Freezing water

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Freezing water

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shadiya

Joined: 02 Feb 2008
Posts: 1285

Posted: Sun Jun 02, 13 10:59 pm Post subject: Freezing water

I didn't do physics at school so can somebody clever please help? I've been wondering for a while about how one might go about filling an ice house, given that these days our winters are mostly mild. Then was reading one of my old farming books (honestly, they really are better than getting a life

) in which it described making giant ice cube trays for the very same purpose. However, as I have no idea how much coldness one needs to freeze how much water, I can't work out whether this is practical or not.

The trays described were about 12 by 24 by 12, inches. Living in Oxford, well, near enough, we don't normally get more than a couple of weeks of snow and as I keep meaning to but have never actually got round to keeping weather records, I've no idea how many days and nights below freezing we get. So what I'd like help with is how long it'd take to freeze that depth of water at say -1, so I can try and guesstimate whether this is one of my more loony ideas or not.

Thank you clever people!

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Mon Jun 03, 13 7:36 am Post subject:

Unless you have a number of cold days and nights, I wouldn't bother. The old ice houses used to take a lot of filling, had to have a drain in the bottom, and ran out after a while. I would stick to a fridge.

You seem to be colder than we are, but I think we would be lucky to freeze or fill one of your trays virtually any year.

If you are thinking of freezing, you need to calculate the energy needed to reduce the temperature of the water you put in the trays to at least 0 deg C. This will be the volume (mass) of the water x the number of degrees of temperature drop. There is then the latent heat of fusion to turn it into ice; 79.72 cals per g of ice. All these calculations are in calories as it is a lot easier.

Say you try to freeze 1000g of water that starts at 10 deg C. You will have to 'lose' 1000 x 10 = 10,000 calories to reduce it to 0 deg C. To then freeze it, you will then need to 'lose' 1000 x 79.72 = 7972 cals. Total is therfore 17972 cals. or near enough 18000 cals, as it is not going to be exact.

If you fill the trays with snow, you need to ram it down hard, leave it to get as cold as possible over a frosty night, then store it before it gets any warmer.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Mon Jun 03, 13 8:07 am Post subject:
As Mistress Rose says it's not going to be practical. However, if you want something to keep temp stable such as a larder for instance then that is much simpler as all you need do is insulate from the surrounding environment and add lots of thermal mass. I have seen some larders made to use air from below ground to help keep things cool and stable. Or build a cellar.

Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Mon Jun 03, 13 8:21 am Post subject:
Tahir has something similar in his new house. He'll provide details, I'm sure. It keeps his nuts cooled but not drafty, or something.

shadiya

Joined: 02 Feb 2008
Posts: 1285

Posted: Tue Jun 04, 13 9:53 pm Post subject:

Nick wrote:

Tahir has something similar in his new house. He'll provide details, I'm sure. It keeps his nuts cooled but not drafty, or something.

Thanks for the very specific instructions Mistress Rose. I'm not sure I entirely understand them but will re read them and hope that brain engages....

I daresay it is a lot more hassle than a fridge but on the other hand, I know how it works (complicated calculations aside), which is more than can be said for a solar pane or a fridge. I know they need a drain and in the olden days, the run off was used to cool things down, much like I used to keep my milk in the river when I lived on a boat. Read an interesting article about a farmer in NY State who has one as he is also off grid. He's decided not to go down the solar route on the grounds that batteries are expensive and poisonous and don't last that long really and I have to admit, I think he has a point. Only an idea at this point and I may well decide that investing in more technology is the easiest thing, I shall have to do a bit more research.

Behemoth

Joined: 01 Dec 2004
Posts: 19023
Location: Leeds

Posted: Wed Jun 05, 13 7:24 am Post subject:

A cool food store can be built without the need for ice but usually involves a cellar/underground/north facing room. Door shuts well, relatively high humidity. Cool air in at ground level piped down to floor level, warmer air vented out the top. There was a book circulating around downsizer sometime ago.

An ice house usually requires acccess to a large pond that freezes to a significant depth or compacted mountain snow.

If you are going to freeze water to preserve food you might as well get a freezer.

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Wed Jun 05, 13 8:01 am Post subject:

I don't think you really need to do the calculations to get water to freeze, but you did ask.

I still don't think it is really on unless you are sure there are going to be about a week of sub-zero temperatures, which I shouldn't think you would get every year. Even the Victorians took to using freezing salts and other apparatus. I haven't studied it, but from the pictures it looks quite complicated.

shadiya

Joined: 02 Feb 2008
Posts: 1285

Posted: Wed Jun 05, 13 10:47 pm Post subject:

Behemoth wrote:

If you are going to freeze water to preserve food you might as well get a freezer.

The whole point is to use natural weather conditions to create ice to use for cooling due to being off grid and not having a freezer...... Not to freeze ice in a freezer and put it in a room to use later, I'm not a complete moron even if I do have some unusual ideas.

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Thu Jun 06, 13 7:26 am Post subject:
Do you want to freeze food or just keep it cool? If the latter, you might do better to use vaporisation rather than trying to make an ice house. Either try Behemoths idea, or cool a box using water evaporating from something. Charcoal works very well, and I know from experience that it takes ages to dry out, so would only need water adding once a day or so.

shadiya

Joined: 02 Feb 2008
Posts: 1285

Posted: Thu Jun 06, 13 11:44 pm Post subject:
It's for a dairy. I need to be able to keep yoghurt chilled to whatever temperature it is that one is required to keep it, for sale later. It's a medium term project which is why I'm exploring options now, attempting to save a bit of time. Chances are that I will have to go down the 'extend the solar' route but it's always worth exploring other options. In my opinion anyway.

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4563
Location: Lampeter

Posted: Fri Jun 07, 13 12:16 am Post subject:
Underground bunker,that will stay cool,what ever the ground heat source people say.

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Fri Jun 07, 13 6:55 am Post subject:
If you want to sell it, you are going to have to convince the right people that your system is suitable all year round. I think Ty Gwyn is right; the only way you will do that is underground bunker or cellar.

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