The science of Freezing. Do Freez Paks work??

[MarkJ]

Now I have a full electrical system upgrade I can have a freezer on 24 hours per day! Yipppppeeeeee!

ICE CREAM!!

But I am trying to be economical with power.

I have put in the freezer some Freez Paks an "ice substitute" that I think contains Sodium polyacrylate

The idea is you freeze them then put them in your picnic basket etc. but I have some in the freezer with the idea that they freeze and then buffer the temperature increase therefore requiring less electricity to operate the freezer.

I did do thermodynamics sometime in the dim distant past ummmmm but my memory....

Is it better to use a Freez Pak or just reduce the excess space with water and foam?

[atoll]

works like a eutectic holding plate,glycol freezes at about -8 celecius depending on the solution.

water freezes at 0deg celcius,so glycol better

[toddedger]

They are going to act like a holding plate. So they will take energy to cool and hold it for a while. Somewhere I heard an idea of using packing peanuts in plastic bags to fill in any dead space between food. I haven't tried it yet, but plan on giving ita try.

[sailorboy1]

Personally all I feel they do is increase the cycle times. So it takes longer for the system to drop the temperature down, and longer for it to heat back up. But that is a plus if you are making more power than you can store.

[senormechanico]

http://www.amazon.com/Arctic-Ice-Tun...rds=arctic+ice

These work great !
Way more efficient than those "blue ice" blocks.

[2Hulls]

They will work no better than putting already frozen food into your freezer, unless they are somehow colder. If you have excess space after loading your already frozen food, yes, adding any extra mass that is already frozen will save you some power. But the key is not expecting your freezer to freeze anything from ambient temperature.

Dave

[Stumble]

There are really two answers here.

The first is once a freezer achieves a steady state (doors closed, and all items at the same temprature) it takes exactly the same amount of energy to maintain a given temp regardless of how full it is. Because the amount of energy needed is dependent on the insulation not the thermal mass.

However there are a few real work caviats.

First is that a full cold box will coast longer between when the compressor needs to turn on. Because the thermal mass takes longer to heat up. But it also takes longer to cool back down again.

Second. By replacing the air inside the box with stuff you decrease the amount of warm moist air exchanged every time you open the box. This will decrease energy consumed.

Third: when you add new, warm items to the freezer the temprature won't spike as high, since the thermal mass acts to absorb heat.

Fourth: froze bottles of water are great to have independent of the energy used just to carry with you on the dink. But don't use those cold packs, they just take up space. At least water bottles can be drunk, and achieve the same effect.

[senormechanico]

The cold packs I listed freeze @ +5 degrees f.
They are a true eutectic.
In other words, they phase change over a very narrow range.
This keeps the average temperature in the insulated space much closer than food.
Water phase changes (freezes/thaws at 32f, and the food around it will follow at roughly the same temp.
I'd rather keep my food frozen until I use it.

[Dockhead]

Originally Posted by Stumble

. . . Second. By replacing the air inside the box with stuff you decrease the amount of warm moist air exchanged every time you open the box. This will decrease energy consumed. . . .

Not enough to be worth the trouble.

Air has a specific heat of about 1006 J/Kg Degree C, compared to 4200 for water. , and air has a density nearly a thousand times less than water. So a complete change of the air inside an empty marine fridge, say 0.1 cubic meters, will require less energy to cool down than a teaspoon of water. Actually, a teaspoon of water, 6cc, can hold about 25 times as much heat energy as 0.1 cubic meters of air. A whole empty fridge full of air holds about the same amount of heat energy as 4 drops of water, in fact.

If this were not so, then front-opening fridges would be disastrously inefficient. In fact, they are not -- as long as they have decent gaskets.

So forget about stuffing anything in your fridge or freezer to reduce the air inside -- waste of time.

[MarkJ]

Originally Posted by Dockhead

So forget about stuffing anything in your fridge or freezer to reduce the air inside -- waste of time.

Blocks of foam would be good, though, wouldnt they? Reduces space and only the surface of the foam cools as its insulates itself.

[2Hulls]

Originally Posted by senormechanico

This keeps the average temperature in the insulated space much closer than food.

What does that mean? You mean colder than food?

The only way they would be a benefit is if their mass is higher than an equal volume of food AND they are colder than the frozen food already in the freezer when you add them. In that case, you will save power until the temperature equalizes within the freezer. After that, very little benefit as stumble described, above.

Dave

[Dockhead]

Originally Posted by MarkJ

Blocks of foam would be good, though, wouldnt they? Reduces space and only the surface of the foam cools as its insulates itself.

It does not reduce the cooling power required, and it interferes with air circulation around your food, which is the only way it gets cooled down. Don't overcomplicate a simple thing. Just put your food in the fridge (or freezer) and don't worry about it.

[Cadence]

Originally Posted by toddedger

They are going to act like a holding plate. So they will take energy to cool and hold it for a while. Somewhere I heard an idea of using packing peanuts in plastic bags to fill in any dead space between food. I haven't tried it yet, but plan on giving ita try.

It sounds as possibly the peanut idea may be self defeating if it causes more open time to find the specific food you are looking for?

Possibly you are more organized than me.

[Dockhead]

Originally Posted by Cadence

It sounds as possibly the peanut idea may be self defeating if it causes more open time to find the specific food you are looking for?

Possibly you are more organized than me.

Not only that, but they may prevent the food from freezing in the first place by keeping the heat in and preventing circulation.

This is not a good idea.

[warrior 90]

Thermal storage is a good idear in combination with solar power.
Since cold space is limited I prefer beer,fruit juice and water for thermal storage