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  • troubleshooting an old passive SHW system

    Aloha,

    I have a 20 year old, passive low pressure solar hot water system in my house. It includes what I think is an 'open?' copper storage tank that has an inflow, outflow, and vent only (no t&p valve) There is a gate valve on the cold side, which then flows to the solar system, and then to the storage tank/backup heater. The drain at the bottom of the tank is plumbed back up to the inflow from the solar HW system. An inventor friend of my Pop's built the whole system for us and he (my Pop) is pretty proud of the thing, though he and I have little idea exactly how it functions.

    In case it helps, some background info - I have a shallow well pump to boost city pressure to my house (tankless) and this system has never been a problem in the past. However, I recently replaced an old leaky hosebib on the others side of the house so there may be a difference in pressure on the system??

    Recently (possibly concurrent to the leak repair but not for sure) water started dripping out of the vent at the bottom of the tank. I have a new HW tank ready to install, as this sucker is old anyway. However, if it is likely another cause I would like to keep the $500 in my pocket, plus I just hate to throw something out just because I'm too dumb to fix it.

    Any suggestions on how to troubleshoot? Mahalo for your ideas. Happy to provide more info if it will help.

  • #2
    Re: troubleshooting an old passive SHW system

    Since this a is a unique system (An inventor friend of my Pop's built the whole system for us) can you post some photos please?

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    • #3
      Re: troubleshooting an old passive SHW system

      some basic pictures would sure help,

      if it is a open system, is there a float on the system, and is it holding?
      Push sticks/blocks Save Fingers
      ~~~~~~~~~~~~~~~~~~~
      "The true measure of a man is how he treats someone who can do him absolutely no good."
      attributed to Samuel Johnson
      ~~~~~~~~~~~~~~~~~~~
      PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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      • #4
        Re: troubleshooting an old passive SHW system

        Below is the link to some photos of the tank. More info: the solar hot water is a pre-heating system. So the cold inlet runs through the solar system's hot water storage tanks, but does not mix.

        The storage tank has an inlet (from the solar) and an outlet (to the fixtures) and the vent that you see leaking, as well as a drain valve on the bottom. The drain valve is plumbed back into the inlet pipe just above the tank, though I don't know why or if the valves should be open or closed...I just recently replaced the hose and have tried every combination I can think of.

        I have no idea what the mechanism is for filling, etc. The only access to the tank is at the bottom for the single element (just changed) and thermostat. The top of the tank jacket is riveted on, though I popped it off, but all I saw was the two pipes (in & out) no valve, float, etc.

        There is possibly a back flow preventer in the system somewhere (required by code) but I am not certain as I don't know what to look for.

        I'm pretty much ready to stuff the new GE 50gal duel element tank in there & forget about it, but any last minute advice is most welcome.

        Last thing...I'm in Hawaii, so there is no freeze concern here, but electricity is $.35 per kW-h so that dribble is costing me a couple dollars a day, lol.

        Last edited by pacsullivan; 12-27-2010, 04:14 PM.

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        • #5
          Re: troubleshooting an old passive SHW system

          not sure if the photo link showed up above...

          http://picasaweb.google.com/pacifics...OPP8avxpdq0Vw#

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          • #6
            Re: troubleshooting an old passive SHW system

            what kind of valve is that? is it a temperature and pressure valve?

            I down loaded the picture and enlarged the view of the valve and not sure what I am looking at,

            with out really knowing that kind of valve it is, I really do not have any idea what to think,


            some explanation of how or how some systems are set up, open loop systems,
            http://www.addzip.com/nes_open_loop_system.htm

            http://www.coseia.org/newsite/119.html

            there are some differences in terminology,

            open loop is or can be that the system solar panel and the water used is the the same water,
            a closed loop is usually has a antifreeze, or a separate water for the panel and uses a heat exchanger, in the storage tank,

            and there are open systems that are not pressurized and normally use a heat exchanger but drain back from the panel,

            and closed systems, that are sealed, off. and use an expansion tank for the water expansion,

            I am not sure from your description on what you have,

            if that is a pressure relief valve leaking than either the valve is faulty or some thing is over pressurizing the system,
            Last edited by BHD; 12-27-2010, 08:55 PM.
            Push sticks/blocks Save Fingers
            ~~~~~~~~~~~~~~~~~~~
            "The true measure of a man is how he treats someone who can do him absolutely no good."
            attributed to Samuel Johnson
            ~~~~~~~~~~~~~~~~~~~
            PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

            Comment


            • #7
              Re: troubleshooting an old passive SHW system

              Thanks for the reply. I'm not sure what type of valve, but don't think it's a t&p valve. It looks like a gate valve put I really don't know. Regarding the system type:

              The solar panels & solar storage tanks are a closed loop, open vented system. The collector water runs from the collectors to the storage tanks and back. Occasionally I have to replenish the water in the system via a hose hook-up at the bottom of the panels.

              The supply water for the house pre-heats by passing through a heat exchange system in the solar tanks above the collectors. It then runs to the copper tank I took photos of.

              I guess the hot water system itself is a closed system. I'm not sure if or how it is isolated from the house pressure, or if the copper tank is okay with the @40psi of pressure in the house system. The tank configuration is a mystery to me...as there is no t&p valve accessible from the exterior of the tank, nor an anode. The only access port is the heating element/thermostat. I tried draining the tank and if I open the drain valve & leave it plumbed to the return line, water comes flowing out of the vent and then it slows down until it stops and then air sucks back into the tank loudly...

              There are no pumps between the solar system and the hot water storage tank. The only pump in the system is the shallow well pump that pressurizes the water supply for the entire house. It was a really low maintenance system for 20 years...just a new heating element a decade ago and the occasional drain. Oh well...

