Re: [Vo]:If 2 heat engines are placed in series their efficiency is lower, and the second law breaks according to Carnot if that can occur!
OK If you change the limits like some do with the Peltier elements using 500C input then you can get higher COP's due to the higher entry level. (and just ignore the heating of the input...) Heat pumps we use in houses are certified - Europe for 0..35C, not for 10..35C - as we live pretty north in average. With 10C input you already can get a COP way above 6 with the proper gas. (well ground water heat pumps do it) Our probe runs between 6..12C and is pretty warm. We are lucky. Older probes here have been to short, are most of the time frozen and deliver below 0C... Your example with COP > 10 uses natural phase changes (T > 80C, water) what is way better than induced phase changes as you don't need a high compression. But such heat pumps definitely are just for industrial process heat recovery add not for common use. J.W. On 10.05.2024 13:24, Jonathan Berry wrote: /Sorry a heatpump (HP) cannot have a COP 30 or 60/ Sorry but they can, I gave you the links. The math also supports this. No, you are right that a regular small house-hold heatpumps operating at 100% power over the rated temperature differential will top out currently at about a heating COP of 5.5. However is it is well made and can be powered at the ideal power level the COP goes up and can be measured at 10+ And that is just the heat being counted, if we count the cold side which is normally ignored when we are trying to heat we get a true COP of 20+ But have you ever wondered who small house-hold heat pumps have a higher COP than larger ones? It is because the smaller heatpumps have everything (for the power level they work at) size larger and closer to optimal. But when operating on an inverter basis, the efficiency can go higher. And the COP of a larger heatpump that isn't working hard out can exceed the rated COP of a smaller heatpump and even outclass it entirely, though there might also be a point of something being oversized but I don't really think it's much of an issue when it is inverter based and you know how inefficient it is to have the cold side outside to have a hard time due to getting too cold and frosting up too much... Note: "A W10W35 water-to-water heat pump should have a coefficient of performance (COP) of at least 5.5. COP" AT LEAST! not at best. I just asked a chatbot, apparently 12.8F might be a plausible range to give a reading over: " 47°F (8.3°C) outdoor temperature and 70°F (21°C)" So I ran with that and based on the heat engine efficiency numbers, at that temp there is a 4.3% efficiency as a heat engine, and that would seem to indicate an absolute max heatpump COP of 29. But at a 2C difference it was a heat engine efficiency of 0.67% and a COP as high as 148! People report to have measured COP's of 11, and I gave you links to very professional examples of COP's up to 30 and explain why 30 can be seen as 60 when you utilize both sides. In theory COP can with some tiny fraction of a C separation across each heatpump go near infinite if ideal (no losses). Of course if you were driving so many you would need to find a super efficient way, but we don't need a COP of 148 even if it is theoretically possible. A COP of 5.5 even without doubling it is plenty, even without running it across a more modest gradient... Just run enough in series to get the efficiency of the heat engine to about 50% while the COP is not much worse than 3 and you not only have a proof of principle but something perhaps practical. But we don't need to build it, the fact is that in theory you can move ANY amount of heat up any hill as long as it is divided up by enough heat pumps that have low frictional losses. We don't need to build it (though we could) to prove that the conservation of Energy is more of a rule of thumb but easily broken in practice if you know how. /Assume a COP of 5 for a single step HP as we have it today in a reasonably good probe heat pump. (mine has 5.5 for heating) / Ok. Can do. /You can neither simply multiply or add the COP's/ I did neither one, well I doubled which is valid (or approximately so) in a single state if you just count the cold side, but generally I didn't add or multiply COP's. /as you must provide e.g. 20x the basic energy to fill the reservoir for the next HP state./ There are probably only 2 Reservoirs (one on the extreme hot and extreme cold ends), and even if there is a reservoir between each one it only takes a moment to reach a steady state condition and then it is as if it isn't there. I am not sure really what you are talking about, what reservoir needs 20 times the energy? I think you have misunderstood something. What we are proposing is very much like Carnot's proposal, 2 Reservoirs, one hot and one cold. There is a high efficiency heat engine connected between two reservoirs turning say with 64% efficiency of the thermal energy to mechanical. If we were to try and make this
Re: [Vo]:If 2 heat engines are placed in series their efficiency is lower, and the second law breaks according to Carnot if that can occur!
