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  • Bad experience with evacuated tubes.

    We installed two 30 tube panels on our roof in 2006. They made 100% of our domestic hot water and contributed a tad to our in-floor heating. We recently ordered 3 more panels to add to the existing 2 because we wish to heat our house even more using solar.
    In order to add on, we had to remove the existing tubes so we could drain the system. While we were removing the tubes we found 23 of the 60 tubes had gone bad. Upon inspection, we found the slim copper tube inside the glass had expanded and split at the bottom. The copper looks like a bloated puffer fish! This released the water inside the copper and made the tubes useless in conducting heat. We live in northern Wisconsin and it's not uncommon to have -20 degrees for weeks on end. We believe the copper inside the evacuated tube froze and burst. We don't know if the vacuum had been lost, and thus lead to freezing? Each tube seems to be completely in tact, no glass is cracked or broken. Even the seal between the glass and the metal looks fine. Can the liquid inside the copper freeze even with a vacuum? And why did 23 of them go bad and not the full 60?

    My husband believes the vacuum still exists in those bad tubes, but the copper still got cold enough to burst. He believes this because there is a stretch of coiled metal going from the glass to the big copper head at the top of each tube. It's the skinny neck part. This neck part isn't insulated. This neck is exposed to that cold air on frigid January nights. Could that cold be entering the neck and traveling down the copper tube and freezing it? He believes this is what happened. He believes the 23 unfortunate tubes were the ones that slipped a bit past the manifold and really got exposed to the cold air. They slipped a bit when we cleaned the snow off them. When I slipped a bit, I mean like 1/4 inch. There's nothing but a strip of plastic on the bottom of the manifold protecting that neck, and the tubes could easily slip a bit beyond that plastic strip. The new Kingspan tubes have a clip to hold them into the manifold so they can't slip. But the necks still aren't insulated. Don't they think cold can penetrate that uninsulated strip of plastic?

    To add insult to injury, Thermomax was bought by Kingspan Solar in 2007, and all tubes sold before that aren't covered under warranty. So we lost our warranty. But since we already have 37 good tubes, racks, and a system in place we will be purchasing 23 more tubes from Kingspan. But we are going to insulate those wire necks ourselves to make sure they don't freeze.

    Also, we never would have known these tubes were bad if we hadn't ordered more panels. We don't annually go up on our roof to check tubes after winter has passed. We never thought it was something we had to do. Kingspan says they've not have any complaints on solar sold to northern climates. But do those panels get checked annually? Maybe they have bad panels and don't know it.

    Looking at our solar data, it seems the tubes went bad after the first year because our production really dropped. We thought it was just a really sunny first year and never thought about it more than that. If we would have done an annual check up, we could have maybe caught it soon enough to be under warranty before Thermomax went belly up. If you wish to install evacuated tubes in a cold climate, be prepared to annually check your tubes.

  • #2
    That's one I have never heard of before but I stopped using Thermomax ne Kingspan several years ago even though they are right around the corner from us. I really don't have an answer for you other than to use Apricus tubes for the additional array. At least if a heat pipe freezes only the heat pipe needs to be replaced. Since the tubes are bad why not try poking a hole in the rubber and see if they are still holding a vacuum. My guess is they are not. That is the biggest failure point on that design of tubes.
    NABCEP certified Technical Sales Professional

    [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

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    • #3
      The heat pipes you are referring to should have a non freezing solution in them - methanol is common. LucMan has told a story about the same problem some time back.

      Maybe this particular model wasn't suitable for the very cold climate.

      Russ
      [SIGPIC][/SIGPIC]

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      • #4
        Windy,

        That sounds very unfortunate. We spend alot of time arguing about the tubes vaccuum seals themselves (all glass vs metal on glass) but rarely discuss the heat pipes. My understanding from the manufacturer of a different company (Apricus) is that the heat pipes actually have distilled water and certain "additives" which they dont really go into. The idea is not to prevent freezing but rather to ensure even expansion of the fluid in the heat pipe when they do freeze to prevent bursting of the pipe. I have cut them open before to find what appears to be enough water to fill a 20 oz soda cap and a copper colored additive but I dont know its exact nature. There is so little fluid in them that there should be plenty of space for expansion w/out bursting.

