Refrigeration....Ice as a battery (change of state) & eutectics

[owly]

My home refrigeration is a machine I absolutely hate. At 65, I've owned numerous refrigerators, and hated every one of them. The worst aspect is that every single refrigerator I've ever owned will occasionally go on a tear and decide to freeze my produce. The thermostats in fridges suck! The problem can be allevated by replacing the thermostat with something like an STC 1000 and a installing a small circulating fan, but this is a pain. In most households the fridge is opened and closed often enough that the crappy thermostats don't cause a lot of trouble apparently.

I have an old time spring house, where I keep produce to prevent this problem. I live in a remote area, and like to buy things in quantity to avoid a lot of trips to civilization. Another and very effective solution is an ice box. An insulated space cooled with blocks of ice does not get down to freezing temps and maintains fairly good temp control.
Many boats use ice boxes obviously. Marine refrigeration is expensive and tends to be maintenance intensive. Ice boxes are simple and reliable so long as you have ice.



Ice has about the same embodied energy as a charged lead acid battery per pound, except that it can be "discharged" 100% forever and never degrades. I had the brainstorm of looking at very small freezers with the idea of freezing blocks of ice on a boat. The idea is that rather than relying on a stupid thermostat to control temp, you simply run the freezer when you have plenty of solar or wind energy as a way to store that energy. You freeze water to use in your ice box. This would eliminate the need to have a big battery bank to run a fridge that mindlessly turns on and off just based on internal temp. You transfer the containers of ice into the ice box, the temp stays uniform. It takes human intervention, but on a boat a chore like that is trivial... you have a lot of spare time.

What I found was a cheap 1 cubic foot freezer at Walmart for about $100 To run it you would need an inverter..... but the draw is going to be fairly small, and most people have an inverter anyway. The freezer is essentially a "throw away" at that price, and about a quarter of the cost of the cheapest marine freezer. It also is mechanically simple with a single sealed compressor / motor assembly, not multiple voltage systems. It should be extremely reliable based on it's simplicity.


The beauty of this is that with an insulated space, you can store as much energy as you want.... you just need more fresh water and containers. Batteries are a fixed value. Granted you cannot light your boat or cook with ice or do anything but refrigerate or cool drinks, but in my experience refrigeration is one of the largest energy loads.
You can of course store heat as well, but it's not quite as simple. Hot water does not have the energy from change of state that ice does. The transition from liquid to solid and back takes up far more energy than simply heating a liquid or solid.
With this in mind there are eutectic materials, generally salts that transition between solid and molten at specific temp ranges. They are well known, but to my knowledge nobody has built marine appliances that for example store heat by transitioning at say 350F so that you can store energy and use it for baking and such. There is absolutely no reason why this cannot be done.
There is a good article on Wikipedia on eutectic materials that explains the concept, and has charts of both naturally occurring eutectic materials and commercially available ones. It is a potentially useful technology, and at least interesting. Water is the ultimate as far as being cheap and having a tremendous capacity for energy storage and release.

Enjoy the read H.W.

Phase-change material

[ttex]

Doesn't sound very efficient to me at all but what do I know.

[Bill O]

Will agree the amount of power needed for refrigeration/freezer on a boat is way up there w/power needed to create hot water.
Did see someone else freeze water in jugs then transfer it to a well insulated cooler for refrigeration. Interesting idea, but not really certain you will be saving any energy in the long run by doing this vs. straight refrigeration. Anyone one have the calculations for this strategy? (Richard?)

[dougweibel]

Storing thermal energy relies on insulation and the rate of energy transfer through insulation (or any material) is dependent on the temperature difference. We keep our freezer at 11 degrees F and ambient temperatures in the boat are usually below 95 F, so there is a 84 degree or less temperature differential for the freezer. The refrigerator is set at 44F, so only a 51 degree or less difference there.