*Sorry a heatpump (HP) cannot have a COP 30 or 60* Sorry but they can, I gave you the links. The math also supports this. No, you are right that a regular small house-hold heatpumps operating at 100% power over the rated temperature differential will top out currently at about a heating COP of 5.5. However is it is well made and can be powered at the ideal power level the COP goes up and can be measured at 10+ And that is just the heat being counted, if we count the cold side which is normally ignored when we are trying to heat we get a true COP of 20+ But have you ever wondered who small house-hold heat pumps have a higher COP than larger ones? It is because the smaller heatpumps have everything (for the power level they work at) size larger and closer to optimal. But when operating on an inverter basis, the efficiency can go higher. And the COP of a larger heatpump that isn't working hard out can exceed the rated COP of a smaller heatpump and even outclass it entirely, though there might also be a point of something being oversized but I don't really think it's much of an issue when it is inverter based and you know how inefficient it is to have the cold side outside to have a hard time due to getting too cold and frosting up too much... Note: "A W10W35 water-to-water heat pump should have a coefficient of performance (COP) of at least 5.5. COP" AT LEAST! not at best. I just asked a chatbot, apparently 12.8F might be a plausible range to give a reading over: " 47°F (8.3°C) outdoor temperature and 70°F (21°C)" So I ran with that and based on the heat engine efficiency numbers, at that temp there is a 4.3% efficiency as a heat engine, and that would seem to indicate an absolute max heatpump COP of 29. But at a 2C difference it was a heat engine efficiency of 0.67% and a COP as high as 148! People report to have measured COP's of 11, and I gave you links to very professional examples of COP's up to 30 and explain why 30 can be seen as 60 when you utilize both sides. In theory COP can with some tiny fraction of a C separation across each heatpump go near infinite if ideal (no losses). Of course if you were driving so many you would need to find a super efficient way, but we don't need a COP of 148 even if it is theoretically possible. A COP of 5.5 even without doubling it is plenty, even without running it across a more modest gradient... Just run enough in series to get the efficiency of the heat engine to about 50% while the COP is not much worse than 3 and you not only have a proof of principle but something perhaps practical. But we don't need to build it, the fact is that in theory you can move ANY amount of heat up any hill as long as it is divided up by enough heat pumps that have low frictional losses. We don't need to build it (though we could) to prove that the conservation of Energy is more of a rule of thumb but easily broken in practice if you know how. *Assume a COP of 5 for a single step HP as we have it today in a reasonably good probe heat pump. (mine has 5.5 for heating)* Ok. Can do. *You can neither simply multiply or add the COP's* I did neither one, well I doubled which is valid (or approximately so) in a single state if you just count the cold side, but generally I didn't add or multiply COP's. *as you must provide e.g. 20x the basic energy to fill the reservoir for the next HP state.* There are probably only 2 Reservoirs (one on the extreme hot and extreme cold ends), and even if there is a reservoir between each one it only takes a moment to reach a steady state condition and then it is as if it isn't there. I am not sure really what you are talking about, what reservoir needs 20 times the energy? I think you have misunderstood something. What we are proposing is very much like Carnot's proposal, 2 Reservoirs, one hot and one cold. There is a high efficiency heat engine connected between two reservoirs turning say with 64% efficiency of the thermal energy to mechanical. If we were to try and make this heat engine drive another identical heat engine connected between the same 2 resivious to act as a reatpump it would fail as each would be matched, even If it was smaller and weaker but just as efficient as a heat engine then as a heatpump over that temperature differential it would have a COP of less than 1 if I'm not mistaken, but not good anyway. However if we had multiple identical reversible heat engines, and one goes between the hot and cold, and the others are placed with one on one hot, one on the cold and other heat engines placed in between. As such they would behave just like a series of resistors across a voltage potential. If you measured the temperature between each one it would ideally be a fraction of the total. Each one by being over a tiny fraction of the full temperature differential is only driven as a heat engine very weakly (low efficiency) that can easily hit a percent or 2 or less. And a 2% efficient heat engine when run as
Re: [Vo]:If 2 heat engines are placed in series their efficiency is lower, and the second law breaks according to Carnot if that can occur!
