What to do with unused space in a home freezer?

[Richard Crane]

Our home food freezer (ca. 14cu ft) is bigger than we really need. I am planning to fill one shelf with 8-12 gallon jugs of water, with the intent of using its high latent heat of fusion to help keep the contents cold during a power outage. Is this volume actually enough to make a meaningful difference? Would this improve the efficiency during regular operation? (I am presuming cold air in the unused volume warms up very quickly, thus needing to be cooled down again.) Could this be improved by adding something to lower the water's freezing point?

 

[Dale]

Make it salt water so it freezes at a lower temperature

 

[sophiecentaur]

You could make an inner space that's very well insulated and keep the food in that. They are built to a price and with 'just enough' insulation to match some sort of spec for a given cavity volume. You could improve on that greatly and I have a feeling that volume for volume, it may be better value. But don't try to freeze stuff down in that insulated core. Have a freezing section that's outside the core.

 

[Nik_2213]

IMHO, if you get a bunch of those inexpensive, plastic cased 'freezer packs', you can jam them into odd corners then easily move some to Fridge or a carry-out chill box as required. Also, you won't have to calculate 'expansion' margins for those brine jugs. Come 'defrost' time, 400g and/or 800g freezer packs are much easier to stow around food in towel nests in buckets than a brine jug.

 

[Red Robbo]

Back in January - and agreed that the weather wasn't particularly warm or cold, just normal for Wales(!) - we had a burst pipe that tripped the consumer unit. Four days later when we returned from holiday to a kitchen that looked like a cross between Niagara Falls and the Somme, I was pleasantly surprised to find the contents of our rather full large A+++ freezer to still be frozen. As we haven't died of food poisoning yet, I would venture to suggest to Richard Crane that as long as he has a well-insulated, modern freezer and doesn't live in the tropics then it isn't worth the hassle.

 

[sophiecentaur]

Back in January - and agreed that the weather wasn't particularly warm or cold, just normal for Wales(!) - we had a burst pipe that tripped the consumer unit. Four days later when we returned from holiday to a kitchen that looked like a cross between Niagara Falls and the Somme, I was pleasantly surprised to find the contents of our rather full large A+++ freezer to still be frozen. As we haven't died of food poisoning yet, I would venture to suggest to Richard Crane that as long as he has a well-insulated, modern freezer and doesn't live in the tropics then it isn't worth the hassle.

Lucky you. I wonder what maximum temperature your freezer compartment reached during the power cut. (A max/min recorder should be mandatory in all freezers, I think). Also, yours was a one-off experiment and the statistics of microbial populations in food could have accounted for the result. You are right in many ways, though in that the recommended storage conditions are well over the top, in most cases. The 'rules' about re-freezing food have changed over the years, partly due to the better initial freezing processes for meat and fish.

 

[Vanadium 50]

I like the freezer pack solution. Bags of ice are also much more convenient than frozen jugs.

 

[sophiecentaur]

This is a harder problem that it might appear. I have been looking at the performance of gel packs and water and, if you want to keep the food 'deep frozen' at well below -10C, I couldn't find any phase change materials to help you. The gel packs are designed for around 0C, which would be too high for freezer food safety. Adding salt will lower the phase change temperature but, so I read, the latent heat goes down. Basically you'd just be using specific heat capacity, which, for water, is only about half the 4.2 J/g /°C at room temperature. That's worth knowing because it means food will warm up faster than you might assume too.
If you can half the thermal conductivity of the total insulation, that would be the equivalent of doubling the mass of water / food, stored in the freezer for a given change in internal temperature. It is a point worth considering. Then there is the advantage that you don't need to freeze down the extra thermal mass.
The cost of insulation is not high. You can buy 50l of polystyrene beads for about £6 (first hit on Amazon and I'm sure there would be a cheaper source) and the insulation doesn't need to be fireproof.
So I still say that insulation could be the way to go! Any comments?

 

[rokytnji]

I cheat when it comes to gel packs

Living in the desert. They come in handy.

 

[Tom.G]

You can buy 50l of polystyrene beads for about £6 (first hit on Amazon and I'm sure there would be a cheaper source) and the insulation doesn't need to be fireproof.

I tried that approach when a cheap landlord installed a cheap refrigerator, not much insulation. I added polystyrene insulation boards (the 4 x 8 foot type with foil facing used on ourside walls, under the shingles), to the outside surfaces. Ended up with a reduced electric bill but the condensation between the 'fridge and the insulation was enough to rust the 'fridge! Oh well.

