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Comment by anticensor | Hacker News Reader

Did they solve the inefficiency problem of peltiers?

They claim 75% better. I doubt this is better than compressors in general but they seem to be going for a niche where a high power compressor does the high load part but when only a litte cooling is needed the compressor is now very inefficient and so the peltier is better. Normal fridges just let the temperature have a wider swing which is good enough for most needs.

> Normal fridges just let the temperature have a wider swing which is good enough for most needs.

These wide swings annoy me. You hear that you shouldn't let your fridge go above 4°C, because that's dangerous. And you obviously don't want your fridge to go below 0°C. But finding a setting where the hottest part of the fridge doesn't go above 4°C (or even 5°C or 6°C) during the hottest part of the cycle and the coldest part of the fridge doesn't go near 0°C during the coldest part of the cycle is really pretty difficult, in my experience.

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

Really? My fridge says 8°C, I think?

Between 3°C and 5°C is the recommended refrigeration temperature

https://www.which.co.uk/reviews/fridges/article/how-to-store...

Christ.

I also run my fridge at 8C, which I think was the default setting when I bought it.

Gonna go change that right now.

8 degrees or just 8 on the 1-10 scale that many of them use?

(I always remember the recommended fridge temperature as 40F, which avoids the confusion.)

I suspect it's that. Most inexpensive refrigerators don't have thermostats. Which seems insane; it cannot add that much to the price.

8C is a perfectly fine temperature for a wine fridge. And they usually have thermostats because a wine fridge is a luxury item. As opposed to keeping people from getting foodborne illness.

> Which seems insane; it cannot add that much to the price.

Be careful what you wish for.

When buying my current fridge, I specifically tried to go out of my way to avoid complexity, but the opening for my fridge is an odd size so my choices were limited. The only fridge I could buy that didn’t have a bunch of crap that’s was guaranteed to break (ice maker, water dispenser [seriously? aren’t most fridges right next to a faucet?], LCD-covered glass panel, etc) that also had a thermostat had a digitally-controlled thermostat. No knob or physical buttons, just a capacitive surface for temperature adjustment and some LCD screens showing the fridge and freezer set temps. (Not the actual measured temps, that would be too useful, just the set temps.)

In hindsight, I probably should’ve just gotten one with a regular dial, but I was a bit fixated on the “real” thermostat. So now I’ve got that to look forward to breaking in 4-5 years and figuring out where the hell to source a discontinued fridge LCD panel from.

> water dispenser [seriously? aren’t most fridges right next to a faucet?

Same reason you'd keep a container of filtered water in your fridge.

...why would I keep a container of filtered water in my fridge? My water comes out of the tap already filtered at my municipal water supplier?

Maybe if I was on a well I would need to filter my own water, but then I definitely wouldn’t trust that job to a fridge.

Many people prefer a cold glass of water compared to the cool to room-temperature water that comes out of the tap (Hence the refrigerator for cooling). Filtering at the individual level is typically done for flavor, because depending on where you live, while the water is probably safe to drink (assuming HN readership demographics), it may or may not be particularly pleasant. Even here in the Bay Area, where we have that sweet, sweet Hetch-Hetchy water, I know people who live in buildings with pipes bad enough that they filter their water.

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.

The yogurts at the back of my fridge still freeze up.

There's going to be a temperature gradient in a typical fridge, if only because one side is getting opened every now and then, and the other is separated by all the products which are inside.

I suppose what they're trying to do here is even out that gradient without running the compressor.

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.

I may consider that the next time I buy a fridge, but the reality is that this isn't something I care deeply enough about to buy a new fridge over.

Maybe you can retro a fan into your current fridge. Nice little project!

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?

The recommendation I've always heard in the Netherlands is 7°C, it's more recent that I've been seeing 4°C on meat packaging in Germany (where I live now). I doubt anyone's fridge is consistently at or below 4° without freezing things constantly, so I've been assuming this is wishful thinking and/or ass-covering on the manufacturer's part and not what anybody actually does. Your 8°C is close enough that it probably makes little difference, though afaik this is an exponential curve (at 14°C it would last far less than half as long) so I'd not be surprised if things spoil a bit sooner than they otherwise would

Even if your products generally meet their "should be safe at least until" date (Mindesthaltbarkeitsdatum, idk if it's the same as "best before"), you might exceed that longevity more often than you do now and thus have less food waste by setting the fridge colder - if food waste is a thing you have in the first place (I'm the type of person that is hungry all the time, opens the fridge when hungry, and isn't super selective (among what I've bought anyway), so food I buy ~always gets eaten before it spoils, but then when I see food waste numbers, apparently that's not the case for everyone so I'm just throwing this out there)

Edit: trying to fact-check myself, I can't find any trustworthy source in Dutch saying your foodstuffs fridge should be more than 4°C. I measure new fridges when moving in and again at least once during the first summer to make sure they stay at or below 7°C when we had the door open a normal amount of times, so I know they're that (and not much cooler, to not freeze items or waste energy). So far, products meet their minimum shelf life date thingy and almost always exceed it. Strange. Maybe this recommendation I heard predates the internet (showing my age here), or maybe every page on the internet assumes that nobody actually measures it properly and so they recommend a value that's half of what's actually safe?

