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Comment by ResNet | Hacker News Reader

It's worth mentioning the recent development of extremely miniaturized (soda can-sized) refrigeration compressors, such as those from Aspen Systems [1]; these allow for efficient cooling in small spaces that just can't be achieved with Peltier-based solutions.

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)

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I remember Adam Savage got something like these to keep from baking his noodle when he made the No Face costume for Comicon. I wondered when those sorts of things would show up for more general usage.

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.

> practically cause brownouts on the electrical circuit

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.

That starting coil can get stalled too, esp if head pressure is still very high. I did HVAC 30 years ago and back then you could reliably thermal-trip residential and commercial systems by simply turning them off then back on within 10-15 seconds. Motor would just hum for a few seconds then 'click. We'd always have to let it equalize for a minute or so before turning back on.

Not sure if that applies to newer systems.

The gas distribution part can be significantly compensated for by "unloading valves" of some kind—this is very common on piston air compressors—but with unloading, a major component of the starting torque is overcoming the angular momentum of the motor and compressor assembly. This is expressed as Locked Rotor Amps (LRA) on a compressor's spec sheet. There are devices that can limit the inrush current to about 25% of the listed LRA.

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.

>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.

Yes, they do tend to be quieter, and as far as I know are the only kind on inverter drive AC compressors. It's also a continuous process without having peaks and valleys in the motor load which probably lends itself to work well with an inverter drive, but I'd have to think about it a little more to say if that's accurate.

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...

I did HVAC work in the late 90's till the late 00's. At that time, only the really expensive, high SEER rating units were variable speed. Cheaper 10-13 SEER systems had scrolls but they were fixed speed.

Awesome, thank you!

That miniature Aspen system is quite amazing. I want one although I have no need for it at all.

That's really fascinating, thanks for the aliexpress link! I'm tempted to get one for regulating the fermentation temperature of beer. (A while ago I saw a peltier cooled rod that dips into the fermenter, but I bet this would be a lot more efficient! - https://web.archive.org/web/20220625100157/https://brewjacke...)

After losing power in southeast Michigan for 3 days, a couple of weeks ago, I began wondering about low-power cooling. Something like a couple of solar panels, a battery of some kind, then a fan for an evaporator "swamp cooler" or something similar. I'd like to be able to cool a single room occupied by 2 adult humans and a couple of 75lb dogs.

How much power do those mini refrigeration compressors draw?

Have you seen the new high emittance paints? You might skip the electricity step with new futuristic paint: https://www.coolingpost.com/world-news/radiative-cooling-pai...

Recently got one of these for one of our operators to put his Red Bull in, he loved it. Seems fairly efficient:

https://singledoorrefrigerated.com/red-bull-mini-fridge-for-...

That's interesting, why is it not being used by PC enthusiast. I haven't seen one incorporated as a PC cooling system.

Both peltiers (look for thermoelectric coolers on Amazon/Newegg) and phase change coolers are used by PC enthusiasts, but it’s not that common because regular liquid cooling is good enough for everyday use, and you don’t need to waterproof everything to protect against condensation when the cooler gets below the dew point. Not to mention mould...

People trying to break over clocking records just use liquid nitrogen: https://m.youtube.com/watch?v=WwJvHJ1hyto

Cooling below the dew point results in condensation. Moisture on a circuit board is bad

Inconvenience is no obstacle to over-clocking.

> 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...

I've tried to use those aspen compressors for several projects but was never actually able to buy one. They're unobtainable.

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.

I don't think it's that recent; water fountains and the like had very small compressors for at least a few decades. What's new is inverter drives.

Gas compressors are fairly different internally to water pumps.

I'm referring to the water fountains that serve chilled water and have a miniaturised refrigeration system.

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