PELLAQUA solar heating 12 m2 struggles to provide DHW in summer

[sylvain52220]

What makes you say that it is not a submerged coil ???

A plate heat exchanger would mean that it would be necessary to add (again) a circulator and vessel etc etc ...

the document https://manualzz.com/doc/14270726/instr ... 0-a-1500-l , page 15 says:

3.Solar exchanger with stratification solar rod
The solar domestic hot water exchanger, placed inside, is made of high quality AISI 316L stainless steel. The solar energy supplied on the primary side is stored in the appropriate zone by a destratification chimney, thanks to the secondary circuit of the heat exchanger. The volume flow in the secondary circuit of the exchanger is optimized by itself by absorbing solar energy. This results in a first rate DHW load, associated with a very high efficiency optimization. The advantage over an external heat exchanger is that neither a secondary pump nor its regulation is necessary. In addition, the radiated losses are lower.

page 14, it looks like a plate heat exchanger which is referenced (3), noted "Solar exchanger with solar stratification rod".

on the page https://www.batiproduits.com/fiche/prod ... 14538.html, we can read :

Key Features
High performance solar tank incorporating a solar plate exchanger, in low position, with inspection hatch. Allows the instantaneous production of domestic hot water and heating. Incorporates a pre-wired regulation, all the hydraulics, circulators and 3-way valves for one or two heating circuits. Forced stratification system optimizing solar gain from buffer and DHW. Available in three models from 600 to 1 liters.

All this makes me think that it is a plate heat exchanger for the solar fluid / balloon exchange.

As for the heat transfer coefficient of around 200W / m2 / K for the exchanger, don't you think it's low?

[sylvain52220]

I don't have many pictures of the installation, here is one of the balloon where we see the connections to the solar circuit on the right and the heating circuit of the slabs

buffer tank

I will get more pictures of the connections to the DHW circuit and the back-up (electric boiler which is not used).

[sicetaitsimple]

As for the heat transfer coefficient of around 200W / m2 / K for the exchanger, don't you think it's low?

You make a mistake, the "K" of an exchanger is not the power exchanged divided by the area and again divided by the deltaT of one of the branches.
Forget it, in my opinion Oekofen knows how to size an exchanger to optimize operation under more or less standard conditions of a solar installation ...
There you have an operating problem, in my opinion a solar circuit flow rate too low, at least under "summer" conditions.
In any case, it is easier at first to confirm (or refute) this hypothesis than to embark on hazardous dismantling, or even to ask yourself questions about the sizing of the exchanger.
Note that you are already a little above (or below, as you like) Okoefen's "rule of thumb", which is 80l of storage per m2 of sensors. It doesn't matter mid-season, but in the middle of summer it can get annoying.

[sylvain52220]

As for the heat transfer coefficient of around 200W / m2 / K for the exchanger, don't you think it's low?

You make a mistake, the "K" of an exchanger is not the power exchanged divided by the area and again divided by the deltaT of one of the branches.
Forget it, in my opinion Oekofen knows how to size an exchanger to optimize operation under more or less standard conditions of a solar installation ...
There you have an operating problem, in my opinion a solar circuit flow rate too low, at least under "summer" conditions.
In any case, it is easier at first to confirm (or refute) this hypothesis than to embark on hazardous dismantling, or even to ask yourself questions about the sizing of the exchanger.
Note that you are already a little above (or below, as you like) Okoefen's "rule of thumb", which is 80l of storage per m2 of sensors. It doesn't matter mid-season, but in the middle of summer it can get annoying.

I'm not talking about sizing here, but looking to check if the performance is consistent.
Higher we evaluated that 10 liters per minute and a temperature differential of 4 ° corresponded to a power of the order of 2700 W (I give the details of the calculation in another post).
The exchange surface of the solar exchanger is 3 m2.
For all this to hold together, the heat exchange coefficient of the material chosen for the exchanger would have to be 2700/3/4 or 225W / m2 / K when we should be much higher. Which can make you think it is clogged in one way or another ...

