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  • Orientation- horizon or vertical

    My roof has a low pitched roof to the West and I have two 4 by 10 hot water panels I bought used. I know these panels are supposed to be oriented so the hot water rises and is collected in a manifold pipe but I would like to orient the panels horizontally to minimize wind load and street visibility. I was wondering if this will affect the performance with a 23 degree rise on the metal roof. The roof is painted white so am hoping for reflectivity benefits.

    Kurt

  • #2
    If you are going to defeat the thermosiphon function by changing the orientation you can always add a recirculation pump.
    9 kW solar. Driving EVs since 2012

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    • #3
      Flipping those will seriously mess up the thermosiphon function. Adding a pump will work, but you'll need a differential thermostat to control the pump.

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      • #4
        I guess this is one of those situations where hacking is warranted and data collection is needed to optimize the function.

        Fortunately the roof's raised metal ribs for attachment allows orientation flexibility. I was going to place them in series which would maximize the thermosiphon effect, I think (vs parallel).

        On another note (maybe a new thread), my current HW demand requirements are lower than what is expected to be delivered via solar esp in summer. However there are simple principles and technologies to convert the excess low level heat to electricity, or application to a dessication membrane to support evaporative cooling. A pump may be mandatory to keep things from melting down.

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        • #5
          Originally posted by KurtP3 View Post
          I guess this is one of those situations where hacking is warranted and data collection is needed to optimize the function.

          Fortunately the roof's raised metal ribs for attachment allows orientation flexibility. I was going to place them in series which would maximize the thermosiphon effect, I think (vs parallel).

          On another note (maybe a new thread), my current HW demand requirements are lower than what is expected to be delivered via solar esp in summer. However there are simple principles and technologies to convert the excess low level heat to electricity, or application to a dessication membrane to support evaporative cooling. A pump may be mandatory to keep things from melting down.
          That would be an interesting experiment. While I haven't dabbled in thermoelectricity, I have read up on it somewhat.

          Basically it's expensive. You need a lot of heat, and cold, too. One side has to be heated, while the opposite side cold.
          Then you get a dismal amount of power out one thermopile‚ÄĒtypically only a handful of watts. (I may not have the name right. Perhaps thermocouple)

          If only i were younger and had lots of money to tinker with.

          Apparently I haven't done anything stupid enough that would cause a time traveler to come back to my time and stop me.

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          • #6
            Originally posted by KurtP3 View Post
            My roof has a low pitched roof to the West and I have two 4 by 10 hot water panels I bought used. I know these panels are supposed to be oriented so the hot water rises and is collected in a manifold pipe but I would like to orient the panels horizontally to minimize wind load and street visibility. I was wondering if this will affect the performance with a 23 degree rise on the metal roof. The roof is painted white so am hoping for reflectivity benefits.

            Kurt

            Do you live in an area where freezing or close to freezing temps. will occur ?

            What's you latitude ? Know that unless you live in at a low latitude, low panel tilts may have sever performance penalties due to poor panel orientation ?

            Unless you have the potable HW storage storage located above the collectors, thermosiphoning will not occur.

            With a direct type system (potable H2O circulated through the collectors) you will need a pump for any water heating to be possible.

            On active water heating, contrary to popular belief, it is entirely possible to pump fluid through a collector from top to bottom with the only energy/thermal efficiency penalty being from the slightly reduced thermal efficiency caused by the slightly reduced flowrate pumping against the thermosiphon head - and that's probably close to zero unless the pump is marginally sized to the duty. Most circulators for active (pumped) residential solar hot water systems produce pumping heads that exceed most any thermosiphon produced head by an order of magnitude or more, so it's not much of a problem in that respect.

            However, care is needed in the piping design if fluid is pumped from top to bottom or "downhill". I did plumb a system "upside down" once but used a motorized ball valve and a timer. Worked fine.

            Also, unless you live in an environment so clean that it's dustless, or don't mind a very frequent cleaning schedule, horizontal panel orientations quickly turn them into shallow sandboxes. Keep at least a 5-10 deg. tilt - steeper if you live in a dry, dusty climate. If it's a low tilt, the panel azimuth is much less important.

            I'm travelling just now. Be back in a day/two.

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            • #7
              Freezing is the norm at 39 lat (Wash DC area) and plenty of rain for the washer effect.

              Now I didn't mention that the roof also has other orientations, but to the ENE and WSW. They are however not adjacent as they fall on either side of a central dormer.The pitch is steeper at those orientations (23 vs 13 deg for the other more level area alluded to originally).

              How might the pipes be connected to achieve thermal siphoning with the diurnal differential exposure?

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              • #8
                As stated previously a pump, glycol, and differential controller are going to be required for the installation that you are proposing, using vertical flat plate panels oriented horizontally in parallel. They will work just fine that way if you slope the panels to wards the manifold, I recommend a min. of a 1/4 per ft. Thermosyphon only works with the storage tank mounted above the panels in close proximity with the panels configured vertically. A dump zone may be required to prevent stagnation temps, and or cooking of the glycol. At 23 degrees the summer production will be high unless there is shading from another part of the house.
                There will be no reflective benefits from your roof, as the roof is facing the same direction as the panels reflecting the sun away from the panels not onto them.
                Last edited by LucMan; 01-13-2020, 10:37 AM.

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