Converting waste heat from refrigerators to electrical energy

[Apache]

How can I preserve energy dissipated out from some devices that always extract heat like fridge?
Do you guys have some alternatives or ideas to convert heat energy to electrical energy that can supply some sensors and indicators?
Thanks!

 

[mfb]

Your question looks a bit unclear to me. What do you mean with "preserve energy"?
Energy is conserved, and if you cool one object, you have to heat another object due to entropy.

Do you guys have some alternatives or ideas to convert heat energy to electrical energy that can supply some sensors and indicators?

If you don't need much power and just want to save cables: Thermocouples?

 

[Apache]

I mean convert the heat dissipated out from device to other form of energy and used for other purposes. Normally we just treat them as heat loss because temperature is too low and it is not much efficient to be converted. So now I am trying to convert heat dissipated from condenser of fridge to electrical energy.
I was thinking like making the air inside a piston to expand after heating by heat dissipated out from condenser under constant pressure.
Under expanding and contracting of piston, the piston drive a simple crank and thus drive a dynamo.
The dynamo then save energy to supply some low voltage, low current drawing electrical elements like thermostat and sensors.
My fundamental in heat is not strong.
Looking forward to some advices. =)

 

[mfb]

I mean convert the heat dissipated out from device to other form of energy and used for other purposes.

You can get a small fraction of that, but the process cannot be very efficient (in absolute numbers) as the temperature difference is small. Even worse: to make it more efficient, you have to make the fridge less efficient. You cannot win that game, and basically everything is too expensive if you just get something like 1W (-> 9kWh per year).