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  • solar collector in garden / possibly / unsure of pipe insulation

    Hello everyone,

    I can't find answers to my question on the forum search (probably because my question is bordering stupidity), so here goes:

    1 = Aim to install solar thermal collectors at the end of our garden, house faces west & end of garden gets sun from 9am. Will build small gazebo to mount evacuated tubes on, facing south.
    2 = From collector to house = 15 metres. Will need really good underground pipe insulation.
    3 = Once reaches house, will be 10 metres to the boiler.

    >>>>>>>>>>>>>

    I'm worried about how effective underground pipe insulation will be. I have 2 options:

    option 1
    Underground pipe insulation:
    110 PVC pipe, water pipes mounted inside, with armaflex insulation + more insulation wrapped round. PVC pipe segments sealed along the 15 metres


    option 2
    dual solar collectors on the roof:
    Solar collector facing east + solar collector facing west. Although will cost more + be a bit of a struggle with planning permission.


    >>>>>>>>>>>>>>


    Key question is, option 1 or 2? (If 1 what % of heat is likely to be lost?)


    thanks / simon

  • #2
    i'd look at underground, closed cell foam insulation, sleeve the pair of pipes inside 5" ABS drain line. Keep it out of the sun, the UV in the desert eats plastics.
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

    Comment


    • #3
      Originally posted by oemodm View Post
      Hello everyone,

      I can't find answers to my question on the forum search (probably because my question is bordering stupidity), so here goes:

      1 = Aim to install solar thermal collectors at the end of our garden, house faces west & end of garden gets sun from 9am. Will build small gazebo to mount evacuated tubes on, facing south.
      2 = From collector to house = 15 metres. Will need really good underground pipe insulation.
      3 = Once reaches house, will be 10 metres to the boiler.

      >>>>>>>>>>>>>

      I'm worried about how effective underground pipe insulation will be. I have 2 options:

      option 1
      Underground pipe insulation:
      110 PVC pipe, water pipes mounted inside, with armaflex insulation + more insulation wrapped round. PVC pipe segments sealed along the 15 metres


      option 2
      dual solar collectors on the roof:
      Solar collector facing east + solar collector facing west. Although will cost more + be a bit of a struggle with planning permission.


      >>>>>>>>>>>>>>


      Key question is, option 1 or 2? (If 1 what % of heat is likely to be lost?)


      thanks / simon
      1.) FWIW, I thought the only stupid question was the one not asked. besides, someone else is probably wondering the same thing but, not wanting to look dumb, afraid to ask. Most of this forum concerns PV, solar thermal is a side issue so maybe not much interest.

      2.) What is the load you are tying to supply and how big is it ??

      3.) What % of the load would you intend to supply w/ solar?

      4.) Are you in a climate where freezing will occur at all, or infrequently, or commonly ???

      5.) I'd start by asking those questions, then answering them before I got to more slightly more detailed design questions about pipe insulation.

      6.) Mike's suggestion is one method I'd endorse, only adding to think long term, like how do I provide access for inspection/servicing. And don't kid yourself into thinking those actions will not be necessary. I'd also add that the piping losses can be a large % of system gains for the size system you may be considering, so keep them as short as possible, that is, put the collectors as close to the load as practical and possible, otherwise you'll wind up with an expensive soil heater (insulation slows down heat transfer but doesn't stop it). Also, FWIW, I've found the more complicated a piping system, the less the insulation job meets expectations, but that's anecdotal. Keep the pipe runs as short as possible.

      7.) Do your solar homework first. it's not like any other heating or energy source. Assuming so will cause problems and waste time/money.

      Good luck.

      Comment


      • #4
        Here is a link to Uponor Ecoflex insulated underground Pex, expensive but is the best way to go. This item saves labor and the insulation is designed for underground use.
        http://www.uponorpro.com/Catalog/Cov...rmal-Twin.aspx
        Prices are list. You can order the length that you need instead of ordering a complete roll.

        Comment


        • #5
          Originally posted by J.P.M. View Post

          2.) What is the load you are tying to supply and how big is it ??

          3.) What % of the load would you intend to supply w/ solar?

          4.) Are you in a climate where freezing will occur at all, or infrequently, or commonly ???

          5.) I'd start by asking those questions, then answering them before I got to more slightly more detailed design questions about pipe insulation.

