chest freezer - energy efficiency tips?

mark_cycling00

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.

Someone told me that I had to keep the chest-freezer full because lots of air in it took more energy to cool. With only basic knowledge of physics this didn't sound right but who knows?

How is the best way to use it efficiently? I know some people also put a blanket over the top-door to add a bit more insulation.

Any tips?
many thanks

oldagetraveller1

Hopefully the outbuilding isn't potentially too cold for the freezer to operate?

I have one in the garage but it is specifically designed to function in there or an outbuilding, with low ambient temps..

[Deleted User]

mark_cycling00 said:

Someone told me that I had to keep the chest-freezer full because lots of air in it took more energy to cool. With only basic knowledge of physics this didn't sound right but who knows?

The air heats up quickly when the lid is open, so then needs to be cooled down again.

The things that you would be using to keep it cool don't do that, so don't need to be cooled down so much.  You can just use bottles of water if you don't want to buy things to fill it.

Put your hand on the lid - does it feel cold or does it feel normal.  If it's feeling very cold, then the blanket over might help, but otherwise not.

Keeping it shut makes the biggest difference sometimes.

mark_cycling00

oldagetraveller1 said:

Hopefully the outbuilding isn't potentially too cold for the freezer to operate?

I have one in the garage but it is specifically designed to function in there or an outbuilding, with low ambient temps..

yeah its one of the rare ones that operate in -20c temperatures.

Of course you need to take steps to stop mice nibbling any exposed cables...

Swipe

I've never had issues running normal freezers (not fridge freezers) in the garage even though they warn against being in environments lower than 12C

xeny

Deleted_User said:

The things that you would be using to keep it cool don't do that, so don't need to be cooled down so much.  You can just use bottles of water if you don't want to buy things to fill it.

Presumably empty bottles would do the trick, or even a sealed cardboard box - you just don't want "unconstrained" air that can be replaced by warmer air while the freezer is open.

ariarnia

xeny said:

Deleted_User said:

The things that you would be using to keep it cool don't do that, so don't need to be cooled down so much.  You can just use bottles of water if you don't want to buy things to fill it.

Presumably empty bottles would do the trick, or even a sealed cardboard box - you just don't want "unconstrained" air that can be replaced by warmer air while the freezer is open.

i would think a milk bottle of water would stay colder than a milk bottle of air. better than free range air but why not just fill the bottles and keep them next to the freezer when not needed?

we used to keep bread in ours. now its full of real food ready for christmas. and the OH has a bottle of vodka in there which he says is to help the efficiency  

Lorian

Don't cover the sides/front/back of it with your blanket if it's a newer model that will be where it's heat exchanger coils will be under the metal skin. They don't tend to be visible on the back only like in older models. Blanket on the lid? Little effect. Some phenolic foam a few inches thick might save some pennies, but wouldn't recover the cost in a reasonable time.

xeny

ariarnia said:
i would think a milk bottle of water would stay colder than a milk bottle of air. better than free range air but why not just fill the bottles and keep them next to the freezer when not needed?

Because the freezer will have to do quite a lot of work (use quite a lot of energy) freezing the water in those bottles. Bottles with just air in them will need far less energy to cool down.

ariarnia

xeny said:

ariarnia said:
i would think a milk bottle of water would stay colder than a milk bottle of air. better than free range air but why not just fill the bottles and keep them next to the freezer when not needed?

Because the freezer will have to do quite a lot of work (use quite a lot of energy) freezing the water in those bottles. Bottles with just air in them will need far less energy to cool down.

i think that only really matters if you are taking the water out regularly and letting it defrost?

there's probably a tipping point between the savings from less cold being lost over a period of time and the cost of freezing the water (which we can probably call a one off cost). 

but my brain isnt a math brain so I can't help with that

i did google and find this which was interesting tho (taking about fridges).

i always thought it was more efficient to keep fridges half full and freezers full (because fridges are closer to room temp and used more often so spend more time cooling things and things cool faster if theres air around them)  

https://www.straightdope.com/21343775/does-a-refrigerator-cool-more-efficiently-when-full

xeny

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.