A flat plate collector heats a larger volume of water to a lower temp - The "getting hotter" means squat. You proved nothing except that you do not understand heat collection units. The total heat units collected by both types is close - proven by many agencies over time.

Have fun tilting your windmills.

[J.P.M.]

What you are looking for is s differential controller with multiple sensors that can control a 3 way valve to change the water flow circuiting ($200) to the heat exchanger.
Vs a pump pack $600 plus. These controllers are readily available. I have one one in stock.
You must be a newby to solar. I suggest you start doing some extensive research before continuing your project as you will be wasting lots of money and effort.

+1 on the research part. There will always be problems. Heading off the most obvious ones before they occur through process and product knowledge is perhaps a better start and a bit more proactive on heading off problems rather than simply meeting all challenges as they appear. If nothing else, you'll get blindsided less.

[LucMan]

Thank you for the info on the pumps but, what I am looking for is the equivalent of two Pumping Stations in one. Stage one would circulate the water from the Array through the tank and back but once the differential is met and stage one shuts down, stage two would kick in and circulate the water from the array through the heat exchanger to heat the house. Right now the system need to be tricked into continuing the circulation by pulling out the sensor from the bottom of the storage tank.

I myself am a product designer and look to solve any and all problems as they arise...I believe the current systems even the flat plate could use a two stage system to better utilize the heat generated.

What you are looking for is s differential controller with multiple sensors that can control a 3 way valve to change the water flow circuiting ($200) to the heat exchanger.
Vs a pump pack $600 plus. These controllers are readily available. I have one one in stock.
You must be a newby to solar. I suggest you start doing some extensive research before continuing your project as you will be wasting lots of money and effort.

[russ]

RJM - This is an old, old topic that has been gone over many times. New to you as we can see by your comments.

A flat plate collector heats a larger volume of water to a lower temp - The "getting hotter" means squat. You proved nothing except that you do not understand heat collection units. The total heat units collected by both types is close - proven by many agencies over time.

Have fun tilting your windmills.

[RJM]

If the heat tubes are filled with an appropriate solution to prevent freezing there will be no failure as it is a sealed copper pipe. Not sure why the rubber seal would fail...maybe the earlier versions used the wrong material but that failure should have little to no affect on the system as it is the copper pipe going into the header where all the energy is transferred.

The probable reason for not guaranteeing the system is most likely because of the heat pipe failures so until that issue is resolved it will be hard to guarantee..once that issues is fixed there should be no problem.

It is true that the systems can get very hot which once again proves how much more efficient the Solar Tubes are since you apparently never have that problem with Flat Plate collectors...you just settled that argument.

Many take to covering the system and using heat dumps to vent off the excess heat BUT if you can use that excess heat for other purposes such as cooling, a process called "Absorption Cooling" check out this link http://www.technologyreview.com/news...ool-buildings/ or helping to dry Fire Wood an idea I thought of since my location is very damp and takes a long time to season my wood. I am sure there are other ways to utilize that heat.

Thank you for the info on the pumps but, what I am looking for is the equivalent of two Pumping Stations in one. Stage one would circulate the water from the Array through the tank and back but once the differential is met and stage one shuts down, stage two would kick in and circulate the water from the array through the heat exchanger to heat the house. Right now the system need to be tricked into continuing the circulation by pulling out the sensor from the bottom of the storage tank.

I myself am a product designer and look to solve any and all problems as they arise...I believe the current systems even the flat plate could use a two stage system to better utilize the heat generated.

Evacuated tubes are prone to vacuum loss, heat pipe failure from freezing, and rubber seal failure at the header depending on the tube type.
Multiply that by the number of tubes in an array and you have many possible points of failure.
Here in NY state most pro installers won't install an evacuated tube system because NSERDA (the state subsidy authority) requires certified contractors to guarantee the complete system for a period of 5 yrs. That is along time to keep an evacuated tube system online with out any issues. Larger array's can cook the glycol because of the extreme temperatures generated during the summer month's. This requires glycol replacement as the glycol becomes degraded and loses it protection properties, and it's viscosity.

As far as a 2 stage pump, Grunfoss (Apha) and Taco make variable speed pumps that can be set to a specific delta T and may be what you are looking for.