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tom66:

--- Quote from: MK14 on June 12, 2023, 02:27:04 pm ---Which (after my rather quick read up on it, so could be a bit or more mistaken) limits the maximum efficiency of heat-pumps, to values which CAN'T exceed 100% over-all efficiency.  Because if it did, it would violate a number of laws of Physics.
--- End quote ---

No.  The theoretical maximum CoP for a heat pump is around 8.5.   Real world units are limited to about 5 in ideal conditions, and around 3.5-4 in real world conditions.  Those are all above 100% efficiency.  The efficiency figure can exceed 100% because the energy to the room includes that which is extracted from the outdoor environment, which you don't pay for.  I guess you could try to measure the thermal efficiency of the whole system including that outdoor heat source but I'm not sure exactly what that would tell you or if it would be that useful as a figure.

MK14:

--- Quote from: tom66 on June 12, 2023, 03:13:21 pm ---
--- Quote from: MK14 on June 12, 2023, 02:27:04 pm ---Which (after my rather quick read up on it, so could be a bit or more mistaken) limits the maximum efficiency of heat-pumps, to values which CAN'T exceed 100% over-all efficiency.  Because if it did, it would violate a number of laws of Physics.
--- End quote ---

No.  The theoretical maximum CoP for a heat pump is around 8.5.   Real world units are limited to about 5 in ideal conditions, and around 3.5-4 in real world conditions.  Those are all above 100% efficiency.  The efficiency figure can exceed 100% because the energy to the room includes that which is extracted from the outdoor environment, which you don't pay for.  I guess you could try to measure the thermal efficiency of the whole system including that outdoor heat source but I'm not sure exactly what that would tell you or if it would be that useful as a figure.

--- End quote ---

I didn't write/explain it well enough.

I meant, 100% efficiency of the overall system, with a combination of the heat-pump and the thermopile, to turn the heat-difference back into electrical energy.  The idea being to generate more electricity (by inventing much high efficiency heat-pumps and thermopiles, than perhaps are available today), than you initially put into the heat-pumps.
Essentially making a device which turns pure temperate back into electricity, while absorbing some background temperature.

I.e. If a room is at 25 deg C, and you have a discharged car battery.  The car battery could be charged up, but the room temperature would fall to perhaps 10 degrees C.

But as Zero999 (and at least one other in this thread), are pointing out.  The existing laws of Physics, don't allow for this.

I.e. You can't do it, it wouldn't work.  (ok, you can try it, but you would end up putting in more energy (electricity) into the heat-pump, than the thermopile, returns as generated electricity.

Because otherwise, it would be more than 100% efficient, overall (i.e. comparing input electricity into mainly the heat-pump, with the generated/outputted electricity from the thermopile).

IanB:

--- Quote from: tom66 on June 12, 2023, 03:13:21 pm ---No.  The theoretical maximum CoP for a heat pump is around 8.5.   Real world units are limited to about 5 in ideal conditions, and around 3.5-4 in real world conditions.  Those are all above 100% efficiency.  The efficiency figure can exceed 100% because the energy to the room includes that which is extracted from the outdoor environment, which you don't pay for.  I guess you could try to measure the thermal efficiency of the whole system including that outdoor heat source but I'm not sure exactly what that would tell you or if it would be that useful as a figure.

--- End quote ---

But CoP is not efficiency.

To relate to what MK14 was saying, you have a hypothetical Black Box, connected to various high temperature sources on one side, various low temperature sinks on other side, and the box does useful work (mechanical work, electrical work, whatever). Heat flows through the box from the hot sources to the cold sinks. Inside the box can be any contrivances you like, including the use of heat pumps.

The efficiency is the amount of heat converted to work divided by the total amount of heat flowing through the device. Conservation of energy says that the maximum efficiency cannot be greater than 100%. Other laws of thermodynamics say you cannot even reach 100%.

tom66:

--- Quote from: IanB on June 12, 2023, 03:24:37 pm ---
--- Quote from: tom66 on June 12, 2023, 03:13:21 pm ---No.  The theoretical maximum CoP for a heat pump is around 8.5.   Real world units are limited to about 5 in ideal conditions, and around 3.5-4 in real world conditions.  Those are all above 100% efficiency.  The efficiency figure can exceed 100% because the energy to the room includes that which is extracted from the outdoor environment, which you don't pay for.  I guess you could try to measure the thermal efficiency of the whole system including that outdoor heat source but I'm not sure exactly what that would tell you or if it would be that useful as a figure.

--- End quote ---

But CoP is not efficiency.

To relate to what MK14 was saying, you have a hypothetical Black Box, connected to various high temperature sources on one side, various low temperature sinks on other side, and the box does useful work (mechanical work, electrical work, whatever). Inside the box can be any contrivance you like, including the use of heat pumps.

The efficiency is the amount of heat converted to work divided by the total amount of heat flowing through the device. Conservation of energy says that the maximum efficiency cannot be greater than 100%. Other laws of thermodynamics say you cannot even reach 100%.

--- End quote ---

I agree, ultimately the heat is just moved so it has to come from somewhere.  I guess such a system would probably approach 100% efficiency at a CoP of >8.5 (haven't done the maths, just intuition).   However, I'm not sure what that would tell you.  Maybe give you a figure of merit for the performance of such a system?  Sounds more like a scientific curiosity than a useful measurement.

IanB:

--- Quote from: tom66 on June 12, 2023, 03:26:52 pm ---I agree, ultimately the heat is just moved so it has to come from somewhere.  I guess such a system would probably approach 100% efficiency at a CoP of >8.5 (haven't done the maths, just intuition).   However, I'm not sure what that would tell you.  Maybe give you a figure of merit for the performance of such a system?  Sounds more like a scientific curiosity than a useful measurement.

--- End quote ---

Engineering comes into it. Every improvement in efficiency comes at a cost (of design, of manufacture, of materials). At some point, the increased cost outweighs the benefit.

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