I have a closet that I am considering converting into a root cellar by using a coolbot. It's not an outside facing closet so I'll have to figure out where the a/c unit would go. I may also be able to mount a cooling unit in the attic above the closet. I would of course insulate the space.
My question is I believe I may be violating the principles of root cellar storage as I believe mechanical refrigeration has a dehumidifying effect on the air. This may be more certainly true if I'm using an air conditioning unit/coolbot system.
I will be storing potatoes, sweet potatoes, winter squash, onions, and garlic.
I know each of these has different needs regarding humidity, and that is what I am trying to figure out.
I suspect the air conditioner will drip condensate, which is the humidity you want to stay in your closet. So you might have to find another way to keep it humid in there. Potatoes want it very humid (95%) while the other things you mention don't. Don't rot your house/closet by accident!
My root cellar isn't humid enough but it gets cold enough. So I store taters and carrots in 5 gallon buckets with damp planer shavings to keep the humidity up inside the bucket. Outside the bucket (in the root cellar), I keep the onions that like it cold but drier (70%??). Entirely outside the root cellar I keep the squash and garlic which like it drier and more like 55 degrees. Farther away I keep the sweet potatoes which like it closer to 60-65 degrees.
Humidity can be gotten around with packaging, damp sand or straw or even an open bucket of water. One issue is that the storage temperatures are very very different, garlic want's 0C (32f) whereas potatoes want 7-10C (45-50) and sweet potatoes need over 12C(54F) or they take cold damage. Humidity requirements vary from 95% right down to 50%. A good list of optimal storage temperatures, damaging temperatures and humidity levels can be found HERE
I'm not sure what you would call my cellar, it's the house cellar but I think it's closer to what people on here call a root cellar than whatever a Basement is. It's Brick, whitewashed uninsulated and has two small single glazed windows facing north with a always open vent. The temperature in high summer is around 13C and in winter about 1 or 2C when it was -18C outside the cellar was at 1C. (there is an insulated central heating pipe that runs through it stopping it freezing in cold weather) I use it to store potatoes(yes it's to cold but it's what I have), carrots, parsnips, onions and garlic. The potatoes are on the floor in hessian bags and keep fine, the carrots and parsnips have to be in wet sand or they dry out the onions and garlic hang from the ceiling. Winter squash and pumpkins are kept in the house in a cool room at around 15C the cellar is way to cold for them. The humidity in the cellar is close to that of outside so about 90-99% all winter.
If you were to keep the area at around 12C (54F) you could keep the onions and garlic for a few months, the squash and potatoes would keep nearly to their maximum and the sweet potatoes would also be happy. You would need to do some packaging on the items that like higher humidity.
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