 

[sophiecentaur]

I tried that approach when a cheap landlord installed a cheap refrigerator, not much insulation. I added polystyrene insulation boards (the 4 x 8 foot type with foil facing used on ourside walls, under the shingles), to the outside surfaces. Ended up with a reduced electric bill but the condensation between the 'fridge and the insulation was enough to rust the 'fridge! Oh well.

Interesting comment. From what you write, it looks as though you put the insulation around the outside of the fridge. Fridges will 'sweat' and there is a regular thermal cycling of the outer skin so I am not surprised that your idea gave you problems. I am suggesting adding extra internal insulation. The thermal cycling inside the fridge is much less and the chill panel (the coldest part of the inside) has a drain which takes the condensate outside and, not surprisingly, that could easily have turned up as condensation between the skins.

 

[Richard Crane]

I like the thought of extra internal insulation - avoids the problem of heavy jugs of liquid and potential leaks -- will explore ideas to implement.

 

[256bits]

I like the thought of extra internal insulation - avoids the problem of heavy jugs of liquid and potential leaks -- will explore ideas to implement.

Good luck!
Lining the interior walls of a chest freezer with insulation will hinder the coils from freezing the food.
some of the food you put in there will then not freeze for a week, which can make for some ghastly culinary disasters and perhaps trips to the doctor and/or hospital. One wants the food to freeze as fast as possible to avoid bacteria growth.

 

[sophiecentaur]

Any extra measure would require some extra considerations. I would never suggest just lining the inside of the freezer. My suggestion was to put already frozen items in ‘local’ insulation. Insulated shopping bags or expanded polystyrene boxes would give extra protection. A frost free freezer would deal with condensation as usual in the intermediate voids - as it does between chicken and beef pieces in their own bags.
I already made the point about freezing stuff down before putting it in extra insulation.

 

[Richard Crane]

To the point about slowing freezing: the metal shelves have refrigerant tubing running underneath, so I should be fine putting food in on those to chill.

 

[sophiecentaur]

To the point about slowing freezing: the metal shelves have refrigerant tubing running underneath, so I should be fine putting food in on those to chill.

A bit of 'management' would be needed here. Things would spend a few days next to the chilling panels / shelves and then be put in the extra insulation.

 

[Tom.G]

Careful you don't cover the thermostat.

 

[sophiecentaur]

Careful you don't cover the thermostat.

That's very true for an ordinary fridge where air should be allowed to circulate. The shelving is usually designed to allow circulation and this avoids hot spots.
But most good freezers will operate chock full and we are told that freezers are more efficient when full. Although that may just be bs. If there are baskets supplied then everything should be kept within them.

 

[Tom.G]

But most good freezers will operate chock full and we are told that freezers are more efficient when full. Although that may just be bs.

As near as I can tell, that is marginally true. A full freezer will have a longer thermal time constant, thus having fewer startup transients per unit time. Not having to cool the evaporator and heat the condensor as often saves a little bit of energy.

 

[CWatters]

Our home food freezer (ca. 14cu ft) is bigger than we really need. I am planning to fill one shelf with 8-12 gallon jugs of water, with the intent of using its high latent heat of fusion to help keep the contents cold during a power outage. Is this volume actually enough to make a meaningful difference? Would this improve the efficiency during regular operation? (I am presuming cold air in the unused volume warms up very quickly, thus needing to be cooled down again.) Could this be improved by adding something to lower the water's freezing point?

Every time you open the door cold air falls out and warm humid air enters and has to be chilled gain. If you fill empty space with anything that traps cold air (or eliminates voids) preventing it falling out then efficiency should improve. This could be jugs of water, empty plastic boxes with lids or even bubble wrap.

Jugs of water/ice have the advantage in a power cut but their shape might not have the optimum packing density to minimise air lost when door opened. Unless you have cubic jugs?

 

[sophiecentaur]

fewer startup transients per unit time

That is true but how much energy is taken in the brief current surge when the compressor starts? I guess that a full freezer just has less air circulation so the heating is less.
A fridge freezer is quite a major part of a yearly electricity bill but people want as much internal space as possible in as small an external volume as possible (at a low price) so 'we' are all stuck with sub optimal efficiency.