Hacker Newsnew | past | comments | ask | show | jobs | submitlogin

> So ask yourself, if more energy came into your home than you put in from the electric socket, where exactly did the extra energy come from?

I notice you didn't answer this question.



I did. The question is for you. I've answered it in several different ways in this thread. There is a sibling comment I replied to which breaks it down even more clearly.

You used the energy from the wall socket to pump the heat from outside into the inside, less efficiently than you could use that heat to generate more electricity or do other work later.

Aka you pumped the energy inside and concentrated it a bit. You didn't generate more energy than you had before. You did make existing energy more useful for you, comfort wise.

Actually operating one, you'll see that the energy cost of a heat pump becomes proportionally higher as the temperature difference gets bigger, so you spend more energy moving the heat when the source is low temperature and the output is high temperature.

Many people have gotten quite frustrated when they end up chilling the ground in their ground source heat pump too much, and they end up with very inefficient systems.

You could do the exact same thing (with better or similar efficiency) by using some other source of thermal mass. Air sourced heat pumps do it with the atmosphere. It's possible to use lakes and other bodies of water.

No net usable power is being extracted from the earth in this scenario. The earth is being cooled in order to heat your house. And heated, in order to cool your house.

Geothermal power systems do produce actual usable power, and they do so by running a heat engine (the opposite of a heat pump) off an extremely large temperature difference from a very large source of underground heat. You can't run a heat engine on the output of a heat pump and produce net power, anymore than you can hook a generator to an electric motor and produce net power.


I quote:

>That is not what ‘power source’ means. You probably want to read up on some thermodynamics and definitions. I’m guessing you think that if you connect the heat pumps output to it’s input, you’ll have infinite energy?

There is no answer in that whole comment to my question. However, you did answer it in the comment I am replying to:

> you pumped the energy inside and concentrated it a bit.

Yes! That's exactly right. But furthermore:

> You didn't generate more energy than you had before. You did make existing energy more useful for you, comfort wise.

This is exactly right, and it is also known as the first law of thermodynamics. [1]. There is no way to produce energy. Even with electrical generation from geothermal, we are moving energy and concentrating it a bit, as you say, just in different forms.

[1] https://en.wikipedia.org/wiki/First_law_of_thermodynamics


Haha, no. In geothermal, you aren’t concentrating shit. Rather the opposite. You’re just moving it down the entropic slope/dissipating it.

And converting (lossily) the form (usually, unless you’re doing geothermal heat - even then you need a heat exchanger).

And it all boils down to ‘within an enclosed system’. With heat pumps the scope is typically within a hundred meters of itself.

With deep geothermal it’s 1+ mile underground and the surface.

There is useful power between 1+ mile down and the surface. There isn’t 100 meters away and the surface - unless you’re sitting on top of a hot spring anyway.


> You’re just moving it down the entropic slope/dissipating it.

Agree on this, however

> In geothermal, you aren’t concentrating shit.

This one is a matter of opinion depending on scope so I'll disagree. You are concentrating it where it's useful. But overall system entropy goes up.


In geothermal, Heat is moved from where it is concentrated (underground) to where it is less concentrated (atmosphere).

There is no point I’m aware of in the process where something gets more hot than it started.


Ground source heat pumps absolutely do concentrate heat. See e.g. https://edwardsroyalcomfort.com/how-warm-does-geothermal-hea..., typical ground temps are around 60F and system output is above 100F.




Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: