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1. Embed this notice
   Rich Felker (dalias@hachyderm.io)'s status on Thursday, 02-Apr-2026 09:40:52 JST Rich Felker

   Hmm, inspired by toots about dynamo phone charging:

   Can you cool your body with a manual-cranked (probably by pedal) AC compressor? IOW can you get it to move more heat than the waste heat from muscle inefficiency?

   • Embed this notice
     cliffle@hachyderm.io's status on Thursday, 02-Apr-2026 09:56:18 JST cliffle

     in reply to

     @dalias ... I am thinking about this more than I probably should be

   • Embed this notice
     Rich Felker (dalias@hachyderm.io)'s status on Thursday, 02-Apr-2026 09:56:39 JST Rich Felker

     in reply to

     • cliffle

     @cliffle Successful nerd-snipe. 😈

   • Embed this notice
     Rich Felker (dalias@hachyderm.io)'s status on Friday, 03-Apr-2026 00:45:57 JST Rich Felker

     in reply to

     • smells of bikes
     • Alex von Kitchen

     @smellsofbikes @Dangerous_beans That's probably assuming body cooling from ambient air (and particularly the airflow over you if you're biking).

     I didn't state this but I was thinking in a more awful hypothetical wet bulb survival type of situation, like if there was no way to move off body heat via ambient air but you had access to food and a manual-crank compressor.

   • Embed this notice
     smells of bikes (smellsofbikes@mastodon.social)'s status on Friday, 03-Apr-2026 00:45:58 JST smells of bikes

     in reply to

     • Alex von Kitchen

     @Dangerous_beans @dalias I lean towards yes if you are an avid cyclist because you can crank out a fair amount of power without much effort. People who do something physical a lot get more efficient at it. I can produce 125 watts indefinitely without sweating. People who don't bike would be working hard to do 75.
     There's an xkcd about how fast you would have to ride for compression heating to warm you up.

   • Embed this notice
     Alex von Kitchen (dangerous_beans@aus.social)'s status on Friday, 03-Apr-2026 00:45:59 JST Alex von Kitchen

     in reply to

     @dalias maybe? Apparently muscles are 20-30% efficient, and coefficient of performance for an air conditioner is 3.5 to 5, so it's close

   • Embed this notice
     Gantua (gantua@pleroma.marchera-pas.fr)'s status on Friday, 03-Apr-2026 03:32:34 JST Gantua

     in reply to
     @dalias This sounds like a violation of the second principle of thermodynamics.
     
     Your body+compressor would be a thermodynamic system that can cool itself using only its internal energy without any external power being applied to it.
     
     In practice, cooling without access to a cold source is very inefficient.
   • Embed this notice
     Rich Felker (dalias@hachyderm.io)'s status on Friday, 03-Apr-2026 03:33:07 JST Rich Felker

     in reply to

     • Gantua

     @gantua Heat pumps don't violate thermodynamics. They utilize the otherwise unusably hot ambient bath to move off heat by raising the temperature of the refrigerant above that through pressurization.

   • Embed this notice
     Rich Felker (dalias@hachyderm.io)'s status on Friday, 03-Apr-2026 04:28:28 JST Rich Felker

     in reply to

     @gantua Yes they can! Heat pumps move away [generally, a lot!] more heat than the work and waste heat that power them, combined. This doesn't violate any thermodynamic laws because they're just moving that heat somewhere else, generally to a "cold source" that's so large it can be approximated as a fixed-temperature cold bath. This cold bath is what makes it not a closed system.

   • Embed this notice
     Gantua (gantua@pleroma.marchera-pas.fr)'s status on Friday, 03-Apr-2026 04:28:30 JST Gantua

     in reply to
     @dalias heat pumps can move heat from a hot source to a cold source when external power is applied to them, because you ignore the heat produced by the external power generator.
     
     If you stop ignoring the heat produced by the external power generator and include it into the hot source, the resulting system cannot cool itself.