Seebeck generator from placing water heater next to freezer

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Discussion Overview

The discussion revolves around the feasibility of using a thermoelectric generator to collect energy from the temperature difference between a water heater and a freezer placed side by side. Participants explore concepts related to energy conservation, thermodynamics, and potential energy harvesting methods.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether a thermoelectric generator could collect energy from the temperature difference between a water heater set at 130°F and a freezer at 5°F.
  • Another participant asserts that a perpetuum mobile is impossible due to the laws of thermodynamics.
  • Some participants argue that while conservation of energy is a valid concern, the insulation of both the water heater and freezer limits the energy available for harvesting.
  • It is suggested that a heat exchanger could be a more effective solution, allowing heat from the refrigerant to warm the incoming cold water, potentially reducing energy needs.
  • One participant mentions that heat recovery chillers already exist, which can simultaneously produce hot and cold water, but notes that such systems are not typically used in residential settings.
  • Concerns are raised about the practicality and efficiency of energy recovery from a residential freezer, especially in regions where air conditioning is prevalent.

Areas of Agreement / Disagreement

Participants express differing views on the practicality and effectiveness of using a thermoelectric generator in this scenario. There is no consensus on whether energy can be effectively harvested or if alternative methods like heat exchangers are more viable.

Contextual Notes

Participants highlight limitations related to insulation, efficiency of electric water heaters, and the specific conditions under which energy harvesting might be feasible. The discussion remains open-ended regarding the effectiveness of proposed solutions.

DWT
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Water heater is set at 130 degree f freezer is 5 degrees f.

Is it possible for a thermoelectric generator to collect energy from these placed side by side?

Would the extra energy used by the heater and freezer due to the presence of the generator cancel out and then some any energy that could be collected?
 
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If I read your question correctly, the answer is:
There cannot be a perpetuum mobile (PMM) in our universe. (Reason: laws of thermodynamics)
 
I am not suggesting a perpetuum mobile, i am asking more about conservation of energy. Since one thing is already hot the other cold couldn't we conserve some of that energy and give it back to grid?
 
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Short answer is "no." A freezer pumps heat from the inside chamber and exhausts it externally in its refrigeration cycle. The outside of the freezer gets warm.

It would be better to have the watersupply going into a water heater jacket where the incoming water is cold, and put your peltier device inbetween the jacket and water tank.

The reality is, its not cost effective.
 
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DWT said:
I am not suggesting a perpetuum mobile, i am asking more about conservation of energy. Since one thing is already hot the other cold couldn't we conserve some of that energy and give it back to grid?
The water heater and freezer are both insulated to prevent heat transfer. That's the opposite of what an energy harvesting device needs. So there really is almost no energy available to be captured and at an extremely low delta-T (because of the insulation), you get an extremely low efficiency.

Broader; the laws of thermodynamics do indeed forbid such a device from being useful, even if it isn't obvious how. The energy required to create your temperature difference must always be greater than the energy gained by harnessing it. In this case, it is particularly bad because most electric water heaters don't even use a heat pump (COP: 4:1), they use resistors (efficiency: 100%/COP: 1:1)
 
protonic_mass said:
Short answer is "no." A freezer pumps heat from the inside chamber and exhausts it externally in its refrigeration cycle. The outside of the freezer gets warm.

It would be better to have the watersupply going into a water heater jacket where the incoming water is cold, and put your peltier device inbetween the jacket and water tank.……

Or maybe just set up a heat exchanger between the two, so that heat from the compressed refrigerant fluid gets put into the cold water entering the tank? This would perform some of the work of heating the water and cooling the refrigerant, practically for free. Wouldn’t that reduce the amount of energy needed to do both jobs? Would probably work best when the water is in motion, so I don’t know how much of a savings it would be. Just a thought.
 
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LURCH said:
Or maybe just set up a heat exchanger between the two, so that heat from the compressed refrigerant fluid gets put into the cold water entering the tank? This would perform some of the work of heating the water and cooling the refrigerant, practically for free. Wouldn’t that reduce the amount of energy needed to do both jobs? Would probably work best when the water is in motion, so I don’t know how much of a savings it would be. Just a thought.
In fact, this product already exists: it's called a heat recovery chiller. It makes process hot and cold water at the same time, instead of rejecting the condenser heat to nowhere useful.

https://www.carrier.com/commercial/en/us/products/chillers-components/heat-recovery/

Really, it's just different in function from a normal water cooled chiller.

It isn't done on a scale as small as a residential refrigerator that I know of though.
 

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