Miscellaneous Questions about Cool Food Storage

Kelly Hart is your host at greenhomebuilding.com. He and Rosana created a large pantry (about 150 Sqare feet) in their earthbag house. Kelly has produced a video, titled Building with Bags: How We Made Our Experimental Earthbag/Papercrete House, which chronicles the adventure of building this house, and shows some of the making of this pantry. Kelly is available to answer questions about what he has done, or consult about other pantry or root cellar projects.

Questions and Answers

Q: I am about to remodel my kitchen (in a temperate to subtropical climate ... Auckland, New Zealand). Could you advise which factors I should build into the kitchen for maximum energy efficiency? I have read to put a vent in the floor under the refrigerator to vent cool air from basement below over the cooling surfaces and so reduce their workload.

A: The idea of venting basement air to help cool your fridge sounds like a reasonable idea, although I have no experience or knowledge of this having been done before. Cold air usually sinks, so I don't know how available it would be to help the cooling, unless it is forced upward with a fan, and then there would need to be somewhere else to allow that air to be replaced. Maybe a tube that was dug several feet into the ground so that it helped cool the incoming air would help. Otherwise I would suggest that you choose the most energy efficient and durable appliances available, and not use electricity to heat things much (i.e. not plan on using the heated dry cycle of a dish washer.)

Q: These #10 cans of freeze dried foods...can one dig a small cellar, say 3x3x3 feet, and put the cans in there, then lay treated lumber over the hole, then cover back up with 12" of dirt and grass...and expect the cans to remain cool and dry? (the longer they stay cool and dry, the better) I suspect the cool will be ok, but am concerned about the humidity...or would it matter, since they are vacuum sealed?

A: I would suggest that you go down even deeper than 3 feet...maybe 5 or 6 (depending on your location) with more soil or insulation on top of the hole to get a more stable temperature. Then if you place the cans in several plastic bags that are tied tightly, the humidity shouldn't get to them and tend to rust the cans.

Q: I'm wanting to store canned foods. I've starting digging into the side of a bank behind my house and I need some instructions. I'm only looking to store no more than 2 dozens jars in it. What materials would be best to use...treated lumber, bricks, etc.? And will it need to be vented?

A: You don't really need much space to store a couple dozen jars, so it doesn't need to be very big. One approach I have heard of is to bury a large garbage can (plastic would not rust) deep enough to be sure that it is below your frost level. Depending on how often you expect to need to get into this stash, you can devise various ways of covering it with enough insulation to assure that it will not freeze. This approach does not require direct venting.

Q: I'm wanting to make a root cellar with access from inside the house and I had a question on an idea I had. Our potential pantry will be 12x14. If I made the root cellar a 10x12 or an 8x10, could I put it within the pantry but underground and the "roof" of the root cellar would be the floor walking space in the pantry?

A: Sure, I think this would work. Both spaces would need separate ventilation to keep the humidity/air temperatures independently controllable. Also it would probably be best to insulate the floor between them.

Q: I am with an undergraduate engineering group at UT developing solar dryers that could be used in Mexico for drying mesquite seeds. We are interested in the idea of using a solar mass to act as an auxiliary heat source. Are there any general rules of thumb for amount of thermal mass and the heat that can be used? We are thinking of having a thermal mass that stores energy during the day and then releases heat that is funneled into a dehydrator. I’m wondering if I can get a substantial amount of heat from an 80 inch x 48 inch surface area of thermal mass (some type of masonry). We are unsure on the the thickness as well. 

A: Most of the rules regarding thermal mass that I am aware of pertain to passive solar home heating. For a dehydrator the ideal amount of heat is likely somewhat higher than it would be for living space. It sounds like you are thinking of having the thermal mass separate from the dehydrator itself. This is certainly possible. Perhaps some kind of arrangement like a Trombe wall would work, where the thermal mass is situated close behind some glazing (facing south) in a well-insulated box. If this box were sealed the mass inside would get quite hot during the day and this heat could then be vented into the dehydrator at night.

The thermal mass is best dark with a matte finish to absorb the greatest amount of heat. If the glazing were covered with insulation at night it would retain more heat. Effective thermal mass can be around 4 to 6 inches thick I would think; if it is too thick it will not release the heat as efficiently. I suggest some experimentation with this. You don't say how big the dehydrator is, so the mass needs to be sized relative to that.

We are interested in testing a thermal mass/trombe wall setup that could also feed into the system once the sun starts to go down. We knew there would be some testing and prototyping, but the 4-6 inches is good place to start. Right now our drying chamber is roughly 4’x3’x3’ for a total of 36 cubic feet of space, but this may change.

Asher Gelbart: My intuition here is that you are over complicating things if you want to do solar drying 24-7 for mesquite pods. No issue with pods cooling down overnight and starting back up when sun comes up. But if they do want to do 24-hr solar dehydrating on a commercial/industrial scale, probably best to use a hydronic system with heat exchangers/fans etc that extract heat from big hot water storage tank when the sun is down. I sketched up a design for such a system many years ago but it never was implemented.

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