Greenhouses forum: Solar can heater for the greenhouse

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Name: Lucky
Sacramento CA (Zone 9b)
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luckyzl230
Jan 30, 2016 2:30 PM CST
Has anyone ever tried a solar can heater for their greenhouse during the sunny days in the winter?
Obviously, solar mass objects would be needed in the greenhouse during night times.
The post below is a small one but the concept works!

https://www.youtube.com/watch?v=UJVC6_yiXTg
Lucky Patrick
Name: Cheryl
Kingwood, Texas (Zone 9a)
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ShadyGreenThumb
Jan 30, 2016 4:43 PM CST
I also wondered if it would work. I have the perfect winter sun elevation fire thus to work. But it would take a large set up to provide enough heat. I wonder if it's worth the effort?
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Name: Lucky
Sacramento CA (Zone 9b)
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luckyzl230
Jan 30, 2016 5:09 PM CST
Same here. If anything. I would think it would use less electricity during the day. I've seen videos of people using these for there homes and garages.
Lucky Patrick
Lakeland Florida (Zone 9a)
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cycadjungle
Jan 30, 2016 8:07 PM CST
I don't think this would work very well for a greenhouse. Am I correct that the cans are empty? If so, they do not retain any heat at night and only work during the day.
So, I have no idea what works way up north, but from what I have seen, if you totally close up a greenhouse during the day, it can get 135f by afternoon because of the greenhouse effect. A closed greenhouse should heat up all you need during the day, its heating a greenhouse at night, for me, is the big concern. Now, heating a bunch of cans filled with liquid would provide heating at night, but 1 cubic foot of water only provides about 65 BTUs per hour so you would need piles of cans of water to make a big difference in heat for night use.
Name: Heath
sevierville TN (Zone 7a)
Beekeeper Houseplants Region: Tennessee
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plantcollector
Jan 30, 2016 8:34 PM CST
I agree with @cycadjungle that heater would be useless for a greenhouse. You only need to heat a greenhouse on a cloudy day and at night.
Name: Lucky
Sacramento CA (Zone 9b)
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luckyzl230
Jan 30, 2016 10:22 PM CST
Thanks for the advice. Didn't think about it that way. I was just think about how the 186 degrees coming out of the vent could heat a barrel of water to release at night.
I live in Sacramento and we don't get a lot of below freezing temps. But, we do average a quite a few days in the mid to upper 30s
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Name: Rick Corey
Everett WA 98204 (Zone 8a)
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RickCorey
Feb 23, 2016 6:56 PM CST
My impression from the video was that the cans were filled only with air: basically large tubes with thin walls.

Thus it had zero heat capacity; it was only a warm air generator, and only generated warm air while the sun shone directly on it.

Maybe a similar device could be built, replacing the large tin cans with small diameter, black-coated copper tubing. Push cold water through the copper tubing slowly and it would come out warm or even hot if it trickled slowly enough.

You could send the warmed water to a 55 gallon drum inside the greenhouse. Maybe insulate it during the day and remove the insulation at night?

Say the "warm" drum sat inside the greenhouse at floor level or slightly sunken.

Each morning you could pump the cool water UP to another drum, elevated, either inside or outside the greenhouse, but hopefully in the sun. Then let it trickle by gravity through the "solar heater" and back into the "warm" drum inside the greenhouse, all day. Then the pump only needs to run briefly each day, and gravity runs all day for free.



The air got so hot because it has such a low heat capacity, and probably flowed slowly through the cans.
It took hardly any sunlight to warm it from 30 F to 180 F.

Cp Air = = = 0.24 BTU per pound-mass x degrees F
Cp Water = 1.0 BTU per pound-mass x degrees F

So water has four times the thermal capacity PER POUND compared to air.
Water is 784 times as dense as water (at sea level and 15'C).

Therefor, water has 3,267 times the heat capacity of an equal volume of air.
For heat STORAGE, use water or rocks, not air.

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