I've seen someone do something slightly like this with a greenhouse. It had a large tank of water in the middle. It was black, so it absorbed sunlight during the day, heating the water, and then that kept the temperature up at night.

I think it also had something to do with an aquaponics setup? Like there were either fish in the tank, or in a "pond," and fish shit water would be cycled out to the plants because fertilizer?

So a bunch of the other comments have mentioned this but you would be creating a thermal battery essentially. These can be useful for smoothing out the temperature changes in that room but it isn't exactly efficient since the only way to heat or cool it is by changing the temperature at the surface of the container.

Adding passive heat sinks like radiator fins would increase the efficiency as it would absorb or diffuse the temperature difference with increased surface area but it would still would be subject to things like the air conditioning turning on and off more regularly when there is a higher ambient temperature delta or condensation when the weather is hot and moisture is high. You've essentially added an inactive water boiler tank in the middle of a room that takes up space and takes a long time to either heat up or cool down and it still would be lagging behind where you want the temperature to be.

You're on the right track to a good idea with trying to store thermal energy but it can be made better with a few tweaks:

• Let's make the tank part of an active system by adding pumps and a heat exchanger that integrates with your current air duct system (assuming you have one). We can heat and cool the tank directly instead of passively so that our time and energy is directed more efficiently.
• Insulate it so that we minimize any unwanted heat changes
• Move it to a utility room or outside so you aren't taking up room space

Now we have a thermal battery that works with your air conditioning system as opposed to against it. This can be paired with other methods of heat/cooling such as a solar system.

But if you're in a dorm or somewhere you can't make changes, it could make sense if you aren't paying for electricity, you actively heat/cool the bucket by putting it in a freezer or on a heater/fire, and you don't mind a large metal container in the middle of the room? Just watch for a lot of condensation when cooling the air.

You see this with normal heating systems. My house has hot air heating with a big burner and vents in the rooms. It is great for instant heat but once it turns off you lose the heat just as fast. And if you dont have a vent in the room it can be pretty cold.

But the house I grew up in had water filled radiators in every room. Took ages to warm up the house but it would transfer an awful lot of heat into the brick walls so it would stay warm for a really long time after the heating shut off.

So in the old house in winter you really didnt notice the heating turning on and off but in my new one it is painfully obvious. I really want to rip it out and get a better system.

Yes, this is called thermal mass, or more scientificly, heat retention. The more stuff you in have a space, the more resilient to change it'll temperature it is. Insulation, is basically putting a bunch of high retention materials in perimeter of a building so that it stays more consistent

I don’t think it’s a dumb question at all. I’m not a physics person but I think what you’re describing is a thermal battery. It’s the reason people put tiles in their ovens for smoothing out hot and cold spots and moderating temperature swings from the oven cutting on and off or opening the door.

Sounds like adobe sorta.

Lots of places in the desert with big walls.

Useful? No, mainly because you need circulation of the air to feel it.