I recently had a discussion about ACs and how they heat up cities.

Then I found an article about theoretical increase of efficiency of acs by using the heat pulled from a room to run a thermoelectric device and getting some of the energy back that was used in the ac.

I‘ve had this downstream thought many times already: since hot air is basically just energy stored. Could we theoretically pull (all?) the energy from the air (depending on desired temp) to cool it and casually fuel our society’s energy needs?

  • Hacksaw
    7·
    10 months ago

    If you only had access to the coal furnace you couldn’t make power. The coal furnace is hot and it’s surrounded by room temperature air. The furnace really wants to heat the air around it and the air wants to cool the furnace because nature generally doesn’t like large differentials. So what we do is we force that heat to turn an engine before it can get to the cool ambient air.

    It’s like a putting a turbine in the way of a waterfall. The water wants to fall, so we force it to turn an engine before it can get to the ground.

    So back to your initial question, an AC is a heat pump. It pumps heat from the cooler inside to the warmer outside. It’s just like if we pumped the the water from the bottom of the waterfall to the top. Yes you can than use that water to generate energy, but you’re the one who pumped it up there in the first place so it’s a bit counterproductive.

    • Haui@discuss.tchncs.deOP
      1·
      10 months ago

      Thats an awesome explanation! Thank your very much!

      So, from this and many other comments and some independent reading on my side, we‘re technically just walking batteries getting fed by the sun, being buried under ground after dying and becoming coal so to speak.

      So, theoretically, we would need to build some way to exhaust the excess heat into space (and could also get work done in the form of electricity) if we wanted to use the current overheating earth to our advantage while cooling it off. Thinking of a giant ac at this point. :D

      But jokes aside, this means that the average laypersons idea about „energy“ is false. We need „work“, not energy. Because the dissipated energy can not perform work anymore. Correct?

      • Hacksaw
        1·
        10 months ago

        Sounds like you’re on the right track there. As far as energy goes, you’re right, when things are dissipated, or all the same, you can’t extract anything. You need a differential, like a hot place and a cold one, a high voltage and a low one, a fast object and a slow/stopped one, a high object and a low one. The higher the differential the more you’re going to be able to extract. If it’s too small you might not be able to get any useful work out at all.