Heating, insulation, ventilation, VMC, cooling ...PELLAQUA solar heating 12 m2 struggles to provide DHW in summer

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sylvain52220
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PELLAQUA solar heating 12 m2 struggles to provide DHW in summer

Unread Messageby sylvain52220 » 18/08/20, 09:19

Hello,

I'm new to this forum. I am turning to you for a technical opinion (s) on the rather average functioning of a solar thermal installation. My parents opted, ten years ago, for a solar heating solution with instantaneous DHW production made up of 12m2 of collectors (60 ° tilt) and an Okofen Pellaqua 800 liter tank. This summer, when the sun is shining (Drôme Provençale), the system is struggling to provide DHW and finding a competent heating engineer does not seem so easy.

Here are the observations made:
- The solar circuit pump is running well, the flowmeter indicates 10 l / min, there does not seem to be any bubbles in the circuit, in any case we do not see any at the level of the flowmeter
- The fluid of the solar circuit rises well in temperature, yesterday at 11:30, it was at 100 ° C
- The pressure in the balloon is 1.5 bar
- The temperature of the tank rises very slowly, to the point that the collectors reach a temperature of 120 ° C which causes the solar circuit pump to switch off, and therefore that no more exchange takes place, while the tank has reaches only 45 ° C.
- The pump starts up again when the sun goes down, obviously not for long ...

What I find strange:
- 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?
- I exchanged the thermometers of the solar circuit valves to validate the temperature difference which is indeed 4 ° C / 5 ° C
- We thought that the bottom of the balloon might need to be purged if there was, for example, any mud, but the water is clear, not loaded ...
- The solar circuit exchanger does not seem to be playing its role, could it be that it is "dirty"?

Their new heating engineer (the one who did the installation is now retired), without trying too hard to understand and indicating that he is not familiar with the equipment, decided to replace the fluid in the solar circuit. Costly operation but totally ineffective in solving the problem ...

You see more checks to do ...

Thank you in advance for your help.

Silvan
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Macro
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby Macro » 18/08/20, 09:29

The exchange between your solar fluid and the water in the balloon is not (or no longer) ... Did this installation work correctly one day? If so ... It could quite simply be that the internal exchanger of the balloon is purely and simply calcified ... Do you have inspection hatches?
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby sylvain52220 » 18/08/20, 09:38

Macro wrote:The exchange between your solar fluid and the water in the balloon is not (or no longer) ... Did this installation work correctly one day? If so ... It could quite simply be that the internal exchanger of the balloon is purely and simply calcified ... Do you have inspection hatches?


Hello Macro and thank you for your message,
The documentation says that there is an inspection hatch, a disc 18 cm in diameter which precisely includes the arrival and departure of the solar circuit.
We will have to cut the insulation of the balloon to check that this hatch does exist on our version of the balloon (PelleAqua 800l sold 10 years ago).

Maybe we could manage to get the plate heat exchanger out, right?

66 page, https://ardante.com/wp-content/uploads/ ... okofen.pdf
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby Macro » 18/08/20, 10:50

It is not a plate heat exchanger .... It is a coil in the balloon ...

https://www.oekofen.com/assets/download ... ktuell.pdf

You will not manage to get it out of the balloon .... But you may also have a plate heat exchanger on the side of the balloon (the fabulous instantaneous heating ....)

To remove the interior of the water heater .... Apart from 800 liters of hydrochloric acid .... : Oops: : Oops: : Oops: : Oops: I do not see too much other solution ...

Or ... If it is not connected to a boiler .... Use the second coil ... Is your water from the network very loaded with limestone ??? perssonelement with material which represents a significant investment .... A water softening would seem essential to me ...
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby sicetaitsimple » 18/08/20, 11:03

If your measurements are representative of reality (10l / min and 5 ° deltaT on the solar circuit) and that I am not wrong, we still arrive at:

4185 * 10 * 60 * 5 = 12.555.000J per hour, i.e. an exchanged power of 3,5kW, which does not seem absurd.
Do you have a way to vary the flow or is it fixed?
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby sylvain52220 » 18/08/20, 12:17

sicetaitsimple wrote:If your measurements are representative of reality (10l / min and 5 ° deltaT on the solar circuit) and that I am not wrong, we still arrive at:

4185 * 10 * 60 * 5 = 12.555.000J per hour, i.e. an exchanged power of 3,5kW, which does not seem absurd.
Do you have a way to vary the flow or is it fixed?


