Metal plates as thermal mass in freezer?

[Lunita]

Thanks everyone for weighing in on this. Yes the salt water works great. We put 1/4 cup of salt in a one gallon milk jug of tap water and freeze it at home. In our cooler or ice box it lasts 3-4x longer, although we do not end up with potable water after that.
I think maximum insulation and air tightness will optimize the fridges and freezer. I will freeze lots of something- water, ice packs or ??? While connected to shore power and experiment with repositioning these to the fridges to reduce energy consumption. Maybe transfer back to the freezer while motoring.
Or just carpet the whole deck with solar panels....

[jheldatksuedu]

It takes no more energy to keep something frozen or cold for that matter once it is frozen or cold as long as it stays in the refrigerator, the only energy is what it takes to keep the air cold around it. Adding mass to the inside of the refrigerator or freezer only changes the length of time before the compressor comes on again, if you add mass it will come on for a longer time, basically using the same total amount of power in the long run. Mass (or a eutectic solution) will help keep things cold longer but then it will take longer to return them to the cold state. The only thing that determines the amount of power required is the insulation and the average interior and exterior temperature, that's what controls the heat transfer through the insulation. If you bring cold from home that reduces power on the boat but increases power use at home.

[Jim Cate]

Originally Posted by jheldatksuedu

It takes no more energy to keep something frozen or cold for that matter once it is frozen or cold as long as it stays in the refrigerator, the only energy is what it takes to keep the air cold around it. Adding mass to the inside of the refrigerator or freezer only changes the length of time before the compressor comes on again, if you add mass it will come on for a longer time, basically using the same total amount of power in the long run. Mass (or a eutectic solution) will help keep things cold longer but then it will take longer to return them to the cold state. The only thing that determines the amount of power required is the insulation and the average interior and exterior temperature, that's what controls the heat transfer through the insulation. If you bring cold from home that reduces power on the boat but increases power use at home.

Exactly, and well said!

Jim

[Lunita]

Now that makes sense to me!
Scratch the metal plates idea. Max out the insulation and keep the fridge door closed!

[Juho]

Additional cold maintaining liquid in the freezer can make sense when the cold liquid is carried to the boat from home (as in the original use case). They may be useful also if one has shore power available at regular intervals. Or when one uses motor only occasionally, or has plenty of some other kind of electricity available only occasionally. One should take into account battery capacity, availability of electricity, and freezer properties when estimating if use of extra frozen liquid makes life easier.

[leftbrainstuff]

Originally Posted by Lunita

Has anyone used non food items in their freezer to hold the temperature down. I wondered about putting some thick aluminum plate material in the freezer and fridge to act like holding plates. They would not take up a lot of room and would allow longer times between compressor run cycles?

Horribly inefficient.

The phase change of a liquid is what you're looking for. The food we're trying to freeze works well.

Or better yet proper insulation (step 1), a proper working refrigeration cycle (step 2).

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[IdoraKeeper]

Originally Posted by senormechanico

Eutectic solutions:

http://www.amazon.com/s/ref=nb_sb_no...rds=arctic+ice

Arctic Ice is for refrigerators and Arctic Tundra is for freezers.
Note the phase change temps. Ice +33.8f, Chillin +28f and Tundra +5f .
We use the biggest size
Tundra when on vacation and want our fridge to work harder using the extra available solar and thereby boosting the apparent size of our fridge/freezer.
We built an insulated bag out of Aerogel specifically made to hold one of the biggest Arctic Tundra cells.
With two Tundras, we switch them once a day.
It's like having a MUCH bigger freezer.
We use the refrigerator version (Ice) with the same bag for a refrigerator if we're only going out for a week or so and don't need more freezer space.

This seems very smart. Can you keep frozen veggies and fish in the bag?

[senormechanico]

A couple of years ago, we used the bag and two large size Arctic Tundra while on vacation in Desolation Sound. We kept everything in the bag frozen hard.
We lived on 320 watts of solar almost exclusively, even heating water with the inverter.
The trick is good insulation (Cryogel, a variation on Aerogel) for the hot water tank and fridge/freezer.

We kept all frozen food in Ziploc bags or vacuum bags and never had more than a half bagful of food, i.e. we could have built the bag smaller than we did.
The bag was made by us to have approximately 3" of Cryogel on all sides, top and bottom in a cube shape and designed to drop into an ama hatch.
(We now keep it under the V berth, as it's more accessible to the galley.)
It was covered with Sunbrella with a zippered top which was sewn by my wife.
Next to it, also under the V berth is another zippered bag which holds a refrigerator block for fresh veggies.
The refrigerator freezer compartment is basically not used to hold frozen food, it's now a "recharging station".
This scheme uses the excess solar we have to effectively enlarge the apparent size of the refrigerator.

