Heaters with low entropy production

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Heaters with low entropy production




by Ortograf-fr » 05/08/08, 15:30

"Low entropy heaters: what are they?"
by Ortograf-fr, July 2008


In practice, heaters with low entropy production are essentially the pompe à chaleur and cogeneration, in other words, combined heat and power production.

The heat pump is of great interest pedagogic, because it proves to those who do not want to hear that the efficiency of a heater can be much higher than 100%.

But it is the systematic development of cogeneration that will minimize consumption energy resources for heating. It does not take the way in France currently.



A - An entropy production is a degradation of energy.

It occurs in particular:

- whenever electrical, chemical or mechanical energy is converted into heat: electric heating, heating with the usual fuels, friction,

and whenever heat is exchanged between two bodies at different temperatures. The greater the difference in temperature, the greater the entropy production.


B - Heating without entropy production would be obtained with an ideal heat pump

Heating without entropy production is impossible to achieve, but it is very easy to imagine.

This is the one that would be provided by an ideal heat pump, the one that would have the best operation imaginable.

Its electric motor would present no friction or Joule effect.

And above all, the part of the heat pump used to heat the apartment would have a temperature very little higher and almost equal to that of the apartment, at the same time as the part of the heat pump which serves to draw heat from the external environment would have a temperature very little inferior and almost equal to that of this medium.

In other words, the two exchanges of heat made by the pump would each time with an infinitesimal temperature difference.


C - An entropy production is equivalent to a loss of energy resources

Physicists and heating specialists know very well how to calculate the efficiency that such an installation could have. It can be called the "theoretical maximum yield". It only depends on the two temperatures involved: that of the air from which the heat is extracted and that of the apartment that is heated.

Let's take numerical examples. To maintain an apartment at 20 ° C, with an outside temperature of 15 ° C, the yield would be sixty, ie, 6000%.

With an outside temperature of 10 ° C, this yield would be 30, ie 3000%.

The efficiency of an ideal heat pump is thus usually about ten times higher than that of real heat pumps, which is itself three or four times greater than the efficiency of 100% of an electric heater.

D - Heaters without entropy production: the ideal new reference to measure the performance of a real heater

All the extra consumption of a real heating compared to an ideal heat pump is a loss of energy resources by entropy production.

In the second previous numerical example, to provide 30 heat joules at the apartment, the electrical energy consumed can never go below a joule.

In this example, if the heating is produced by an electric heater, on 30 joules consumed by this radiator, 29 represent a consumption of resources related to an entropy production and that, as such, we can hope to reduce.

The actual heat pump shows that one can already do better than an electric boiler, since it will consume about 10 joules instead of 30 to provide the same heating. But its balance sheet is still ten times lower than the best benchmark and we can hope to do even better.

In conclusion: a yield of 100%, which translates a heating without loss of energy, is no longer the ideal to achieve in terms of heating. The ideal efficiency of heating without entropy production will never be achieved, but the energy efficiency of low entropy heating far exceeds 100%, as shown by heat pumps, whose yields are commonly located between 300% 400%.


E - To minimize entropy production, it is necessary to reduce as much as possible
- the number of energy transformations
- the number of heat exchanges
- and also temperature differences which allow these exchanges of heat.

This last point has an immediate practical consequence. For heating with a heat pump, a home will consume less electricity if it is designed to be heated by 30 ° C circulating in the soil, than if it is designed to be heated by water to 60 ° C circulating in radiators.


F - All traditional heaters are incompatible with a good management of energy resources

It has been seen above that the 100% efficiency of an electric heater was in fact extremely poor. For heating with traditional fuels, it's almost as bad.

This is due to the fact that the heat exchanges take place with very large temperature differences. The production of entropy corresponds to the fact that the starting heat is "high temperature" heat and that it is found in the form of low temperature heat to reach the places of stay.

Typically, the energy provided by the fuel oil can in some cases give mechanical energy with a yield exceeding 60%, as is the case for some boat engines. It means that the energy provided by this fuel has a theoretical maximum convertibility exceeding 60% to provide electrical energy.

