Peltier vs. compressor-based cooling (2019)
labincubators.net
labincubators.net
An interesting project I've seen using one of them is this portable chiller suit to cool the human body on-the-go, intended for relief of Multiple Sclerosis symptoms [2].
For DIY/prototyping, there are a bunch of Chinese manufacturers now producing compressors of these sizes along with the appropriate driver board for the variable-speed AC motor [3]. I'm excited to see how this technology will be applied elsewhere in time.
[1] https://aspensystems.com/vapor-compression-refrigeration/
[2] https://hackaday.io/project/4729-bringing-cool-relief-to-mul...
[3] https://web.archive.org/web/20220916231432/https://www.aliex... (archived as of time posted for future readers)
Isn't part of what makes these work also linear compressors? The old on/off models have gotten better over time, but when we were kids, some of them would practically cause brownouts on the electrical circuit. Too much startup current. So for electronics you need someone with a smoother transition.
That's because a compressor has an odd property... The motor requires substantially more starting torque than running torque. That's because the cylinder can be stuck on the compression cycle pushing against a cylinder of gas, and has no momentum to get it through. Also, the very first compression typically has far more gas in it (because the 'cold side' is actually warm before it starts).
If nothing were done to compensate, the motor would stall, overheat, and burn out.
Designers of fridge compressors have instead added a very high current starting coil, which will provide massive amounts of torque to get the thing going for a few seconds. Sometimes that might be 20 amps or more for a few seconds. When the motor is spinning fast enough, that coil gets disconnected.
On most air conditioning compressors today, a scroll plate compressor is used, which doesn't have the unloading problem of the piston type of compressor.
Just replied to the same comment wondering if this has changed. I used to help my dad install residential and commercial HVAC systems and all of the compressors back then were piston type. I would tick him off by getting impatient when we were testing by calling for cool too soon after shutting it down and tripping the thermal beaker. (Come on dad it's hot up here!!! lol)
I imagine the scroll type are probably quieter as well and probably work nicely with inverter-based drives.
I did go back and look that there are sometimes valves used in scroll AC compressors. Even with that the full compression cycle is much more gradual, and continuous happening over ~3 revolutions of the compressor instead of half a revolution for a piston so there's not a slug compressed gas to hold the compressor back in the same way as a piston compressor.
This pages has some diagrams that shows the spiral plates and compression cycle pretty well. https://www.sciencedirect.com/topics/engineering/scroll-comp...
Not sure if that applies to newer systems.
> Vaseline is popular as it is a fairly easy application and can usually be removed by running the motherboard through a cycle in the dishwasher.
https://www.icc-usa.com/prepping-a-system-for-subzero-overcl...
People trying to break over clocking records just use liquid nitrogen: https://m.youtube.com/watch?v=WwJvHJ1hyto
How much power do those mini refrigeration compressors draw?
https://singledoorrefrigerated.com/red-bull-mini-fridge-for-...
There are now also some similarly sized compressors from other manufacturers as well, some that run on 12v. Lots of other options other than aspen.
Either I am misunderstanding what is being said there, or the article author misunderstands how physics works.
The self heating (for better or for worse) of a peltier is generated at the cooling chamber edge.
This is in excess of the heat being removed from the refrigerated area.
Air conditioners have the warm-running compressor outdoors, but refrigerated indoor appliances release that heat into the room along with the heat transferred from inside the refrigerator. And then the AC encounters further inefficiency as it next removes this heat from the room.
Even the motor of a ceiling fan warms up a room (gradually) if there is no AC and windows/doors are not open adequately to let that heat escape.
Ceiling fans have big motors and are best outdoors like at a tiki bar.
https://www.meerstetter.ch/customer-center/compendium/71-pel... has some nice plots and explanation of how performance varies with deltaT.
A constant current driver can also be important - PWM results in increased joule heating. For 50% maximum constant current joule heating is (V/2)^2/R but when duty-cycling with 50% PWM, it's V^2/(2*R). Moving the scaling factor out from under the ^2 makes the savings more pronounced at lower deltaT as well. But constant current is more complex, especially with larger peltiers.
I cants really speak for Carnot cycle coolers, but they can often be effectively duty-cycled and can be placed remotely so the compressor waste heat can be vented into the room. Performance still degrades with dT though.
