Hacker News Reader

Comment by nine_k | Hacker News Reader

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.

View on HN

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.

"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.

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)

Reply on news.ycombinator.com