dry ice for refrigarator?

[radarbob]

this could sound like a dumb question, but would having the capacity to produce dry ice be helpful in an off-grid event? i would think your average home refrigerator could be turned into a giant ice chest by adding some blocks of dry ice. I have no idea how much you would need to cool each cubic foot. i saw a guy on youtube make it with what looked like a pillowcase, a fire extinguisher, and duct tape. After a 10 second burst, he had a handful of packed "snow". If you could keep your fridge going you could use up whatever you had in it before starting on your short-term (canned) supplies and then your long-term (freeze dried) stuff. A few years back we had a hurricane here and lost power for several days. our local supermarket was open with emergency lights, selling canned and dry goods (no meat, produce, dairy, or frozen) to only customers who had cash, since the debit/credit machines didn't work. Anyway, even though we were super careful about opening it, we still lost most of what we had in the fridge and its freezer. we weren't prepared then, and ended up eating cold cereal with canned milk, peanut butter on crackers, and box macaroni and cheese cooked on the camp stove. how about it, folks? i figure if anyone would know the answer, it would be someone on here!

 

[mibro]

Hoo boy.

Interesting question but the short answer is where are you going to get large quantities of dry ice during an emergency? Much easier to buy and store a small (2kW) generator and the gas to run it. The hot setup for the zombie apocalypse is a chest freezer which does not spill cold air when you open it and is therefore very efficient.

Because we can't "see" electricity it's easy to wildly underestimate just how much work it does for us, both for cooling and heating.

A typical modern refrigerator uses 350 kWh per year, or about 1 kWh per day.

1 kWh = 3,600 kilojoules

A refrigerator is a "heat mover" and does something weird - it moves a lot more heat than the electricity it uses. So a refrigerator using 3,600 kilojoules of electricity might move as much as 18,000 kilojoules of heat out of the contents of your refrigerator. But let's say 10,000 kilojoules of heat energy moved per day.

The latent heat of sublimation of dry ice is 571 kJ/kg and 10,000 divided by 571 is about 17.5

So.....ballpark number.....you'd need about 17.5 kg, or about 38 lbs of dry ice per day to keep the contents of your refrigerator (edit - both compartments, freezer and fridge) - cold. If the dry ice started at a lower temperature than its sublimation temperature you would need less, but you're not going to get that with the fire extinguisher/pillowcase method.

 

[radioman]

Storing enough co2 to make enough dry ice to make any difference would cost big money. Initial cost, tank rental, space to put 10 cylinders, etc... One fire extinguisher would only make enough dry ice to cool a shoe box. As stated above a generator would be a better bet and you can use it for many other tasks.

 

[MisterHappy]

Refrigerators and dry ice have been around for a long time. The market has spoken.

It's a specialized item, for limited uses. As stated above, it's probably best for you to have more main-stream backups for cooling needs.

That said, I've heard that a few chunks in a 2-liter coke bottle, half filled with water, then tightly capped, and tossed a good distance away is AWESOME

 

[Kevin_NH]

For a refrigerator only, a SWAG would be about 10 pounds/day.

So.....ballpark number.....you'd need about 17.5 kg, or about 38 lbs of dry ice per day to keep the contents of your refrigerator cold. If the dry ice started at a lower temperature than its sublimation temperature you would need less, but you're not going to get that with the fire extinguisher/pillowcase method.

38 pounds of dry ice per day would be about right to maintain a freezer.

For a refrigerator only, a SWAG would be about 10 pounds/day. Up until about WWII, US homes used to get water ice delivered for their home icebox, a home would go through about 50 pounds a week (25lbs twice a week, according to grandpa). That was sufficient to keep milk and meat at a reasonable temperature, even with the primitive insulation available at the time. Grandpa says they didn't keep frozen goods in the "ice box", if they wanted ice cream, they'd chip ice off the block and get out the rock salt and hand-cranked churn.

If you could keep your fridge going you could use up whatever you had in it before starting on your short-term (canned) supplies and then your long-term (freeze dried) stuff. A few years back we had a hurricane here and lost power for several days. our local supermarket was open with emergency lights, selling canned and dry goods (no meat, produce, dairy, or frozen) to only customers who had cash, since the debit/credit machines didn't work. Anyway, even though we were super careful about opening it, we still lost most of what we had in the fridge and its freezer.

I don't think dry ice would be a great option for long term outages, but if you had access to an efficient dry ice machine and a large supply of CO2 cylinders, selling dry ice could be a very profitable venture after a major storm.

If you don't open the fridge, you only need to run a generator every 4 hours or so to keep the contents from going off. A fully-stocked freezer can go even longer.

 

[mibro]

Up until about WWII, US homes used to get water ice delivered for their home icebox, a home would go through about 50 pounds a week (25lbs twice a week, according to grandpa). That was sufficient to keep milk and meat at a reasonable temperature, even with the primitive insulation available at the time.

Fascinating piece of trivia, thanks.

That 50 lbs of ice was keeping a relatively small amount of food at what was probably a somewhat higher temperature than a modern fridge. OP's fridge/freezer has probably about double the total interior volume of your Grandpa's icebox.

If you don't open the fridge, you only need to run a generator every 4 hours or so to keep the contents from going off. A fully-stocked freezer can go even longer.

Refrigerators with vertical doors make absolutely no friggin' sense from an efficiency perspective.

Here's a guy in Australia who's adapted a chest freezer as a fridge using 0.1 kWh per day, 36.5 kWh per year, so about $8 per year of electricity at 22 cents/kWh.