Redundant heat pump

[marcel]

Hello.
I just read Hic's delusions about internal compression. Wire locked, since stupid, but that asks me a question a little silly too. I assume my ignorance!
The efficiency of a PAC falls with the increase of the temperature delta.
When the delta is big, would it be more profitable to create redundancy. A heat pump heats an external and isolated exchange zone while remaining in a delta with very good COP. For example, it goes from -10 to + 5 ° C. There, a second PAC will change from + 5 to + 20 ° C inside the house. Would the total consumption of the two PACs be higher or lower than that of a single machine filling the same delta with a very poor COP?
What is the buffer zone? A neutral room very well insulated and can store the heat mass. Or a direct interchange between the two PACs. Or a liquid tank ???

I'm waiting for your shots !!!

[dedeleco]

PACs, even with 50 staggered small deltaT as suggested with 2 instead of 1 will be at best, limited by the Carnot principle either COPmax = Ts / deltaTglobal with T in Kelvin absolute or T = 273 + T ° C

DeltaT = 10 ° C gives COPmax = 30 for 10 ° C to 20 ° C !!!

The actual PACs of the trade are very far from that (fluid adapted to a rather precise temperature) and thus one could gain a little, but illusory, because the real ones do not give infinity for deltaT = 0 ° C, like the theorem of Carnot !!!

[Forhorse]

PAC is taboo! We will all be exhausted!

[Christophe]

Good question thank you for asking! (nothing to do with that of Hic which was the idea but inverted to want to cool a room with an open fridge ...)

It's not easy to answer ... I would say that it is "kif kif" or worse because you only postpone the problem of the delta N times ... and the losses of each compressor will therefore accumulate. ..

To be on it is necessary to take a PAC datasheet and compare the COP / delta curves ... and make the overall assessment ...

There is one package in this document: https://www.econologie.com/la-technologi ... -3389.html

[marcel]

Thank you for the tracks Christophe.
Must see according to the gear, indeed.
But hey, I'm a thermodynamic buzzard !!!
It's complicated too, because there may be variables like the type of PAC. For example if you do air / water on the first and water / air on the second with better exchanges than air / air everywhere.
And again, if you do some sort of thermal storage in the buffer chamber when conditions are favorable ...

Finally, it reminds me a little the principle of stage compressors: from an energy point of view, it is curious to cumulate mechanical parts adding their losses, but on the other hand it gives good results.

[Christophe]

It's complicated too, because there may be variables like the type of PAC. For example if you do air / water on the first and water / air on the second with better exchanges than air / air everywhere.
And again, if you do some sort of thermal storage in the buffer chamber when conditions are favorable ...

That's why there's only one good way to answer it: analyze the actual PAC features! And for that Dimplex doc is ideal!

Finally, it reminds me a little the principle of stage compressors: from an energy point of view, it is curious to accumulate mechanical parts add their losses, but on the other hand it gives good results.

Uh it does not give good results from a performance point of view but the staged compression is the only method that exists to increase pressure ...

[chatelot16]

it is the same formula of carnot which limits the output of a heat engine, or determines the theoretical maximum COP of a heat pump

physics is very logical ... 2 perfect heat pump in cascade or only one will have the same maximum theoretical coop

the problem is that a real commercial heat pump has a cop significantly worse than the maximum possible, as usual nothing is perfect

the only thing to do to aprocher of the theoretical maximum COP is to put a big compressor of good quality with low loss ... big hoses of gas to avoid the pressure losses, big exchanger for not to have a drop of temperature

therefore the opposite of normal heat pumps, miniaturized at the expense of efficiency

to make good heat pump and powerful performance would have another advantage, more longevity

the heat pump is not bad in principle, rather say that there are bad

[marcel]

Sorry Christophe, I was not clear, when I spoke of "good results" for the staged compressions, I was referring to the objective reached, that is to say to go up to high pressures, and not to the output which accumulates losses of each floor ... obviously.

I stick to the charts in two or three days.

@Chatelot
The problem is not to deal with a maximum COP, but on the contrary to refer to the minimum COP in a large delta T °, ​​in the worst conditions for an ordinary machine with a limited real COP and not " theoretical". We can always say that we only have to heat with wood when it is very cold !!! and forget about PAC in these cases.
My question is therefore more about the opportunity, or not, to continue using PACs to overcome significant temperature gaps. Because putting two PAC in cascade to fill less than 20 ° it would be absurd for sure.

[chatelot16]

Stored compressor and refrigerating machine, it is completely diferent

when you want to compress a gas heating and harmful: if you compress too much pressure in a single stage it heats up a lot and consumes a significant mechanical power to make a useless heat: so we share the compression in several stages to lose less energy. mechanical energy in heat

for a refrigerating machine it is the opposite: the change of temperature during the compression is precisely the aim sought: thus compressing in a single stage is the best solution to approach the maximum of the theoretical COP: to improve the heat pump it does not There is no need to change the cycle, but just to improve the quality and the dimension of each element ... and there is a lot to be gained

there is only one case where the refrigerating machine is made in cascade: to make very low temperature: it is impossible to find a refrigerating fluid functioning of the ambient temperature at -200 ° C: one is therefore obliged to put more refrigerating machine in cascades with different fluid

[Christophe]

when you want to compress a gas heating and harmful: if you press too much pressure in one stage it heats up a lot and consumes significant mechanical power to make a useless heat : So we share the compression in several floors to lose less heat energy in heat

In the end it is kif kif no?

That one compresses at once to 200 bars or on 5 stages, thermodynamically the heating is the same not? Only it will go up a lot less T ° shelves ...

It's far from the thermo courses ...

Easy to check with pv = mRT ...

mR = constant = pv / T

The staged compression is, I think, therefore more related to material resistance issues (structural and T °): the higher you compress, the smaller the piston is ...