If you want to store something at 350F+ as a heat source and the ambient temperature is 70F then that is a 280 degree temperature difference. With the same insulation value as I have in my freezer the rate of heat loss will be 3.3+ times higher than in the case of my freezer, so even with a proper phase change material storing heat for cooking is going to be inefficient due to heat loss.

Using an old fashion ice box is great if you can freeze ice at home and use that to get by for some number of days. Notwithstanding the potential efficiency benefit or lack thereof, for long term cruising our freezer is fully utilized for its intended purpose - keeping frozen food frozen. There is no room to be freezing large blocks of ice.

[Stellar1970Cat]

I prefer compressor fridges over ice boxes. All that melting water soaks the food.
I was born in Finland on our farm where we did not have fridge until I was about 10.
So dad cut big blocks of ice from the lake and took them behind the house on the north side which did not get much sun.
Ice was covered with sawdust. So we had ice all the way to the end of summer if I remember right?
Additionally we had a freshwater spring on our cellar and that was always cool but did not freeze in winter. Dairy products were stored there.
Then we got a fridge so running for milk to the cellar was not needed.

Going without a fridge now here in tropical Australia would be too hard and I would spoil food.
My 200W solar and 100Ah lithium battery supplies enough power to run my 40 litre fridge, TV and other gadgets.

[CaptTom]

I missed this back in May when it was first posted. I actually like the idea: Buy a small freezer and use an ice box instead of a refrigerator.

This solves several problems: Consume some excess electricity from solar or motoring. Keep the ice box just above freezing all the time. Store the "cold" for later use without consuming much electricity. And best of all, keep your ice cream rock-solid, rather than that half-melted state it comes out of a standard marine refrigerator/freezer in.

It would be fairly trivial to put some water bottles (maybe one-quart milk jugs) in the freezer when electricity is plentiful. When frozen, put them in the fridge and freeze some more. Then, when the sun isn't shining, leave frozen jugs in the freezer and it will use minimal electricity to keep them (and your ice cream) cold.

That solution is available to anyone today. Using other materials to store heat would become a design and engineering project. A worthy goal, but nowhere near as easy.

I could even see this working if you don't have an ice box. Just put the frozen water bottles in your regular marine fridge so it doesn't have to work so hard.

[owly]

Originally Posted by CaptTom

I missed this back in May when it was first posted. I actually like the idea: Buy a small freezer and use an ice box instead of a refrigerator.

This solves several problems: Consume some excess electricity from solar or motoring. Keep the ice box just above freezing all the time. Store the "cold" for later use without consuming much electricity. And best of all, keep your ice cream rock-solid, rather than that half-melted state it comes out of a standard marine refrigerator/freezer in.

It would be fairly trivial to put some water bottles (maybe one-quart milk jugs) in the freezer when electricity is plentiful. When frozen, put them in the fridge and freeze some more. Then, when the sun isn't shining, leave frozen jugs in the freezer and it will use minimal electricity to keep them (and your ice cream) cold.

That solution is available to anyone today. Using other materials to store heat would become a design and engineering project. A worthy goal, but nowhere near as easy.

I could even see this working if you don't have an ice box. Just put the frozen water bottles in your regular marine fridge so it doesn't have to work so hard.

You get the idea..... Water / ice .... doesn't wear out or need maintenance, it costs exactly nothing. A freezer with a significant mass of frozen goods really doesn't need to cycle mindlessly. Your deep freeze will remain frozen for days when there is a power outage. Bottles or milk jugs full of ice can maintain a fairly constant temperature in a well insulated ice box.
Cold plate refrigeration systems are an improvement over the dumb systems on most boats... but there is a lot of room for improvement. Optimally they would have an eutectic solution, of significant capacity, and would be designed to operate when there was surplus power, and not when there wasn't power going into the system from solar, etc. They would be linked to an intelligent charge controller of some sort that would first assess the state of the solution, then the battery state, or vice versa, or however you configure it. The big thing about storing energy that way is that you get 100% return... Not to mention reducing the need for batteries.