[sicetaitsimple]

For all this to hold together, the heat exchange coefficient of the material chosen for the exchanger would have to be 2700/3/4 or 225W / m2 / K when we should be much higher. Which can make you think it is clogged in one way or another ...

No, no, I insist! Your calculation of K is completely wrong, and therefore you cannot compare it to more or less normative values.

https://www.barriquand.com/fr/actualite ... ode-emploi

[Christophe]

As for the heat transfer coefficient of around 200W / m2 / K for the exchanger, don't you think it's low?

You make a mistake, the "K" of an exchanger is not the power exchanged divided by the area and again divided by the deltaT of one of the branches.
Forget it, in my opinion Oekofen knows how to size an exchanger to optimize operation under more or less standard conditions of a solar installation ...

I answer to you 2 both the performance unit of an exchanger is expressed in W / m².K (or W / m².C) and it depends on the fluid speeds (cold and hot) and on the type of fluid obviously (oil is not water ... glycol water is not domestic hot water ...) ...

The purely theoretical sizing of an exchanger is rather complex and it must go through test phases to obtain the real values ​​of this K according to these parameters.

K of 200W / m². C ° is rather low but where did you find this value?

Here is a course on heat exchangers, you will see that a plate exchanger in a buffer tank is utopian .. batieproduct tells nonsense ..

See page 13:

iup-me-heat-exchanger-2.pdf

(2.65 million) Downloaded times 1080

http://gsi-energie.univ-rouen.fr/IMG/pd ... ique-2.pdf

A finned heat exchanger, I'm fine ... but not a plate heat exchanger. A plate heat exchanger requires 2 circulators. I don't think there is a submerged circulator at the bottom of the balloon!

Page 14 it is the finned heat exchanger (car radiator type which could be suitable in the bottom of a buffer tank)

From your photo (phew we understand better) indeed it is possible that this is a finned heat exchanger seen where the entry / exit is located (it is different from the first documents you gave! In short ...)

If it is full of lime, it is normal that it does not exchange anything ...

If the ball is well designed you should be able to take it out through the trap door.

Go to work !

[ENERC]

- The temperature difference of the solar circuit fluid at the inlet and at the outlet of the tank (therefore of the solar exchanger) is only 4 ° C or even 5 ° C while the fluid is at 100 ° C and the tank at 30-40 ° C (the fluid enters at 100 ° C and comes out at 95 ° C) - is this normal in your opinion?

Not for me. Wouldn't there be a large layer of limestone deposited on the coil?
With 60 degrees of difference between the coil and the water, it must have cooled a lot more than that.
(seen Christophe's post: I agree, we must clean the outside of the coil)

[Christophe]

Not for me. Wouldn't there be a large layer of limestone deposited on the coil?

Hey you're lagging behind !! Must follow !! It is a finned (plate) exchanger!

Otherwise agree with you it stinks of fouling! External see internal ???

Sylvain did not answer my question on the pressures of the solar circuit.

[Christophe]

We must look at page 52/53.

Why an extra vase or circulator?

Because obviously we don't have the same definition of the plate heat exchanger ... See the course I just posted.

ps: you don't necessarily need a vessel if the circulator pumps the DHW from the buffer ... but we are no longer in this situation. There is indeed a solar-buffer exchanger at the bottom of the tank and it is most likely a hydrostatic finned exchanger.

[Christophe]

Okay friends, a picture is worth 1000 words (headache in this case) ... it is indicated on the plate but I take offense at this name since a plate heat exchanger requires a circulator on the secondary and I do not see circulator submerged or pumping water from the buffer ... In short, it's a detail but sorry it would have avoided some headaches!

pellaqua_vue_interne.jpg (115.11 KiB) Viewed 1786 times

The confusion probably comes from the fact that it is possible to install an EXTERNAL plate heat exchanger on this model !!

Screenshot_2020-08-18 Price list - PDF Free download.png (26.59 KiB) Viewed 1786 times

Not given elsewhere!

ps: why there are 2 heating circuits ??? (as long as we are in the grip ...)