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 less efficient heat
engine is a more efficient heat pump!
That is the message of Carnot's theorem, but another thing of Carnot's
is the equation that tells us the efficiency of a heat engine.
η = 1 - Tc / Th
We take the cold temp in Kelvin, divide it by the hot temp and then
subtract the result from 1 then multiply by 100 to get our efficiency
in percent.
So at -200C on the cold side and -190C on the "hot' side we have,
after adding 273.15 K 73.15 K which we divide by 83.15 =
0.8797354179194227 subtracted from 1 gives us a 0.12 which we
multiply be 100 to get the percent: 12% efficiency.
Interestingly if we drop the cold side to 0.0001 K and the hot side to
10 K we get 0.00001 which subtracted from 1 x 100 gives us an
efficiency of 99.99999%! At just 10C (K) difference!
Just why the cold side being almost perfectly cold skyrockets the
theoretical conversion efficiency... I am not clear on. And this
should be called into question at another time, but I wonder if it is
related to how hard it is to pump heat from something almost at
absolute zero looking at it in reverse? IDK, but whatever.
But if we have a more normal temp range for our 10C difference of 15C
and 25C then...
25+273.15 = 298.15 and 15+273.15=288.15 So 288 / 298
= 0.9664429530201342 subtracted from 1 then x 100 = 3.4%
Ok, staying at a middle temp of 20C...
70C (343K) hot side and 100 C/K colder at -30C or 243 K then 243/343
then subtract from 1 and multiply by 100 for percent and we get 29.15%
Ok, so by having 10 times more heat potential difference we have close
to 10 times more conversion efficiency at turning heat into energy.
And by using 10 heat pumps each just contributing 10C difference
between their hot and cold side we have a COP that might be quite high.
The heat pumps each feel a mechanical feedback at about the 3.4% level
(they have to input in theory 3.4% of the heat they move).
3.4 / 100 That is a COP of 29.
So once we have a COP of 29 and the other way we have a conversion
efficiency of 29%.
Even though this is the max theoretical conversion efficiency at this
temperature differential and not a real world value, the potential is
clear, we can put in 100W, get 2.9KW of heat and get 29% of that back
so 841W out!
You can of course go further, but while for practical application the
maximum efficiency of a heat engine is important, and putting too many
heat pumps in series sounds absurd, we can just focus on the
undeniable fact.
That there is no way the second law of Thermodynamics is consistent
with what we know for an absolute fact.
That a heat engine and heat pump (heat engine run in reverse) have
VERY different and inverse efficiencies over large and small
temperature differences.
It is easy (in theory even if expensive) to put 2 or 200 (reversible)
heat engines in series to make them less effective as a heat engine
and more efficient as heat pumps.
And you can still tap the difference between the hot and cold sides to
achieve a conversion efficiency in reality of above 50%
And as the COP from a heat pump can be VERY high (30 and higher) it's
only an issue of making this practical, not a question of if it can be
done both in practice and in theory.
/"But there have been some materials detected that can improve this
further like thermo (Peltier-) elements."/
Well it is an interesting point that between every heat pump in the
series you could actually put a heat engine (which a peltier is
really) and you could get a little energy out, it won't really affect
anything (a little heat will be turned into energy but in this case
it's not really lost, that which is transferred is meant to be transfered.
This allows us to gain little bits of energy, but it is not worth the
bother unless there is a suitable difference in temp, if it is 1C it's
pointless (but then the max theoretical COP is 274!) the energy from
it is negligible.
Having said that there IS a way to do it, if you put a bunch of heat
pumps in series there is going to be on the hotter half of the
heatpumps, after the fluid giving up it's extra heat to the hot side
and expanded it is col, likely colder than the ambient.
So let’s say we have ahot revivor at 100C (+273.15 = 373 K) and 0C (0
+ 273.15 K) so we 273/373 = 0.7319 subtracted from 1 = 0.268 x 100 = 26.8%
Ok so 26.8% efficient.
But from 100C to 50C we get an efficiency of 13.4%
From 50C to 0 C we get an efficiency of 15.4%
For an average of 14.43% with 2 heat pumps in series but 26.8 for 1.
This then means the only issue is how many you need given the real
world issues.
And I'm happy to discuss that, but first let's just basc in the
(ironic) warmth of entropy being reversible.
Heatpumps are reverse Carnot engines and have a much higher COP in
respect to heat gained but *not to current gained!!!!!!!*
Even more interesting are quantum level processes in nano particles
where one could achieve the doubling of IR photon energy by
suppressing some emission bands. This could be used in solar panels.
J.W.
On Fri, 10 May 2024 at 01:20, Jürg Wyttenbach <ju...@datamart.ch> wrote:
Youtube physics usually is self satisfaction of people that have
no clue of the simplest things. So I almost never watch this garbage.
A heatpump is not a Carnot process as *you obviously supply
additional energy*! 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! *
The best Carnot process (multi stage turbines) today delivers a
conversion rate of about 61% always target is current.
But there have been some materials detected that can improve this
further like thermo (Peltier-) elements.
Heatpumps are reverse Carnot engines and have a much higher COP in
respect to heat gained but *not to current gained!!!!!!!*
Even more interesting are quantum level processes in nano
particles where one could achieve the doubling of IR photon energy
by suppressing some emission bands. This could be used in solar
panels.
J.W.
On 09.05.2024 14:39, Jonathan Berry wrote:
After 200 years (1824) the second law of thermodynamics is
disproven.
https://en.wikipedia.org/wiki/Carnot%27s_theorem_(thermodynamics)
Simply Carnot argues that if the efficiency of a reversible heat
engine was variable based on how it is made or the gases etc,
then the second law of conservation would be broken.
"A heat engine *cannot* drive a less-efficient reversible heat
engine without _violating the second law of thermodynamics_."
(excerpt from the Wikipedia article below the image)
So what happens when you take 2 reversible heat engines and put
them in series (one touches the hot side, one the cold side and
they join in the middle with potentially a small thermal mass
that is thermally equidistant to the hot and cold side)???
Well, we know what happens, according to Carnot!
The lower the thermal potential the lower the efficiency at
turning heat into mechanical energy and therefore the less
mechanical energy is developed when driving heat (operating the
heat engine as a heat pump)...
Which is to say that with a lower temperature differential a
heatpump operates with more efficiency.
So a heat engine constructed to act like 2 or more reversible
heat engines will break the conservation of energy.
There is a company that is making cascading heatpumps which can
keep a high COP over a much larger temperature differential.
https://www.youtube.com/watch?v=wSgv5NwtByk
The point is that it is absolutely possible to turn uniform
ambient heat into electrical power and heating and or cooling
with current technology...
And it is easily explained in a way that cannot be denied,
clearly 2 heatpumps cascading have a higher COP, same as saying
clearly 2 reversible heat engines in series have a lower
conversion efficiency and therefor a higher COP as a hatpump,
precisely the scenario that made Carnot assert 200 years ago
would destroy the second law of thermodynamics.
Jonathan
--
Jürg Wyttenbach
Bifangstr. 22
8910 Affoltern am Albis
+41 44 760 14 18
+41 79 246 36 06
--
Jürg Wyttenbach
Bifangstr. 22
8910 Affoltern am Albis
+41 44 760 14 18
+41 79 246 36 06
