A compressor based cooler gets a COP of about 4 in the real world. I'm pretty sure this is an apples to oranges comparison to an expert (I am not one of those) but a factor of 3+ increase in COP is fairly noteworthy -- if it holds up.
(This is an area which is really hard and details matter. Heat is basically impossible to measure directly, and the indirect measurements are fraught with peril. Getting it wrong was a large part of why people thought they had demonstrated cold fusion)
That is, if you want to chill your cabbage to 4.3 degrees C, your room temp should be not more than 5.6 degree C. Or... if it's 25 degrees outside, in an ideal case your cabbage is 23.7 degrees cool.
Btw, max theoretical COP increases rapidly as T'hot - T'cold shrinks to zero. Your practical AC or fridge delta T is much more than that, depending on the weather.
What they’ve done here is add a point of failure, use additional materials as well as a traditional heat pump, and called it “AI” and “eco friendly”.
Never have I seen more prime VC bait.
And you dont get to stack Peltiers to increase COP, only to increase delta T.
Still, Peltiers are super cool and I have some ideas for their use od they get slightly better. Advances are super welcome.
I didn't actually have a use for it. It was just neat that it actually worked.
I understand the basic physics of it perfectly well. It's just one of those things where you expect basic physics to be overwhelmed by friction or something.
The thinness of Peltier devices bothers me. Amazing temperature differences… without any room to insulate such!
Unusually effective heat insulation is exactly how they work. (This is tempered by eg radiative losses, so making them thicker doesn't work better.) placing poorer heat (vs electrical) insulators between peltier material is counterproductive, similar to using resistors to improve conduction between copper wires
Don't ask me for a better explanation :)
As to why COP or even Carnot efficiency hasn't been thrown out in favor of temp-difference independent efficiency metrics like exergy.
I can't tell you either
I haven't seen it in any physics thermodynamics book, and only mech eng. seem to know what it is, and then only in the US.
Faires (undergrad MIT Thermo book from the 50s) makes no mention of it as far as I can tell.
But that isn't a mathematical expression. At best, it would appear to be energy * maximum_Carnot_efficiency (for heat engines anyway)
But it seems not to be adding very much, since Carnot efficiency depends on delta_(T). The OPs point that exergy doesn't depend on T is tautological since T has already been accounted for by the Carnot expression.
If one makes the walls thick, then they end up with a hole for the Peltier device and somehow sandwich two heatsinks on the device while maintaining insulation around it.
Perhaps easier to deal with in CPU cooling and such since one side is simply smacked into the thing being cooled.
The direct-contact neck cooling plates are an absolute lifesaver. Keep the sun off the back of your neck and chill one of the best heat sink locations exposed on your clothed body.
When I looked a while ago there wasn't really a clear winner or high quality unit. There is the "Coolify" series that are much more expensive but still somewhat middling reviews overall.
I'd say they are super hot, but it depends from which side you look at it.
Stacking a bunch of these Peltiers to give more temperature difference would give a pretty low CoP. Say, for a 13°C temperature difference you'd have to stack 10 of them and use 10x the power. It's even worse actually as the hotter ones have to also pump the waste heat from the cooler ones.
The design ΔT of ~10°C is the typical return-to-supply air ΔT.
Just an idea of course, but I'd not write new tech off as "ok but just 1.3 degrees who cares" when the claimed COP is so insanely good without first trying it out
A brick wall is on the heavy side and you'd be able to store a whopping 1/8 of a ton of AC in ten feet of brick wall. It'd save about 0.1kWh of AC power use. A whole house will have many lengths of wall but also multiple tons of cooling requirements, so that doesn't help much. And how are you going to distribute those small temperature differences without wasting a ton of power?
And that's after you figure out how to trap a temperature difference in your walls for more than a day.
>A compressor based cooler gets a COP of about 4 in the real world.
Real life refrigeration usually isn't very interested in a difference of 1.3 C. The Carnot COP for this temperature drop near ambient conditions is, I believe, around 200. When you consider a cooling technology relative to the Carnot efficiency (or COP) you get a better idea of what the efficiency means in practice. For an AC unit blowing 10 C air on a 40 C day, the Carnot COP is about 10, while real units get less than half that. But I think that's still better than the Peltier effect getting less than 10% performance relative to Carnot limits.
That said, 1.5C is tiny.
Might as well not use a refrigerator if your ambient temperature is that low.
One side would have been ~23C and the other 24.3C.
> is ~15 for temperature differentials of 1.3 °C.
I want to build a wine cooler in my basement ~20-24c, and I want it at ~16c. Is that low enough to be reasonably efficient?
They can be designed to move a specific amount of heat or to cool at some delta-T below the hot side (and due to inefficiencies the hot side can climb above ambient temperatures too, raising the “cold side” above ambient!)
I ran through a design exercise with a high quality TEC and at 8°C delta-T for a wine cooler you could expect a COP of around 3.5–4 (theoretically). This is pretty good! But below the 2.5V max to do that you’re only able to exhaust up to around 40W. For a wine cooler this is not so bad. For a refrigerator it’s a harder challenge because the temperature drops when the door opens, and if someone sticks in a pot of hot soup, it’s important to eject that heat before it raises the temperature inside to levels where food safety becomes a problem. For a CPU it’s basically untenable under load because it’s too much heat entering the cold side thus temperatures will rise.
https://fluffyandflakey.blog/2019/08/29/cooling-a-cpu-with-t...
Things often overlooked:
- Most TECs are cheap and small and come without data sheets, so people tend to become disillusioned after running them too hot.
- You have to keep the hot side cool or else the delta-T doesn’t help you. For a wine cooler this is probably no big deal: you can add a sizable fan and heat sink. For CPU cooling it becomes a tighter problem. You basically can’t win by mounting on the CPU; they are best at mediating two independent water-cooling loops.
- Q ratings are useless without performance graphs. It’s meaningless to talk about a “100W” TEC other than to estimate that it has a higher capacity than a “20W” TEC.
- Ratings and data sheets are hypothetical best cases. Reality constrains the efficiency through a thousand cuts.
When I think about TECs I think more about heat transfer than temperature drops. If you open a well-insulated wine cooler once a week then once it cools it will only need to maintain its temperature, and that requires very little heat movement. Since nothing inside is generating heat you basically have zero watts as a first-order approximation. For the same device mentioned above, it stops working below 1V, and at 8° delta-T that’s a drop in COP to around zero but it’s also nearly zero waste. If you were to maintain a constant 2.5V, however, it would continue to try and pull 40W to the hot side. This would cause the internal temperature to drop and your COP would decrease even though the TEC is using constant power. The delta-T would in fact increase until the inefficiencies match the heat transfer and everything stabilizes. In this case that’s around a 20° drop from the hot side, assuming perfect insulation.
Unlike compressors, TECs have this convenient ability to scale up and down and maintain consistent temperatures; they just can’t respond quickly and dump a ton of heat in the same way.
edit: formatting of list
It's like trying to swim against the current - the faster the river flows, the harder it is to move forward at the same rate.