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  • A solar greenhouse!

    Hello everyone, I'm Luca and I write from Rome, Italy. I'm new to the forum and am looking for help in solving a problem.
    Thank you in advance who will want to help me out ))

    So, I'm building a greenhouse for cacti and other succulents, the topic is how to heat in winter the greenhouse using solar panels and a boiler or solar water heater.
    persp_01.jpg

    I know the basics of an electrical system, I can manage a little with the water pipes, I work with wood, I use a welder, but I'm not an expert in renewable energy, I have only approximate ideas, but I definitely want to finish my project. the more so that it begins to get cold

    And I must premise that my goal is not to go below 8 degrees at night, but also during the day if the temperature drops just below 8 °.

    Here is the description of my idea:

    -1. I want to make an underfloor heating system, then put in the greenhouse floor (which is simply a dirt surface) a tube (the green plastic that is used for plumbing in the house), buried approximately 5 cm, placed as a serpentine.
    Hot water passes into the pipe and heats the ground and the greenhouse. You can see it in photo 2.
    foto 2_interno serra e serpentina.jpg

    -2. The heating must start when the thermometer detects a decrease of the temperature below 8 °, then it takes a temperature sensor, unless it is too complicated, and then solving with a timer.

    -3. The greenhouse measures 18 meters x 8 meters x 3.80 h, is covered with a PVC sheet, not dual layer. During the winter the doors are closed.

    -4. The greenhouse is located in Rome, Italy, then the temperature is mild, but in the months of January and February can reach 0 to -2/-4 or down at night, and even more.

    -5. I do not want to use a hot air burner fueled by diesel.

    -6. I understand that solar energy systems can be of two types: isolated, and there is no need of batteries or connected to the mains supply: here is to understand what is most suitable for my purpose, taking into account that I could also create a paneling, say, 6 meters x 8 meters, so as to have electricity for other purposes.

    7. There to understand even if the system is closed-loop or not, and if it is a closed circle maybe it takes a pump

    ok, this should be exhaustive, I expect your suggestions!

    a warm greeting to all the forum community!

  • #2
    About your only hope would be to build water storage into the greenhouse and use solar thermal panels to provide the hot water.

    You need to go to the double layer covering for the greenhouse for sure.

    One more sure thing is that you don't want to use solar PV for heating purposes.
    [SIGPIC][/SIGPIC]

    Comment


    • #3
      I have a solar heated greenhouse, a solar water heater, and a good friend has a solar-heated hydronic system in his floor. So, putting those things together, I can offer a couple things.

      First, as Russ said, a storage tank of heated water in or near the greenhouse is your best best. If you can bury it in the floor, even better, or build a "vault" into the floor and put a tank in it so you have maintenance access. Above the floor and the tank tanks up room better used for the cacti.

      Your needs do not sound prohibitive, and a solar-heating panel [water in pipes in a glass-fronted box type of collector] would heat up your storage water just fine.

      You will need at least two pumps. For your needs, these can be small pumps. One pump to circulate water from your storage to your collector box, and another to circulate the warmed water through your serpentine pipe layout beneath the greenhouse floor. My friend tried to use one pump for all of it, but it reguired him to have sets of valves he manually closed and opened and it was a pain. There are automated systems available, but they are rather pricey.

      The pumps can easily run off PV-generated electricity. Both my friend and I do this.

      You want a differential controller [thermostat] to control the pumps. The controller compares the various temperatures involved and turns on and off the pumps. You might need two controllers: one to operate the floor circulating pump and one to control the storage tank/solar collector set-up. Very simple to set up and use. Mine is operating hands-off. These controllers are not very expensive, though they range in price according to whether you want digital read-outs, computer records, etc. I've seen them ranging from US$ 75 to several hundred dollars. The controllers need a small amount of electricity and mine runs off the same PV as my pumps. [My pumps are 12 volt DC.] Often a controller will operate over a wide range of voltages and either AC or DC, as mine will.

      You will have to put pencil to paper and decide how much water storage you will need to accomplish your heating goals and also how much of a PV system [how many panels, etc.] you will need to run the pumps. Probably very modest needs on the PV part if you go with efficient pumps. You will also need to decide how many gallons per minute you want to run through the hydronic system and that will determine the pump capacity.

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      • #4
        You may want to consider running your radiant tubing ( the plastic heat tubing with the warm water) through the soil in the beds where the plants are growing.
        This is a more direct method used in green houses that supplies the heat directly to the root of the plants, less heat required, higher efficiencies for solar hot water panels.
        Just another idea for you.

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        • #5
          Earthship

          I built my solar heated 'greenhouse' in 2000----an Earthship.
          http://www.earthship.com/

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          • #6
            Originally posted by russ View Post
            About your only hope would be to build water storage into the greenhouse and use solar thermal panels to provide the hot water.
            Russ, I am considering that for my redneck greenhouse made of used sliding glass doors. Thought I would put a 250 gallon or so water tank inside with a solar batch heater. Would need to figure out best way to move the water around during the day. Considered a solar pond fountain pump cannibalized to make it work only when sun was shining.

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            • #7
              Use a thermosiphon panel - system
              [SIGPIC][/SIGPIC]

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              • #8
                Yep, thermosiphon is not one I have learned about yet. Sounds very technical and engineered. As opposed to my hatchet job engineering of the solar pond pump circulator. Why do I always lean towards the hillbilly version of everything?

                Comment


                • #9
                  Originally posted by rhawkman View Post
                  Why do I always lean towards the hillbilly version of everything?
                  I'm kinda the same way. I LOVE repurposing, so a lot of my stuff winds up being makeshift. It keeps the price down for me so I just concentrate on good craftsmanship.

                  BTW I think a pump would work way better than a thermosiphon system. That's just my humble opinion though.

                  Good luck and keep creating,
                  Green

                  Comment


                  • #10
                    Originally posted by rhawkman View Post
                    Yep, thermosiphon is not one I have learned about yet. Sounds very technical and engineered. As opposed to my hatchet job engineering of the solar pond pump circulator. Why do I always lean towards the hillbilly version of everything?
                    Look up in the wiki thermal siphon solar water heater - no moving parts - where you are you want a drain back system I suppose - a little more complicated but not much
                    [SIGPIC][/SIGPIC]

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