ice chest option

[walt]

Since this is more of a trailer sailer problem, Ill put this here.

Next year, if things go to plan, Im going to spend more time on my 1990 Mac 26S - mostly docked in marina's, sometimes on anchor.

Ive thought about an elecric fridge to make life easier but these very much complicate things. 200 amp hours of battery capacity I currently have is marginal and gets worked hard using up battery life (assuming about 35 amp hours per day for a small fridge). Adding the fridge just about triples my existing power needs and since it can just about deplete the battery in a few days, you need a large solar panel plus probably some sort of gas generator backup. I sort of looked at the cost of this (fridge, about a 100 watt solar panel, maybe a 40 amp battery charger and a Honda 1000 watt generator to supply AC to the 40 amp charger) and on the trip I am planning, the cost just to add the fridge would be better spent (and make the wife happier) on hotel rooms near the marina.

However.. in looking at this, I was wondering about having a two ice chest system where one ice chest held the food and the second ice chest just held ice. There would be some sort of heat transfer between the two ice chests - maybe as simple as pumped air circulating between the two ice chests through two insulated air ducts - one cold, one warm. You would just put for example blocks of ice in the "ice only" chest and the air pump would tranfer the "cool" to the food ice chest. Maybe some sort of metal "heat sink" would aid in tranfering cold from the ice to the air that would be pumped to the food ice chest. The "ice only" chest would be always clean so you could even use it for ice cold drinking water when the ice had melted. Just thow in a fresh block of ice every few days.. The DC power draw could be very low as in the idea above, you would only need to keep a small fan running.

Would this work.. has it already been done?

edit - sort of like the attached drawing??

 

[Johnb]

If you are mostly in marinas and have access to shore power a $80 dorm fridge will serve you well. Then have a good cooler and get ice when you need to. Dry ice is another option.

 

[walt]

Yep.. or just a regular ice chest like I already have been using and overall works fine. For some reason, I have this urge to modify SOMETHING on the boat before this trip... sometimes without any really good reason..

 

[kloudie1]

Use one or two of the newer insulation technology ice chests,like the Coleman Xtreme line . Freeze drinking water in clean gallon or half gallon plastic jugs and drink the water when it melts. Freeze prepared food sealed in good zip-lock bags and use that for some of the ice.. Much easier and no power draw. would use less ice than fan forced boxes.

 

[shemandr]

I think it was GOB magazine that had a recent article about using alcohol /water in freezer bags and a low voltage fan to enhance cooler performance. Sort of like your heat sink. I like your idea of separation of the ice from the food. Let us know how you work it out.

 

[walt]

I dont know if I will try this idea.. but its interesting.

I did this quick using google.. hopefully its correct but I calculated that 2 gallons of ice going from frozen to just thawed has the same energy as a 58.7 amp hour 12 volt battery. But if you do things right (ie, a closed air circuit like in the diagram so the drip water doesnt taste like a hot dog), you get the "power" from the ice but after its spent of its energy, you get to drink it. If a block of ice is around around 2 gallons, the energy of it is not that much different than a group 24 wet cell battery. Except with the battery, you can only use 1/2 of the energy. With the ice, you get to use 100%.

I dont know how many gallons are in a "standard" block of ice but here is a little refinement on that idea so that you could load in two or three blocks of ice. You would want the clean ice chest and the air ducts to all be very well insulated.

Here are the numbers for that calculation

it takes 80 calories to freeze 1 gram of water (this is going from just above 0C to frozen).
1 watt*hour = 859 calories
1 gallon water = 3785.4 grams

2 gallons * 3785.4 grams/gallon * 80 cal/gram * 1 watt hour/859 cal
= 705 watt*hour

At 12 volts, 705 watt*hour = 58.7 amp hours

 

[John23883]

This is easier

The main problem I see is the air all around the ice and in the box. The more mass the more cold is held, air pulls the cold away and makes the unit inefficient.

