Cold Plate / Thermoelectric?

[LakeSuperior]

Peltier cooling or thermoelectrics effciency depend on the thermal gradient or difference in temperature. The larger the temperature gradient the worst the efficiency...more power (more current through the thermoelectrics) is required to move the same amount of watts of heat. So for the 90 degree day and a 40 degree refrigerator temperature efficiency is bad (don't forget about the efficency of the heat exchanger on the back side of the TE, count that fan also.) However, if the refrigerator is well insulated then not much energy (heat) is required to be removed to maintain temperature and so the TE's may do the job OK even if the gradient is large.

One has to do the engineering to look at the trade-off...cost, power, weight, functionality, install, insulation on the refrigerator walls, etc.

I can see advantage to using a switchable water/air cooled system for the TE's. However, the complexity is probably not worth it.

[wolfenzee]

Originally Posted by LakeSuperior

Peltier cooling or thermoelectrics effciency depend on the thermal gradient or difference in temperature. The larger the temperature gradient the worst the efficiency...more power (more current through the thermoelectrics) is required to move the same amount of watts of heat. So for the 90 degree day and a 40 degree refrigerator temperature efficiency is bad (don't forget about the efficency of the heat exchanger on the back side of the TE, count that fan also.) However, if the refrigerator is well insulated then not much energy (heat) is required to be removed to maintain temperature and so the TE's may do the job OK even if the gradient is large.

One has to do the engineering to look at the trade-off...cost, power, weight, functionality, install, insulation on the refrigerator walls, etc.

I can see advantage to using a switchable water/air cooled system for the TE's. However, the complexity is probably not worth it.

As far as trade offs:
Wieght is not too much of an issue I have just added (am addding) a few batteries (total of 4 deep cycle marine and 1 8D), a diesel cook stove all new counters (tile) and cabinets.
Because I gutted out the galley to do this and am building the starboard side galley (galley is on both port and starboard with counter behind companionway) around a modest ice box space is not a problem.
The ice box is going to be very heavily insulated and is below the waterline, the additional fan/heatsink I have for the TE was designed for a computer but is used for this application (2 fans incredibly low draw fans)
Most importantly I am not trying to make is *cold* just cool enough to keep food and there is a section behind the food (loaded seperately from the top) for ice.

[witzgall]

While Peltier coolers are very cool technology, You will find that they just draw too much power for use when there is not an engine, or grid power, to supply the juice. The only advantage they have is the cost of components, and perhaps they are a a bit simpler in design. Adding batteries only increases the amount of time you can run without recharging the batteries. An inefficient cooling system will simply be false economy, and when things get hot in the summer (even in AK) you will find that they simply won't be able to keep up with the cooling requirements. If you do go this way, make sure you install some type of temperature monitoring device, so you can be alerted if your food drops to unsafe temperatures.

I would suggest you experiment with these if you have not already done so, before committing to this cooling technology.

There is an ebay seller with Isotherm kits for very good prices right now. One option that works and is efficient - there are others.

Chris

[LakeSuperior]

Again, for certain applications TE's could be the way to go. They would weigh less and take less volume than a cold plate refrigeration system, they are cheaper, more reliable, and they would probably be easier to install. OK, they are mostly not as efficient thus requiring more power under certain conditions. However, the power requirement may not out weigh the other criteria listed.

The power penalty (difference between the two systems) becomes less if refrigeration box insulation is made better. Less heat transfer into the refrigerator means less that has to be removed.

Roughly, you can estimate the heat transfer into your refrigeration box with your insulation and allow for some opening and closing (use). Assume constant temperature boundary conditions. Then look up the TE efficiency curves as a function of the temperature difference and add the power needed to run the fans. Compare this power estimate to the power needed to run the cold plate.

[witzgall]

I woud add to your info below that the differential between ambient temperature and box temperature would need to be low. If you are trying to keep a box 38 and the outside temp is 95+, then TE is not going to work, no matter how much you are ok with the increased power consumption.

Chris

Originally Posted by LakeSuperior

Again, for certain applications TE's could be the way to go. They would weigh less and take less volume than a cold plate refrigeration system, they are cheaper, more reliable, and they would probably be easier to install. OK, they are mostly not as efficient thus requiring more power under certain conditions. However, the power requirement may not out weigh the other criteria listed.

The power penalty (difference between the two systems) becomes less if refrigeration box insulation is made better. Less heat transfer into the refrigerator means less that has to be removed.

Roughly, you can estimate the heat transfer into your refrigeration box with your insulation and allow for some opening and closing (use). Assume constant temperature boundary conditions. Then look up the TE efficiency curves as a function of the temperature difference and add the power needed to run the fans. Compare this power estimate to the power needed to run the cold plate.

[SURV69]

My coleman cooler works much better at night.

Late afternoon to mid-morning, the unit "makes" things nice and really cold.

After mid-morning until the evening coolness, I'm careful not to open the unit more than absolutely necessary with the idea that the insulation will keep things cold enough until evening comes again. It would help if I placed a paper bag over the top(under the lid) to keep things cold during those very few times I open the unit.

In this respect the Coleman unit works wonders for me and When I'm away(at home), I have the unit programmed to run a few times from about 7pm til 9am. During the day I have it running from about noon to 3 pm.

I have kept milk(1%), cream(for coffee) and my cheeses and such for more than a week with no problem.

AFTER all, up to 35-40 degrees below ambient 65-75 degrees(Ohio's nightime temperatures), along with the natural coolness of being on the water means the cooler only needs to act as a "cooler" during the day.