        Three days ago I would have told you I never heard of a heat pipe bursting but just two days ago I recieved a call of a burst heat pipe up in Nome Alaska. We are a bit more fortunate as its a sydney tube so the heat pipe can be removed and replaced in the same tube. They have 150 tubes operating for a little over two years now so it appears to be an isolated incident. What you say about the exposed neck of the heat pipes may have some merit to it as sydney style tubes don't have the heat pipe exposed to the open air at all, but they don't sit in a vaccuum either.

        I think you should press a little harder to get your tube cost covered as one of the major selling points of the tubes are their cold weather performance, especially for what you must have paid for that brand. I know for a fact they have recalled tubes in the past few years and you certainly have a good case to make here.

        John

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        • #5
          more bad experience

          I installed 90 tubes of Apricus collectors in 2008. I had some problems of my own creation relative to circulation and air separation in glycol loop, but over the first two years heat production dropped dramatically. When I removed all tubes for inspection I found that the bulbs on top of heat pipes of about half of my tubes had disengaged from the manifolds. (Heat pipe had migrated downward within the tube).

          Apricus was not forthcoming about sharing the fact of a product redesign (spring plate assemblies) which I incorporated after being reluctantly supplied necessary parts. After reassembly of system, installing an additional 30 tubes (now 120 total) I find my collection is still much less than when new. I have found condensation in one evacuated tube which I suspect may be symptomatic of a progressive loss of vacuum affecting many of my tubes. While reinstalling my tubes there were one or two which were plainly not creating as much heat as the rest (The bulb did not pass the sizzle test after half an hour in the sun).

          I am interested in hearing more about similar unhappy experiences of others. With respect to split heat pipes, I don't think insulation of tube necks can be relied upon to prevent this problem. I have had one (out of 120) heat pipe split, so perhaps Apricus has figured out what to do to minimize that, but insulation is not meaningful when there is no source of heat within the tube. You have to assume it will get pretty much down to ambient temperature.

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          • #6
            How to test heat pipes without taking the evacuated tubes apart.

            Burst heat pipes are very common and most consumers don't know until their system is putting out nothing. Apricus, Sunrain, Thermo-max all have their problems. There is suppose to be 10 mil of water in each heat pipe about one inch so insulating the neck of the condensor will not help this problem. Apricus mixes a copper compound in the water to take up expantion but if there is too much water or not enough copper they burst. Someone mentioned that some company's use methanol but I doubt it as it is against the law as it is highly toxic and if ther was a failure on a pure water system it would poison your water. If you want to test an evacuated tube for performance all you have to do is use an infered thermometer on the outside of the glass tube. In full sun put the thermometer right against the glass on the bottom of the tube. Your pump must be running for this to work. Check every tube. Tubes with failed heat pipes will register a 3 to 4 deg. celcius higher reading as the heat pipe is not extracting the heat to the manifold the way it should. Faulty heat pipes when pulled out turn completely black and cooked to death. If you want to check a heat pipe heat some water to close to boiling and put the bottom end in the water. If you can touch the condensor in 30 seconds it's toast. Good ones will have a natural copper color and cook your hand, 200 celcius. These company's will tell you that they have never, ever seen this, but they are lying. Most company's designed these systems for warmer climates so they are playing catch-up on cold weather design. Where I live -20c is just a nice day to go fishing. Hope this helps.

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            • #7
              @ solar guru - You intend to say solar teacher?

              1) Heat pipes are very difficult to find any decent information on.

              2) No system should have the water to be consumed running through the collector or header. Very few places have water clean and soft enough to allow that. The system can still freeze which requires a separate loop for the water to the tubes/panels.

              3) To use methanol or other antifreeze solution other than propylene glycol requires a double walled heat exchanger to prevent the solution from getting into the potable water - nothing different and nothing new. With the mandatory double walled heat exchanger it is definitely not against the law.

              4) infered thermometer? maybe you intend to say infrared thermometer - never heard of the other thing. An IR thermometer to measure temperature is the worst idea one can come up with - let 10 different people measure the temperature of an object and you can easily get 10 different temperatures. Everything depends on the emissivity of the material at that temperature and the emissivity setting of the IR device.

              A digital thermometer with a contact probe will provide an accurate result.

