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Staying cool without refrigerants: Next-generation Peltier cooling

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Re: Staying cool without refrigerants: Next-generation Peltier cooling

#81

Post by tasty_freeze »

theluketaylor wrote: post #59
bob1029 wrote: post #29

Earlier quoted context omitted.

I've been thinking about what it would look like to convert my GE fridge into a minisplit (i.e., move the compressor, condensing coil & fan outside). You can buy R600a on Amazon right now. One $60 can will charge the system ~5 times.

With home HVAC, fridges, water heaters, and dryers all using now able to use of dependent on heat pumps I wonder how long it be before we see modular appliances that connect to coolant lines where the temperature differential is supplied by a central high efficiency heat pump. Cars already have heat scavenging that can move heat from where it's being created through losses to places where it's valuable, like the cabi…

That is an interesting thought, but I assume that the working ranges of the different appliances are different so there would be some complexities and inefficiencies getting them all connected to a common circulation loop. If there was a thermal equivalent of a transformer used for alternating current, that would be amazing.

Re: Staying cool without refrigerants: Next-generation Peltier cooling

#82

Post by szvsw »

closewith wrote: post #15
szvsw wrote: post #13

Earlier quoted context omitted.

FWIW, in a typical apartment or single-family home, refrigeration uses a fraction of the energy that space cooling (also via a refrigeration/vapor compression cycle) requires on a warm day (and probably year round too unless in very mild climates). The psychrometric chart path is different so there are of course differences in the amount of energy required for the sensible and latent components, but the real differen…

Definitely not the volume of air. The thermal mass of air is tiny. The difference is in the thermal mass of the building and the surface area exposed to the sun.

Sure I was playing a little fast and loose there, but (a) the large surface area of the home (and resulting conductive transfer through the walls + convection transfer via infiltration through gaps) is directly a result of the fact that you need a significantly larger volume for humans to move around in and live in than you do to store food and (b) even if we do look directly at the volume of air, the difference is significant since at the end of the day, since for any given constant deltaT, your energy spent is still linear with mass or volume. And we are talking about roughly 2-3 orders of magnitude difference in air volume between a house and a refrigerator.

Anyways, if you write out all of the heat balance equations, you get a few W/m2 of flux on the inside wall of the home and a few W/m2 of flux on the inside faces of the fridge, assuming a typical wood frame construction in summer time and steady states all around.

So yes, of course multiplying the flux through the home’s wall by the surface area of the home results in a massive heat gain value compared to the heat gain conducted through the surface of the refrigerator, but that’s arguably precisely because of the two different volume requirements.

Re: Staying cool without refrigerants: Next-generation Peltier cooling

#83

Post by szvsw »

rcxdude wrote: post #69
closewith wrote: post #15

Earlier quoted context omitted.

Definitely not the volume of air. The thermal mass of air is tiny. The difference is in the thermal mass of the building and the surface area exposed to the sun.

Also the area that needs insulating, and in the extremes the amount of air that needs to be exchanged with the outside to make the house livable, and the heat generated by the people living in it (stick a 100W lightbulb in a fridge and see how cold it can get). The insulation is actually solvable, and for heating can basically remove the power requirements: a house heated and using heat exchange on air leaving vs ent…

Yep, PassiveHouse standards which typically include an extremely tight envelope which forces installation of outdoor air supply famously can get away with just a few hundred watts of heating capacity because of heat exchange on the incoming and outgoing airstreams!

Re: Staying cool without refrigerants: Next-generation Peltier cooling

#84

Post by rcxdude »

fghorow wrote: post #27

For those worried about tiny COPs from these gizmos, trawling through the actual paper -- as well as the PR from JHU APL -- in this HN post [1] shows claims of COPs of ~15 for Delta Ts of 1.3°C. 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…

ugh, reading the paper, their methodology is kinda crap. They basically just guess what the thermal resistances in their system are, and use air temperature measurements to figure out the heat flow. This is not how to measure heat flow accurately. It might be OK as a comparison with whatever TEC they tested with, maybe, but it's not at all something I would trust to compare to another test setup. If their box is more insulative than they think it is, their results are gonna look better than reality. This can be validated at least approximately by just putting a heater in the box that's dissipating a known amount of heat and looking at the temperature rise, but it seems they didn't even do this. And in general the regime where you've got small temperature differences is where your systematic error in a system like this can become huge and distort the results by multiples.

(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)

Re: Staying cool without refrigerants: Next-generation Peltier cooling

#85

Post by electroglyph »

delusional wrote: post #39
duskwuff wrote: post #5

Earlier quoted context omitted.

> I've wondered what became of the tech. Remember that Peltier coolers don't make heat disappear - they just move it from one side of the cooler to the other, and produce a lot of additional waste heat in the process. There are better ways of transferring heat from a hot IC to a heat sink nowadays - like liquid cooling for really high-performance systems, or capillary-action heat pipes for more typical needs.

> There are better ways of transferring heat from a hot IC to a heat sink nowadays Peltiers were always a bad way to move the heat. What they offered was the ability to go below ambient, which at the time could improve overclocking. Peltiers of course lacked the capacity to actually take you there with any decent load, but in theory it could. It never really made much sense for consumers, and once consumers realized…

peltier on the liquid reservoir might be worth trying...

Re: Staying cool without refrigerants: Next-generation Peltier cooling

#87

Post by mousethatroared »

nine_k wrote: post #19
cosmotic wrote: post #9

Earlier quoted context omitted.

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 frid…

"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...

Re: Staying cool without refrigerants: Next-generation Peltier cooling

#88

Post by burnt-resistor »

WarOnPrivacy wrote: post #2

I used peltier coolers on K6 processors 1M computer years ago. They worked great and lasted about as long as the PCs did. Not long after I bought mine, they disappeared from cooler offerings. I've wondered what became of the tech.

They made both the problem of power consumption and removing waste heat infinitely worse. Instead, I used liquid cooling with a copper block on one side and a heater core from an RV on the other. It was so efficient, it didn't even need a fan so long as the radiator fins remained somewhat vertical. I recall it used a pink additive to distilled water. That was bank in the day when you had to make double sure the very large PVC tubing was kink free, clamped properly, and oh the joys of removing air from the system.

Re: Staying cool without refrigerants: Next-generation Peltier cooling

#89

Post by Sharlin »

elzbardico wrote: post #79
Tistron wrote: post #16

What I want is a silent refrigerator, will this bring that? pray

Move it outside a cabinet, let it free stand. I found out that my nice kitchen niche for the refrigerator acted like a nice resonance chamber for the frequencies the compressor generated. I can barely hear it now.

If the cabinet is poorly designed (or ventilation is otherwise obstructed), it will also retain heat, making the fridge have to work harder.
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