AcuTemp Refrigerator

rustystud

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My freezer when running seems to almost pull a vacuum in the freezer box. The lid doesn't want to come up like a vacuum is holding it down. My downstairs deep freeze does the same thing after I close the door. Those wires you have checking on the temperature could be interfering with that whole process.
 

DieselAddict

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Sounds like your system is not running properly. Could be those wires coming out of the cooler box letting in warm air. Like I mentioned earlier, mine froze 2 gallons of water in under 6 hours.
Certainly a possibility. The wires are very fine so I would expect the leakage would be minimal.

The second unit has just broken through the barrier at around 11 hours to freeze 8.5lbs of water. That indicates a heat transfer rate of around 110 btu/hr. I'm going to let it run a bit longer so the trend graph shows the temps dropping below freezing.
 
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CMPPhil

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Hi

How about using one of these (set to cooler not to freezer) and the Cool Shirts they use in racing? Or would the thermal load from cooling a person be more than they could handle?

Cheers Phil
 

DieselAddict

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How much ice do you go through in a stint and how long is a stint? We use water bottles in ours and refreeze them with dry ice track side.

I'm going to try and get a peak at the label on the compressor to see what capacity it is.

As the unit is I don't think is practical to put in a race car. Too big and bulky. The compressor and other bits may be salvageable to build a custom unit for that application.
 

DieselAddict

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Hi

How about using one of these (set to cooler not to freezer) and the Cool Shirts they use in racing? Or would the thermal load from cooling a person be more than they could handle?

Cheers Phil
Looking at the datasheet for the compressor and the MAX capacity is well within the range of what would work for a coolshirt refrigerator.
 

rustystud

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I managed to snap a photo of the label on the compressor. It is a Danoss 101Z0200.

The attached datasheet for the compressor indicates the capacity of the compressor. The values I've recorded are within the reasonable range of what you would expect for this unit.
So like I said all along, it is as capable as any house freezer. Yes it "can" freeze something put in it. It doesn't have to be frozen first.
 

DieselAddict

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Sure it can freeze something. It will take a good bit longer to do so than a home freezer will based on the tests of the two units I have. I stand by my original statement that is isn't well suited for dumping a bunch of stuff inside to freeze. It is better suited to keep things already frozen in that state.

To eliminate the probes as cause for the freezing times I reset and used freezer bags with water in place of the milk jugs. They have a little better geometry in regards to volume/surface area ratio.

I had a total of 8 lbs of water that started off at 46 degrees F. The water took approximately 11 hours to cool and freeze solid. The time is based on watching the condenser discharge temperature to detect when the compressor started cycling again after the heat load was placed in the chamber.

If you calculate it out it comes out to about 110 btu/hr average over that time. That is the same basic result as the test with the milk jugs.

So maybe the units I have are down on capacity or their insulation is degraded. Totally possible. The seals are in very good condition as they had been recently serviced per the documentation.

Screenshot-2018-3-12 HeaterMeter BBQ Control.png
 
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NATCAD

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It seems like a sealed water bottle with big thermal mass would be much harder to cool than a larger open mouthed container i.e. mixing bowl full of water.

I'm hoping to use mine to make ice in trays and I expect these would freeze very quickly compared to a sealed item with a certain depth to it.
 

DieselAddict

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The time will be the same if the mass of the water is the same. What may be different is where all the ice ends up. On an open container some water will evaporate then deposited somewhere else. The total energy however is the same. The amount of energy it takes to freeze a gallon of water is always the same.

What I think would make more difference is spreading the water out so it had more surface area. That would push the evaporator temperature higher which will move the compressor up into a higher capacity area on its pumping curve. In that case the water would freeze maybe as much as twice as fast.

Still the total energy is the same. The rate the compressor can move it changes based on the evaporator/condenser temperatures. The colder it is the lower capacity the compressor has.
 

rustystud

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Sure it can freeze something. It will take a good bit longer to do so than a home freezer will based on the tests of the two units I have. I stand by my original statement that is isn't well suited for dumping a bunch of stuff inside to freeze. It is better suited to keep things already frozen in that state.

To eliminate the probes as cause for the freezing times I reset and used freezer bags with water in place of the milk jugs. They have a little better geometry in regards to volume/surface area ratio.

I had a total of 8 lbs of water that started off at 46 degrees F. The water took approximately 11 hours to cool and freeze solid. The time is based on watching the condenser discharge temperature to detect when the compressor started cycling again after the heat load was placed in the chamber.

If you calculate it out it comes out to about 110 btu/hr average over that time. That is the same basic result as the test with the milk jugs.

So maybe the units I have are down on capacity or their insulation is degraded. Totally possible. The seals are in very good condition as they had been recently serviced per the documentation.

