[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.