On the other end, you can for some applications, use "R-290" which is just highly pure propane. Typically waist high commercial ice cream freezers will use a fully sealed R-290 system.
And finally there is also "ammonia phase change" refrigeration, which can be done with a compressor, but also a "generator" which is essentially just a propane or electrical boiler which creates the high pressure side of the system, also with no moving parts. You will typically find these in highly portable and mobile applications, such as RVs.
Their other experiments are worth a read as well :)
The tubing isn't pinched shut, it's just pinched to restrict the flow. I believe it's to create a bottleneck where pressure can build up between the "hot side" and the "cold side" of the refrigerator. Before the pinch the compressor is driving gas into the pipe, where it meets resistance at the pinch point and compresses to liquid, shedding heat. Then after that point a narrow jet of compressed refrigerant squirts into a lower pressure part of the pipe and starts to evaporate, expanding and taking in thermal energy again.
Of course, the refrigerator already has some valve to do this, but the author mentions that it may not be designed for the pressure differential needed for propane, so you can make your own with a pinched tube.
Liquid refrigerant flow is restricted when it flows through the orifice. This causes the pressure to drop which causes the refrigerant to flash/boil. While the refrigerant is flashing/boiling, it is absorbing heat from the surrounding environment.
Ideally the charge amount should be such that the evaporator is fully frosted, but not much more than that.
The basic way of working it is basically
* lowering the pressure of gas causes it to cool, increasing it causes it to heat
* creating standing wave in a gas in pipe means the low pressure part will be cold, high pressure part will be hot, and the difference will equal to basically pressure induced thermal difference
sooo a fancy speaker in the tube. Already stuff that can be bought, just didn't get to the level required for consumer stuff.
Supposedly they can be pretty efficient too. Would also be basically noiseless, as the ultrasonics are limited to the cooling tube and easier to dampen anyway.
https://blog.vinfolio.com/2016/09/13/does-vibration-ruin-win...
EDIT> For a reaction A + B -> C, the more chances molecules of A and B have to get into contact, the faster the reaction could run since chemistry is just atoms bumping into atoms. Stirring or shaking can bring more unreacted A's and B's together.
European energy is super expensive right now, fridges normally use quite a lot of energy, and peltier fridges use quite a lot more than normal fridges.
In case you are unaware: The European efficiency rating system is in fact percentile-based on some fictional reference appliance which is adjusted every few years [0].
A fridge with an "A" rating you bought 15 years ago would not get an A rating today.
(This sounds weird, but fights the problem that when the system was based on absolute values instead of percentiles, nearly fridges started being rated A, A+, A++ or A+++ to the point that the scale was very opaque to consumers.)
[0] https://en.wikipedia.org/wiki/European_Union_energy_label#Re...
Well, some of them do.
Unless the genius who designed your kitchen put the fridge directly next to the dishwasher, whose job it is to keep hot steam inside for a long time.
Yeah, don't put the box full of hot steam next to the box filled with cold stuff.
(I rent, so I can change nothing about this arrangement.)
How is it possible to use more energy, but produce less heat? Are they comparing a tiny peltier cooling box to a full sized refrigerator?
EDIT: I guess you could argue it produces less heat if it moves less heat from inside the refrigerator, but that's not really an upside
I'm not aware of any point in the input/output temperature chart where peltier wins on efficiency.
It doesn't appear this article will make it clear if such a thing is possible, since it lacks any hard numbers relating to the technologies it is comparing.
Here's an example: https://www.amazon.com/dp/B07KZLJ7PB
Peltier coolers have one thing going for them- they have no moving parts*. That's it. Which means they still have their niche! But everything else about them is awful compared to other cooling solutions.
*in practice most applications use fans for the heat sinks.
This is why heatsinks on CPUs have fins: to increase the surface area where the heatsink is in contact with the (hopefully cooler) surrounding air. The windings of a radiator are very much the same idea.
In a traditional compressor based system this huge surface area is the radiator in the back and technically it also only "moves the heat" to the surface of that radiator. But give the size of that radiator it will be effective at transfering that heat to the surrounding air.
A peltier cooler with a smaller surface area needs a heat sink and or some form of active cooling (airflow, water etc).