I arrived at this order of magnitude also ~ 2800W for 4 °.
The doc says that the surface of the solar exchanger is 3m2 (page 13 of (1)), that would give a K of 2800/3/4 = 233 W / m2 / K, is this consistent? I have read elsewhere that we are rather at 1.5-2kW / m2 / K for a stainless steel plate heat exchanger (Page 14 of (1), on the diagram, it really looks like a plate heat exchanger, but I am not Sure. Same thing on pages 16 and 17.)

I can change the speed of the solar pump (Grundfos UPM3 SOLAR). Going up or down, after more than 5 minutes, the effect on the temperature difference is almost imperceptible.

Are you thinking of scaling on the solar fluid side or on the balloon side? What I find it hard to understand is that the water in the balloon is in a closed circuit. There is no continuous supply of limestone, there can only be limestone introduced during the first filling.

(1) https://manualzz.com/doc/14270726/instr ... 0-a-1500-l
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby sicetaitsimple » 18/08/20, 12:39

sylvain52220 wrote:
I can change the speed of the solar pump (Grundfos UPM3 SOLAR). Going up or down, after more than 5 minutes, the effect on the temperature difference is almost imperceptible.


It is normal that you do not detect anything really noticeable on the solar fluid deltaT, on the other hand if for example you went from 10l / mn to 15l / mn with the same deltaT, your exchanged power is multiplied by 1,5. You have to try for a full day, leaving the flow at, for example, this 50% increase (or 20, or 30 ... depending on what is possible)

sylvain52220 wrote:Are you thinking of scaling on the solar fluid side or on the balloon side? What I find it hard to understand is that the water in the balloon is in a closed circuit. There is no continuous supply of limestone, there can only be limestone introduced during the first filling.


I am not really thinking of scaling, because indeed the two circuits which exchange are closed circuits, with possibly some minimal contributions.
Last edited by sicetaitsimple the 18 / 08 / 20, 12: 52, 1 edited once.
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby Christophe » 18/08/20, 12:46

Same: the primary solar fluid circuit cannot be fouled since it is in a closed circuit!

Check your magnesium electrode ... If it's eaten it's not a good sign ...

If the coil is really clogged with limestone on the DHW side (to be checked if possible visually) you can clean the limestone with a few liters of hydrochloric acid or white vinegar ... I would say 10% of the tank's capacity (that's already 80L of acid!)

White vinegar will last longer but since it is DHW it is preferable.

It is a fairly large site and requires at least 48 hours without DHW ... time for the chemical action to take place.

Another possible cause: the circulator which is tired ... it is because it is running that you have the flow you need.

In your place, I would start by testing with another circulator.

Send us pictures of the installation.
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby Christophe » 18/08/20, 12:58

sicetaitsimple wrote:I am not really thinking of scaling, because indeed the two circuits which exchange are closed circuits, with possibly some minimal contributions.


Yes, but on the DHW side it is still an open circuit ... fouling occurs on the open side ...

This tank does not have a DHW exchanger, it is a classic design ... the 2 exchangers heat the total volume of the tank.
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Re: Solar heating 12m2 struggles to provide DHW in summer

Unread Messageby sicetaitsimple » 18/08/20, 13:02

Christophe wrote:If the coil is really clogged with limestone on the DHW side (to be checked if possible visually) you can clean the limestone with a few liters of hydrochloric acid or white vinegar ... I would say 10% of the tank's capacity (that's already 80L of acid!)


I don't think so, because if I understood correctly there is an exchanger between solar fluid and "heating" fluid (the 800l), and then an exchange between "heating" fluid and "DHW water" via a coil embedded in the heating fluid tank, in which the DHW water circulates.
But here the problem is a priori at the level of the first exchange, the low temperature of the DHW being only a consequence of the fact of a "heating fluid" not rising sufficiently in temperature, until the circuit is triggered. "solar fluid" by overheating in the middle of the day.
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