Cool rooms are as important as cool people! Stop underestimating them, I warm you!

Heating is just a warm jumper. Energy sounds more like a gimmick on it's own but cooling, now that is interesting.

Have wondered about water cooling my sofa but not sure how easily to get tubes you can lay on and pump water through and be comfortable to lay on. Cooling the water is fairly easy, ice cubes short term and heat pump aquarium chiller if you want it to run for a long time is probably the most reasonably sized/priced option.

Modifying an old fridge or freezer could also work if you drill a hole through it to have a bucket inside cooling down and pump water from that.

Having a big hand-made tank of water in the house is overall a bad idea. Having a thermo-accumulator in a region where the idea of water-cooled sofa doesn't sound too crazy is even worse idea.

You can buy buckets for very little. Why is it a bad/worse idea?

The water container obviously depends on how you are cooling it, if its in a fridge then it needs to fit but if using an external chiller you could use pretty much anything.

Was gonna do this to some servers once, but for something as thermally insulative and porous as couch fluff, I'd try water cooling a radiator in the couch that just moves cold air throughout

What kind of radiator though? Normal radiators are solid and not comfortable to sit on.

I'm thinking something like an AC one, bout halfway between the bottom of the ass to the ground, the just a little box fan or so to move the air around.

Kinda like some cars have for the seats.

If its a fan wouldn't it be cooling the room rather than the person? The idea is for it to be highly targeted to largely just be cooling the person.

No no I'm thinking leather couch, the fan in where the springs and stuff are to keep the air contained (enough), but also blow the fan with the coldest air right at the ass.

So like its water advection from fridge to radiator, conduction from radiator to the air/fan, then advection to almost right up to your ass where it conducts to the leather.

There is foam inside the sofa though. How are you sticking fans inside that? This is part of the keep it comfortable problem. If tubes can be made comfortable enough then they are probably a decent option. Or perhaps a cold blanket ontop instead?

Remember water which isn't sterile (and manipulated in a glove box under sterile circumstances) accumulates mold, bacteria, assorted nasty protists etc.

Depends on what you do with it, but yeah. Got an aquarium so aware of some of the things water can like doing if neglected. But for a bucket cooling reservoir you could also just add chemicals to keep it clean enough or replace it periodically.