Looking at Portable Freezer Fridges

[brownoarsman]

Originally Posted by MarkJ

I had the feeling Engle was about double the price of Dometic. I could be wrong.

Mine was about $400 and the Engle $800 but its been about 4 years and the putty keeping my eyes in is a bit flaky.

Nope, that's still about right. It's a serious chunk of money to get an Engel vs a dometic, with, at least according to the earlier outfitting retailer, the advantage being the reputation for longevity.

[Capella]

You will see plenty of Engel units on the back of utes in the hottest parts of Australia. Usually 10+ year old, and still working as good as a new unit.

They are not cheap, and the compressor makes more noise than the Danfoss (they have a proprietary compressor design, main benefit is no startup surge), but for long-term use, beats the cheapies all the time.

I have 2 of them - fridge and freezer. Still new, no problems.

[roygee]

Originally Posted by a64pilot

I may likely due to cost buy a Whynter myself, I also like the digital temp display.
They seem to get good reviews from the RV crowd, however it seems no one has put one on a boat?

I love mine, works great on freeze or cool, and cannot hear it run. Beer can be adjusted {temp} to where their are giblets of ice when you open it, so good! 12 0r 125 volt and seems to keep very good, would recommend the insulated cover.

[txg]

Have no idea about todays Engel fridges, but we still use the 14L Engel that was installed in the boat by the builder. And that means it is 39 years old now... That is what i call quality!

[brownoarsman]

I did receive this spec sheet from Dometic - unfortunately they did not answer my direct question of whether the compressor size or cooling elements differ between models. It does appear like everything above the 28 liter draws significantly higher watts, but that's the only indication I see of different internals. However, average amp-hours used are pretty much identical, which probably goes to show that cooling air is relatively easy as long as you don't open the box and the boxes are equally well-insulated. So, still not sure what to make of it.

[Schrewsburyduo]

We got the arb An amazing product. We run two solar panels total 120. Have stayed at anchor for 5 days last yr without running the engine once. The fridge draws very little. Highly recommend it.

[PetePetePete]

I recently bought a Engel MR040F-U1...

It can fit 35 1 liter bottles of water in it.

Assuming the water is 75(f) and the ambient temp is 75(f).

How long should it take for those bottles of water to freeze solid?

I currently have this unit and this scenario. I plugged the unit in at 7PM and loaded the 35 bottles. 12 hours later the bottle as "cool/cold" but not frozen.

Is this a reason for concern?

Thanks,
Pete

[captstu]

A liter or water - I remember from high school - has a mass of about one kg.

35 liters of water ==> 35 kg (from elementary school)

. . . btw, this is supposed to be funny, not insulting. Please forgive me if I missed the target.

One liter of water changing to ice liberates about 333.55 kG of energy.

So, 35 liters to water changing to ice is 35 x 333.55 = 11674.25 kg

Now the numbers get easier. 1 kilowatt second = 1 kilojoule so:

11674.35 kg / 3600 seconds in hour = 3.24 kWh.

Now the numbers get more manageable. The numbers above are all at 100% efficiency - generally thermodynamics is nearly that efficient.

So we have to estimate the efficiency of your engle.

The best chart I have says the Dometic CFX-95Z22 (I think this is the best efficiency on the market) consumes 70 watts when running. Assuming yours runs all the time, it consumes 70 *24 = =70-24 = 1680 Watts ( 1.68 kW) per day and if it runs at 100% efficiency should take:

3.24/1.68 = about 2 days

to cool your collection of water bottles. This is about right except!!!!

Most refrigeration units run at well over 100% efficiency since they move heat rather than making or destroying (??) heat. The SEER numbers on home air conditioners reflect the fact that they move more heat than they would "make" if they were just heating the air with electricity.

So, the conclusion is if your new freezer takes two days or so to freeze the water it is working about correctly given the reality of insulation, and other loss factors.

If you want to know more google James Clark Maxwell (you probably heard of him without his first name). Maxwell helped develop the Maxwell–Boltzmann distribution, a statistical means of describing aspects of the kinetic theory of gases. His ideas lead directly to refrigeration were first described in what was then a joke: Maxwell's Demons. Maxwell's demon is a thought experiment created by the physicist James Clerk Maxwell in which he suggested how the Second Law of Thermodynamics might hypothetically be violated.

He was correct - turns out refrigeration equipment such as your freezer and home air conditioner routinely exceed the theoretical maximum efficiency of such devices - Clark would be pleased at your question and the resultant answer.

[PetePetePete]

Yeah... I screwed up. It holds 35 500ML (1/2 liter)!! LOL...

Let me see if I can use your formula to see where I should be...

[basssears]

Originally Posted by PetePetePete

Is this a reason for concern?

I'll let the math, err, speak for itself (wish I could have figured it all out that way). But as far as comparable experience I do not think that is reason for concern. Nothing is free when it comes to energy transfer, so to transfer energy (heat) out of the water faster you would need to draw more power (so think your household fridge/freezer with no limits on power draw)... to only sip 2.8amps when running like the Engels, you have to by definition be moving less heat (energy) out of the water.

For reference, we have the same model and when we start a trip we have four gallons of water we want to freeze... takes about 3 days to get everything good and frozen hard.

I see everything on Engel's site is discounted by a significant amount right now:
Portable Top-Loading - Shop by Fridge/Freezer - Fridge Freezers
... wish I'd had those prices last year...

[captstu]

All we can figure with the theory is the order of magnitude - one factor we can't easily figure is that as water freezes, ice is a better insulator than water since it doesn't circulate any longer.

The theory predicts it should take about 2 days to freeze a freezer full of water - but the efficiency of the compressor system is unknown, and the insulating factory of the ice is hard to measure.

I tried this once and found a very, very small fan inside the freezer improced the speed of freezing.

Anyway, it was fun to write and maybe a little helpful.

Your freezer is probably working the best it can.

When I used to camp a lot a a kid, we pre-froze the food with liquid nitrogen - maybe we could do that on board. During the day when the motor is running, extract nitrogen from the air, cool it to a liquid, and spray it on the food or water bottles.

What an idea!

[brownoarsman]

Pulled the trigger on the dometic cfx-35; still $200 less than the Engel, and currently the lowest price it's ever been on Amazon (even lower than the 28). Hopefully I won't regret it for at least ten years!

[a64pilot]

The most efficient cooling system is one that the compressor is sized so that it runs continuously. A larger compressor that cycles is not as efficient.
However it's not practical for one to run continuously because it would never cool something that was put into it that was warm and would not stay as cool on a hot day, so some efficiency has to be given up so that you have enough cushion to get through these events.
However these efficient units have very small cooling systems and very little capability to remove heat, or they would draw more power.
This is where multi speed compressors come into their own, but are these little units multi speed?
Just a function of the system, want high efficiency, you give up how fast it will cool to some extent.
Wanna cool fast, then you have to have a larger more power hungry system. Thermodynamics isn't just a good idea, it the law right?

[PetePetePete]

They are starting to freeze. Not solid, but still, definitely freezing. Not all of them. We're right around the 18-20 hour mark... (I added more later)...

I am wondering about the very slight noise that it makes almost like a slight metallic rattle. Hard to explain. Not sure if just a vibration, normal noise, or what?...

[a64pilot]

Many have commented that the Engels swing compressor makes a rattling type of noise.