          6.) Mike's suggestion is one method I'd endorse, only adding to think long term, like how do I provide access for inspection/servicing. And don't kid yourself into thinking those actions will not be necessary. I'd also add that the piping losses can be a large % of system gains for the size system you may be considering, so keep them as short as possible, that is, put the collectors as close to the load as practical and possible, otherwise you'll wind up with an expensive soil heater (insulation slows down heat transfer but doesn't stop it). Also, FWIW, I've found the more complicated a piping system, the less the insulation job meets expectations, but that's anecdotal. Keep the pipe runs as short as possible.
          Thank you. To answer 1 by 1:

          2) = It is to supply hot water heating only. 400 hot water tank, with some solar heating from evacuated tubes with this spec:
          60 tubes
          Collector Gross Area = 10(m2)
          Collector Absorber Area = 5.6(m2)
          Annual Output* 5926(kwh)
          Daily Output (litres) at 50°C = 540 litres (average)

          3)I am not expecting this to supply all hot water, all the time. I'm expecting it to contribute at least 50% annually. The 400 litre tank also has an electric element

          4) Freezing climate? Infrequently between Dec to Feb, a week here & a week there it can get as low as -15 deg. C. Here is an average climate graph.

          trench2.png

          5) Totally agree with you. Hence appealing to this forum. The situation of the house + surrounding houses is such that end of garden position is best. Otherwise it would mean doubling collectors on West facing roof and East facing roof.

          6) Agree again. This is my design for the trench pipe. Continuous length of pex, wrapped in R5 to R6 to a total diameter of 300mm. I expect approx R20 insulation value for the entire length (15 metres pipe / 50 foot pipe)

          trench4.PNG



          Originally posted by LucMan View Post
          Here is a link to Uponor Ecoflex insulated underground Pex, expensive but is the best way to go. This item saves labor and the insulation is designed for underground use.
          http://www.uponorpro.com/Catalog/Cov...rmal-Twin.aspx
          Prices are list. You can order the length that you need instead of ordering a complete roll.
          Thank you so much. The nearest available in France I will contact them.

          Originally posted by Mike90250 View Post
          i'd look at underground, closed cell foam insulation, sleeve the pair of pipes inside 5" ABS drain line. Keep it out of the sun, the UV in the desert eats plastics.
          Thanks. Definitely bury the pipe in a trench with access. I will upgrade the pipe from 4.5inch to 11.8 inches diameter.

          Comment


          • #6
            Originally posted by oemodm View Post
            Thank you. To answer 1 by 1:

            2) = It is to supply hot water heating only. 400 hot water tank, with some solar heating from evacuated tubes with this spec:
            60 tubes
            Collector Gross Area = 10(m2)
            Collector Absorber Area = 5.6(m2)
            Annual Output* 5926(kwh)
            Daily Output (litres) at 50°C = 540 litres (average)

            3)I am not expecting this to supply all hot water, all the time. I'm expecting it to contribute at least 50% annually. The 400 litre tank also has an electric element

            4) Freezing climate? Infrequently between Dec to Feb, a week here & a week there it can get as low as -15 deg. C. Here is an average climate graph.

            [ATTACH=CONFIG]4222[/ATTACH]

            5) Totally agree with you. Hence appealing to this forum. The situation of the house + surrounding houses is such that end of garden position is best. Otherwise it would mean doubling collectors on West facing roof and East facing roof.

            6) Agree again. This is my design for the trench pipe. Continuous length of pex, wrapped in R5 to R6 to a total diameter of 300mm. I expect approx R20 insulation value for the entire length (15 metres pipe / 50 foot pipe)

            [ATTACH=CONFIG]4223[/ATTACH]





            Thank you so much. The nearest available in France I will contact them.



            Thanks. Definitely bury the pipe in a trench with access. I will upgrade the pipe from 4.5inch to 11.8 inches diameter.
            Two brief comments:

            1.) I'd never use PEX for any application involving solar thermal, the design temps. are usually too high or off design conditions can easily make them that way.

            2.) I'd put the supply and return in their own sleeves with as much insulation as possible. The close proximity of the supply and return lines as sketched with the relatively small amount of insulation between them will allow the inlet fluid to the collector to be heated by the fluid returning from the collector on its way back to the storage tank, thereby cooling that fluid. Keep the lines apart with insulation to the greatest extent possible to the limits of cost effectiveness. You do not want them in thermal communication. Keep'em apart.

            Comment


            • #7
              Originally posted by oemodm View Post
              Thank you. To answer 1 by 1:

              2) = It is to supply hot water heating only. 400 hot water tank, with some solar heating from evacuated tubes with this spec:
              60 tubes
              Collector Gross Area = 10(m2)
              Collector Absorber Area = 5.6(m2)
              Annual Output* 5926(kwh)
              Daily Output (litres) at 50°C = 540 litres (average)

              3)I am not expecting this to supply all hot water, all the time. I'm expecting it to contribute at least 50% annually. The 400 litre tank also has an electric element

              4) Freezing climate? Infrequently between Dec to Feb, a week here & a week there it can get as low as -15 deg. C. Here is an average climate graph.

