ᐅ Sudden increase in HVAC system performance – all filters are clear
Created on: 8 Dec 2016 14:13
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spyron
Hello everyone....
I am currently experiencing an issue with the built-in ventilation system in my Stiebel Eltro LWZ 404 SOL.
For the past two days, the system’s performance / airflow volume has increased noticeably, which has also resulted in a significantly louder noise level.
The power settings (level 2 during the day, level 1 during setback) and the associated configurations have not been changed. My first thought was that clogged filters might be causing the increase in performance, but I recently replaced all the filters and they still appeared clean upon inspection. This includes the filter behind the heat exchanger cassette.
When I went to check the filters, I noticed that even with the ventilation temporarily turned off, a lot of air was still being drawn in from outside and blown out. I had to turn the system off completely in order to inspect the filters without the fan running.
My assumption (as a complete layperson) was that the fan running despite the ventilation being off is probably used to supply the heating / hot water system with heat from the surrounding air. Since it is currently quite cold outside (around 0°C (32°F)) but the electric backup heater only activates when it reaches the bivalence point at -5°C (23°F), I can imagine that the ventilation unit has to work harder (i.e., exchange more air) than it would at above-freezing temperatures. In principle, this would be understandable. (Could someone please confirm whether this assumption is correct?)
What I don’t understand, however, is the increased performance of the central ventilation system. Normally, an increased airflow for heat recovery related to heating / hot water should not necessarily affect the ventilation system’s airflow / performance, or am I mistaken?
If these are unrelated, do you perhaps have any ideas what else could be causing the increased ventilation system performance? As I said, everything was running normally up until 2-3 days ago. Currently, we turn the ventilation completely off at night, even though the ventilation otherwise was not causing any issues.
I would really appreciate your help. Any hints or suggestions are very welcome.
Good luck, Florian
I am currently experiencing an issue with the built-in ventilation system in my Stiebel Eltro LWZ 404 SOL.
For the past two days, the system’s performance / airflow volume has increased noticeably, which has also resulted in a significantly louder noise level.
The power settings (level 2 during the day, level 1 during setback) and the associated configurations have not been changed. My first thought was that clogged filters might be causing the increase in performance, but I recently replaced all the filters and they still appeared clean upon inspection. This includes the filter behind the heat exchanger cassette.
When I went to check the filters, I noticed that even with the ventilation temporarily turned off, a lot of air was still being drawn in from outside and blown out. I had to turn the system off completely in order to inspect the filters without the fan running.
My assumption (as a complete layperson) was that the fan running despite the ventilation being off is probably used to supply the heating / hot water system with heat from the surrounding air. Since it is currently quite cold outside (around 0°C (32°F)) but the electric backup heater only activates when it reaches the bivalence point at -5°C (23°F), I can imagine that the ventilation unit has to work harder (i.e., exchange more air) than it would at above-freezing temperatures. In principle, this would be understandable. (Could someone please confirm whether this assumption is correct?)
What I don’t understand, however, is the increased performance of the central ventilation system. Normally, an increased airflow for heat recovery related to heating / hot water should not necessarily affect the ventilation system’s airflow / performance, or am I mistaken?
If these are unrelated, do you perhaps have any ideas what else could be causing the increased ventilation system performance? As I said, everything was running normally up until 2-3 days ago. Currently, we turn the ventilation completely off at night, even though the ventilation otherwise was not causing any issues.
I would really appreciate your help. Any hints or suggestions are very welcome.
Good luck, Florian
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Bieber08159 Dec 2016 06:47We recently experienced something similar, but I couldn’t make sense of this statement:
When the insect screen at the outdoor air intake (supply air) gets dirty over time in our system, the fan power increases accordingly. The volume flow remains constant (otherwise the power/speed would not need to increase). If it gets too loud for us, we clean this filter.
Recently, the sound of our mechanical ventilation with heat recovery changed suddenly—from normal (quiet) to jet engine noise in an instant. We turned it off and went back to sleep, but the real cause was actually the supply air screen (insect screen) freezing due to sudden fog. Cleaning it the next day resolved the problem.
I’m somewhat reassured to know that others have had similar experiences.
spyron schrieb:
For two days now, the performance / air volume flow of the ventilation system has significantly increased
When the insect screen at the outdoor air intake (supply air) gets dirty over time in our system, the fan power increases accordingly. The volume flow remains constant (otherwise the power/speed would not need to increase). If it gets too loud for us, we clean this filter.
Recently, the sound of our mechanical ventilation with heat recovery changed suddenly—from normal (quiet) to jet engine noise in an instant. We turned it off and went back to sleep, but the real cause was actually the supply air screen (insect screen) freezing due to sudden fog. Cleaning it the next day resolved the problem.
I’m somewhat reassured to know that others have had similar experiences.
I probably misinterpreted this as a layperson and therefore described it incorrectly: I attributed the louder noise from the ventilation to an increase in airflow, but the airflow probably stayed the same and only the fan speed increased – just as you described.
It’s amazing what a little fog in cold temperatures can cause.
Anyway, I’m glad that it’s all relatively harmless and that it happens to others as well.
You really have to come up with something like this on your own. It’s not mentioned in any manual, and no heating technician prepares you for this.
All the better that you can at least get competent and quick help here.
It’s amazing what a little fog in cold temperatures can cause.
Anyway, I’m glad that it’s all relatively harmless and that it happens to others as well.
You really have to come up with something like this on your own. It’s not mentioned in any manual, and no heating technician prepares you for this.
All the better that you can at least get competent and quick help here.
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Bieber08159 Dec 2016 13:31We should still discuss the type of fresh air inlet ... (Note to self ... I will come back to this).
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Bieber081515 Dec 2016 08:13By now, I believe I have understood the issue. Air drawn through the intake grille causes cooling of both the air and the grille itself (wind chill effect), which may lead to the dew point being reached or passed. In suitable weather conditions, the grille then freezes over. Even without frost, the condensation creates an unsightly streak on the façade. We actually have a flush-mounted plastic grille over the intake opening, sealed all around with silicone (or similar) against the render. After six months of use, a subtle streak caused by running condensation is already visible underneath the grille in the center.
I think we will install a weather protection hood or something similar in the medium term. So, a metal hood that covers the opening at the top somewhat and ideally includes a drip edge for the condensation.
How is this situation for you?
I think we will install a weather protection hood or something similar in the medium term. So, a metal hood that covers the opening at the top somewhat and ideally includes a drip edge for the condensation.
How is this situation for you?
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