chest freezer - energy efficiency tips?

ariarnia

xeny said:

I thought that was what you were suggesting with 

>keep them next to the freezer when not needed?

i.e. shuffling them in and out as stuff left/entered the freezer.

Freezing water is horribly energy intensive as there's a phase change involved. https://byjus.com/physics/latent-heat-of-water/ is looking at it the other way round but:

>melting ice requires as much heat as warming water from 20°C (68°F) to 100°C.

Removing that much energy from the water to take it from a liquid to ice is going to far exceed any saving due to not having to cool air that has flowed into the freezer down to freezing.

I vote for empty bottles. Also less effort to move around in the freezer so you can close it again faster after you find your food.

yes but we fill the freezer probably quarterly (some bits in and out each month but we try to run it down then properly stock up). so at the start of the quarter when the freezer is full there would be no space for the water bottles. then over time the freezer would empty and bottles put in. (like now we're all full for christmas. but the freezer will probably be half empty by 1 jan and we'll have a quick look at boxing day reductions but probably not do a proper freezer shop until the end of feb or maybe march if we have a lot of christmas leftovers from the freezer to use for easter lunch do a proper then restock)

my thought is that once the bottle was frozen then that's the energy needed to keep it cold until the next restock. so there will be some tipping point between freezing the bottles and the heat loss saved.

i'm not sure that empty bottles would have the same saving. but that's the kind of math i can't do. it just seems to me that shuffling empty bottles around to find things would take more time and lose more heat than full bottles (there not the sturdiest of things and you dont want to take the air in them out of the freezer as it would warm up quite quickly in the kitchen completely defeating the point but if you pull out a bottle of frozen water and put it on the floor for a min to find something then it'll sill be frozen when you put it back in.) 

something like milk or bread (that you would eat anyway and might save you a trip to the shop mid week) could be a good option as a thermal sink. 

getmore4less

Just fill the freezer with boxes(of air)

As you get/produce fill the boxes

Use stuff out of the boxes.

Big chest freezers stuff migrates to the bottom.

Boxes make it easy to organise and rotate.

Amazon delivery or supermarket not hard to find.

They are fine unless you let them defrost then  just change.

Bread is an alternative mainly air.

k_man

ariarnia said:

xeny said:

I thought that was what you were suggesting with 

>keep them next to the freezer when not needed?

i.e. shuffling them in and out as stuff left/entered the freezer.

Freezing water is horribly energy intensive as there's a phase change involved. https://byjus.com/physics/latent-heat-of-water/ is looking at it the other way round but:

>melting ice requires as much heat as warming water from 20°C (68°F) to 100°C.

Removing that much energy from the water to take it from a liquid to ice is going to far exceed any saving due to not having to cool air that has flowed into the freezer down to freezing.

I vote for empty bottles. Also less effort to move around in the freezer so you can close it again faster after you find your food.

yes but we fill the freezer probably quarterly (some bits in and out each month but we try to run it down then properly stock up). so at the start of the quarter when the freezer is full there would be no space for the water bottles. then over time the freezer would empty and bottles put in. (like now we're all full for christmas. but the freezer will probably be half empty by 1 jan and we'll have a quick look at boxing day reductions but probably not do a proper freezer shop until the end of feb or maybe march if we have a lot of christmas leftovers from the freezer to use for easter lunch do a proper then restock)

my thought is that once the bottle was frozen then that's the energy needed to keep it cold until the next restock. so there will be some tipping point between freezing the bottles and the heat loss saved.

i'm not sure that empty bottles would have the same saving. but that's the kind of math i can't do. it just seems to me that shuffling empty bottles around to find things would take more time and lose more heat than full bottles (there not the sturdiest of things and you dont want to take the air in them out of the freezer as it would warm up quite quickly in the kitchen completely defeating the point but if you pull out a bottle of frozen water and put it on the floor for a min to find something then it'll sill be frozen when you put it back in.) 

something like milk or bread (that you would eat anyway and might save you a trip to the shop mid week) could be a good option as a thermal sink. 

Anything that warms up quickly with low thermal mass/capacity (e.g. bottles of air), also cools down quickly, so require less energy to recool once returned.

Full bottles with higher thermal mass/capacity can absorb much more heat when out of the freezer (even if still feeling cold), so need more heat/energy removing when returned (or first added).

Extra thermal mass in the freezer is useful to:
 Keep the freezer cooler when adding new contents (to protect other contents, or cool newer ones quicker).

Keep the freezer cooler in the event of a power cut.

Temporarily move to the fridge to cool that down for the 2 scenarios above.

Use in a cool box.


So while there are benefits to extra thermal mass, energy saving is not one of them.

Also, I am not sure why empty bottles would take longer to move than full ones?

ariarnia

k_man said:

Also, I am not sure why empty bottles would take longer to move than full ones?

i'm trying to imagine it in my head (and i'm not great at that)

i'm thinking of trying to avoid taking the bottles of air out of the freezer because in the kitchen they will warm up very quickly and completely void any saving made from having them in there in the first place. 

but if i take a frozen bottle of water out of the freezer then it won't really lose any cold much at all and they can go right back in. 

so it would take me more time to find something in a freezer full of empty bottles than one where i could just lift out the bottles of water for a minute. if that makes sense? 