[wolfenzee]

I live on my boat year 'round and have been doing so with just an ice chest for a couple of years. Shore power is usually available and when it is not I have two deep cycle marine and a marine 8D for "house batteries"...keeping that in mind Walmart has 4cf refrigerator/FREEZERS that run on 110v for about $135 (using 1.5amps, 290kwh/yr at land lubber temps), even with the power loss of the inverter the 8D battery will run one of them for 4-5 days (longer if I throttle it down) that is more than twice as long as a block of ice. From the point of view of a live aboard having a real fridge with a freezer is quite a luxury. I will be building space for an ice chest under the counter next to the fridge for when I have access to ice but not power. A real refrigerator would even be worth getting a small generator for. Just the savings in meat sales at the grocery store will pay for the fridge in less than a year. I agree that this is not efficient for when I am sailing the tropics...but if I ever get there I'll deal with it then.
Though living comfortably on a boat may be considered sacrilege by some...aren't you supposed to suffer

[wolfenzee]

There is room in my galley for this.

[wolfenzee]

With the fridge I have an L-shaped counter and U-shaped galley. I am building it in such away so when I can afford the Nore-cold ice box conversion kit (about $900) I can build in an under counter refrigeration system and have a U-shaped counter. I will have the tile counter piece ready to drop in seamlessly, until then the counter piece and face board will form part of a shelf over the fridge. Until I can afford a "proper" marine 12v DC refrigeration system I will have to put up with a 110v AC stand-up (32.5"h x 18.5 x 18.5")refrigerator/FREEZER....I can have my ice cream and eat it too

[Jace]

This may make me sound green, which I am, I don't even have a boat yet, anyway, why couldn't someone put all of their cold necessities-beer, milk, cokes-in a weighted bag and simply drop it down 300 or so feetand let it dangle? I would think it would be cold enough down there, and when you wanted something just electric wench it up, or use a 6 or 8" diameter spool with a to retrieve it. A 1/8" nylon cord with 1" thick hub seems to me wouold do the trick.

[wolfenzee]

Originally Posted by Jace

This may make me sound green, which I am, I don't even have a boat yet, anyway, why couldn't someone put all of their cold necessities-beer, milk, cokes-in a weighted bag and simply drop it down 300 or so feet and let it dangle? I would think it would be cold enough down there, and when you wanted something just electric wench it up, or use a 6 or 8" diameter spool with a to retrieve it. A 1/8" nylon cord with 1" thick hub seems to me would do the trick.

Well for something like that to work I would have to get a very water tight box (probably fiberglass), weight it with lead (to compensate for the air space at least 100lbs of lead)....lead and fiberglass are not very green. Then instead of grabbing some food out of the fridge on a cold winter night I would have to go topside in the rain and/or snow, winch up the box, wipe off the slime, mud and assorted critters that had accumulated on it......it was bad enough just getting stuff out of a cooler in my cockpit covered by an awning.
As far as green.....the fridge I am getting uses very little power and am looking into wind and solar for my boat.

[wolfenzee]

I live in Washington State, in winter the water temp is 45F (55F in summer) .....wouldn't work for ice cream and other frozen stuff also is not advisable for most "perishable" foods for long times...will keep the beer cool though I guess..my water tanks are below the water line and drinking water is nice and cold.

[GordMay]

Nearly 3/4 of all food-related illnesses are the result of poor temperature control.

Following the simple rule “Keep hot foods hot and cold foods cold” can prevent many food borne illnesses from occurring.

Bacteria that cause food borne illness multiply quickest between 4̊C and 60̊C (40̊F - 140̊F). The Danger Zone is this temperature range in which bacteria and spoilage bacteria grow quickest.

Lower temperatures prevent the bacteria from growing to dangerous levels.

Temperatures above 60̊C will kill the bacteria.

Keep cold food cold by storing in a refrigerator at 4̊C (40̊F) or below.

Keep hot food hot by maintaining it at 60̊C (140̊F) or higher.

Anything between, is the Food Danger Zone.

[LakeSuperior]

Cans of beer dropped to a depth slightly greater than 15 ft...below the thermocline in Lake Superior one summer, were crushed enough to leak. We lost six or seven cans on that tragic incident.

[GordMay]

Originally Posted by LakeSuperior

Cans of beer dropped to a depth slightly greater than 15 ft...below the thermocline in Lake Superior one summer, were crushed enough to leak. We lost six or seven cans on that tragic incident.

A tragedy on two levels; the first being that you felt the need to submerge the beer.


The average summer temperature of Lake Superior is about 40 degrees Fahrenheit; hence (even near the surface) immersing beer in the Lake water will result in a very Well Chilled beverage, only suitable for American swill.

➥ Michigan Sea Grant Coastwatch

➥ Michigan Sea Grant Coastwatch

We North Americans like to say we could never drink warm beer, like those weirdo Europeans; but those that feign disgust at a warm beer have probably never had a real beer. While it is true that the toilet water flavoured swill that most N. Americans drink is best served cold, it is only because it tastes revolting, unless it is cold enough to numb your taste buds.

Chilling below 15.5 ̊C/60 ̊F starts to reduce taste awareness and reduces it significantly below 10 ̊C/50 ̊F.

While this may be acceptable for beers without an appreciable aroma or taste profile, beers brewed with more than basic refreshment in mind reveal their flavours more when served unchilled—either cool or at room temperature

Michael Jackson’s* Serving Temperatures:
Well Chilled (7 ̊C/45 ̊F) for "light" beers (pale lagers)
Chilled (8 ̊C/47 ̊F) for Berliner Weisse and other wheat beers
Lightly Chilled (9 ̊C/48 ̊F) for all dark lagers, altbier and German wheat beers c
Cellar Temperature (13 ̊C/55 ̊F) for regular British ale, stout and most Belgian specialities
Room Temperature (15.5 ̊C/60 ̊F) for strong dark ales (especially trappist beer) and barley wine.

* “Michael Jackson's Great Beer Guide”

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