Sorry a heatpump (HP) cannot have a COP 30 or 60. Assume a COP of 5 for a single step HP as we have it today in a reasonably good probe heat pump. (mine has 5.5 for heating) You can neither simply multiply or add the COP's as you must provide e.g. 20x the basic energy to fill the reservoir for the next HP state. To heat 1000l from 10 to 50C you need 25'000 Liter of water at 10C if you take out 2C. So the base COP goes in with a factor 20 in the total COP equation. Thus you must divide 25 by 20 for a first second step. In average by 10. Thus initial total COP = 5 + 25/20! Also the cooling does only count if you can use it. Normally in winter you must heat. The optimal solution would be to combine the fridge with a heat pump but a good fridge today uses only 300W/day J.W. On 10.05.2024 03:49, Jonathan Berry wrote: Not sure why but this isn't forming into proper paragraphs... / / /"Youtube physics usually is self satisfaction of people that have no clue of the simplest things. So I almost never watch this garbage."/ The video is covering the work of a company cascading heat pumps. As such the temperature differential over each heat pump is a fraction of the total over all the heatpumps, there is a potential feedback instability effect they have resolved. But cascaded heatpumps are an accepted thing with improved COP over a given total temperature difference and the video isn't making claims about the second law, that's me, and well Carnot... / / /"A heatpump is not a Carnot process as *you obviously supply additional energy*!"/ It is a carnot process though and the carnot process gives us the efficiency limit. A reversible heat engine if you supply it with kinetic energy can generate a temperature differential, this is why it is called reversible, you don't get energy from it, you reverse it and put energy in to move heat. To do this you obviously need to supply it with energy just as we do with a heat pump. /"You must calculate in the Carnot conversion rate of energy gained --> electricity to get the proper conversion factor as the current for the heatpump must be produced too* and subtracted!"*/ Yes, however the COP of a heat pump (electrical power in .vs heat energy gain on the hot side) over a low temperature differential can be 5, 10, or 30 or potentially more if the temperature differential is low enough. Note that in a single stage heatpump we can actually double that COP by just counting both the hot and cold outputs as both being beneficial outputs! If a heatpump can deliver four times more thermal energy than the power going in (and for now assuming the heat from the input power is not seeping inside) then wit has a COP of 4, but we ignore the cooling COP of 4 on the other side, that is "free cold" and in terms of a temperature differential to put a heat engine on both are sources of energy, but between the hot and cold sides is a higher conversion efficiency than between the hot and ambient and the cold and ambient. Which is the point I am making, if you divide the heat potential the COP of the heat moving ability of a heat engine or heat pump it improves relative to the energy it takes to drive it. /"The best Carnot process (multi stage turbines) today delivers a conversion rate of about 61% always target is current."/ 61% is a fine conversion of heat to to energy since heatpumps can manage a COP of 30! https://www.sciencedirect.com/topics/engineering/recompression COP 30 "typically COP of 10–30 can be achieved" with a MVR heatpump. https://www.gea.com/en/assets/304829/ COP 20 You can have 30 times more heat energy moved and that's just looking at the heat energy gain, ignoring the energy below ambient on the cold side, so with that a COP of 60!... Now granted my whole point is not that this if done with a single heatpump it would not be efficient when you run steam turbines over 1C, 10C or so, so it does not matter how well it was design, because to gain efficiency for conversion of thermal energy we need as great a temperature difference as possible, but there is no reason we can't put multiple heat pumps in series each working over a small temperature range just as we put batteries in series. And we can do the same with heat engines which are just Carnot heat engines under a different name not designed to be reversible but conceivably can be redesigned to be reversible. And again, the point of this post is to point it out from the other direction, according to Carnot if a reversible heat engine can be made more or less efficient (while still not having frictional losses, poor thermal insulation etc) then the second law would fail. And as putting two in series makes it less efficient (as Carnot would himself assert if he had thought if it and apparently he managed not to)... well then the second law fails, it CANNOT be true if this is a reversible heat engine, AKA, a heat pump, as a
