Freezer on cut off timer with solar

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Freezer on cut off timer with solar

Postby patullose » Tue Feb 12, 2013 7:15 pm

hey guys, got a question.
Someone told me that they use a off timer on their Freezer during the day to gain as much as they can from their feed in Tariff and set the freezer to turn on at night.
i thought they where bonkers, BUT When we had a power black out for 2 days, i opened my freezer to find everything still very frozen so i'm thinking of doing the same. (just for 6-8 hours a day)
Has anyone does this, does this actually work out to be beneficial? or does your freezer use twice as much energy when it turns on again??
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Re: Freezer on cut off timer with solar

Postby Tracker » Tue Feb 12, 2013 8:18 pm

patullose wrote:Has anyone done this..... does this actually work out to be beneficial?

The good suggestion has been made, to take some PET Drink bottles and part fill with a saturated Salt Solution.. Place these at the top of the freezer..
They will absorb the cold ;) whilst running and tide you over in the OFF period, which unfortunately happens to be when it's hottest..

I had planned to do this, but have gone a different road of actually installing a PV/Battery system to run the refrigerators etc.

You can easily and cheaply buy a remote measuring thermometer..
Try it - freeze those bottles at the TOP - MUST be the top (Heat rises)
Let the thermometer show you just how it's working... Adjust the number of bottles to suit your needs

7/8 fill them and squeeze the air out...
..
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Re: Freezer on cut off timer with solar

Postby Tracker » Wed Feb 13, 2013 8:36 am

.
If you want to find out some experience with the practice of using saturated salt bottles, ask Gordon, who proposed the worthy venture.
Btw.. it would likely work best with a frost free freezer, as during cooling, the coldest location is at the air vent at the top... so you can freeze the notes fastest, there
..
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Re: Freezer on cut off timer with solar

Postby Tracker » Thu Feb 14, 2013 4:28 pm

.
PS - I am trying to put my own advice into practice....
Be prepared to "Play" with the salt concentrations.. Remember that we need to get the solution to "Change State" ie to actually freeze, and so far, you can be pretty certain that a "Saturated Solution" won't likely work.

I am actually trying Sodium Nitrate, as I had a very saturated solution, and I have progressively diluted it, trying to get it to actually freeze.. Still Trying..

I can see that an ideal would be a full sized-finned-heat-sink with a TUB on top (with the salt solution there in). All. Mounted to the roof of the freezer...
..
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Re: Freezer on cut off timer with solar

Postby GaryJonassen » Thu Feb 21, 2013 11:11 am

I suggest running a watt meter for a week wit the timer and then a week without a timer and see what the differences are. this should show if the total comsumption changes. Be aware of the different weather and the times you open the freezer that may impact on your results.
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Re: Freezer on cut off timer with solar

Postby GaryJonassen » Thu Jan 15, 2015 1:19 pm

See the nice graph here that shows the temp profile of Salt water VS Temp.

http://antoine.frostburg.edu/chem/senes ... -ice.shtml
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Re: Freezer on cut off timer with solar

Postby Tracker » Thu Jan 15, 2015 7:43 pm

..
As you say - most interesting, and far easier to see what the differences are..

So to get the best freezing temperature using NaCl, you use about 20% salt by weight, and you get a freezing point about -20C

I think I read correctly that it makes no difference what "SALT" was used..

Indeed Interesting Graph..
..
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Re: Freezer on cut off timer with solar

Postby GaryJonassen » Thu Jan 15, 2015 9:13 pm

Using different salts will give you a different result.

http://www.phasediagram.dk/binary/calcium_chloride.htm

What you want is something that freezes solid and that gives you the energy of the phase change to compete with on the melt. Most freezers are about -16 to -22 DegC so the salt solution will never achieve this unless you can get to -21.1DegC; almost regardless of what concentration you started with.
We need a salt that causes a eutectic at -15 DegC. KCl (Potasium Chloride) has a eutectic at -10.7 Deg C (see Page 604) so would suite most Freezers.
https://books.google.com.au/books?id=Z8 ... ic&f=false
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Re: Freezer on cut off timer with solar

Postby Tracker » Fri Jan 16, 2015 8:30 am

..
Visually, how would you observe an eutectic freeze..

Using Sodium Nitrate, I know that it takes FAR longer to turn solid WRT pure water, so, in a dumb way I assume it is doing what I think, and conversely, when in the old esky, remains frozen for much longer... ;)


I never was all that keen on Chemistry ... :oops:
..
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Retired Engineer and keen PV experimenter - Always ready to learn and share.
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Re: Freezer on cut off timer with solar

Postby Tracker » Fri Jan 16, 2015 8:36 am

..
PS... I am assuming that this all leads back to the concept of operating a freezer on Solar Power and then using the surplus "Cold Power" to cover the Off period...

Obviously, the correct freezer would be needed..
One where the motor cycles according to Freezer Temperature, and not the Produce Section ...
And then, there should be a freezer fan that runs either 24/7 or on demand.. ie via a separate thermostat..
..
.
Retired Engineer and keen PV experimenter - Always ready to learn and share.
2 x CMS2000 (fan cooled) GCI and SE 170W panels
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Governments won't save the world :-) They will just TAX it :-(
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