Heating circulator mounted hot side ... why?

[Christophe]

Everything is in the title: the heating circuit circulators are always mounted (at least in the recommended assembly) on the "hot" side, that is to say "outward" circuit ... or:

a) these circulators are cooled by the fluid (dixit Grundfos) .... and a fluid from a "go" heating circuit will therefore cool less well than a return ...

b) the thermal losses of the fluid in the circulators are also greater (undoubtedly a few tens of watts of difference but it is always that of gain ...).

At the time I was told that it was a story of fouling (obviously it is better for dross to stagnate in the boiler than in the circulator?)

Do you have any other reasons?

[elephant]

Now that you say it, it challenges.

For the rest, you have to make the trade work, right?

[Did67]

Perhaps so that at all points, the circuit was always overpressure, the boiler was a resistance to flow, like the circuit itself.

So the pressure curve, if you "draw" your circuit "flat", with the pressure curve, is maximum at the outlet of the circulator (static pressure P + pump HMT), and decreases by step, at each " chicane ". It is minimum, at the boiler outlet, just before suction by the circulator. It can be so weak that the pump "cavitates"!

So by putting the "pump" at the start, you add the HMT released by the pump, to the static pressure in the circuit. Under no circumstances, except at the outlet of the boiler, before the circulator, can you have a vacuum.

If you are sucking, your pressure in the circuit will be the static pressure - the HMT at the height of the pump. And so on by "going up".

So you can have traps in depression. And "infiltrations" of air at levels in depression (if not dripping tap) ...

Finally, I think ... I am not a heating engineer. But I'm trying to apply some basic physics principles ...

[Christophe]

I understand your reasoning did67 ... except that the static pressure of a heating circuit, being around 2 bars (mini), there is no risk that there is air infiltration in the circuit ...

The only difference by putting the circulator upstream of the boiler is that the total pressure at the inlet of the "heat distribution" circuit will be reduced by the pressure drops of the boiler (I think they are all the same low compared to the other losses. of a circuit ... to be checked in a technical manual)

Here is a very simplified diagram to illustrate your idea of ​​constant pressure drop:



Source: https://www.econologie.info/share/partag ... H2Sl5E.pdf

Otherwise after a little reflection and following your remark, I wonder if it is not a history of cavitation ... because if there is a risk of cavitation in the circulator (therefore air at the outlet of the circulator) , this air will go into the boiler instead of into the first radiator or trap ... so this would be precisely to protect the boiler in the event of cavitation (avoid air in the boiler ... more damaging than in the fitted circuit traps) ???

[Christophe]

But the calculation of the static pressure is supposed to avoid cavitation ...
See the formulas for this subject: https://www.econologie.com/forums/vase-d-exp ... t9118.html

[Did67]

You forget that your pressure drops at each stage of your circuit, after each elbow, each fitting, each tap, each radiator ...

So from a maximum at the output of the circulator (= static pressure + HMT of the pump), you descend to each level ... to arrive at the ini at the entrance of the circulator. It is this mini that causes cavitation.

If you put your circulator at the inlet of the boiler return, you operate in "suction"; you have a mini at the entrance of the circulator which is equal to static pressure - HMT.

If your circuit is still at 2 bars, I don't think there is a problem. But you know very well that an installation is designed so that the user does not take care of it ... So if your static pressure drops gradually, I think that the risk is less great of operating in delivery (static pressure + HMT) rather than aspiration (static pressure - HMT). The risk of going under the pressure triggering the boiling is infinitely lower!

In any case, I see no other reason!

Finally yes, another, but I do not believe it too much: in the time, the circuits were "open", with a container vented on the roof. We could not therefore "aspire" without risk of defusing, I think. But I doubt that since, by simple habit, nobody would have asked the question?

Otherwise, indeed, it would be logical to put the circulator on the return, to make it operate at a lower temperature, etc ... In short, the question of departure would have all its meaning. I can hardly imagine that all the specialists are stupid and never thought of that. It may flatter the ego, but hey, don't take us for geniuses either!

[Christophe]

I went to see my nice plumber ... (well, rather my plumbing supplier since I tinker myself).

He confirmed the hypothesis of the pressure, that the circulator had to be in point "high" compared to the boiler (the departure of a boiler being often "at the top" and the arrival at the bottom) but said that it it was above all a story of mud ...

Yes did it is also, perhaps, a story of habit ...

In fact it is rather a constructor of a circulator that should be asked?

[Did67]

but said it was mostly a story of mud ...

There, I do not understand: for a given HMT, it results, in the circuit, a given speed of circulation.

I do not see what the upstream / downstream of the boiler changes! ???

Would the boiler serve as a decnator ????

[elephant]

Most likely indeed: if the circulator is at the bottom, it will get bogged down when stopped.

(sorry, I think my sentence is not very pretty )

[Christophe]

Would the boiler serve as a decnator ????

Absolutely!

The boiler is the part of a heating circuit where there is the most volume ... therefore "dead volumes" also ...

(not including your elephant parenthesis)