You might find this video interesting:
He references this Wikipedia page which contains info on the thermodynamics of rubber bands:
Applied Science is a great channel. The guy builds all kinds of wild stuff including his own scanning tunneling microscope. It’s fun watching him solve problems.
Sometimes I feel like I’m shouting into the void…
The energy loss is the same as if you had compressed a piston, let the hot gas cool, and then let it expand. You get back less mechanical work than you put in, but can use it to pump heat (in either direction).
At any rate, I second that Applied Science is a great channel.
Vacuum chamber will definitely slow the heat transfer. But it will radiate.
If you were directing that at me, I did see what you said. That’s why I thought you and others might like the video - a direct application of the thermodynamics of rubber bands.
If you thought I was trying to make the point you already made, my apologies. I wasn’t very cleat about that.