How long does a freezer stay frozen when the power goes out?

Re:How long does a freezer stay frozen when the power goes out? by ghaff on Sunday August 09, 2020 @10:55PM (#24105016)

I'd have to do the calculations but wouldn't you be better off with a solution that just barely froze at freezer temps? Because of latent heat of melting? i.e. you want it to freeze--just at as low a temperature as possible given the freezer temperature.

Your basic point makes sense to me though of course thawing isn't even.

ADDED:

Doing the calculation. It takes 334 joules to melt 1g of water vs. about 4 joules to raise that same gram of liquid water 1 degree. Freezer temp is supposed to be about -18 degrees Celsius.

So the latent heat of melting is a bigger deal than a few degrees of raising liquid temperature. So you should have ice packs maybe somewhere in the -10 degree range which is what I assume commercial ice packs do.

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Re:How long does a freezer stay frozen when the power goes out? by gnopgnip on Monday August 10, 2020 @12:36AM (#24105599)

Completely saturated salty water freezes right around -6F or -21C. And most home freezers are set to right around that for energy conservation reasons, but max out even lower. So you could use any briny water and it will phase change before your food melts.

I'm surprised a 12v based deep freezer that runs off a reasonably sized solar panel is not more popular/affordable. With the right amount of thermal mass, and good insulation, and a small battery you could greatly extend how long your food stays cold. There are a lot of people who live in places where snowy weather or high winds and loss of power is an eventuality. In an emergency losing your food is a bigger concern than just the cost of the food.

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Re:How long does a freezer stay frozen when the power goes out? by pedrocr on Monday August 10, 2020 @08:44AM (#24108634)

If you're going to the trouble of doing solar it might be better to just do a small system with batteries to power other things as well like this:

https://fridge0.branchable.com/

Or go a bit higher end and put a larger solar and battery instalation with an inverter that can power the whole house. As solar panels and lithium batteries come down in cost that's becoming increasingly attractive for rural areas where the grid is flaky the best of times.

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Re:How long does a freezer stay frozen when the power goes out? by Gibbon1 on Monday August 10, 2020 @06:09AM (#24107490)

12V/120V freezers do exist and are marketed towards RV, camping, and off grid markets. Disadvantage is they tend to be smaller, cost more. But they are very efficient. Where a residential freezer might draw a couple of hundred watts dual voltage fridges draw 25-50 watts. And automatically switch between 12VDC and 120VAC. So they can be connected to both shore power and a battery at the same time and it 'just works'

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Re:How long does a freezer stay frozen when the power goes out? by ghaff on Monday August 10, 2020 @07:49AM (#24108245)

There are also propane fridges/freezers but they are also smaller. (Though at the point where you have a large propane tank, you could arguably just as well have a backup generator.)

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Re:How long does a freezer stay frozen when the power goes out? by Gibbon1 on Monday August 10, 2020 @05:11PM (#24114033)

My impression is the big advantage of absorption fridges is they will run off a tank of propane for a long time. But Downside they are very slow to cool down and running off AC/DC they aren't very efficient.

But yeah cheapest thing to do is get a furnace transfer switch and a generator. That seems to be how rural people in the upper midwest avoid freezing to death when the power goes out in the winter.

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