Ice as a battery

[billgewater]

It seems to me that what we are considering is a thermal bank issue. So if we look at many vessels, you already have one (variable yes). The fresh water tanks. The thermal capacity of a cubic meter of water is enormous.
A limitation here is that you probably don’t want lumps of ice in the water tank. These can cause considerable damage, so possibly using the phase change heat body is a bit problematic.
Also, the greater the difference between the ambient temperature and the water temperature in the water tanks then the greater will be the heat change loss. (Newton’s Law of cooling). So insulation would be an issue, but we are not talking about great temperature differences here.
Maybe a dedicated water tank that is designed specifically for this purpose. The water could be a reserve potable water supply.
So here are two possible scenarios. In the first you would use the excess power e.g. solar, wind, spinning prop. to run a compressor/heat exchanger to actually cool the water in the tank(s). Or you could just run the gen. set for a longer period of time and a use that power to cool the water via the existing refrigeration system. Or even as a subsystem from the propulsion engine.
The greater the temperature drop the better until the temperature differential becomes too great. Avoiding ice formation i.e. being restricted to a minimum of just above 0 degrees C. probably being preferential.
How can you then use this “cold bank”? There are two possible ways. It can be used to cool a non-freezer refrigerator cabinet. This would require a very small low pressure water pump and some control mechanism, but would only be of direct value if the water temperature was low enough. Or it could be used as a preferred sink for the heat produced by a compressor which should improve the efficiency of the freezer system when the compressor system is in full flight. The compressor/heat exchanger would have less work to do.
Alternatively, use the heat created by the compressor during normal daytime freezer operation to heat the water in the tanks. This heat could then be used if needed to warm a cold cabin during a cold night. Or even pre heat a bunk.
Reversed Carnot cycles and efficiency/cost of plumbing would be of concern. However, the current hard working marginal freezer systems we now use generally have short on off cycles to preserve food. Hold over is often far too short etc. Freezers are often the PITA issue on many boats. Particularly in the tropics where everyone wants to go!
It’s probably all about numbers, but most boats do actually carry around this great potential heat store. Could it not be used somehow? Are there any such systems around?

[buzzstar]

Originally Posted by hpeer

GREAT and practical discussion guys. Thanks a lot.

We have an Aerogen6 wine generator and two 315 watt solar systems.

I do not really want to hijack the thread (which is interesting because I used the system without knowing it had a fancy name; Owly had kept it simple and descriptive) BUT how does one generate wine? I want one.

[Pete7]

Originally Posted by john61ct

Google "polar tubes"

Seawater makes a decent eutectic solution, would like to know if adding more salt will usefully raise the phase change temp.

Or is there a source for engineered solutions reasonably priced?

I suppose you could buy some of these which are quite popular camping items:


https://www.amazon.co.uk/Value-Money...freezer+blocks

[john61ct]

No I meant the fluid in bulk.

2" tubes can hold a pretty large volume, part of the physics of staying frozen longer, dozens of little boxes would not be as effective.

My idea is to fasten holding clips to the underside / inside of the box lid, so the (always dry) tubes are suspended above the contents.

The bench seat cushion can cover the box opening while I'm swapping the new tubes in from the freezer, minimizing the cold-air loss.

[Zhyachts]

Originally Posted by owly

Make ice while the sun shines. To paraphrase an old farmer's adage. Batteries weigh up rapidly, and have a short life expectancy. LIPOs and other Lithiums have not lived up to their billing in serious voyaging . The technology is not mature enough, nor is the hardware reliable enough as far as I can determine.

The best storage medium is "work done". That is to say do work while you have energy. The most obvious case is ice. Instead of running a refrigerator that mindlessly cycles based on a thermostat, day or night, it only makes sense to make ice while you have energy. An "ice battery" is cheap, and never wears out. Water can be frozen and thawed an infinite number of times. I did the weight calculations on water / ice, as compared to battery storage some time back, and found that it outperforms lead acid batteries in energy stored per pound, unless you run them down more than is recommended. It does it at what amounts to zero cost, and zero maintenance. Lithium batteries will outperform ice on a pound for pound basis, but at a very high cost in comparison. I propose running a freezer when one has surplus energy, freezing ice to use for an ice box. The whole affair could be a single system with a tiny circulating fan, or it could be a simple as transferring frozen containers from freezer to ice box. Higher gravity beer actually works quite well as an "engineered fluid"
H.W.

You are right. I always recommend putting at least three quart bottles of salt water, about 80% full, in boat freezers. Takes about three days to freeze solid, but acts as a great "battery" when power off.

http://ducktalk.net/eve/forums/a/tpc...61/m/599104112

[owly]

Originally Posted by Zhyachts

You are right. I always recommend putting at least three quart bottles of salt water, about 80% full, in boat freezers. Takes about three days to freeze solid, but acts as a great "battery" when power off.

