Where can I find how to design a cold room storage building?
I have a 12x12 shed that I use as cold storage for tree seedlings for about a month each spring. The present construction is 2x4 walls with fiberglass insulation. The building is wrapped with strawbales, and has 16" of cellulose insultion in the attic.
I have 12 barrels along the walls filled with water, supported on pallets, and with 4" of styrofoam scraps floating on top. The barrels freeze solid in winter.
During the winter, the door is left open and the ceiling fan left on. This chills the ground under the slab.
All 4 sides of the shed have 4 layers of nominal R2 insulated tarps to reduce ground conduction.
This system works, but I've outgrown it. I want to scale up to a 20x20 building, giving me about 3 times the area.
I'd like to get away from the barrels, and instead put a pit in the room that I would flood with water 2 inches at a time to freeze. Build with a permanent set of concrete pillars space to accept pallet sized 'floor' units. Or put in floor supports that span the pit. These would also stop the ice from floating up when the next layer of water was added.
But now I get into the limits of my knowledge:
What is the right slope for the pit? I don't want to cast a swimming pool, I'd rather a dirt pit lined with an impermeable liner if necessary. Too steep, and the sides slump.
What is the right way to make the walls? The desired environment for the use period is 1 degree C and 95+% humidity. Vapour barrier is normally put on the warm side of the wall, but leaving the inside unprotected with such a humid environment seems like a bad idea too.
My thought is to have a fan in the space between the movable floor and the room space, controlled by a thermostat near the ceiling. I'm not sure if the fan blowing over the surface of the ice will move sufficient coolth from the ice to the room. How do I figure heat exchange between moving air and wet ice?
What is the proper design for foundations for such a building? Frost depth here is about 5 feet. But that is based on a building that is heated for at least part of the year. Do I need a different foundation for a building that much of the year is at or below freezing.
Should the foundation be insulated from the surrounding ground? Here best practice is to angle a slab of styrofoam 4 feet out and down from the gradeline/foundation line. The notion is that the increase in path length for conduction outweighs the shallower depth of the bottom edge. But for a room designed to be cold, would it have the same design.