(this is one of the strangest conversations i've tried to have on here. and that includes the one with the person building a room made of mattresses in there living room )

k_man

ariarnia said:

k_man said:

Also, I am not sure why empty bottles would take longer to move than full ones?

i'm trying to imagine it in my head (and i'm not great at that)

i'm thinking of trying to avoid taking the bottles of air out of the freezer because in the kitchen they will warm up very quickly and completely void any saving made from having them in there in the first place. 

but if i take a frozen bottle of water out of the freezer then it won't really lose any cold much at all and they can go right back in. 

so it would take me more time to find something in a freezer full of empty bottles than one where i could just lift out the bottles of water for a minute. if that makes sense? 


(this is one of the strangest conversations i've tried to have on here. and that includes the one with the person building a room made of mattresses in there living room )

While the full bottle will feel colder than the empty one if both are taken out, it will have absorbed more heat (because it is still colder, as energy transfer rate relates to difference in energy levels/temperature), so will use more energy to cool back down when put back in.

Or put it another way, if an empty and full bottle are taken out, the empty bottle gets warm quickly, but uses little energy to do so, and then stop getting warmer.

The full bottle takes a long time to warm up, but using energy all that time to warm up, and at a faster rate than the empty one did, even when the empty one was warming up (apart from the instant both were taken out)

Taking the empty bottle out is not worse than taking the full one out, but is actually better.

And I too remember the den in the living room thread 😆

ariarnia

k_man said:

ariarnia said:

k_man said:

Also, I am not sure why empty bottles would take longer to move than full ones?

i'm trying to imagine it in my head (and i'm not great at that)

i'm thinking of trying to avoid taking the bottles of air out of the freezer because in the kitchen they will warm up very quickly and completely void any saving made from having them in there in the first place. 

but if i take a frozen bottle of water out of the freezer then it won't really lose any cold much at all and they can go right back in. 

so it would take me more time to find something in a freezer full of empty bottles than one where i could just lift out the bottles of water for a minute. if that makes sense? 


(this is one of the strangest conversations i've tried to have on here. and that includes the one with the person building a room made of mattresses in there living room )

While the full bottle will feel colder than the empty one if both are taken out, it will have absorbed more heat (because it is still colder, as energy transfer rate relates to difference in energy levels/temperature), so will use more energy to cool back down when put back in.

Or put it another way, if an empty and full bottle are taken out, the empty bottle gets warm quickly, but uses little energy to do so, and then stop getting warmer.

The full bottle takes a long time to warm up, but using energy all that time to warm up, and at a faster rate than the empty one did, even when the empty one was warming up (apart from the instant both were taken out)

Taking the empty bottle out is not worse than taking the full one out, but is actually better.

And I too remember the den in the living room thread 😆

this is where i dont think i follow. the whole problem we are trying to 'solve' is the cost of reheating hot (room temp) air that gets into the freezer when its open. 

if my freezer is set to -18 (i dont actually know what ours is set to) then the contents will be stable at around -18 (i know freezers cycle on and off so theres some fluctuation).

if i have a bottle of water at -18. then in a minute in my kitchen it will warm up by a couple of degrees. when i put it back in my freezer the average temp in the freezer will still be close to -18 and the freezer will only have to work to reduce the temp again by a couple of degrees. 

if i have a bottle of air then in that minute i think it will be at or nearly at room temp. it will definitely be a lot warmer than the bottle of water. so if i put it back in the freezer the average temp in the freezer will be higher than the average temp in the freezer full of water. 

i know what you are saying about the time it takes to warm or cool something depending on its density but 1kw of energy is 1kw of energy (that's the same for heating as it is cooling) so if a space needs heating or cooling by 1 degree then the time it takes to do that might be longer but i don't see how the total energy needed to do that would be... 

i understand what you are saying about water changing from a liquid to a solid but in this situation it stays a solid throughout. if we were letting the water get to room temp and then put it back in then i would follow. but in this situation the air reaches room temp but the water remains frozen. that (in my brain at least) is the difference. 

k_man

ariarnia said:

k_man said:

ariarnia said:

k_man said:

Also, I am not sure why empty bottles would take longer to move than full ones?

i'm trying to imagine it in my head (and i'm not great at that)

i'm thinking of trying to avoid taking the bottles of air out of the freezer because in the kitchen they will warm up very quickly and completely void any saving made from having them in there in the first place. 

but if i take a frozen bottle of water out of the freezer then it won't really lose any cold much at all and they can go right back in. 

so it would take me more time to find something in a freezer full of empty bottles than one where i could just lift out the bottles of water for a minute. if that makes sense? 


(this is one of the strangest conversations i've tried to have on here. and that includes the one with the person building a room made of mattresses in there living room )

While the full bottle will feel colder than the empty one if both are taken out, it will have absorbed more heat (because it is still colder, as energy transfer rate relates to difference in energy levels/temperature), so will use more energy to cool back down when put back in.

