At our community farm sites, people come once a week or so to pick up produce (fruit and vegetables, no meat, dairy, or eggs). We need a way to keep the produce fresh without electricity.
I was thinking that I would dig a shallow trough in the ground and line it with plastic. It would be maybe six inches deep. Large clay pots would be stood in the trench, and then the trench infilled with sand, and then filled with water. The sand would keep mosquitoes away from the water. Two plastic buckets would be nested together, and then placed in each clay pot. The space between the two buckets and the pot would be filled with sand. The inner bucket would be capped with its lid. An insulated lid of some sort would be placed over the top of each pot.
A chicken wire enclosure would be built around and over the whole thing, with a locking lid, to keep animals or unauthorized humans from tampering with it.
The vegetables would be put in the inner bucket as they were harvested. Then, when somebody arrived to claim their produce, they would unlock the lid, pull out the inner bucket marked with their name, and put in the bucket they are returning from last time.
This is in dry, windy Colorado, so evaporation will not be a problem. Rainy days here tend to be quite cool, even in the summer, so the days when evaporation is not working will not matter.
This is in dry, windy Colorado, so evaporation will not be a problem.
Well, not having enough shouldn't be a problem! Is there a potential for too much?
Where does the water come from? Figure ~1' diameter for your buckets... is this big enough? And at that size, are we talking a 20' trench? A 50' trench? Starts to turn into a lot of pots and insulated lids if you have a large customer base!
How much water will a trench of whatever length evaporate? How far do you have to run a hose or carry a bucket to replace it? Still have plenty of water onsite by September?
I'm a bit skeptical of the physics here... With only the bottom 6" in the damp sand, these big pots would have a lot more surface area exposed to the hot, dry wind than to the cool, damp sand. Seems like the key would be for the pots to wick up enough moisture to play a major role in the cooling process; will they? Otherwise that upper portion is just a heat collector... While this worked for amphorae way back when... IIRC those were relying on seepage from inside.
I would expect that shading this whole setup would be important. I guess the thing I like best about this idea is you can easily test it out in a 1-pot size!
We have plenty of water on site, and the hose spigot is right where we want to build this. And yes, it is in the shade. Whether the water will wick up properly is one of the potential problems I seen, too.
Sounds like most of the worries I had are addressed by your site, convenient!
If the pots don't wick enough on their own, what about adding some extra wicking? Something like fabric sheets, running from inside the pot, passing under the insulated lid, and then down into the wet sand?
I guess another thing to consider is the wind; is it a benefit because it accelerates the evap. cooling? Or is it a problem since a hot wind will be a heating force despite the accelerated evaporation? A wind break wouldn't have to be very high to bounce much of it over the top of a low-lying system like this, or a semi-permeable barrier might strike a better balance.
If full-on earth-tube construction doesn't work, perhaps something of the principle could be used in a scaled down way, allowing air to travel under a windbreak, along the top of some more wet-sand trench with a cover over it, before reaching the pots?
Location: Denver, CO
posted 3 years ago
I like the idea of adding something to the pots to wick water. Maybe I could just use the buckets and wrap them in some sort of sheet running down in to the water. Terracotta is expensive. And we would need a lot of them. Cloth is a better wick then terracotta.
I think the wind would be an advantage; it would carry off a lot of water vapour. We don't really get hot winds here.
It will be interesting to build one unit and see how it works!