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  • Need help with DIY pool solar design

    Hello all.

    I'm new here so please forgive some of what may seem like simple questions. I've been researching this for a week and can't find some of the answers I'm looking for.

    I am in the middle of designing a solar system for my small inground pool. I am located in the Mayan Riviera in Mexico. Our swim season is usually around March to Oct. with unheated pools depending on the weather. Winter freezing is not an issue. In the summer, my pool is around 30C-32C (86F-90F) and gets about 5, maybe 6 hours of sun per day. With that information, here are my questions:

    1) With freezing not a factor, do I need a vacuum break on the panels? I don't want them to drain if not necessary in order to work on the pump upon startup.

    2) I am planning on making coil type collectors using polyethylene pipe. I calculated 10' head due to friction loss threw 200 feet of 3/4" pipe (1 collector). If I use 5 collectors, is the dynamic head 5x the single collector or equal to it? This is unclear to me given what I've read.

    3) If the recommended flow rate is 5gpm threw the collector, I need 25gpm total threw the bottom manifold in order to supply this flow rate to the five collectors. Is it better to use 1-1/2" pipe or 2" pipe for the manifolds? The rest of my pool plumbing is 1-1/2".

    4) Currently, I have a single speed 3/4hp pump. My current setup turns the pool over in around 5 hours. Based on my total dynamic head calculations, this pump should be producing around 25gpm based on it's performance curves. Assuming this pump is sufficient to get the water on the roof (about 20' vertical), and given the siphon effect of the water coming down off the roof, would it be better to have a two speed or variable speed pump, higher speed to lift the water, then lower speed to circ. the water and save energy (electricity rates are crazy here)?

    If you could help me out with this it would be greatly appreciated. I want to do this right the first time.

    Thanks in advance.
    Dave

  • #2
    Originally posted by davestew View Post


    2) I am planning on making coil type collectors using polyethylene pipe. I calculated 10' head due to friction loss threw 200 feet of 3/4" pipe (1 collector).
    I suspect that the polyethylene pipe, being plastic, will not do a good job of warming the water. Black painted metal (aluminum or copper) will be a LOT more efficient at collecting heat. When you paint, you want the thinnest layer of paint possible, to not have it insulate it from the pipe. Additionally, you'd want the collector in a wind proof "glass oven" box, to keep the pipe warm.
    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 Mike90250 View Post
      I suspect that the polyethylene pipe, being plastic, will not do a good job of warming the water. Black painted metal (aluminum or copper) will be a LOT more efficient at collecting heat. When you paint, you want the thinnest layer of paint possible, to not have it insulate it from the pipe. Additionally, you'd want the collector in a wind proof "glass oven" box, to keep the pipe warm.
      That is wrong on many levels
      Chlorine in a pool will destroy copper or aluminum very rapidly. Polyethylene pipe although it may not be as UV resistant as copper will last longer and be much more cost effective in the long run. DO NOT put in an enclosure ( Ask Solar Industries about the GL series of pool collectors) You are on the right track although the materials used in commercial pool collectors will be more UV resistant the principle is the same. Keep in mind however that as the temperature drops the BTU output of the piping used will drop with it. Commercially available unglazed pool collectors will generally stop producing heat when the pool temperature is about 20 degrees warmer than the ambient air.
      If freezing is not a problem then the drain down vacuum breaker is not necessary
      If 5 collectors are used the friction head should be the same if they are in parallel at the lower flow rate.
      Install a flow meter on the collectors before upgrading the pump they are less expensive than installing a new pump.
      Generally make the pipes to and from the collectors the same size as the existing pool piping.
      Last edited by Naptown; 09-06-2011, 10:52 PM.
      Rich
      WWW.solarsaves.net

      NABCEP certified Technical Sales Professional

      http://www.solarpaneltalk.com/showth...Battery-Design

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

      www.gaisma.com

      Comment


      • #4
        I never claimed copper or aluminum would last long just that they will collect heat faster. Plastic, you can't enclose.
        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


        • #5
          A couple of links for you -

          1) Black pipe coil pool heater http://www.mmattera.com/bin/Solar_Pool_Heater_Coils.jpg

          2) Black pipe coil pool heater http://rimstar.org/renewnrg/solar_po...ter_diy_fp.htm
          [SIGPIC][/SIGPIC]

          Comment


          • #6
            Thanks for the info. The rimstar link is the one I got most of my information from and is the type of collector/system I wish to build.
            I am still not clear on the pressure loss threw the collectors. If one collector has approx. 10 feet of head, all 5 total in parallel will also create only 10 feet of head? Can you explain why this is the case and not 50 feet of head?

            Thanks!

            Comment


            • #7
              In parallel there is no apparent increase in pipe length - no increase in pressure drop.

              There will be a bit additional due to fittings and balancing valves but shouldn't be much.

              In series you would be correct - the pressure drop would accumulate.
              [SIGPIC][/SIGPIC]

              Comment


              • #8
                Ok, so when calculating the head threw the collectors, do I use 5 gpm (flow threw one collector) or 25gpm (total flow threw the feeder pipe)?

                Comment


                • #9
                  use one collector
                  Rich
                  WWW.solarsaves.net

                  NABCEP certified Technical Sales Professional

                  http://www.solarpaneltalk.com/showth...Battery-Design

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

                  www.gaisma.com

                  Comment


                  • #10
                    If the total flow is 25 gpm then you need to consider two separate sections -

                    1) For the coils (5 each) you would use 5 gpm

                    2) For the common piping you would use the 25 gpm

                    You will probably have to balance the flow using valves - add the drop across these into the calculation.
                    [SIGPIC][/SIGPIC]

                    Comment


                    • #11
                      Thanks for all the info. I just have one more question regarding the pump. I am thinking of upgrading the pump to a two speed pump to save energy. Once the water is flowing through the system and collectors on the roof, would the low speed on a two speed pump be sufficient to circulate the water given the siphon effect of the water coming back down? It would be great if I could run the pump longer (to produce chlorine through my salt generator) and still have an efficient flow through the solar collectors all while saving energy....

                      Also, I've a lot of the coil type collectors use 1/2" polypropylene pipe. Do you think it's better to use 1/2" or 3/4" for flow, heat gain, etc.?

                      Thanks,
                      Dave

                      Comment


                      • #12
                        dynamic head would be lower in 3/4 and there will be some siphoning effect to the collector. I hope it does not freeze there or you will be removing or replacing your collectors every year.
                        Rich
                        WWW.solarsaves.net

                        NABCEP certified Technical Sales Professional

                        http://www.solarpaneltalk.com/showth...Battery-Design

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

                        www.gaisma.com

                        Comment


                        • #13
                          Read the information at the URLs I provided for you for starters.
                          [SIGPIC][/SIGPIC]

                          Comment


                          • #14
                            Why would I be replacing the collectors, because I don't have a vacuum break? In any case, it doesn't freeze here. January temps average around 25c/13c high/low (77F/56F), and the sun is still pretty hot during the day.

                            Comment


                            • #15
                              Sorry I saw where you were after I posted.
                              Rich
                              WWW.solarsaves.net

                              NABCEP certified Technical Sales Professional

                              http://www.solarpaneltalk.com/showth...Battery-Design

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

                              www.gaisma.com

                              Comment

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