[ErikFinn]

Coleman - Coleman - Cooler Ice Pack - Coleman Ice Packs - Chillersâ„¢ Hard Ice Substitute - Large

Hi guys, is this product similar to what has sometime been mentioned as Blue Ice, or Arctic Ice?

Imagine this scenario: I have some solar panels but not a big battery bank nor a genny nor want to run engine to charge batteries. With boat in tropics and anchoring, would I be able to save some amps by filling my freezer with these during sun shine hours when I'm getting excess charging from solar, and then moving these "chillers" in to the fridge side sometime in the afternoon or evening, and shutting off the fridge for the night when I have no solar charging? Would this make sense or is it plain stupid?

Do people commonly do something like this?

In this post I'm not looking for information on how to build a perfect cruising fridge/freezer, just interested if these "chillers" are usable in a sail boat and used in in what way? Just keep in freezer and dont move them? Do people find it troublesome to keep doing something like this?

Cheers.

[a64pilot]

Your better off with a very good, well insulated cooler and putting the blue ice into that, than you are with a Peltier chiller.
I believe the cheap styrofoam coolers are actually not that bad from an insulation perspective if money is an issue.
I'm not so sure say a Yeti cooler is as good as one cheapo styrofoam cooler, put inside of another cheap cooler?


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[Cruisingscotts]

Little info on on heat transfer in refrigeration. 1st off you are not making anything cold. You are transfering heat from one place to another. This part is very important!! There is a very big difference between the efficiancies and process for a unit that will freeze and a unit that will cool. In a cooling process you are only transfering heat (BTU's or Jouls) via sensible heat transfer. The efficiany and rate of heat transfer is relatively small. It can be sped up by increasing evaporater surface area or adding already frozen items like jugs of saltwater or some Eutectic solution. When you get to freezing something then you are talking about Latent heat transfer, The energy transfered in Latent heat transfer IE a change in state of the water from liquid to solid is astronimocally higher than sensible heat transfer. Once this phase is complete and the water is frozen, then you are back to sensible heat transfer and subfreezing, with a very similar energy transfer rate as subcooling.

Insulation does one thing only it tries to maintain the heat or energy in one space, a well insulated box will not allow outside heat to transfer into the cool box or freezer. The latent heat transfer of BTU's into the refrigerant as it boils is the point in the cycle that is going to give you your most bang for your Kilowatt hr or amphr. That exchange of energy is captured in the change of state in the media in the water bottles holding plate etc. It takes heat or BTU's to revesre that state of change frozen to liquid which is still a latent heat transfer and the more efficiant exchange. Where as a large mass like a block of aluminum will get cold, its molecules while not change state and therefore no latent heat transfer will occur. With that in mind when we are freezing food stuffs we are freezing the water in the food. Most types of food will have a coefficiant factor based on there given water content to calculate the amount of BTU's required to freeze to a given core temperature, for practical application all you need to know is that big Dorado is going to act just like the bottle of Water or the blue freezy thing.

A Eutectic solution is a solution with a lowered freeze point. Since as above, everything is based on water, a Eutectic solution will lower the temperature that the latent heat transfer occurs making it ideal for energy storage when trying to maintain a water based medium at freezing.

[newhaul]

Originally Posted by ErikFinn

Coleman - Coleman - Cooler Ice Pack - Coleman Ice Packs - Chillersâ„¢ Hard Ice Substitute - Large

Hi guys, is this product similar to what has sometime been mentioned as Blue Ice, or Arctic Ice?

Imagine this scenario: I have some solar panels but not a big battery bank nor a genny nor want to run engine to charge batteries. With boat in tropics and anchoring, would I be able to save some amps by filling my freezer with these during sun shine hours when I'm getting excess charging from solar, and then moving these "chillers" in to the fridge side sometime in the afternoon or evening, and shutting off the fridge for the night when I have no solar charging? Would this make sense or is it plain stupid?

Do people commonly do something like this?

In this post I'm not looking for information on how to build a perfect cruising fridge/freezer, just interested if these "chillers" are usable in a sail boat and used in in what way? Just keep in freezer and dont move them? Do people find it troublesome to keep doing something like this?

Cheers.

To answer your question yes it will work just fine assuming you are using excess power generation from solar to run refer after batteries are full charged. Think of it as the blue ice being a battery for your fridge in essence you are storing energy in freezing the units when power is available to use when it is not available. This is the same principal as a holding plate system.