In other words, high temperature heat is already amputated by an entropic haircut compared to the electrical energy, but this haircut represents a few things compared to that which occurs when the same amount of heat is degraded to reach the premises that is heated.


G - The device that best minimizes the entropy production caused by heating is cogeneration.

In this case, the heat used is simply the low temperature heat rejected by a thermal power plant or by any generator.

We have seen that, in order to minimize the production of entropy, the number of energy transformations, the number of heat exchanges, and the temperature differences that allow these exchanges of heat must be reduced as much as possible.

The cogeneration heating perfectly fulfills these conditions, because it only transforms a low temperature heat often called thermal rejection, to give another heat low temperature, that which is desired for our places of stay. We can consider that the heat of departure is recovery and that it is practically free of charge for the energy resources consumed.

It corresponds well to the theoretical balances of the heaters with low production of entropy.

...........

Possibility of giving talks on the theme: "heaters with low entropy production."

Contact us.


To download this document in pdf format in two copies on one page, click here:

http://www.alfograf.net/ortograf/images/tract/paj-472-807-chauffages-fpe-presentation-tract.pdf


Ortograf-en
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by Ahmed » 08/08/08, 19:57

I am not a thermist, but can not help but react to this curious text.

All leaves me the unpleasant impression that the theoretical aspect fascinates its author to the point of forgetting the reality.
Admittedly, this concept of entropy is interesting but it leads us quickly into considerations which, instead of shedding new light, only succeed in obscuring these problems.

Based on the comparison between an electric radiator having a yield of 100% (by definition) and a heat pump, it shows that under good conditions, in practice, it can restore about 3 times the amount of energy absorbed.

It's forgetting a lot of things:
These 100% of local efficiency of the electric radiator do not have much significance, since it does not take into account losses in the production and transport of electricity. Because of these losses, only a fraction, about a third reaches the meter (the yields vary according to the production methods, the nuclear, majority, would be inefficient because operating at low pressure *, transport losses would be evaluated at 10% in average).

So the CAP is only regaining what is lost: hello entropy!

And still I do not place myself in good operating conditions: in case of cold a little intense, the performance of the CAP (air / air or air / water, the most common) drops quickly and may even be below the electric heater when an electrical resistance defrost the condenser.
"The heat pump is of great educational interest, because it proves to those who do not want to hear it that the efficiency of a heating device can be much higher than 100%."

Note also that a water radiator, considered alone, heated by what one wants, also has a yield of 100%; it is also irrelevant to speak of efficiency in the case of heat production since it is the most degraded form of energy.

Without criticizing paragraph B where assumptions are supposed to support later reasoning, one can not help thinking that, paradoxically, the (classical) CAP would have an extraordinary yield if only it were used to produce hot summer and cold winter ... : Cheesy:

Let's talk about cogeneration where the author sees, with good reason, interesting possibilities: the fact that we recover what is usually lost, the author wrongly infers that the yield is well above 100%. This is true only in relation to the production of electricity with loss of heat, and, in itself, these figures greater than 100% are absurd since we can not expect to derive more from a fuel than it contains.

I had noticed the same logical drift in the case of the condensing gas boiler: recovering the latent heat of the water vapor makes it possible to approach a little more of this value, not to reach it and even less of to go beyond it. Let's say it's a business approach ...

* If you have reliable sources confirming or denying this data, I am a buyer.
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by Other » 08/08/08, 22:29

Hello
It's forgetting a lot of things:
These 100% of local efficiency of the electric radiator do not have much significance, since it does not take into account losses in the production and transport of electricity. Because of these losses, only a fraction, about a third reaches the meter (the yields vary according to the production methods, the nuclear, majority, would be inefficient because operating at low pressure *, transport losses would be evaluated at 10% in average).


It is a bit strong the 1 / 3 that arrives, maybe for a thermal power station, but a hydraulic barrier? Online losses are not as important as that even on 1000km

I think you have to compare a calorifer electric resitance and a heat pump from the domestic meter.
To say 3 is in the ideal conditions, on average it is more often 2 sometimes 2,5 what is already better than a simple heating resitance.
To reduce its electric consumption for the heating of 50% it is already interesting ..