We use this in the cooler. http://www.walmart.com/ip/Arrow-H2O-2.5-Gal-Slimline-Beverage-Dispenser-Blue/15915151

The opening in the top is about 3 inches, so you cut the corner off of the ice cube bag and pour in. I replaced the spigot with a cap I found that fits so it won't get bumped and leak. When the ice melts, we take out as much water as we need to drink and add another bag as needed without removing the water. The cold water adds mass and helps to keep things cold. The water is always drinkable and the cooler doesn't get full of water and get on the food.

For $7, I'd try this first.

 

[walt]

That looks like a great idea to me, I may look for something like that - way simpler than the electric fridge. The only issue would be that often a bag of ice is partically frozen so it would not be easy to get the bag of ice into the container - but with a three inch diameter opening, maybe not too bad. I wonder if there is something like that which works with a block of ice.. maybe that is what I should make if I cant buy something.

But for discussion, if the clean ice box was very well insulated along with the air ducts, there should be very little heat loss. Just depends on the quality of the insulation. The main heat loss would be from cooling the pumped air in the close circuit - but that is also how the energy tranfer is supposed to work.

 

[dscribner]

Let's throw this in there

Ice 1/2 BTU

Melting Ice 144 BTU

Cold water 1 BTU

Just as more energy is required at the freezing point, a jump in energy is occurs at the melting point.

So, have three ice containers

1) 30% rubbing alcohol

2) 15% rubbing alcohol

3) Straight water


# 1 starts to melt first and really drops the temp.
# 2 stays solid longer due to the lower temp but finally kicks, thereby dropping the temp
# 3 is wondering WTH are we waiting for? Finally, a day late a BTU short, starts to melt . . . and drops the temp.

It will extend the cooling time by as much as 100%, according to some.

 

[walt]

One more thing on this idea.. if you did something like the idea in my previous post, how much power would the fan consume?

I have been using a system sort of related to this in my house (Denver) for the last couple winters where I have a passive solar air heating panel outside and pump air through it to heat my house. It is here http://analogengineering.com/project/solar_space_heater.html

In this system, I have a fan that consumes 27 watts and I get heat out of this system that is about the same as a small space heater on the 1/2 setting - about 750 watts.

Below are some calculations and if right (??), say that the power that needs to go to the ice chest to keep it cold is about 7.34 watts. If I scale the fan needed to transfer 7.34 watts similar to what I have had working in my house for two winters now, the fan I need for the ice chest would only need to be .26 watts.

A .26 watt fan might be hard to find but a 1 watt computer 12 volt fan is fairly easy to find so I think a 1 watt fan would be about what I would try.

A 1 watt fan uses .083 amps or 2 amp hours per day. I would take about 8 watts of solar to supply this. If you could find the mininum size fan from the model (which may be to small?), you would only need about 3 watts of solar to keep the fan running 24 hours per day.

I probably won’t do this unless I get really bored when I am retired and REALLY need to modify something just for something interesting to do..

--------------------

Ice chest uses 7.34 watts to stay cold.. Previously I calculated that a 2 gallon block of ice contained about 705 watt*hour of energy. 2 gallons is actually between the typical 10 to 20 pound weights block ice comes in but say this 2 gallons lasted 4 days or 96 hours. The power the ice chest used is then just 705 watt*hours/96 hours = 7.34 watts..

 

[kloudie1]

Not trying to be a (cold) wet blanket, but here are some things to consider.. Heat intrusion is what you are fighting with any chiller that holds stuff below ambient temperature. Heat intrusion is a function of the surface area that the heat is travelling through, the amount of insulation, the difference in temperature between inside and outside the chiller, and the heat transfer coefficient, both inside and outside the chiller. More surface area exposed to warm temp outside is more heat transfer= more ice loss. Two boxes and the hoses will lose a lot more heat than one bigger box.. Heat transfer coefficient increases with flow (generally) so boxes and hoses with moving air inside will lose more heat than boxes with still (or less flowing) air.. To make ice last a lot longer in your climate, I believe you'd be better to have the ice in a bottle or bottles and cover the box with a blanket (maybe microfiber) that you could keep wet to lower the temperature outside the box to decrease the heat transfer rate. The temperature of a wet thing approaches the dew point temperature .. so like this morning, the temperature outside a box covered with a wet blanket would be 10 degrees F cooler than a box not covered.. decreasing the heat transfer rate a lot!
Using a little in line computer fan would decrease your amp draw a bunch.. Something like this draws about 0.2 ampere.. so 5 hours run =1ampere hour..

