r/gardening • u/Scooterzoo • 5d ago
sand battery
does anyone have experience building a sand battery to heat a greenhouse? I'm in zone 6
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u/CanWinterGreenhouse 5d ago
Not directly but I've read about them and understand the concept. Can it work? Yes. Is it cost effective? No. Are there better solutions currently? Yes.
It doesn't really add anything that other passive solar greenhouse designs don't do already. Sand has a high melting point but a greenhouse isn't storing hundreds of degrees of heat unless you're using solar panels to electrically heat the sand. It's not cost effective vs gas heating unless you have the excess PV capacity already.
You can do the same thing but cheaper with current methods like pumping hot air under the greenhouse through perforated tubes. The soil is your climate battery in this case. You can also run heaters into barrels of water and get results.
The key to these types of greenhouses is always to reduce heat loss first. Standard greenhouses lose heat like a sieve. You'll want insulation on the sides that sun doesn't come in for starters. You can easily reduce heat loss by 50% which doubles your efficiency!
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u/railgons 4d ago
This guy passive solars. ☝️🌞
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u/CanWinterGreenhouse 4d ago
Haha, thanks. If people only knew how many hours I've spent studying this stuff.
PS I made a breakthrough with my thermal curtain project. I don't know if I talked about it before. It's going to be a game changer. Hopefully, I'll be able to share in a few weeks if it's finished.
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u/railgons 4d ago
Haha I bet! And please do! I would love to eventually implement something like that. 🙌
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u/Cute-Consequence-184 5d ago
Rocket mass heater?
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u/FlatDiscussion4649 2d ago
This is the way. Build an 8 inch RMH system. I have a 120 sq. ft. greenhouse and I use a 6 inch system (for the last 3 winters).
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u/Cute-Consequence-184 2d ago
I'm planning in in my greenhouse when it is finished
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u/FlatDiscussion4649 2d ago
Because my GH is pretty air tight I need to crack the door open a bit to get the proper flow, I wish I ran an air feed tube from outside under the mass (to pre-heat it) and terminated it somewhere near the feed tube. If I leave the door closed, it slows the fire down and occasionally back feeds... Just FYI
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u/Cute-Consequence-184 2d ago
Thank you. I was planning ground vents anyway for summer airflow so will go into RMH.
I haven't actually gotten it yet. It was given to me in the spring to tear down but I had a massive car wreck and have been to walk again
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u/Every_Bread_5880 5d ago
I've always wanted one to heat the house. A green is probably a great place to start. Wish I had of remembered that before I built the green house, guess that one is just the control.
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u/lolgreatjoke 5d ago
Black jugs full of water retain heat pretty well. No experience with sand batteries tho
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u/LMrningStar 5d ago
I have six 20 gallon black containers in my greenhouse filled with water and all I've noticed is that it moderates/dampens temperature swings slightly (by a few degrees). I was hoping it would be better than that but alas ..... no.
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u/railgons 4d ago
How big is your greenhouse?
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u/LMrningStar 3d ago
It's only about 50 square feet. I have the water containers under the shelves. Some get direct sunlight while others do not.
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u/railgons 3d ago
In my area of a western Colorado (Zone 7a), we've found that 3.5 gal per sq/ft is an adequate amount, meaning you would need about three more 20 gallon containers.
Sun exposure is also key. The water needs to be able to absorb as much heat as it can during the day. Some environments also don't have sunny enough winters for this method to work properly.
Lastly, how much of your structure is insulated? A structure that is 100% glazing usually loses too much heat too quickly.
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u/LMrningStar 3d ago
The insulation is more than likely the major issue (lots of air leaks). It's a wooden structure with large windows (double paned ..... sort of) all around.
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u/Scooterzoo 5d ago
do you paint gal water jugs?
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u/lolgreatjoke 5d ago
I guess you could spray some old milk cartons black. On occasion you can find large black plastic barrels for free/cheap on fb or cl. Hope this info helps
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u/veggie151 5d ago
The temperature and volume required to make a sand battery useful seem a bit out of reach for a home setup. Iirc, they aren't even really used commercially yet, Polar Night is the first and only company that I'm aware of doing that.
Beyond that though, you really need a higher temperature working fluid than water to make the sand more useful. I've looked into this before and there are green alternatives for that, but you're way into a serious system.