Dry Ice ?

[Captain Bill]

Originally Posted by hellosailor

Simes-
"it is easy and effective to make at home " Yes, but let's not neglect the laws of thermodynamics and all that nice stuff, shall we?
You're dealing with a perpetual motion machine here. No matter what you make, you're still only "transforming" and in order to get BTUs out of the icebox, you've got to invest energy into whatever is cooling it. I suspect that either you will need a source of BTUs aboard the boat to make the dry ice, or you'll need an incredibly bulky and expensive CO2 source.
Things that are easy at home, often rely on things that ARE easy at home. like plugging in a mains power cord, sadly absent on most small craft.<G>

I defense of Simes he has not neglected the laws of thermodynamics. By using stored liquid CO2 to create dry ice he is simply expending all of the energy to cool his ice box on land along with all of the equipment weight. I have used an 8 lb block of dry ice in a 5 day cooler with a couple of bags of ice. Everything we put in it was frozen solid. The ice did not even begin melting for a week. I did keep the cooler on deck to prevent the CO2 from building up in the cabin.

[hellosailor]

Bill, Simes, I don't say it CAN'T work out, just that it sounds like a perpetual motion machine, i.e. you're getting something for nothing compared to conventional refrigeration. There are many ways to refrigerate things. Commercial systems have used liquid ammonia for a long time but home systems tend to use "freon" heat exchangers these days. There are propane and kerosene (paraffin oil) FLAME systems still in use too.

But generally the energy to compress and liquify a gas, and the expense of the cylinders and maintaining them, and the bulk of it, etc., etc., make dealing with compressed gasses unheard of for "domestic" refrigeration. If you can rent CO2 bottles for 160L, the odds are that you can also go to a local supplier and simply buy the blocks of dry ice for 5L instead. And save all the space--and hazard--of the compressed or liquified gas tanks. That you've got a convenient local source for the gas at all is unusual.

So if it does work out for you, I think you'll be making history. I'd be curious to hear how that works out, six months or a year down the line.

I know dry ice is a great way to cool things, but making dry ice yourself, and doing that at a competitive price, is something else again. I can make it from my fire extinguisher, but that's also about $20US per 10 pounds of gas to refill. Way more expensive than just buying the dry ice at the supermarket.

[Captain Bill]

Hellosailor, It comes to mind that you actually don't know how refrigeration systems work. To put it simply some form of energy, wether it be electricity, propane, or cng, is used to compress a gas, (Freon, Ammonia,etc) which heats it up. The gas is then cooled using a heat exchanger to ambient temperature, but still under pressure. Ideally this gas will turn to a liquid because of the pressure. This liquid then flows to the heat exchanger inside the refrigerator where it passes through an expansion valve which reduces the pressure causing the liquid to flash into a gas. The problem is that that process requires heat (just like boiling water). It has to get that heat from somewhere so it absorbs it from the inside of the refrigerator making it cold. That process of flashing a liquid to a gas requires heat no mater what the liquid is. CO2 stored under high pressure such as in fire extinguishers or Simes tanks is in fact a liquid at room temperature. Releasing this pressure rapidly causes the liquid to flash to a gas. In the case of CO2 this happens so rapidly because of the extremely high pressures involved that it cannot absorb the heat rapidly enough from the surroundings and the gas part absorbs so much heat from the existing liquid that some of it freezes solid as dry ice. This is the snow you describe from discharging a fire extinguisher. If you do it in a confined space or insulated space you can collect that snow and use it for cooling an ice box. The difference between the CO2 method and a convensional refrigeration system is that the CO2 method is an open system where the refrigerent is not reused. It also means that all of the power usage is done at the recharging plant on land and does not require any power usage on the sailboat. Also as long as the liquid CO2 is stored in the tank it can be stored indefinitely with no additional expenditure of energy. One can argue that the compressor units, batteries and recharging system used to power conventional refrigeration weigh more than the tanks of CO2. Now buying dry ice at a supermarket may in fact be cheaper, but how much dry ice can you find on a six week passage. If you can make your own once a week you'll have no problems but you can't buy it in the middle of the ocean. The nice thing about this plan is there is almost nothing to fail. The only thing I can think of that might is the valve on the tank and this is unlikely. With conventional refrigeration there and a huge number of potential failure points. Take it from a guy who spent a couple of days trying to get a muffin fan repaired in Rum Cay last year.It's kind of like arguements about watermakers. It's certainly cheaper to fill your tanks from a garden hose or maybe even to buy RO water on a remote Island. But the argument falls apart when you are in the middle of the ocean and out of water. There is no perpetual motion involved here. Instead of paying for the energy using onboard systems he is simply paying for the enrgy use at the CO2 plant.

[Captain Bill]

Pleas note that I did put paragraphs in my previous post but for some reason none of the stuck when I posted the message.

[hellosailor]

Bill, I know how they work. The point is not that they all heat or compress or whatever, but that they are all closed cycle systems. They don't throw away the refrigerant every time it is cycled! With the dry ice system, you are throwing away the coolant every time the CO2 sublimates and wafts away. It is different from every other system, in that it is an OPEN cycle, not a closed cycle.