              [ATTACH=CONFIG]4222[/ATTACH]

              5) Totally agree with you. Hence appealing to this forum. The situation of the house + surrounding houses is such that end of garden position is best. Otherwise it would mean doubling collectors on West facing roof and East facing roof.

              6) Agree again. This is my design for the trench pipe. Continuous length of pex, wrapped in R5 to R6 to a total diameter of 300mm. I expect approx R20 insulation value for the entire length (15 metres pipe / 50 foot pipe)

              [ATTACH=CONFIG]4223[/ATTACH]





              Thank you so much. The nearest available in France I will contact them.



              Thanks. Definitely bury the pipe in a trench with access. I will upgrade the pipe from 4.5inch to 11.8 inches diameter.
              Some brief comments:

              1.) I'd never use PEX for any application involving solar thermal, the design temps. are usually too high or off design conditions can easily make them that way.

              2.) I'd put the supply and return in their own sleeves with as much insulation as possible. The close proximity of the supply and return lines as sketched with the relatively small amount of insulation between them will allow the inlet fluid to the collector to be heated by the fluid returning from the collector on its way back to the storage tank, thereby cooling that fluid. Keep the lines apart with insulation to the greatest extent possible to the limits of cost effectiveness. You do not want them in thermal communication. Keep'em apart.

              3.) There will be summer days when the tank temp. may exceed +80 deg. C. Check Temp. & pressure rating of the tank, valves, & other equipment, ESPECIALLY SAFETY VALVES AND OTHER RELIEF DEVICES.

              4.) Allow for pipe thermal expansion especially in long, straight runs.

              Comment


              • #8
                Originally posted by J.P.M. View Post
                Some brief comments:

                1.) I'd never use PEX for any application involving solar thermal, the design temps. are usually too high or off design conditions can easily make them that way.
                Agreed - in building the system I have I went through a lot of discussions on that point.
                [SIGPIC][/SIGPIC]

                Comment


                • #9
                  Originally posted by J.P.M. View Post

                  1.) I'd never use PEX for any application involving solar thermal, the design temps. are usually too high or off design conditions can easily make them that way.

                  .
                  What would you recommend? (in continuous length would be great)


                  Originally posted by J.P.M. View Post

                  2.) I'd put the supply and return in their own sleeves with as much insulation as possible. The close proximity of the supply and return lines as sketched with the relatively small amount of insulation between them will allow the inlet fluid to the collector to be heated by the fluid returning from the collector on its way back to the storage tank, thereby cooling that fluid. Keep the lines apart with insulation to the greatest extent possible to the limits of cost effectiveness. You do not want them in thermal communication. Keep'em apart.

                  I have taken your advice in modified image below.By the way, is it possible to assume how much heat will be lost in percentage terms?

                  Detail:
                  1 = Each flow will be mounted in its own insulated pipe, where:
                  A = Styrofoam or cold cell foam wrapped around solar panel pipe
                  B = Leak detection
                  C = Radiant insulation, foam layer
                  D = 300mm PVC drainage pipe
                  F = Gravel trench fill

                  trench8.JPG


                  Originally posted by J.P.M. View Post

                  3.) There will be summer days when the tank temp. may exceed +80 deg. C. Check Temp. & pressure rating of the tank, valves, & other equipment, ESPECIALLY SAFETY VALVES AND OTHER RELIEF DEVICES.

                  4.) Allow for pipe thermal expansion especially in long, straight runs.
                  I will hire a professional to advise on the safety side. Thank you for your warning. Inside the 300mm drainage pipe will be a gap for any expansion.

                  thank you again
                  Attached Files

                  Comment


                  • #10
                    I think CPVC pipe is rated for high water temp, as long as you use CPVC fittings and glue.

                    The pipe themal expansion occurs in the length, so there needs to be some right angle bends where the pipe can get some motion
                    here and click on the IMAGES link at the top examples of U joints, and pipes that pop out of the ground
                    https://www.google.com/search?q=pipe...rmal+expansion
                    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                    solar: http://tinyurl.com/LMR-Solar
                    gen: http://tinyurl.com/LMR-Lister

                    Comment


                    • #11
                      Originally posted by Mike90250 View Post
                      I think CPVC pipe is rated for high water temp, as long as you use CPVC fittings and glue.

