Hi, I am building a large root cellar, 25'x80' and if anyone has any advice on any ventilation systems that would be much appreciated. I am wanting to keep the temperature at a pretty constant 10 degrees celsius. Has anyone build of or know of any root cellars this large? Any info would be great! Thanks
That is a large root cellar! What are you going to fill it with? Whole lotta potatoes!
Two key concepts for ventilating an underground root cellar-
Oxygen rises, and Carbon Dioxide sinks. So depending on what you will store, that will be important.
Vegetable, mushrooms, cheese, and fermentation all release carbon dioxide, so you need to plan for the air to exit the room from near the floor level, and have fresh air drawn in near the ceiling.
Running your air intake pipes underground for 20-30 feet before they enter the cellar will temper the air quite nicely. That way, if it is super hot, or if it is below freezing outside, the air entering the cellar will be a much more moderate temperature by the time it reaches your cellar.
Our cellar is much smaller, more like 16x16. It is passively ventilated, non-electric. There are two seperate rooms, one for animal products/ferments, one for vegetables. We love it. It is fully underground, with just one wall accessable for entry without stairs. The temperature does fluxuate through the year, not on a daily basis, but seasonally. It is definitely colder in spring than fall.
Thanks so much for the info! I will be storing squash, onions, sweet potatoes, potatoes, turnips, carrots and parsnips. Possibly in two different areas. No dairy for the moment! I would like it to be as passive as possible and I am concerned about condensation in my ventilation system and therefore growth of bacteria and mold! I am counting on the ventilation pipe underground to cool and warm air as needed but I am unsure of how to maintain a relatively constant temperature (here winter can go down to 25 and summer up to 30). How exactly do you know 20-30 feet would be sufficient to temper the air? Thermal mass calculation??
'relatively constant temperature' is relative. if your outside temps have large seasonal differences, your temps inside your cellar will have swings seasonally as well. basically, you can put crops in the passive cellar in fall, once the cellar has cooled off. it will stay cold through the winter and into the spring, but it will definitely warm up by may/june. so a passive cellar works well for storing crops from november to april, not year round. to help cushion the temp swings, we put down a 4" layer of blueboard insulation over the top of the concrete structure before backfilling 2 feet of soil. the walls are not insulated, just deeply buried underground. we used a large commercial refrigerator door to minimize heat transfer through the one part of the cellar that has contact with the outside air.
the crops you mentioned are mostly suited to cellar storage, but not squash. a cellar in winter would be too cold and damp for squash to store. they are better in an above ground structure that is warmer and drier. onions will do much better hung in mesh sacks from the ceiling than in bins, so it is good to have metal hooks in your ceiling for hanging.
you might calculate carefully the amount of volume you actually need for storage. a full cellar will be more stable with temperature compared to a large cellar with a lot of empty air volume. when you run the calculations, you may be suprised by how much root crops fit into how small of a volume. and cellar construction is not cheap with all the concrete and rebar, not to mention earth moving costs.
I didnt run any mathematical calculations for the air tempering. mostly just went off of local country wisdom, for what that's worth. if your pipe runs are too long, you wont move enough air to ventilate. our climate is fairly severe, with winters averaging around 25 degrees F, and summer average around 75 degrees F. the cellar buffers this, but not like a thermostatically controlled refrigeration room would. the air exchange is very slow, you cannot feel the air moving generally at the point where the pipes enter the cellar.
for the vent pipes, I used corrugated pipe with drainage slits, so any condensation drains into the soil. no problems there with mildew. make sure you screen the pipes for rodents, that would be a more likely problem.
consider the cleanability of the materials you use in construction. we chose all concrete walls and ceiling, coated with many layers of lime. easy to wipe down and disenfect, and the lime is strongly anti-fungal and anti-bacterial.
part of our floor is concrete slab, easy to clean for cheese and ferments. part of our floor is gravel, good for drainage and humidification. if we water down the gravel, it keeps the ambient air humidity levels very nice for the vegetables.
hope those suggestions are helpful. like I said, we really love our cellar, and I think every farm should have one.