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  1. #1
    starloc's Avatar
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    Default DIY solar heating for greenhouse

    somewhere on the internet ( it may have been on here ) , i saw someone who had set up a powerless solar heater for a greenhouse, using convection to circulate the water,
    it was very simple setup, maybe not easy to get right, but it was easy to set it up

    Does anyone know where it could have been?, or know how to do it

    its something similar to a car radiator for the solar panel and tubes taking the hot water upwards to circulate the heat into the greenhouse and back down after its cooled?
    Last edited by starloc; 13-03-2011 at 08:35 AM.

  2. #2
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    Not seen that one Starloc, but if using solar power, wouldn't you want to store the heat somewhere (as per Dick Strawbridge heat sink) as surely if the sun is hot enough to power a panel the greenhouse would be hot anyway?
    "We can complain because rose bushes have thorns, or rejoice because thorn bushes have roses."-- Abraham Lincoln

  3. #3
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    Ive been given a 100ft by 20ft greenhouse ( will be up as 50 by 40 ) but im putting it up in Bulgaria so during the summer it will be very very hot ,so i can solve that easily... open all the doors around the edge of it to keep it cool,
    but in the winter it can drop very low so im going to need to warm it by 15 to 20 degrees C , the sun is hotter in bulgaria, but the temperature is usualy lower i the winter

    Im trying to avoid any large bills for heating it,i could use a generator but its noisy and fuel costs are high, Bulgaria doesnt have very good electric supply if last year is anything to go by and where we are there is no gas, just propane bottles , everything is done by wood

    i can use a heater run on wood or similar to heat it by having a hollow floor and letting hot air circulate

    Due to the temperature outside , im going to have to cover the glass to prevent sunlight getting in if the temperatures are cold inside, so its probably easier to insulate it all with thin polystyrene sheet all over to prevent heat loss, it has wooden shutters to close inside, i will insulate these

    hopefully the only electric i will use will be from a vertical wind generator

    Ive seen people say they have heated up the greenhouse from outside with a car radiator, the heated water during the day circulates to radiators higher up inside the house so the water circulates , but never seen any figures on how much heat they can produce area for area, any plans for a system they have used that works would be good!

    for storage ive seen mention of using a drum of water in the circuit that heats up, some say an old chest freezer works and is insulated ( but would look bad! )
    Last edited by starloc; 13-03-2011 at 02:12 PM.

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    Very low tech I know, but barrels of water along the sides - you make the tops of the barrels into benches. I don't know the exact thermal properties of the set up but you can look it up and its free as the water stores any heat during the day - might off set any other heating costs considerably.
    Jiving on down to the beach to see the blue and the gray, seems to be all and it's rosy-it's a beautiful day!

  5. #5
    starloc's Avatar
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    Quote Originally Posted by King Carrot View Post
    Very low tech I know, but barrels of water along the sides - you make the tops of the barrels into benches. I don't know the exact thermal properties of the set up but you can look it up and its free as the water stores any heat during the day - might off set any other heating costs considerably.
    Id forgotton about that one, some time ago there was a post on the citrus growers forum where someone did that in the winter to stop frost damage

    Its probably a good idea to use it even with heating as it will reduce costs and probably make temperatures more stable

  6. #6
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    If you are talking about heating water on a hot sunny day and storing this to use over night with out using any electricity then the setup would have to be gravity circulation.

    I know this works as a friend and I did an experiment a few years ago just for fun and not in a gardening situation.

    First we obtained a second hand single panel radiator 4` long x 2` high. This was set on end in a purpose made wooden box that had been painted black inside. (not sure if that made any difference).

    We then led the 22mm flow (hot) pipe from the top of the radiator to a plasitc 10/4 gallon tank some 3ft higher than the highest point on the radiator and connected this pipe as the top most connection some 2/3 of the way up the tank. The 22mm return (cold) pipe was lead from the bottom of the tank into the bottom of the radiator. The setup was filled with a hose pipe. It was a hot sunny summers day and the 8 gallons of water reach hand washing temperature in about 90 minutes.

    The thing to remember when dealing with a gravity fed system is they are prone to air locks to avoid this the flow pipe must rise continuously from the heat source to the storage vessel and the return pipe must likewise fall continuously.

    The main problem that I can foresee is that at night the tank becomes the heat source and therefore this must be lower than the heat emitter's it is going to serve.

    Hope this gives you some ideas Colin

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    I've been interested in this topic for a while but the weather always seemed to work against it.

    From my school days, if I take a 40 gallon water butt (180 litres) and I manage to get the temperature during the day to 30 degC then I have a heat source that will give out heat as it cools.

    If I want to keep my greenhouse at 10 degC minimum then my water butt will cool by 20 degC.

    Each litre of water gives out 4.2 kilojoules of energy for each degree it cools so my water butt will give out 4.2 x 180 x 20 = 15,120 kJ of energy.

    If I want my water butt to last all night - say 14 hours in winter/spring - then I can convert the 15,000 kJ of energy into watts.

    15,000 / 60 secs / 60 minutes / 14 hours = 0.3 kW = 300 watts.



    So if I can raise the temperature of my water butt to 30 degC every day from its starting temperature of 10 degC I would have a reasonable heater.



    The problem comes from the heat loss from the greenhouse over night.

    If I replace all my glass in my 10 x 6 greenhouse with double glazing this 300 watt heater will keep the inside at 10 degC only when the outside temperature is above 5 degC. So I would need to use 2 water butts both heated to 30 degC every day to keep the plants at 10 degC when it gets to freezing point outside during winter.



    The physics says it should/will work (providing you double-glaze the greenhouse with proper double-glazed panels) but only if you can get the water butt temperature up to 30 degC on dismal, overcast winter days.

    And I've never seen any DIY plans that would guarantee this in England's climate without spending an absolute fortune!!!!!!!




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    Last edited by teakdesk; 14-03-2011 at 02:36 PM. Reason: Typos
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    Pots.... I've got an old radiator rusting in the garden... I feel a project coming on!!!!!





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    The proof of the growing is in the eating.
    Leave Rotten Fruit.
    Nitrogen, Phosphorus, Potasium - potash.
    Autant de têtes, autant d'avis!!!!!
    Il n'est si méchant pot qui ne trouve son couvercle.

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