Twenty years ago there was a company trying to commercialise thermoelectric cooling based on a vacuum gap: https://web.archive.org/web/20031213235132/http://www.coolch...

They claimed 55% Carnot efficiency based on a 30-100 angstrom gap maintained by piezoelectric controllers, and a method to construct large electrodes with matched surfaces so that the gap could be maintained over a large area. It all sounded plausible but never went anywhere as far as I know.

Incidentally that means all their patents will have expired...

What if you use the technology in places where you actually want to maximize heat conductivity?

I'm thinking of the separation walls in counterflow heat exchangers (only useful at the end where the incoming stream is closer to its end temperature than the delta offered by thermoelectrics I guess). Can it do whatever it does across a temperature gradient?

that's an idea but would you not have to power each one which then destroys efficiency anyway

I didn’t know this, and it jumps out to me because 10k is pretty much the exact difference between room temperature and wine fridge tenperature - I wonder if this is actually not a horrible application for peltiers?

You can get 4 COP with a regular air cooled chiller and up to 7 COP if you add an evaporative cooling tower.

Variable frequency drives have made running pumps and fans a lot more efficient, even residential HVAC equipment is starting to get EC motors or VFD driven A/C motors. I can run my 10,000 BTU (1kW) window unit at 68F for an entire month in the summer and it only costs $50 due to the variable speed fans and compressor pump.

What’s the use case for peltier coolers, wearable cooling?

Thanks for the link. One of the projects I'll probably never get around to is a thermoelectric-augmented fan coil unit for air-to-water heat pump retrofits. The existing emitters (and crucially the in-wall distribution piping that's expensive to insulate and vapor seal after the fact) would stay just above the dew point, and then the augmented fan coil would work to remove latent heat (humidity) by dropping a bit below the dew point via thermoelectric coolers that reject heat into the return piping.

It's a relatively small delta-T and in most climates a relatively small fraction of the overall cooling load, so it might just barely pencil out.

Nah. Heat pumps are ~10-100x more efficient than thermoelectric. Thermoelectric is just inefficient mechanism and is inherently difficult to scale up as the more electricity gets generated so does more heat which inhibits the temperature gradient you’re trying to utilize. There’s a reason water cooling is preferred instead of peltier to ferry heat away from electronic.

Magnetocaloric is super interesting though as an alternative to heat pumps. Likely the next big revolution in this space.

> Mechanical cooling is extraordinarily space consuming.

You'd wind up taking up even more space with a TEC solution at these efficiencies. To replace a 5-ton condensing unit you'd have to reject on the order of 50-100kW of heat.

Wait, won't thermoelectric cooling need a LOT more surface area to have any comparable cooling performance to compressor-based systems?

For sure this doesn't replace mechanical cooling.

But efficiency is extremely important in this context, not just for saving energy, but because the inefficiency manifests as heat generated, which undermines the intended refrigeration. So as far as Peltiers go, a doubling of efficiency is like a 3x ~ 4x improvement in effectiveness. Peltiers are already used for cooling in some contexts (eg. cooling CCDs) and this greatly grows the envelope for where they can be effectively employed.

I'm not sure why we would want to replace mechanical systems. A portable AC unit with 10,000 BTUs uses ~650wh these days, and it'll turn a 50m^2 apartment into an icebox. That's not much more than a flagship GPU pulls. This is also about the least efficient class of aircon you can get.

Sure less energy usage is always better, and if we could get the same out of mere single digit wh power draws that would be cool. But I don't think thermoelectrics are ever going to get us there.

IIRC there is an application in solar panels where thermo electric cooling could play a role if we could get the efficiency just slightly higher.

I’m not sure what they mean by “traditional materials” here, but from their paper the COP is in the range of 1.3 - 6.8 depending on heat load which is similar to a modern household refrigerator. So yeah, it really does seem to be good enough to replace mechanical cooling.

The paper also references a Samsung hybrid refrigerator that already uses a thermoelectric device to improve efficiency (probably by letting the compressor operate in a more efficient mode most of the time).

According to the paper Samsung uses a bulk TEC device with a COP of 1.2 - 3 depending on heat load. That’s already fairly close to mechanical cooling. If it wasn’t it wouldn’t have made sense for Samsung to use it in a refrigerator whose whole selling point is efficiency.

I mean, clearly the 100% improvement is for the high heat load COP relative to that Samsung device, right? From 3 to 6.. and I think 6 is better than most commercially viable mechanical cooling solutions, no?

One step at a time... it would be astonishing if any thermoelectric device can leapfrog mechanical compressors.

> can't move the heat very far.

Heat pipes (as in CPU heatsinks) can passively move the heat up to a feet away. Far enough to allow effective insulation between cold and hot side. From there you can move the heat further away with a fan.

HN hasn't been a good place for technical discussion in at least 5-6 years, maybe longer.

X is much better for this kind of stuff these days (just follow the right people and stick to the following tab)

It’s the day before a holiday in the US. No one is thinking, we’re all just knee-jerk existing for another handful of hours and then… Then we engage in that once a year ritual of lighting up explosives and making a pilgrimage to the ER, where no one can afford proper treatment. /s

Happy 4th all!

(With apologies for the wildly off topic comment)

Presumably night vision on drones and missiles and things suddenly gets a lot smaller and deadlier?

I’ll watch your video later when I get home. Mostly leaving a comment so I can find it easier later.

Freezing food waste prior to composting it results in much faster breakdown in the compost.