Staying cool without refrigerants: Next-generation Peltier cooling

That's still a lot hotter than I'd like my refrigerator, to be fair to OP.

The time it stays above 4C unless you're opening the door of your refrigerator all the fucking time is mostly negligible in terms of the difference it will make for bacterial growth.

The foodstuff itself is loaded with water, it won't have an excursion dangerously above 4C just because you opened the door and the air temperature raised a few degrees.

If you are really worried about it (you shouldn't), and you don't keep your refrigerator full, add a few water bottles for thermal mass.

Put a thermometer in a plastic bag (to keep it dry) in a jar of water in your fridge, you'll likely find the temperature of items inside the fridge much more stable than the air temperature.

Why should that be dangerous? I have never heard that.

I have always had my fridge at 8°C and never had something dangerous happen to me. I have never come across fridges that were way cooler, apart from fridges of friends in Canada and the US. What's the reasoning?

You should buy a fridge with a fan in the cooling chamber. My Samsung fridge has a nice fan and associated ducting to circulate air and keep temperatures ~uniform.

If you buy something good like a Sub-Zero it will stay within 1 degree of the set point.

> You hear that you shouldn't let your fridge go above 4°C

Really? My fridge says 8°C, I think?

While Peltier cooling have low efficiency wouldn't it be ideal in some cases like:

- energy source is solar, DC already and abundant.

- cold climate so the fridge can contribute to heating the room

Anyway good to know those small electric cooler with Peltier effect must be consuming a lot electricity.

That is wrong, COP is expressed as a ratio, not a percentage (efficiency is expressed as a percentage, which is COP * 100). And as others have said, both efficiency and COP are dependent on ΔT both in refrigeration and thermoelectric cooling.

"that is, it produces 35 W of cooling per 1 kW consumed."

No, they don't. First, without defining a delta T, efficiency is meaningless (unless its a Carnot cycle).

Second, the efficiency is (depending on op. point) higher than 100%. See [1]. You can pump 20 W of thermal power with 2 A @ 4 V = 8 W

20 W of cooling for 8 W of work, or an efficiency of > 200%. This is common to all refrigeration cycles, and frankly for a puny 10C, it sucks.

[1] https://www.datasheethub.com/wp-content/uploads/2022/10/data...

A steam railway engine is a lot better than you would think. They were more efficient than diesel engines when diesel took over - the diesel engine needs much less human labor and so was cheaper overall, but for efficiency steam was better. (Note that diesel technology has improved since the 1950s, so I don't know how they compare now)

There's some commercial options for this, but it's not common. Usually, these devices just have their own compressors, because they all pale in comparison to the heat pump(s) used for climate control. For example, I have a HP water heater, and its heat pump is about 1/3 of a ton, whereas most homes need 3+ tons for climate control. Fridges are a fraction of that.

For HP clothes dryers, there's no efficiency to steal from somewhere else, because they use both the hot and cold coils - similar to (the same, really) dehumidifiers.

The tradeoff would also be running high-pressure refrigerant lines everywhere. That would require EPA certification (in the US, anyway) to connect/disconnect an appliance, and it would probably be less reliable. These sealed-system units are generally pretty reliable, because the refrigerant is installed at the factory under ideal conditions, and there's no connections that are made later that may be done poorly.

That is an interesting thought, but I assume that the working ranges of the different appliances are different so there would be some complexities and inefficiencies getting them all connected to a common circulation loop. If there was a thermal equivalent of a transformer used for alternating current, that would be amazing.

Likely high speed compressors --- the oldest hermetic systems used an induction motor running at 1800 RPM, then later they went to 3600 RPM, and now they're running on a VFD that possibly goes much faster. By making it pump faster, they can use a smaller compressor and reduce costs, at the expense of longevity and noise.

They use lighter lubricant oils than were historically used, which allows more vibration. It’s also why compressors burn out far more quickly than they used to.

In an "open home" concept I guess it might make sense, but I've never lived in a place like that.

I guess all of the places I've lived the kitchen was always its own room, maybe adjacent to the dining room if anything.

No new appliances (>10y now I think about it, they came with the house.)

New appliances are far better than old ones here. Especially old ones that (I assume) haven't been maintained and so are working far harder than they used to. I've lived in places with old ones that were fine and old ones that were awful, both. I've had much more consistently good results in places with newer ones.

Skill issue on the manufacturer's part. I live in a studio and never hear the fridge. This is part of a fitted kitchen, though, but I doubt the panel hiding the fridge makes that big of a difference.

Just today I ordered a 32dB Liebherr; the previous one had 35dB and could be heard all around the studio (I measured the noise using a dedicated sound meter).

Also the area that needs insulating, and in the extremes the amount of air that needs to be exchanged with the outside to make the house livable, and the heat generated by the people living in it (stick a 100W lightbulb in a fridge and see how cold it can get).

The insulation is actually solvable, and for heating can basically remove the power requirements: a house heated and using heat exchange on air leaving vs entering can be heated a lot just by having people inside it, let alone the other energy they use for other purposes. It's just more expensive to build this way, and with cheap energy it can a long time to pay back. Cooling you can't push down past the heat generated inside the house divided by the COP of your cooler, though.

Sure I was playing a little fast and loose there, but (a) the large surface area of the home (and resulting conductive transfer through the walls + convection transfer via infiltration through gaps) is directly a result of the fact that you need a significantly larger volume for humans to move around in and live in than you do to store food and (b) even if we do look directly at the volume of air, the difference is significant since at the end of the day, since for any given constant deltaT, your energy spent is still linear with mass or volume. And we are talking about roughly 2-3 orders of magnitude difference in air volume between a house and a refrigerator.

Anyways, if you write out all of the heat balance equations, you get a few W/m2 of flux on the inside wall of the home and a few W/m2 of flux on the inside faces of the fridge, assuming a typical wood frame construction in summer time and steady states all around.

So yes, of course multiplying the flux through the home’s wall by the surface area of the home results in a massive heat gain value compared to the heat gain conducted through the surface of the refrigerator, but that’s arguably precisely because of the two different volume requirements.

You can also stack them, but you need ever-increasing areas of TEC and corresponding power consumption. I think a triple-stack is sometimes practical if you want to get something to well below ambient and it doesn't really generate much heat itself (and you don't really want to use a traditional cooler due to size or vibration or something similar)