a question trots me for some time,
why do not we extract the energy of the fluids present on earth (water and air) by cooling them? the process requires energy, but could not this same energy be extracted from this same fluid? thus, the machine will feed a part of its production
There is no question of several sources of heat but of "could this same energy not be extracted from this same fluid" and therefore from a single source of heat !!
the answer :
This is a story of performance and temperature level (too low): in the current state of technology we can not self-power a heat pump .... but nothing in theory prevents it in fact. ..
In the future, if we develop PACs with COPs of 10 or higher and systems for converting thermal energy at low temperatures with good yields (1 / 3), then it is conceivable that a PAC can be self-powered. .
does not speak either of several heat sources, nor of Carnot, but of self-powered heat pump !! with in addition "good yields (1/3)" which leaves you perplexed because Carnot limits to deltaT / T is for 10 ° C between hot and cold at 300K a maximum ideal yield of 1/30 !!!
The new answer
We would not shoot with NOTHING but with the (weak) hot source delta source.
does not specify cold and hot sources.
The extreme case I know is the Atmos clock by Geiger Lecoultre which draws its energy from the movement of minute variations in temperature in a room (one degree is enough) with the cold and hot source in turn related to the minute temperature variations in the day. This clock that I own is a movement that goes back to life forever!
So we could make a PAC using the difference in temperature between day and night (10 ° C) with a compressor with engine using these same sources, what you suggest in your answer without specifying ??
I think the first question was not aware of the limits of Carnot's principle !!
But you can suggest as bone to gnaw, very useful, the realization of a self-powered PAC using as sources the difference in temperature between day and night, or that between air and earth, in winter or summer. and giving temperatures in the houses higher than those of the hot spring running the engine, and thus creating a third hot spring!
It would be a Canadian self-powered PAC well by the difference in temperature between well and outside air!
In my opinion nobody has considered it, nor tried seriously, but it is technically possible since during tests it was possible to operate engines with the temperature difference between surface and seabed (20 ° to 30 ° C).
It is possible to turn them into a fridge or PAC a priori !!