> I doubt anyone's fridge is consistently at or below 4° without freezing things constantly.

My refrigerator is typically between 3-4°C, never had any problems with things freezing.

Crazy, I'd think the fluctuations would be way too big. How long does it normally run for when it does a cooling cycle? Is that temperature throughout the fridge or only on certain shelves?

Ours (well, our landlord's) runs very consistently for 40 +/- 3 minutes, with just over 1h30min in between during normal use, or 1h54min if it was closed the whole time (like at night). The temperature of products, as measured with a cheap infrared thermometer that's probably off like 10%, varies between 2 and 7 degrees, but it's not very consistent between shelves (top seems warmer but then the very bottom one, that is only half deep, is as warm as the top again). The products I checked have all been in there for days; reflectivity may be part of the difference, not sure. I don't know what the air temperature difference is at the beginning and end of a cooling cycle though

It's closer to 2-3°C in the drawers at the bottom and 3-4°C at the shelves at the top. However, it's very consistent otherwise.

I can't tell you how long it runs for because the compressor is too quiet for me to hear, sorry. Maybe if I had an energy monitor on it. Sounds like a fun idea.

Thanks for that explanation!

The Mindesthaltbarkeitsdatum is the deadline to which the item may still be sold by the vendor, iirc.

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.

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

I think the 4C recommendation is an average. There is not magic in ~1% temperature difference from 3 to 6. Just slightly different rates. Which again slow, but do not stop when it is at low end compared to high.

> you shouldn't let your fridge go above 4°C, because that's dangerous.

Dangerous how?

75% better than "utterly awful" is an improvement, but you're still going to be searching for applicable niches with a microscope.

There are many applications for peltier cooling in industrial settings, i.e. sensor devices (or, actually, microscopes with CMOS sensors). Those have to be temperature stabilized to minimize noise while also be IP rated, i.e. no air cooling. 75% efficiency gains would be awesome here.

Yet I'’d love to see real-world power consumption numbers compared to traditional fridges

Would a peltier element allow for a more constant temperature? Or can you turn a peltier up and down easily? With a compressor based system it's always been "on or off", something that can ease up and down would be nice.

What exactly does "75% better" mean? 75% more cooling per watt? 75% less distance from theoretical ideal?

Traditional Peltier devices operate at ~10% efficiency (COP of 0.5-0.7) compared to vapor-compression systems (COP of 2-4), but recent advances in thermoelectric materials like bismuth telluride alloys and segmented elements have pushed lab efficiencies to ~15-20%.

It's clearer to think in terms of "efficiency relative to ideal Carnot efficiency".

Compressor systems use twice as much energy as an ideal system, while Peltier systems use about 10x as much.

The article says they have made peltiers 75% more efficient than existing ones.

OK, a typical Peltier device has 3.5% coefficient of performance, that is, it produces 35 W of cooling per 1 kW consumed.

Fine, let's expect that the new tech doubles the efficiency, to 7%. Still, to my mind, pretty wasteful, on par with a steam railway engine. A Peltier element is good in cases where you can afford a large heat removal device, but need precise temperature control and no moving parts. For a home fridge, I'll take the sound of the compressor and the temperature fluctuations of a 400% efficient compressor-based heat pump over a Peltier element any day.

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.

A common use case: coolers. You don't want a whole compressor, but you do want to keep your hot dogs safe and your beer drinkable. It's not very efficient but it's enough for short periods.

There are mini-compressor based coolers available now if you look for them. They cost a little bit more, and obviously have more weight than a peltier, but I think are worth it if a bag of ice isn't viable by itself because they will run for way longer than a peltier setup.

I considered putting some in our under-sink reverse osmosis tank, to cool the water. Couldn’t come up with a way to exhaust the heat well enough to even look at how much electricity it would have cost me though - probably too much to make it worth it.

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)

"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...

Oh, indeed I was wrong; COP of Peltier elements is much higher than I had gleaned from online charts, not the order of 0.03 (3%) but can easily reach values above 1.0 (100%) and be e.g. 0.5 (50%) at ΔT = 30C, enough for a home fridge.

Still a bit far from compressor-based designs, but not negligible, and almost doubling the efficiency is indeed a serious advance.

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.

> In the Bespoke AI Hybrid Refrigerator Samsung launched in 2024, the compressor operates under normal conditions such as routine storage and retrieval, while the Peltier device activates alongside the compressor during high-load situations — like when storing large amounts of groceries or placing hot food inside — thereby enhancing both cooling performance and energy efficiency

I'd choose a fridge with a larger compressor.

Larger compressor would probably mean short cycling though. That has its own downsides.

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