SOME FREEZER TRICKS - Topic

The low tech solution is often the best. Canned beer is a good choice for an "engineered fluid" if it is fairly high gravity. Because it convenient to handle in a nice light weight container with an extremely high thermal conductivity. It must be one of the higher gravity beers, or it will rupture the can. Around 6% and upward is best. Throw a dozen or so cans is the freezing unit, and later remove and store in a highly insulated cooler for later use. Experience (not personal) shows that this works. I know houseboaters who use a small household chest freezer as an ice box, and load it with 6 packs, the number depending on how long they will be gone, sometimes as much as a week or 10 days. They simply plug it in at home before leaving to allow the beer to freeze. The items to be chilled are layered. Things like meat on right on top of the beer, fresh salad greens and such at the top, etc.
On a sailboat using this strategy would be different. You would manually transfer the six packs back and forth from freezer to ice box or storage. Another daily chore, but a quick one.

H.W.

[owly]

Someone mentioned watermakers as being a high cost accessory........... Quite true, but parts to build them are not prohibitive, and the pump can be an ordinary pressure washer pump with a suitable 12 volt motor driving it. You could run it from 120 volt ac, but then an inverter also needs to be running. The technology is fundamentally simple, and information on how to build one, including Utube videos are out there.
I consider a watermaker to be an essential piece of equipment. It eliminates the need to carry large amounts of water for long passages, though one would be a fool to depend entirely on one. "Murphy" is alive and well out there. Shore water is questionable at best IMHO in many parts of the world, and may be laced with chlorine. If not chlorinated, treatment aboard is a virtual necessity. Even bottled water is questionable..... It's just water in a bottle. You can see through it, but you cannot see what's in it, and don't know where it came from, and worse yet, you are subsidizing a packaging industry that's producing a huge amount of the waste that we see in our oceans. In some places, such as the Cape Verde Islands, you may have difficulty even buying water from what I've read.

Water Water Everywhere, nor any drop to drink............

H.W.

[john61ct]

Yes making water is an alternative "load dump" for excess power.

So is heating water, running dehumidifiers or cooking with a crock pot.

I know guys run aircon off solar too, only after the bank is above 95%, and only when they don't need to get it to Full that day.

[hpeer]

Sorry guys for the typo, it should have been WHINE generator. Im sure we all know where to find them.

[Pete7]

Originally Posted by owly

Shore water is questionable at best IMHO in many parts of the world, and may be laced with chlorine. If not chlorinated, treatment aboard is a virtual necessity. H.W.

HW, there is Fluoride in our water, some is as high as 0.435mg/l.

However, I would have to travel many thousands of miles before I found a country were the average water quality wasn't suitable for drinking. How about you? Which are the nearest countries with undrinkable water to you.

Pete

Oh and the fluoride, well it's natural.

[olaf hart]

So how do you set up a switching system so the freezer switches on after the batteries are fully charged?

Is there some way to maintain battery trickle charging while the freezer is running?

[john61ct]

Frater Secessus, member in cheapRV forum has a howto posted, I'll try to find it.

Otherwise can be done via custom Arduino project, built into some controllers (wind I think) or of course easiest is manually.

You need to size your load(s) so enough amps are left over for the last few hours long tail charging. Easy enough for HWS to derate current, I think "rheostat"?

But definitely DIY electronics skills and motivation needed in any case

[olaf hart]

I guess if the freezer had a voltage threshold switch around 12.7 or 12.8 volts, it would only switch on when the battery bank was full and solar or wind chargers were working.

If it was draining the batteries too much, their voltage would drop past the threshold, and the freezer would switch off.

Similarly, at night, it would switch off when the solar wasn’t charging.

Any issues with this from the brains trust?

[decktapper]

Originally Posted by john61ct

No I meant the fluid in bulk.

2" tubes can hold a pretty large volume, part of the physics of staying frozen longer, dozens of little boxes would not be as effective.

My idea is to fasten holding clips to the underside / inside of the box lid, so the (always dry) tubes are suspended above the contents.

The bench seat cushion can cover the box opening while I'm swapping the new tubes in from the freezer, minimizing the cold-air loss.

Hello John:
did you consider having the freezer and refrigerator side by side with two small holes between them and a small fan operated by a thermostat?

[OzePete]

Hi Olaf,
suggest reading about our ECO2 power management method, standard on all Ozefridge marine refrigeration systems. We have been doing this for many years and I think you will get some ideas there for your project. See: http://www.ozefridge.com.au/?page_id=24 (Lower down that page)
Cheers OzePete