[Juho]

I assume that you have lots of extra electricity available on daytime from your solar panels. In that case it makes sense to me not run to the freezer at night, and let the freezer run all day (or as much as it needs to, to regain what was lost during the night).

It would be better for the frozen stuff to have constant temperature in the freezer all the time, but maybe small differences are not too bad for your needs.

This daytime freezing approach can work also so that you keep the freezer full all the time (ice is plastic containers if nothing else). But special coolers are of course better if you have the space available and you can find a good balance between available electricity and freezing/melting of the coolers.

The first thing to do on my to-do list would however be to improve the insulation as much as possible. That is the cheapest and well working partial solution to the problem. Check those possibilities first.

[RaymondR]

Originally Posted by jheldatksuedu

It takes no more energy to keep something frozen or cold for that matter once it is frozen or cold as long as it stays in the refrigerator, the only energy is what it takes to keep the air cold around it. Adding mass to the inside of the refrigerator or freezer only changes the length of time before the compressor comes on again, if you add mass it will come on for a longer time, basically using the same total amount of power in the long run. Mass (or a eutectic solution) will help keep things cold longer but then it will take longer to return them to the cold state. The only thing that determines the amount of power required is the insulation and the average interior and exterior temperature, that's what controls the heat transfer through the insulation. If you bring cold from home that reduces power on the boat but increases power use at home.

The above quote says it well regarding steady state temperature and energy balances.

On page 35 of Nigel Caulders Refrigeration For Pleasure Boats he illustrates a number of graphs for eutectic fluids. Y axis is temperature, X is % of solute. The solutions are all water based. The graph for glycol mixes does not have a eutectic point but has a notation that below a certain temperature the fluid "sets to a viscous mass" indicating separation. This appears to happen at about minus 44 degrees F. He also explains that antifreeze solutions are not suited to eutectic refrigeration because the eutectic point tends to change over a range of temperatures, the extremely low temperatures required by the antifreeze solutions and, the separation of glycol and water as the water freezes tends to remain in the tank as glycol is heavier than water. He does not mention alcohol water solutions anywhere as a eutectic fluid.

Page 18 provides a graph indicating the effectiveness of insulation. The BTU loss per square foot of icebox per 24 hours versus inches of insulation curve is not linear and shows that after 4" the law of diminishing returns tends to kick in fairly savagely after you achieve 4", still helps to have more but not as effective after 4".

Eutectics were used with large, engine driven compressors in order to exploit the high refrigeration capacity of these compressors over a short period to minimise the cycling time.

Be mindful that solar panels as a source of electricity on boats is a relatively recent phenomenon and when I built my boat 28 years ago I made no provision for panels as they were horrendously expensive and did not produce much power. I now have 520 watts of the damned things and am becoming concerned about their effects on stability.

In the absence of the large ice block the eutectic systems exploit the low capacity DC powered compressor systems we use on boats need to cycle constantly through the day and night to maintain the required temperature in the box.

Not a problem during a nice sunny day when the solar panels are providing lots of electricity but not so good during the night when consumption is high anyway because we are running lights and entertainment systems and sometimes navigation systems.

I am in the process of rebuilding my constant cycling 12V refrigeration into a 12V eutectic system in order to transfer electrical power usage during the night when the panels don't produce power to the day time when I have an excess of power from the panels.

To answer the original question - you have the right idea in wanting to "store cold" in your ice box you just need to improve your methods. In the short term the ice in a container solution one may purchase at the supermarket is a good way to go as you are emulating a eutectic system with them but in the long term building the fridge or freezer is a better solution.

You can now buy off the shelf 12V eutectic systems which tends to indicate that the manufacturers have recognized the value of electrical load shifting.

It will be interesting to see when this starts to enter the domestic refrigeration and air conditioning market with the proliferation of rooftop solar.

[Juho]

Originally Posted by Juho

I assume that you have lots of extra electricity available on daytime from your solar panels. In that case it makes sense to me not run to the freezer at night, and let the freezer run all day (or as much as it needs to, to regain what was lost during the night).

It would be better for the frozen stuff to have constant temperature in the freezer all the time, but maybe small differences are not too bad for your needs.

This daytime freezing approach can work also so that you keep the freezer full all the time (ice is plastic containers if nothing else). But special coolers are of course better if you have the space available and you can find a good balance between available electricity and freezing/melting of the coolers.

The first thing to do on my to-do list would however be to improve the insulation as much as possible. That is the cheapest and well working partial solution to the problem. Check those possibilities first.

One afterthought. It would not harm to add one more battery. Maybe that would be enough to do the night shift. You could then forget the problem of switching the freezer on and off.