So while it may be easier to throw away CO2 while you are on a short trip, throwing away the coolant and consuming it as well as "power", makes the approach resource intensive. OK, so's a diesel genset and sometimes that is the right way to go. But as I already said, I don't thnk the economics of buying, storing, handling, compressed and liquified gasses are going to work as compared to any conventional system. Conventional systems usually have become the way things are done--because of their success at working best. Unless I misread the OP, he wants to use this on an ongoing daily basis--not just for a week or two cruising. I'm betting that's going to wind up consuming a lot more CO2 and being a lot more expensive than it seems.

I don't know his local economics, but here in the US buying dry ice is cheaper than getting CO2 refills, WAY CHEAPER. Compressed gas tanks, tank rentals or leases or deposits, hydrostatic testing and inspections if you own them....it gets expensive fast. Way more expensive than conventional refrigeration.

So we'll see, if he posts some numbers and results months down the line. Or, if the amzing new way to cool an icebox wafts away, like sublimating dry ice. (Oh, and if you vent that ice box through a potable water line, you get free soda water out the drain at the same time. Conventional fridges can't do that!)

[svcambria]

Checking out the Cole Palmer site, I get a 3:1 conversion of LCO2 to dry ice as well.
Your projected use is .5 kg/10 days, so about 18 kg/year, so you would need 54 kg of LCO2/year. At $100/15 kg you will be spending about $360/year on "fuel".
Yeti box is about $300. Funnel kit $135. Cylinder about $400. Capitalization about $400+$300+135 = $835.
First year's use $360 + $835 = about $1200
Second year's use - add another $360 = about $1560
Third year's use - add another $360 = about $1920
Eleven trips to fill up the tank.

An Engels 60 quart power efficient stirling engine cooler is about $1200. An 80 watt solar panel is about $400. Regulator about $50. Capitalization = about $1650.
First year's use = $1650
Second year's use = $0
Third year's use = $0

Somewhere shortly after two years use the cost of dry ice will exceed the cost of acquiring and using a powered refrigerator.
Some people don't want a solar panel on board; some don't want to use electricity. Their choice, but economically dry ice just doesn't compete.

[Simes]

You are right, It does not add up. As such we will not be using Dry Ice to cool our Cooler.

The long term costs are high (er) ans the on-going problems around finding and storing cylinders just does not make good sense.
We are going to go down the well trodden route of an Isotherm air cooled unit and replace it when it fails.

Many thanks to all for the spirited attacks and defense of the idea and principals.

Original thought, is an original idea . . . . .

Simes

[ZeroTucker]

I agree. Besides the scare of asphyxiation, according to a dry ice website, they say that the liquid CO2 would have to be stored. This seems like it would consume a lot of space and there is weight involved in that. I agree and think that is it probably not the right fit. Sorry.

[roger.waite]

Short of asphyxiation, CO2 poisoning occurs with persistent exposure to relatively low concentrations. E.g. sleeping in cabins that are less well ventilated than thought. Symptoms include nagging headaches. FYI

[osirissail]

"Symptoms include nagging & headaches." I had better find the source of CO2 in my boat that has been affecting my wife.

[rebel heart]

You'd be hard pressed to find a more difficult way of killing yourself than with carbon dioxide poisoning from dry ice. It would take *a lot* of dry ice, and the normal amount of draft in a vessel would easily solve any problems. And the symptoms are much different than carbon monoxide poisoning. You'd have a splitting headache and feel out of breath long before you died. And again, that's if you had *a lot* of dry ice and tape-sealed every possible vent to the exterior.

Anyway, the problem I've noted with using it is that it's too cold. Putting 5 pounds in an regular ice box ended up with exploded beer bottles and ice crusted food that needed to be thrown out. If you're going to use some, just make sure you test it out first to figure out the right amount. Don't just go buy a bunch, throw it in the ice box, and call it good.

[FreeSC]

I have used dry ice extensively in the ice cream truck business and recently on a sailboat delivery.

first... you will have no adverse effects using dry ice on a sailboat... don't even give it any thought ... it is "mental masterbation"!!

second "enviromental effects" ..get real I'm sick of this political buzz .. in this case you are simply recycling co2

third... why the hell would you buy this "funnel" when you can make it for $15 at the local hardware store

Last .. I have tried "homebrew dry ice methods... while they do "work" they are horribly inefficient..

in summary..if it blows your skirt up... then go for it..

on my delivery I put 20# of dry ice in the bottom of a boat ice box (typical boat box deep!) covered it with 25# of ice then 3 towels doubled over to insulate the food from freezing... then packed the cooler with food and 20 # of cubed ice on top...... we had a seperate cooler for drinks (except milk) to keep the openlid time of the main cooler to a minimum ... worked well for a week... a week tops!!

dry ice for any long term cooling..even making it aboard...no way go for a 12volt frig and big battery band and supplemental charging..

[JanetGroene]

Maybe I went through this thread too quickly but did I miss the warnings about ruining food and exploding bottles because dry ice is too cold? I guess if you come and go from the same port all the same and know where to get dry ice, it could work but I can't image cruising with it and having to find a new supply in each port of all.

[hellosailor]

Janet, I'd expect dry ice to be like any other industrial commodity: Unknown to the average Joe, but present in any reasonably-sized city (especially including ports) if you asked around. Ice cream carts, pushcarts of all kinds, food delivery services, Fedex/DHL/UPS shipping offices, air couriers...they all use dry ice.

Like fork lift batteries: Business just doesn't run without them, you just won't find them in Staples or WalMart. And if there isn't a local store that sells them...congratulations, you've finally gotten into the boonies!