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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

#51

Post by rcxdude »

moffkalast wrote: post #34
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…

15 is absurd, regular peltiers get like 1.05 at most don't they? That's like inventing the warp drive but for cooling.

You can get a COP of ~3-4 out of regular TECs, but only at pretty low temperature differences. That's the killer, fundamentally the TEC material itself is thermally conductive and heat really wants to flow back the other way, so no matter how well it moves the heat, it winds up fighting against the heat load generated by itself. A refrigerant based heat pump works much better because the heat basically only moves in the direction the refrigerant itself is moving.

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

#52

Post by tormeh »

iLoveOncall wrote: post #35
NuclearPM wrote: post #33

Earlier quoted context omitted.

Why?

Not OP but it's a massive nuisance if you live in a studio. People don't realize how noisy a fridge is until there's one in the room that they sleep in.

Skill issue on the manufacturer's part. I live in a studio and never hear the fridge. This is part of a fitted kitchen, though, but I doubt the panel hiding the fridge makes that big of a difference.

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

#53

Post by bluGill »

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…

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)

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

#54

Post by HPsquared »

ethan_smith wrote: post #20
anticensor wrote: post #4

Did they solve the inefficiency problem of peltiers?

Traditional Peltier devices operate at ~10% efficiency (COP of 0.5-0.7) compared to vapor-compression systems (COP of 2-4), but recent advances in thermoelectric materials like bismuth telluride alloys and segmented elements have pushed lab efficiencies to ~15-20%.

It's clearer to think in terms of "efficiency relative to ideal Carnot efficiency".

Compressor systems use twice as much energy as an ideal system, while Peltier systems use about 10x as much.

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

#55

Post by bob1029 »

esseph wrote: post #46
Tistron wrote: post #16

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

You can hear your refrigerator???

The latest wave of appliances is really fucking loud for some reason.

I think they're using different kinds of motor windings, bearings, insulation, etc. it's not related to the refrigerant or other system parameters. I've had older r600a fridges that were dead silent compared to anything sitting in a Best Buy showroom right now.

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

#56

Post by dijit »

nandomrumber wrote: post #32
palata wrote: post #30

Earlier quoted context omitted.

> You hear that you shouldn't let your fridge go above 4°C Really? My fridge says 8°C, I think?

Between 3°C and 5°C is the recommended refrigeration temperature

https://www.which.co.uk/reviews/fridges/article/how-to-store...

Christ.

I also run my fridge at 8C, which I think was the default setting when I bought it.

Gonna go change that right now.

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

#57

Post by userbinator »

palata wrote: post #30
mort96 wrote: post #28

Earlier quoted context omitted.

> Normal fridges just let the temperature have a wider swing which is good enough for most needs. These wide swings annoy me. You hear that you shouldn't let your fridge go above 4°C, because that's dangerous. And you obviously don't want your fridge to go below 0°C. But finding a setting where the hottest part of the fridge doesn't go above 4°C (or even 5°C or 6°C) during the hottest part of the cycle and the coldes…

> You hear that you shouldn't let your fridge go above 4°C Really? My fridge says 8°C, I think?

8 degrees or just 8 on the 1-10 scale that many of them use?

(I always remember the recommended fridge temperature as 40F, which avoids the confusion.)

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

#58

Post by mort96 »

javiramos wrote: post #42
mort96 wrote: post #28

Earlier quoted context omitted.

> Normal fridges just let the temperature have a wider swing which is good enough for most needs. These wide swings annoy me. You hear that you shouldn't let your fridge go above 4°C, because that's dangerous. And you obviously don't want your fridge to go below 0°C. But finding a setting where the hottest part of the fridge doesn't go above 4°C (or even 5°C or 6°C) during the hottest part of the cycle and the coldes…

You should buy a fridge with a fan in the cooling chamber. My Samsung fridge has a nice fan and associated ducting to circulate air and keep temperatures ~uniform.

I may consider that the next time I buy a fridge, but the reality is that this isn't something I care deeply enough about to buy a new fridge over.

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

#59

Post by theluketaylor »

bob1029 wrote: post #29
Tistron wrote: post #16

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

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 cabin or battery pre-heating. Especially in cold climates it feels like homes should be next.

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

#60

Post by madaxe_again »

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…

The delta of 1.3C is critical there - peltier cooling drops precipitously in efficiency as the delta increases, and struggles to hit a COP of even 1 in real world scenarios. Their figure works out at about 6.5% Carnot efficiency, whereas a normal heat pump is usually nearer 45% over a much broader range of temperatures, as you can separate the hot and cold sides completely. Not so with a peltier wafer.

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.

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