              Russ
              Last edited by russ; 07-13-2011, 03:25 AM. Reason: added
              [SIGPIC][/SIGPIC]

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              • #8
                Even if methanol or ethelyne glycol were used in the heat pipe of an evacuated tube there would be no problem as the header and tube connections are by necessity double walled.
                NABCEP certified Technical Sales Professional

                [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

                [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

                [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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                • #9
                  Heat pipes and methanol

                  If there is a company that uses methanol in their heat pipes please put their name down. I agree the condensor and the manifold create a double wall just haven't found a manufacturer yet that uses methanol. Sorry for my spelling on infrared thermometer (didn't know this was a spelling bee), but we have used this system for finding faulty heat pipes and works flawlessly and saves removing lots of vacume tubes that you wouldn't have too. We build closed loop systems using propylene glycol which is non toxic and actually used in foods and skin creams. Methanol on the other hand can be absorbed through the skin and is very toxic. If you like expense and inefficiant things, then double walled heat exchangers are perfect. In some places they are law because of installers that use methanol and ethylene glycol in their closed loop. My original post was to do with finding faulty heat pipes not the closed loop. We have changed hundreds using this method and it WORKS.

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                  • #10
                    The internet and cell phones have made people forget all about spelling or sentence structure. inefficiant?

                    An IR gun has it's uses for a rough temperature measurement - just forget accuracy with the things. A digital thermometer does the same. Glad you are happy with your method of locating bad tubes.

                    We are quite aware of the properties and uses of propylene glycol.

                    Oh gee! Methanol being so toxic - less than most household cleaners? Any chemical is to be treated with respect. Taking a bath in methanol or a few thousand other things is not recommended.

                    About using methanol in heat pipes - I have read that some where in the past. I have looked for that reference several times as I was wanting to know more but most parties treat the composition of the fluid as a secret.

                    Why they want to use water is beyond me - lousy selection for cold areas and the claim to fame for vacuum tube type collectors is they work better in colder areas.
                    [SIGPIC][/SIGPIC]

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                    • #11
                      Heat Pipes

                      You read it Somewhere? I'm sure you'll find it somewhere! A manufacturers name is what I was asking about. Another reason that methanol might not be the best fluid in a heat pipe is that it is flammable and explosive in the right concentrations. The heat pipe must be brazed closed while hot (which is what creates the vacume in the heat pipe) so what you have is a little bomb and a brazing torch....you may have to try this and let me know how it works out. I have been trained by 4 different solar thermal manufacturers who send out the very best tech. people they have....they don't send out grammer teachers. I originally posted to help people find bad heat pipes. I own and work in this business everyday, not just read about...somewhere.

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                      • #12
                        No use in trying to be nice to some people it seems.

                        Provide links for water in the heat pipe if you can please. I would like to learn more about the things. Not word of mouth.

                        Your understanding of manufacturing processes seems to be lacking. You drive around a car/pickup using gasoline/diesel and you are OK - right? Forget the bomb crap

                        Welding creates a vacuum in the heat pipe? Maybe you misunderstood someone. If any is created in that manner it would be so small as to not be noticeable.
                        [SIGPIC][/SIGPIC]

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                        • #13
                          Heat Pipes

                          My knowledge might be lacking in spelling but I wouldn't try brazing a top on my fuel tank (don't forget the bomb crap Russ). If you don't believe that sealing something that is hot and cooling it creates a vacume try the old grade one test of filling a plastic bottle half full with hot water, sealing it and then cooling it. A heat pipe that is not sealed for what ever reason will not function as the distilled water soon leaks out of the heat pipe and then there is nothing to make steam. Ethylene glycol doesn't work either as it can't withstand +300c. and breaks down. The steam rising into the condensor and changing state from a gas to a liquid is how such high temperatures are reached in evacuated tube systems unlike flat panels. If you would like to learn more right from the horses mouth you should take a course from a manufacturer the way I have and then go out and install a couple thousand tubes. I posted a testing method for heat pipes that works because WE do it....don't just talk about it. I didn't come on here for a spelling lesson just to help people check their systems without taking every tube out which only creates allot of work, broken glass and frustration.

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                          • #14
                            Link to Heat Pipes

                            As requested here is a link to heat pipes http://en.wikipedia.org/wiki/Heat_pipe and if you scroll down that page it clearly says Solar Thermal and a couple of sentences later...distilled water. There are many different uses for heat pipes and depending on the application may use different fluids. There are heat pipes used for cooling a lap top which may use different fluids. Acetone is actually on of the top picks for replacing water but because of it's volitile nature is not allowed.

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                            • #15
                              From your wikipedia article - [I]The vast majority of heat pipes for low temperature applications use some combination of ammonia (213
                              [SIGPIC][/SIGPIC]

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