View attachment 721588
Well I can test my "2 gallons" of water again (16 Ibs) but I'm sure the results will be the same again. I'll start tomorrow.
Since you proved the compressor is a standard R134 compressor that also confirms what I said all along that this unit is a "Real" freezer not some "Toy" .
It also "froze" solid the water I put in it and I'm sure it will do it again under 6 hours. Of course you won't believe me again, but I will do it anyway.
Now for all those who believe the military buys "Junk" and "Toys" to help save the lives of the troops I have nothing to say.
To add one more thing. Any freezer will take awhile to freeze something solid. They excel at "keeping" things frozen. That goes for any freezer. Just so we are comparing apples to apples. This is not some "flash freezer" but neither is a standard freezer.
 
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DieselAddict

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I'm not at all implying these are toys. Far from it. Its a significant piece of gear that serves a specific and needed purpose around the world. Not just in the military. These things according to the manufacturer are sold to military and aid groups alike to transport fragile medical supplies all over the world. No doubt they save lives.

For me this is an interesting puzzle. I'm working under the assumption that yours did freeze 16lbs of water in 6 hours. That is around a 4x amount of energy transfer than what I measured with mine. That is a significant difference. If there is something amiss with the 2 units I have and they are capable of that energy transfer rate I will have a different application in mind for them.

Edit - When you do your test if you are able to download the trend from the controller I would love to see the data.
 
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Hummermark

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Hi,

After all all of these posts I am now brain washed into wanting one (it's like an advert, if you see it often enough you want one!)

who has them them for the best price in the US or as you guys in the US say, who has the best deal?

thanks Mark
 

DieselAddict

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I bought mine via the classified here on the forum. I would say that is always a good option.

You might get a better price if you want to roll the dice and buy directly from one of the auctions. I saw lots of 5 units going for a few hundred bucks. I think the ones I have came from one of the lots I was looking at based on the serial numbers. On the plus side they were tested and verified to work. That is certainly worth some extra $$.

There are several on fleabay. I think they are asking too much though. I would say if you can get working units in the $500-600 range you are doing OK.
 

DieselAddict

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The next step in the experiment is to try and calculate the thermal performance of the insulation. I have my 8lbs of ice in the unit and I've set it to idle. It is still collecting the temperature data in the chamber. I'll monitor the chamber temperature and when the ice has melted I'll calculate the heat transfer coefficient of the insulation.
 

rustystud

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Well after performing my experiment again, and getting the same results I decided to put a gallon of distilled water in my house refrigerator. It took 5 hours to freeze solid this gallon of water. So I went searching on the internet and found some interesting answers. As long as the freezer is able to hold a temperature at least 4 degrees below 0 Celsius during the freezing process, then it will freeze water at a constant rate with known variables. These variable rates depend on such things as the purity of the water, the amount of water (pints compared to gallons) and the thickness of the container and the material of that container. Example, copper will freeze faster then plastic containers.
Now since our little freezers will hold at -10 C when freezing our water, then it is safe to assume that it will freeze anything put in it. Just like any standard freezer out there. I used 16 pint water bottles. Diesel Addict used 2 gallon jugs of water. Since larger volumes of water take longer to freeze then smaller bottles we both came up with accurate times. My house freezer took 5 hours to freeze a gallon of "pure" water in a full freezer. My military freezer took 5 hours ( I checked every hour this time) to freeze 16 pint bottles solid.
So Like I mentioned at the beginning of all this. This freezer will freeze just like the "big" boys. It is not a "Toy" . It is an extremely high quality piece of equipment that will operate on 12V DC, 24V DC ,120 Volt AC and on it's own internal batteries. There is no freezer that I know out there that does this and operates with a real compressor using R134 Freon . Not even a Travel Trailer freezer like "Norcold". Norcold and it's fellow trailer freezers actually use's a very inefficient compressor system and cannot operate with such varied types of voltage like this unit does. Granted this military freezer cannot operate on "propane" .
Now I think we have given this subject all the attention it deserves so lets move on.

For those who want to know more on this subject, here's an interesting discussion on this issue from several engineers.
https://www.quora.com/Thermodynamic...freeze-while-at-a-temperature-of-32-degrees-F
 
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DieselAddict

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If your freezer is holding at -10c that does indicate you have a good delta-T to move out the heat from the water. What was the chamber temperature when you concluded the test?

Edit - The volume I was using was 8.5 lbs in the first two tests with 4lb 4oz each in a 1/2 gallon milk jug. The third test was using four quart freezer bags each with 2lbs of water (total of 8lbs).

The math in the referenced article is how I'm calculating the heat transfer rate.
 
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