              Comment


              • #8
                Re: troubleshooting an old passive SHW system

                Can you provide a schematic of your system?
                Sounds interesting.
                Thank you.
                I'd take an educated guess - but I'm unqualified.
                It ain't just soot, it's paydirt.
                "I swear, wherever Gift goes, argument follows." -Youtube comment

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                • #9
                  Re: troubleshooting an old passive SHW system

                  here's a quick diagram...added to the photo link. Mahalo for your help & ideas!

                  Ben

                  http://picasaweb.google.com/pacifics...OPP8avxpdq0Vw#

                  Comment


                  • #10
                    Re: troubleshooting an old passive SHW system

                    OK that is basically a thermo siphon batch unit, for the solar being used to pre heat the water,

                    as far as the way it is plumbed, if there is a "hot" and "cold" marked on the tank the solar should be going into the cold side and it should have a dip tube,
                    but and it looks like to me that the washing machine hose was added to the drain and the possibly a drain on the solar side of it,

                    my guess is what your calling a vent is some type of relief valve,

                    If there is not a place for a T&P valve in the tank one should put in a tee on the hot out, and put a T&P valve, on the top of the tank at what should be the warmest place in the tank, it is not the best with the tee but better than no T&P valve, or a t&P vale in the middle of the tank, as one could be developing steam in the top of the tank and not set the valve off in the lower cooler water,

                    I can not say I really under stand why it is plumbed the way it is with two locations to allow the solar heated water into the tank,

                    but one may be better to see if there is a dip tube in the tank where the solar goes into the tank, on top, if there is NO DIP TUBE, put the t&p valve in that nipple and then use where your "vent" (valve or what ever it is), is to put your solar hot water into the tank, as it is about mid way on the tank,

                    below is picture of thermo siphoning batch solar system,
                    Attached Files
                    Push sticks/blocks Save Fingers
                    ~~~~~~~~~~~~~~~~~~~
                    "The true measure of a man is how he treats someone who can do him absolutely no good."
                    attributed to Samuel Johnson
                    ~~~~~~~~~~~~~~~~~~~
                    PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

                    Comment


                    • #11
                      Re: troubleshooting an old passive SHW system

                      I think you're right about the 'vent' being a relief valve of some sort, and I suspect that is what has gone bad.

                      If I open the tank drain for a few seconds, hot water drains out of the 'vent' and then stops, it sucks in a big gasp of air, and then it takes a few minutes for the leak to resume. Problem is, I don't know how to fix it.

                      I DO KNOW that it is not a temperature issue, as the symptom repeats itself regardless of the temp of the water, and also repeats itself as long as there is even a small amount of water pressure going to the system.

                      I am highly confident in the original design, both for the history (20 years without a problem) and the reputation of the guy who built the system. I suspect the dip tube only goes down part way, and that the washing machine hose (which I replaced, but an older one was in the original design) may be there to allow flow to revers back to the solar heat exchangers in the event of a temperature inversion. Does this make sense?

                      Either way, I gotta get hot water going again so I am going to replace the old tank with a new 50 gal electric, and consider adding it back in later as additional storage if I can figure out what is wrong with it.

                      Thanks again for your help, and unless there's any last minute advice on how to fix the 'vent' or 'relief valve', or whatever it is, I guess I have to just do what has become the American way (though I disdain it) and replace the whole contraption.

                      Aloha from Kauai!

                      Comment


                      • #12
                        Re: troubleshooting an old passive SHW system

                        there may be a tag or numbers and name on the valve and that may help Identify it my guess is one would just take a pipe wrench and unscrew it,

                        If you take a regular hot water heater, and just run the water from the solar panels into the cold pipe you should have much the same system as you have now, just a different tank and you have more heating elements

                        the difference is that instead of ground temperate water entering the tank it would Pre heated from the solar panels and may not need much additional energy to bring up to your user temperatures, put in a T&P valve as recommend by the manufacture of the water heater, (T&P temperature and pressure valve).

                        with out seeing the tank and the valve and possibly opening it up (take off a few pipes and look inside or to see if there is a dip tube in it, I really do not know what the correct way to plumb your current tank, but my guess is what I said above, and add a T&p valve to the hot out fitting,

                        not trying to beat you up here with this statement, but you may want to get a pro plumber in to help you, to put in the water heater, as you do not seem to be confident with the leaking valve/vent

                        ~~~~~~~~~~~~~

                        info on a water heater, and what the inside of a tank looks like,
                        http://www.theplumbinginfo.com/water...water-heaters/
                        Push sticks/blocks Save Fingers
                        ~~~~~~~~~~~~~~~~~~~
                        "The true measure of a man is how he treats someone who can do him absolutely no good."
                        attributed to Samuel Johnson
                        ~~~~~~~~~~~~~~~~~~~
                        PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

                        Comment


                        • #13
                          Re: troubleshooting an old passive SHW system

                          Thanks again for following my efforts & advising. The new tank is in and all is well with the hot water supply. Was getting nervous there as we have guests at our B&B and it was getting to be a problem.

                          The reason the old tank was so much trouble: there was no valve accessible from the exterior of the tank. That vent pipe went straight in through the insulation jacket into the copper wall, nor sure what it does inside the tank. The dip tube for the cold in was also not removable, just welded through into the tank., as was the hot out. I still don't know what the mechanism was for filling/venting, just a copper elbow protruding as you see in the photo. I will see if I can take a look inside the tank one of these days when I have time. Would still like to add it back in in series with the other tank for more storage.

                          Your help was much appreciated. and yeah, sometimes it is better to call a pro. I may yet do so to optimize the system performance, as the current tank is not ideally configured for the solar pre-heat.

                          Thanks & Happy New Year!
                          Last edited by pacsullivan; 12-28-2010, 10:39 PM.

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