                      The pipe themal expansion occurs in the length, so there needs to be some right angle bends where the pipe can get some motion
                      here and click on the IMAGES link at the top examples of U joints, and pipes that pop out of the ground
                      https://www.google.com/search?q=pipe...rmal+expansion
                      I used copper to the heat exchanger due to this problem. If the system is stagnant the collectors can become hotter than plastics allow.
                      [SIGPIC][/SIGPIC]

                      Comment


                      • #12
                        Originally posted by russ View Post
                        I used copper to the heat exchanger due to this problem. If the system is stagnant the collectors can become hotter than plastics allow.
                        A conventional T&P blowoff valve should be used near the high/hot point of the collector.
                        http://www.watts.com/pages/support/tp.asp?catId=64


                        THE MAXIMUM SERVICE TEMPERATURE FOR CPVC IS 200°F.
                        THE MAXIMUM SERVICE TEMPERATURE FOR PVC IS 140°F.
                        pex has a maximum operating temperature of 180F
                        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                        solar: http://tinyurl.com/LMR-Solar
                        gen: http://tinyurl.com/LMR-Lister

                        Comment


                        • #13
                          Originally posted by oemodm View Post
                          What would you recommend? (in continuous length would be great)





                          I have taken your advice in modified image below.By the way, is it possible to assume how much heat will be lost in percentage terms?

                          Detail:
                          1 = Each flow will be mounted in its own insulated pipe, where:
                          A = Styrofoam or cold cell foam wrapped around solar panel pipe
                          B = Leak detection
                          C = Radiant insulation, foam layer
                          D = 300mm PVC drainage pipe
                          F = Gravel trench fill

                          [ATTACH=CONFIG]4225[/ATTACH]




                          I will hire a professional to advise on the safety side. Thank you for your warning. Inside the 300mm drainage pipe will be a gap for any expansion.

                          thank you again
                          1.) How much heat will be "lost" (assuming through the piping) is a big topic in itself. One indication of how big is the size of a decent heat transfer text. Then consider as a 1st approx., probably better than a third of that text deals with conduction - most of the method of heat transfer under consideration in this thread. A fascinating subject and quite a bit larger than can be scratched at here. I'd respectfully suggest this shortcut as a start: a.) Crash course yourself on a basic heat loss equation, Q = U*A*(Delta T) , the terms used and what the concept is all about. Broadly, that's the eq. that describes heat loss b.) Design the system such that the total incurred piping losses for the entire system are less than about 10% or so of the total system gain on either an instantaneous or time integrated basis. A little homework on theory on your part is necessary. I can't/won't help on that.

                          2.) I'd scrap the PEX and the plastic for pressurized systems. IMO, they are no better than ways to design problems into a system. For solar stuff, I'm a big fan of copper and sweated joints, maybe some screwed joints for fittings etc. that will need service/changeout along the way. While speaking of changeout and piping, don't forget isolation valves unless you want to keep draining the system every time it needs service. Don't cheap out on fittings and don't forget to stroke the valves on a regular basis so they don't crud up and freeze in position sooner than they otherwise would.

                          3.) Piping design includes may things. Hand in hand with thermal expansion considerations go piping support requirements. Make them strong enough and the material appropriate for the service, but at the same time not so rigid they act as expansion restraints that wind up causing more problems than they solve.

                          4.) Russ, and I believe others have suggested a website called "builditsolar" or some such name. It's not bad and talks about the kind of things you're dealing with here.

                          Bon Chance, mon ami.

                          Comment


                          • #14
                            Pex ratings are 80 psi at 200 F. 100psi at 180 F extrapolating you get 240F at 40 psi. Selecting the correct T&P valves is extremely important.
                            If you connect to the collectors with a minimum of 8 ft of copper tubing you will be ok. There would have to be multiple failures in the system safety controls before the pex could fail.

                            Comment


                            • #15
                              Originally posted by LucMan View Post
                              Pex ratings are 80 psi at 200 F. 100psi at 180 F extrapolating you get 240F at 40 psi. Selecting the correct T&P valves is extremely important.
                              If you connect to the collectors with a minimum of 8 ft of copper tubing you will be ok. There would have to be multiple failures in the system safety controls before the pex could fail.
                              Opinions vary and I respect those of others, especially knowledgeable designers, but for the labor involved and the PITA of failures if/when they occur, especially for limited access or inspection situations or more likely no inspection or maintenence, I'll pay a bit more in time/$$'s for sweated and tested copper and build, husband and save my factors of safety for the Rube Goldbergs, incompetent installers and DIYers to chew up.

                              Comment

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