 

[walt]

Yep.. one big ice chest would be more efficient but there are some convenience things which might be nice with the separate box to just hold the ice.

Just thinking a little regarding the one big ice chest, you could probably make something using thin plywood plus epoxy/glass on the inside and the pink Styrofoam insulation from the hardware store that worked way better than the plastic ice chests. It’s nice to keep the food and the ice separate so maybe build the ice chest with separate compartments for food and ice. The melting ice might still be drinkable but also might take on the flavor of the food in the chest.. But it might not be too hard to make sure the melting ice stays away from the food..

edit.. maybe one big ice chest but two seperate lifting covers - one over the ice, one over the food. Also, a 12 volt computer fan mounted in the structrure that seperated the food and the ice would help distribute the cold air. Have a switch for the fan "somewhere" so you could turn on the fan when you wanted to.

 

[AWalker]

I freeze gallon jugs of drinking water. Works good, lasts a long time, cold drinking water without all the little plastic bottles. If you want to increase the time it is cold, buy a little 12v lunch box type cooler and gut it and install into you big cooler.

 

[walt]

for the particular problem Im looking at.. we want to go to the Seatle area (wifes relitives) then work our way North to the San Juan islands. We might be living on and off the boat for a couple or maybe three weeks and Id liike to have a cold ice chest on board. I would be able to get ice either in bags or in cubes during this time..

 

[Gene Neill]

I recently started experimenting with dry ice for the food cooler. My exact process needs tweaking, but I was pleased to find I could easily keep two people's perishables quite cold for three days. With refinements, I think I might be able to stretch it to four.

The beverage cooler just uses regular ice, starting with anything frozen that can be. I still need to replenish the ice daily though, especially since we enjoy a cocktail or two (or three) in the evenings, which puts a bit of strain on the ol' ice supply.

 

[seadaddler]

Summer

Do a search right here in this forum under Summer's travels in a 26s like yours
up and down the west coast of Florida for some maybe helpful idea's what he did.
Nick

 

[LloydB]

Checked the cold pop temp in my fridge it was 50 deg F. thought it was colder than that. then just checked water temp at Tacoma 54-55 degrees F. if it were me it would be pop over the side on a string and everything else frozen then into the ice chest with a chunk of dry ice on top to limit access. just a thought of the moment.

 

[John Nantz]

Dry ice = carbonated food

It's true, dry ice will keep things cold ....

Dry ice is another option.

however, it will also cause food to taste carbonated like sodas. For example, ever had watermelon that was kept cool with dry ice? It's different!

Also, the gas is heavier than air so if you sleep onboard the lower part of the cabin can fill up with the gas from the melted dry ice. This is deadly if not noticed.

Dry ice will keep things really cold but find out about some of the downsides and handle with care.

 

[shemandr]

When cruising, even when we had refrigeration we kept a cooler for drinks and other items which we would be in and out of the cooler for. I think this reduced the burden on the batteries for the fridge.
When we didn't have refrigeration, we froze everything including water. We could go almost a week before we had to go to the spam. We kept another cooler, for drinks then too.

 

[Kestle]

I have a Mac 25, and I use a cooler next to the sink for frozen stuff, and am designing a drink cooler to go under the starboard seat by the winch. So far, the plan is to build it out of pink HD foam, with 2 inches on three sides, and one on top (dye to the foam cushion).

Jeff