[bigattichouse]

A lot of people throw around 5% efficiency for Peltiers, and it's just not true - it depends heavily on the temperature differential and current vs. IMax. You can (with care) drive them >2.0 COP.

This isn't anything like a compressor or heatpump system, but Peltiers get a bad rap... they move heat really well if you're not pushing them to the edge.

Here's a nice chart. At 10k difference and 0.1 current max, you're over 2.5 COP. https://www.meerstetter.ch/customer-center/compendium/71-pel...

[wrigby]

I didn’t know this, and it jumps out to me because 10k is pretty much the exact difference between room temperature and wine fridge tenperature - I wonder if this is actually not a horrible application for peltiers?

[NortySpock]

Found a wine fridge at the thrift store last month, pulled the model number, realized it was basically a Peltier cooler and a fan, and thus likely to be still operational. Powered up just fine, so...

$10 and an hour of deep cleaning later, and now we have a wine cooler in our basement. I don't recall the specs or power consumption offhand, but it does keep my beverage-of-choice a few degrees cooler than ambient. :)

[knowitnone]

power consumption is worst than compressor system

[frankus]

I think the gotcha is that you need a beefy heatsink and fan (and power for the fan) to keep the hot side anywhere close to room temperature.

[quickthrowman]

You can get 4 COP with a regular air cooled chiller and up to 7 COP if you add an evaporative cooling tower.

Variable frequency drives have made running pumps and fans a lot more efficient, even residential HVAC equipment is starting to get EC motors or VFD driven A/C motors. I can run my 10,000 BTU (1kW) window unit at 68F for an entire month in the summer and it only costs $50 due to the variable speed fans and compressor pump.

What’s the use case for peltier coolers, wearable cooling?

[frankus]

I'm not sure of the exact reasons but you don't really see vapor-compression heat pumps in the tens- to low-hundreds-of-watts range. So I suspect there are some scaling factors where the reduced size/noise/complexity of a solid-state device starts to be more important than the extra energy that it uses.

I think most of the commercial bed cooling systems are thermoelectric (ChiliPad, Eight Sleep) and they seem to work fine, but by the time you get to the scale of a small fridge or dehumidifiers the products are generally awful.

[londons_explore]

machining metal parts to tight tolerances when they're only a millimeter wide is awfully expensive.

But making tiny things with lithography is really cheap (in volume).

The middle ground is what one needs for a 10 watt vapor compression pump. And to my knowledge nobody has built a 1 watt pump with lithography - although an array of electrostatic scroll compressors does look like it could work.

[frankus]

Thanks for the link. One of the projects I'll probably never get around to is a thermoelectric-augmented fan coil unit for air-to-water heat pump retrofits. The existing emitters (and crucially the in-wall distribution piping that's expensive to insulate and vapor seal after the fact) would stay just above the dew point, and then the augmented fan coil would work to remove latent heat (humidity) by dropping a bit below the dew point via thermoelectric coolers that reject heat into the return piping.

It's a relatively small delta-T and in most climates a relatively small fraction of the overall cooling load, so it might just barely pencil out.