Or put it another way, if an empty and full bottle are taken out, the empty bottle gets warm quickly, but uses little energy to do so, and then stop getting warmer.

The full bottle takes a long time to warm up, but using energy all that time to warm up, and at a faster rate than the empty one did, even when the empty one was warming up (apart from the instant both were taken out)

Taking the empty bottle out is not worse than taking the full one out, but is actually better.

And I too remember the den in the living room thread 😆

this is where i dont think i follow. the whole problem we are trying to 'solve' is the cost of reheating hot (room temp) air that gets into the freezer when its open. 

if my freezer is set to -18 (i dont actually know what ours is set to) then the contents will be stable at around -18 (i know freezers cycle on and off so theres some fluctuation).

if i have a bottle of water at -18. then in a minute in my kitchen it will warm up by a couple of degrees. when i put it back in my freezer the average temp in the freezer will still be close to -18 and the freezer will only have to work to reduce the temp again by a couple of degrees. 

if i have a bottle of air then in that minute i think it will be at or nearly at room temp. it will definitely be a lot warmer than the bottle of water. so if i put it back in the freezer the average temp in the freezer will be higher than the average temp in the freezer full of water. 

i know what you are saying about the time it takes to warm or cool something depending on its density but 1kw of energy is 1kw of energy (that's the same for heating as it is cooling) so if a space needs heating or cooling by 1 degree then the time it takes to do that might be longer but i don't see how the total energy needed to do that would be... 

i understand what you are saying about water changing from a liquid to a solid but in this situation it stays a solid throughout. if we were letting the water get to room temp and then put it back in then i would follow. but in this situation the air reaches room temp but the water remains frozen. that (in my brain at least) is the difference. 

Water needs more energy to be heated/cooled compared to air (about 4x* even if we ignore latent heat of phase change/melting), so the energy required can't be based just on the temperature.

In the scenario the energy required to re-cool the bottles must be the same as the energy added while they were out (although as fridges are actually a form of heatpump, it isn't quite true, but the energy required is proportional).

More energy is added to the water in the full bottle, than the air in the empty one, as the water stays colder while it is out, and the energy going into it is proportional to the temperature difference.

(Made up numbers at 12C ambient, temp diff x time )
Empty bottle

First 5s -18C 30x5J
5- 30s -12C 24x25J
30s to 60s 0C 12x30J
60s onwards 12C no more energy added

Full bottle

First 5s -18C 30x5J
5- 60s -17C (approx) 29x55J
60s h 120s etc -16C 28x60J

So the full bottle, even though it is colder, needs much more energy removing once returned


I will try and think of a better explanation, but energy required to heat something, absolutely depends on what the thing is.
The same way as if you open the freezer, and let all the cold air escape and replace with ambient, it only takes a few minutes to cool it back down. But fill with food, at room temperature, it takes many hours, even though it is the same volume of stuff to be cooled.

ETA: specific heat capacity of water is about 4x that of air, by mass, but by volume (as air is much less dense) is approx 3000x higher.

QrizB

mark_cycling00 said:

I have a new chest freezer in an outbuilding (plus a two drawer freezer compartment in the kitchen fridge-freezer)
There isn't much in the chest freezer yet, it's huge but I should have crops to freeze after next summer.

Do you have room in the kitchen to empty the chest freezer and turn it off until next summer? That would be the most money-saving option.

If you're not opening the chest freezer often, there's not much point trying to stop the air exchange with bags/boxes/bottles.

Also note that chest freezers are much less prone to losing their cold air than upright ones!

ariarnia

k_man said:

I will try and think of a better explanation, but energy required to heat something, absolutely depends on what the thing is.
The same way as if you open the freezer, and let all the cold air escape and replace with ambient, it only takes a few minutes to cool it back down. But fill with food, at room temperature, it takes many hours, even though it is the same volume of stuff to be cooled.

if you want to then it'll be interesting to read but i think this might just be one of those things my brain can't get around

i just can't see the point of replacing air with air in bottles if those bottles are going to get warmed up anyway when your trying to find something. but i do know that freezer packs work to keep things cold in the car or on picnics. 

i beleve when you say freezers are differnt. my little brain just can't follow the why. 

[Deleted User]

Depending on the context, either is better.  Water takes a huge amount of extra energy to cool and freeze (so a big fixed cost at the start), but on each opening of the freezer there would be less exchange (so less cost each time you go in the freezer).  Given the difference in specific heat capacity and the latent heat of fusion, however, it's in the tens of thousands of 'door opens' to switch outweigh that first cost.  So unless you're opening the freezer hundreds of times a day, air is likely better overall.

Bottles that you don't take out of the freezer are better than bottles that you do (obviously).

So that means you should put all the bottles (probably of air) at the bottom and put your food on top of them in a chest freezer.  Or at the back of the shelves with the food in front in an upright freezer.

Also makes it easier to see and get to the items you want.