HN Reader

Thermoelectric cooling is pretty inefficient, because the materials need to balance competing requirements:

- Good thermal insulator - Good electrical conductor - Good semiconductor

This is because the hot & cold sides are sandwiched closely together as a PN junction, so once you move heat from one side to the other, it just leaks right back. Mechanical cooling doesn't have this problem, because the hot & cold sides are separated by thin bits of tubing. This makes the thermal leakage a "minor annoyance" in a mechanical system as opposed to "literally the whole problem we're trying to solve" as it is with thermoelectrics.

One work-around is to stack lots & lots of thermoelectric coolers on top of each other. That reduces the temperature difference at each individual PN junction, which in turn lowers the leakage. That's what this team is doing, but using layers that are only a few nanometers thick, so they can fit dozens or hundreds of junctions in a single package.

The paper[1] has some actual details, like this:

Under low-heat-pumping, with minimal role of parasitics, TFTEC modules offer four times the Coefficient of Performance (CoP) advantage over bulk devices. As an example, system-level CoP with a 16-couple TFTEC module is ~ 15 for small temperature differentials of 2 °C, pumping about 1.2 W heat load using 80 mW of electric power. Such small-scale high-CoP cooling is relevant for distributed refrigeration or compartmentalized refrigeration as well as for use in future electronic thermal management

They also note that the maximum cooling power density depends inversely on thickness, and this is where the thin-film TECs like this gets most of their improvements from, compared to millimeter thick regular TECs.

Just a quick scan before going to bed, but looks interesting for certain applications.

[1]: https://www.nature.com/articles/s41467-025-59698-y

> the APL team achieved nearly 100% improvement in efficiency over traditional thermoelectric materials at room temperature

Peltier effect refrigeration has very low efficiencies (5%) so while this is an amazing accomplishment it will not replace other more mechanical cooling methods.

A lot of people throw around 5% efficiency for Peltiers, and it's just not true - it depends heavily on the temperature differential and current vs. IMax. You can (with care) drive them >2.0 COP.

This isn't anything like a compressor or heatpump system, but Peltiers get a bad rap... they move heat really well if you're not pushing them to the edge.

Here's a nice chart. At 10k difference and 0.1 current max, you're over 2.5 COP. https://www.meerstetter.ch/customer-center/compendium/71-pel...

I need this for my compact compost freezer [1]

[1] https://www.envirofreezely.com/

Most IR cameras use Peltier cooling so better coolers should lead to better cameras.

So, these devices.... turn heat into electricity? Where does the electricity go, back into the system it's powering?

there are other alternatives for refrigeration

https://en.wikipedia.org/wiki/Thermoacoustic_heat_engine

it should be pointed out that thermoelectric cooling that was able to outperform mechanical pumps, would still be mostly useless for on device cooling as it cant move heat any distance, with it's own heat stuck in the same box or package, making design pivot around that limitation.

From the abstract:

>system-level coefficient-of-performance is ~15 for temperature differentials of 1.3 °C.

There's a long way to go. As far as I know, the leader in condensed-phase refrigeration cycles is still the sodium iodide ionocaloric method, which blew past all of the competing methods (magnetocaloric, elastocaloric, thermoelectric) when it was announced in 2022:

https://www.science.org/doi/10.1126/science.ade1696

...but the temperature drop of 25 C is just barely practical for air conditioning in warm (but not desert) climates.

It’s astonishing how here, in an ostensibly technical forum, the vast majority of comments are left by people who did not even skim the article. At least read through the informative comments left by those who did read it before giving your venerable opinion based on the information that was already in your head? I mean, isn’t the point of an article or paper to present new, novel information?

So it's a better Peltier element? The article only seems to compare it to existing thermoelectric devices and not standard refrigeration units so I'm going to assume they haven't gotten even close to that efficiency. If they had I would assume they wouldn't shut up about the fact.

Also one of the biggest if not the biggest downside of these chips is, unlike a split refrigeration circuit, the front gets cold while the back gets hot which means you can't move the heat very far.

Thermoelectric cooling needs as much research as possible. Mechanical cooling is extraordinarily space consuming. CHESS has the potential over the next 10 years to largely replace vapor compression in most systems other than the most extreme gradients or scales. They are small enough to incorporate into most devices and would allow smaller devices more thermal load. In some ways I think efficient TEC like CHESS could be more useful than room temperature super conductors.

Obligatory video on the inefficiencies of thermoelectric cooling/Peltier elements from Techonology Connections: https://www.youtube.com/watch?v=CnMRePtHMZY

I thought Magnetocaloric cooling [1] was what will kill "traditional" heat pumps, but if we will have something with even fewer moving parts that is awesome.

[1] https://www.youtube.com/watch?v=qcscUoP8FNk