Question: problem of oversized granulated boiler?

[blogophil]

Hello,

I am equipped with a HERZ PELLETSTAR 20 Biocontrol wood pellet boiler from 2005
The house is 150m2 for approximately 420m3 and 27,5m2 of glazed areas with wooden shutters. The attic floor is currently covered with 20 + 10 mm of rock wool. The rectangular house is attached on the west side and 1/3 on the south side to other buildings of the same height
Hot water is produced by the boiler in winter.
Finally we are 4.

For winter 2005/2006, the boiler was put into service at the end of November and we consumed 4,5 tonnes of pellets. At the time, the attic was not insulated (no rock wool on the attic floor).
For winter 2006/2007, I put in place 20 + 10 mm of rock wool in the attic. We consume 4 tonnes of pellets.

In March 2007, we changed the extractor. It seems it was a known defect of this model of boilers, in fact the extractor was very easily clogged with dust, which caused strong vibrations of the latter. The new extractor is twice as powerful as the old one told me the person intervening, it now operates the boiler in "high temperatures". Data written on the extractor: 190m3 / h.

The behavior of the boiler changes radically. With the old extractor it operated between 50 and 110 minutes (ignition and extinction time included) continuously before taking a break with a hearth temperature at 33% power of the order of 300 to 400 °.

With the new extractor, it operates for approximately 12 to 15 minutes (ignition and extinction times included) and ignites between 1 and 1,3 times per hour. At 33% power, the hearth temperature is around 600 ° to 630 °

These figures come from the collection of operating data supplied by the boiler.

This winter I will again consume 4 tonnes of pellets.

I read on this site that for the performance of a wood pellet boiler to be optimum it should operate at least 40 min for 10 min shutdown. With me it's the opposite.

With the insulation provided, I would have expected a drop in my consumption of pellets, but it remains stable.

Does the change of the extraction motor and the short operating time of my boiler have anything to do with it?

Note there is a buffer tank of about 40 liters. Isn't it too small?

My installer is absent subscribers. Can someone enlighten me on my situation. Am I the victim of an oversizing problem or should my installation be modified (larger buffer tank) to take into account the new extractor?

Thanks for your help

[jean63]

I am not equipped with a pellet boiler, but there have already been discussions on this subject with competent people.

There is another person who has the same problem of overconsumption.

You have to search with the search engine and perhaps contact the relevant people by private message (PM).

Bonne chance.

PS: is it really that huge 4 tons? it's 4 X 250 euros / T = 1000 euros per year ....... it's ok with the DHW !!

[blogophil]

PS: is it really that huge 4 tons? it's 4 X 250 euros / T = 1000 euros per year ....... it's ok with the DHW !!

I could be satisfied with this answer indeed. It is an acceptable budget for an individual house.

But as the functioning of my boiler is in contradiction with what I can read on the right and on the left, I wonder if there is not matter to do better, especially taking into account the work of insulation that I have made.

And then I like to understand and be sure that things are "well done" according to the rules of the art. If the modification made by the manufacturer were to have an impact on my installation, it would have been desirable that I had been informed. On paper it regulates between 6,4-21,9 kW. I have the impression that the new engine has changed these technical data and that it regulates rather around 15-25kW. It goes up to almost 800 ° at 100%, which I had never seen with the old extractor.

With the old extractor, it rotated quietly at 33/50% or 6,5-10kW.

[Philippe Schutt]

I suppose you had a bistre formation on the fins of the extractor, and then everything sticks to it and it appears an imbalance.
with a stronger extractor, the T ° of the fumes is higher, more bister, more problem, but yield a little lower.
I would be curious to see what is the temperature of the fumes leaving the boiler?
in my opinion, 120 ° are necessary to be quiet.

[blogophil]

Yes it should be bistre. A technician had told me at the time to hit the fins to make them fall while waiting for the change ...

At level T ° 120 ° mini see rather 150 °

I don't care about all the calories I throw in the air

[dirk pitt]

what would be interesting to know is what was the flow rate of the previous extractor compared to this one and if an adjustment of the parameters was made in the regulation.
in fact, the regul sends a speed setpoint to the extractor but as it is no longer the same, its flow is increased in the same ratio as the air flows between the old and the new.
it seems that this boiler has only the smoke extractor to regulate the air supply, (no booster fan like on the okofen), so by increasing the extraction flow, we also increase the flow d air and draft. Burning at a higher temperature is favorable for less burnt. the main thing is to know in what proportion it is done. maybe there was not much missing in flow to the old extractor and that with this one, there are far too many.
I'm almost sure that we need to touch up the extractor speed settings and that it hasn't been done. It is not normal for a pellet boiler to work for only a few minutes. Consumption is an indicator but not so precise as that to know if the boiler works in the best conditions. Indeed, we can often only compare the annual consumption which can easily vary by 20% from one year to the next depending on the severity of the winter. In addition you have modified the insulation so you cannot know exactly the expected consumption.
It would be interesting to know how to regulate the regul because with an extractor well regulated in speed (before) it had to regulate slowly, ie: after a phase of stop, it starts with 100% then when the water temperature boiler starts to rise it slowly drops to try to stabilize the water temperature. If the extractor is oversized, the drop in speed setting will not really cause a decrease in power, so the water will rise faster in temperature, so the regul will very quickly go from 100% to 10% of power.
The buffer tank is an aid but is not essential with a well-sized modulating boiler

[Philippe Schutt]

I agree with your estimate for the current minimum power of 15kw. there is a problem here, namely that you no longer have the machine (power, efficiency) that you bought.

[Christophe]

Note there is a buffer tank of about 40 liters. Isn't it too small?

Isn't there a typo?

For the rest: 4 tons is quite reasonable ... what region are you in?

[dirk pitt]

additional info after taking a look at the technical doc of the boiler: if you say that the heating cycles last 12 to 15 minutes INCLUDING the start and stop phases, it means that there is really a problem because it would mean that it almost never goes into the regulation phase.
Indeed, the doc indicates a maximum ignition phase of 300 sec (5min) which can be shorter if the ignition detection is done before: say 3mn
then the start-up phase intended to create a correct ember bed at high power normally lasts 5 min (unless the factory parameter has been modified).
after 3 + 5 = approximately 8 minutes, it switches to combustion regulation mode. If the water temperature is already too high, it tries to slow combustion, but as the fan is oversized, it still rises too quickly and when the water is at max temp, it triggers the extinction phase which is set to 3 min (according to the doc). or 3 + 5 + XX + 3 = 12 to 15 minutes therefore the phase where the boiler is in hard regulation from 1 to 4 MINUTES !!!!!!
I confirm that this is not normal. in addition, from an environmental point of view, it is zero because the boiler works very little in phases of good combustion and a lot in transient phases (starting and stopping) where the releases are significant.

[blogophil]

Note there is a buffer tank of about 40 liters. Isn't it too small?

Isn't there a typo?

For the rest: 4 tons is quite reasonable ... what region are you in?

For the volume of the balloon, I make by eye, 10l more or less. It is interposed between the boiler and the exchanger for the DHW and the radiators

Otherwise I am in the Rhône