Second system extension extension.

[Stinsy]

I sometimes put a ziloc bag of water in the freezer during times of excess solar production. This can later be placed on the top shelf of the fridge to save energy as it defrosts.

Not sure if this is a waste of time...

Today I've cranked the freezer down to -25℃ and the fridge down to 3℃. Normally I have them set to -18℃ and 6℃. I'll try to remember to set them back to normal once the sun has gone down...

[openspaceman]

I sometimes put a ziloc bag of water in the freezer during times of excess solar production. This can later be placed on the top shelf of the fridge to save energy as it defrosts.

Not sure if this is a waste of time...

Today I've cranked the freezer down to -25℃ and the fridge down to 3℃. Normally I have them set to -18℃ and 6℃. I'll try to remember to set them back to normal once the sun has gone down...

I have done the same but wonder if it may be more sensible to run the freezer at -17C but put a plastic container with a saturated brine solution in, freeze that during the day at -19 and set the freezer to -17 over night. Ideally a second thermostat on a time switch would automate things.

The freezer seems to have been my biggest drain last night

[AE-NMidlands]

I thought there was something funny about specific heat of water mixtures... (i.e. water is so abnormal that mixing it with anything always reduced the specific heat.) Maybe you want the brine to depress the freezing point so you have a liquid coolant which can convect, rather than a solid block of ice with more "cold" in it but maybe a slower heat gain because conduction through it is slower? https://www.engineeringtoolbox.com/sodi ... _1187.html has


A
p.s. just dug further and found that while water is twice almost anything else (4182) ice is only 2090 J/kg degC - still above most metals though. https://www.engineeringtoolbox.com/spec ... d_391.html It is below saturated brine, at about 3300.

[openspaceman]

I was more looking to the saturated brine reaching the point where the water freezes and salt precipitates out of the remaining solution, over time the whole bucket of brine freezes giving out its heat of fusion (334kJ/kg) with a saturated solution this should be a bit above 18C. Then overnight as the ice melts the temperature hovers at that level until the brine all turns back to liquid. Basically is stores 1/10 of a kWh of cold per kg.

My freezer seemed to consume 0.6kWh last night so 6kg of brine frozen during the day may have been enough to prevent it switching on overnight. Of course it means losing 6 litres of capacity.

Mind physics lessons were a good while ago so figures should be taken with a pinch of...

[Stinsy]

Let's do this!

Freezer was set to -14℃ overnight. By 11am this morning my batteries were 70% full and filling fast even though I'd been out in the PHEV and it was charging at 6A (c. 1.4kW). So I added 45g of salt to 1.5L of water, put it in the freezer and set the freezer to -25℃. The plan is to set the freezer back to -14℃ when the sun has gone down and the melting brine should keep the temperature below the thermostat temp therefore the freezer will stay cold without using power.

[Joeboy]

Let's do this!

Freezer was set to -14℃ overnight. By 11am this morning my batteries were 70% full and filling fast even though I'd been out in the PHEV and it was charging at 6A (c. 1.4kW). So I added 45g of salt to 1.5L of water, put it in the freezer and set the freezer to -25℃. The plan is to set the freezer back to -14℃ when the sun has gone down and the melting brine should keep the temperature below the thermostat temp therefore the freezer will stay cold without using power.

Interesting, looking forward to the results. I'll be doing my massive ice cubes tomorrow in Turkey.

[openspaceman]

I will be watching the result too but to get to 0 Fahrenheit I think you will need 26% salt by weight.

So I think you need to dissolve 310 grams of salt in 1.5 litres of water.

It will only work if the brine solution turns to solid ice plus salt at the lower temperature and then turns back to saturated brine at the higher temperature.

I have put a digital thermometer in my freezer but the temperature is below its range and just reads "lo" (a bit like my moisture meter on my logs atm).

[Stinsy]

Right. Results. (Sorry to hijack your thread @joeboy).

I left the jug in the freezer from 11am-ish to 8pm, by that time it had partially frozen. I set the freezer to -14℃ overnight overnight and by morning the jug was completely frozen.

I wanted the jug to freeze in the daytime and defrost (at least partially) overnight. So that part is a “fail”. Maybe my freezer struggles to achieve super-low temperatures on a very hot day?

Anyway I moved the jug to the top shelf of the fridge last night because it is forecast to be cloudy today, so the energy will still be used…

[Joeboy]

Right. Results. (Sorry to hijack your thread @joeboy).

I left the jug in the freezer from 11am-ish to 8pm, by that time it had partially frozen. I set the freezer to -14℃ overnight overnight and by morning the jug was completely frozen.

I wanted the jug to freeze in the daytime and defrost (at least partially) overnight. So that part is a “fail”. Maybe my freezer struggles to achieve super-low temperatures on a very hot day?

Anyway I moved the jug to the top shelf of the fridge last night because it is forecast to be cloudy today, so the energy will still be used…

No hijack at all, over here in Turkey when it gets above 40 deg the fridges can and do struggle a bit. Our old rear radiator fridge certainly did. So much so that last year I got a new one in Marmaris. Both sides of the fridge freezers flanks are the hear emitters. That's a lot of radiant surface, so far it has performed flawlessly. Also get rear cooled fan assisted units. In saying all that, can't do much to dump heat when it's 40+. That's when we close the curtains and run the a/c low.

I think your idea has merit. Possibly by making oversize ice blocks on solar or overnight on go faster and then sitting in front of a room fan thru the day.

[Stig]

I've been taking ice packs out of the freezer and sitting them on the bedside table overnight the last couple of nights*, then putting them back to re-freeze in the morning. Don't know how much it helps but anything's worth a try to get a better nights sleep at the moment!

*Don't put your phone next to them as there's quite a puddle of condensation in the morning.