I've been looking for a big used side by side for at home (refrigerator / freezer). The plan is to create an "ice wall" between the freezer and the fridge, and completely eliminate the controls in the fridge. It would be entirely ice cooled. The freezer would keep the ice wall frozen.


I've lost count of how many refrigerators I've owned over the last 50 years...NONE of the modern ones regulate decently. They all take temperature excursions. All you have to do is buy a bunch of produce and they will decide to freeze. Only some of the older ones with the hanging freezer compartment do a decent job of temp regulation. Thermostats seem to stick for no apparent reason.. other people seem not to notice or care. I've replaced thermostats with brand new factory thermostats, and they do the same thing. Part of the problem is junk quality components, and part is the lack of any air circulation. I've re-engineered the temp control system in my current big GE side by side......... It works properly now, but it's absurd to have to do that... and far too complex.

[owly]

Originally Posted by OzeLouie

In bold above you have described the type of systems our small family company builds in lots of 12 to 48 depending on model.
Eutectic, phase change, holdover refrigeration.
They are the 'cat's meow" benefiting because of their far greater COP performance, far less inefficient daily start ups and automatically storing most of the daily required thermal energy when power supply is abundant, therefore reducing battery demand. It's a no-brainer.

If any member wants help upgrading an existing system to eutectic holdover, or building same, we are now communicating via video (Zoom, absolutely no obligation)

Here we are, hands on and hard at it!
Attachment 248107 Attachment 248108

Finally someone is recognizing the need!! Alternative energy does not have someone controlling the "throttle" like the grid. You can't throw more generators on line at will. It is always in a state of either shortage or surplus and has to be balanced out in some way. Batteries are a very poor solution. They have a limited cycle life, and are expensive. The only really suitable batteries for the grid are flow batteries like the Vanadium Redox, etc. Refrigeration is for me at least, by far my largest load, and it operates mindlessly, and that means that if I were to go to alternative off grid energy, I would have to have a considerable battery bank just for refrigeration. Ironically heat and cold are easily stored...... Light for example is not, but is an extremely minor load.

A homestead....... long since tumbled down.... near where I live had a very innovative refrigeration system. It had a cellar beneath the kitchen, a well with a hand pump, and troughs, and a chute. During the winter they filled the troughs, let them freeze, tipped them out and slid the blocks of ice down into the cellar where they were buried in sawdust for summer refrigeration. Unlike most homesteaders, this cellar was under the kitchen, and a counterbalanced dumb waiter simply lowered the items to be refrigerated into the cellar, and brought them up to the kitchen as needed.

Being that the homestead was mostly collapsed when I discovered it, I didn't immediately figure out what was going on.....The dumb waiter to the kitchen, the sawdust, meat hooks and shelves, chute and troughs, gave it away. Mr Mitchell.... who nobody remembers... had many innovations, and this was one of his most ingenious. One member from Finland was complaining about how inconvenient and wet ice boxes were......... and that is true, breaking off chunks of ice and carrying them into the house to an oak icebox was a poor solution...... but hardly the ONLY way to use ice for refrigeration........ or the best one.

The era of reliable continuous power from hydro and coal is drawing to an end. Demand metering / pricing is in our future. Those of us who are able to take advantage of low rates in off peak hours will benefit.


On boats this is really a no brainer. The more you can take advantage of peak power the less battery capacity you will need. Make ice while the sun shines... make water while the sun shines, cook meals while the sun shines, etc..... or while the wind blows....If your battery capacity was mostly used for electronics and lighting, very little would be needed.


............ From what I've seen of eutectic solutions, the heat of fusion is virtually always far less than that of plain water, meaning that far more solution is needed for the same storage. Ice is very optimal for refrigeration........ but not for maintaining freezer. Temperatures. That tells me that a two fluid system would be optimal. My "ice wall" refrigerator would be perfect for eggs, milk, veggies, meat (non frozen), etc, but an eutectic solution would be desirable for maintaining freezer temps.


H.W.