You forget the water / air sytem the water of the earth is always at 12c even when it is -25 out and the thermo pump water / air is efficient first we do not need to heat the air at 40c like a sytem to the water a 32 is enough in the ventillation to heat a house at 25 c

I have this syteme for almost 20ans and I live in a climate where it sometimes falls -30 with 6,6kw of power that provided to heat all the house in addition the summer air conditioning ..

Andre
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by minguinhirigue » 08/08/08, 23:03

Regarding the condensing boiler, the fact is that the yields are today more than 100%, compared to the lower heating value.

It is a scam mounted because the PCI does not take into account the energy transmitted to the vaporization of water molecules from combustion. The best condensing boiler therefore remains under the 100% yield compared to the higher heating value.

Regarding the crazy idea of ​​cogeneration with an efficiency greater than 1, it seems that ortograf_fr speaks about it. What he says is more like: "cogeneration is free heat since it is the" rejection "of another use ..."

Nevertheless, there are some fadas who like to imagine fuel heat and cogeneration systems:

This Shaddock system is a cogenerator, which operates a heat pump. Without taking into account the temperatures and especially the temperature differences specific to the operation of these technologies in series, one can dream of drawing from 100 Wh, up to 60% "noble", and 40% thermal, with a heat pump, the 60 % noble become in real conditions up to 300% thermal (COP of 6 for the best commercial water / water pumps). Either in total, by recovering calories from the cogenerator, 330 Wh of thermal energy produced by the combustion of 100 Wh primary ...

Even more crazy, the car offered on the forum, which works from a battery activating a heat pump, which heats an engine, which produces electricity for the battery and for the car's advance ... The balance sheets are held, except that the number of temperature and operating temperature differences is limited: low thermal amplitude for good efficiency of the heat pump, large amplitude for good motor efficiency! It's not about to turn ...
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by Christophe » 09/08/08, 09:01

I have not read everything (nothing in fact) but the title makes me think of the PACES ...

Heat Pump with Spontaneous Flow.

You know? Otherwise it's there: http://www.new-energy-paces.com/

For those who are not afraid download and read this doc: http://www.new-energy-paces.com/brevet.zip

the proposed car on the forum, which operates from a battery activating a heat pump, which heats an engine, which produces electricity for the battery and for the car's advanced


I missed that I think ... where was it?
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by minguinhirigue » 09/08/08, 09:12

https://www.econologie.com/forums/voiture-el ... t2057.html

here it is, the idea is to operate with diffuse solar energy in the atmosphere, to capture calories to activate one or two stirling engines ... :D

Except that, as stated above, there is no clarification on the compatibilities of technologies ...
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by Christophe » 09/08/08, 09:14

Ah ca date 2006, a good digging of Topic in perspective!
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by Ahmed » 09/08/08, 15:21

Thank you André, for your interesting reflections. I think that our differences, which are only apparent, are simply the result of a different context.

Perhaps you did not notice that I was careful to delimit the area of ​​validity of my remarks. This is the French situation where nuclear power is largely predominant, where the most common type of heat pump is air / air. In Canada, given the hydroelectric potential, the data are obviously radically different.

I think you have to compare an electric heater and a heat pump from the domestic meter.

For the consumer, this may be true, but from an ecological (and even technical) point of view, what matters is the entire production / consumption chain.
To say 3 is in the ideal conditions, on average it is more often 2 sometimes 2,5 what is already better than a simple heating resistance ...

I said 3 "in good conditions", because indeed it is much more often below.

To reduce its electrical consumption for the heating of 50% it is already interesting ...

In the French context, and because of the modes of electricity production, it is unfortunate to use a "noble" energy to end up with heat, which is a degraded form. What is more with a low yield.
Where the cost of electric heating dissuades users, the generalization of the use of the CAP would, because of the lesser unitary consumption, only boost the use of electricity and increase overall consumption.
In addition to the global impact *, I also see the disadvantage of an impossibility for the user linked to this system, to opt for other solutions depending on the possibilities or future constraints.

* An intensive use of electric heating implies a more developed nuclear power plant as well as the more frequent use of conventional thermal power plants to cope with the peaks of winter electricity consumption, even due to the impact of temperature variations.
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