Hello,
After the first few days in my new home, I’m having some issues with the heating system. Somehow, it feels like something isn’t working 100%... it heats very irregularly. In my experience, it only heats properly when as many rooms as possible are set to flow. Once most rooms have reached their temperature and only 1 or 2 are open, the system quickly cycles on and off...
- We have about 140 sqm (1507 sq ft) of floor area
- Underfloor heating throughout the entire house
- A Junkers Cerapur ZBS 22/100 S-3 MA gas boiler with hot water generation (22 kW)
- 17.5 cm (7 inches) calcium silicate stone + 14 cm (6 inches) external thermal insulation composite system (ETICS) (no special energy-saving regulations)
As mentioned, when only a few heating circuits are open, the boiler turns on (starting at about 25°C (77°F) flow temperature), heats up quickly (up to about 45°C (113°F) flow temperature), then drops off rapidly and starts again. So the heating circuits are only heated sporadically...? If I turn on more heating circuits, the warm-up time is longer and it gets warm... is the boiler oversized, since it heats single rooms poorly?
After the first few days in my new home, I’m having some issues with the heating system. Somehow, it feels like something isn’t working 100%... it heats very irregularly. In my experience, it only heats properly when as many rooms as possible are set to flow. Once most rooms have reached their temperature and only 1 or 2 are open, the system quickly cycles on and off...
- We have about 140 sqm (1507 sq ft) of floor area
- Underfloor heating throughout the entire house
- A Junkers Cerapur ZBS 22/100 S-3 MA gas boiler with hot water generation (22 kW)
- 17.5 cm (7 inches) calcium silicate stone + 14 cm (6 inches) external thermal insulation composite system (ETICS) (no special energy-saving regulations)
As mentioned, when only a few heating circuits are open, the boiler turns on (starting at about 25°C (77°F) flow temperature), heats up quickly (up to about 45°C (113°F) flow temperature), then drops off rapidly and starts again. So the heating circuits are only heated sporadically...? If I turn on more heating circuits, the warm-up time is longer and it gets warm... is the boiler oversized, since it heats single rooms poorly?
I have done some more research and found similar cases... It seems that the boiler produces too much heat in a short period (which explains the rapid rise in the flow temperature)... this heat cannot be removed quickly enough (since only a few heating circuits are open)... it quickly reaches the maximum set flow temperature of about 50°C (122°F) and then switches off... the flow then carries away the heat (which causes the rapid drop in flow temperature)... at around 25°C (77°F) it switches back on and the cycle repeats.
The burner runs only for a few minutes at a time... which likely means about 150 to 200 burner starts per day... and that with already fairly cold temperatures at the moment...
When the desired room temperature is reached, the controllers automatically switch off... and only switch back on when the temperature drops below the set point... I have 11 heating circuits throughout the house... but as mentioned, only 2-3 are open at a time... I can’t increase the temperature in the rooms just to make the burner run longer, can I?
I guess the heating engineer will need to come again...
The burner runs only for a few minutes at a time... which likely means about 150 to 200 burner starts per day... and that with already fairly cold temperatures at the moment...
When the desired room temperature is reached, the controllers automatically switch off... and only switch back on when the temperature drops below the set point... I have 11 heating circuits throughout the house... but as mentioned, only 2-3 are open at a time... I can’t increase the temperature in the rooms just to make the burner run longer, can I?
I guess the heating engineer will need to come again...
WPIC has covered most of the points.
I just looked up the heating system online.
It’s a very powerful system. In my opinion, it’s way oversized.
It can heat >>250 sqm (2700 sq ft) of living space……Power to the People! A 22 kW heater for 140 sqm (1500 sq ft)! Wow. Who did the calculations here? Unbelievable!
We have a usable area of 135 sqm (1450 sq ft), KfW 70 standard (Q_p and H_t trending towards KfW 55). Our (very small) condensing boiler has a nominal output of 14 kW (11 kW for heating, 14 kW for domestic hot water); and even that is far too large and doesn’t modulate down enough. Even at 23% (minimum modulating output of about 3 kW), you’re often still using too much power. It took me many weeks with numerous adjustments to stop the unit from cycling so often. Less than 10 burner starts per operating hour.
In your heating system documentation, I didn’t see where the minimum modulating output is specified. I probably missed it, but I’d estimate about 4-5 kW.
That’s too much for a modern house of your size.
The heating curve also needs to be significantly lowered. 45°C (113°F) supply temperature for underfloor heating? I run my panel radiators at 40-45°C (104-113°F) and it feels comfortably warm; but that’s definitely not underfloor heating.
That raises alarm bells for me. 28-32°C (82-90°F) is okay. But usually, no more is needed.
Your heating operation definitely needs a serious review. As it is now, it simply won’t work properly! Since you’re unlikely to replace the heating system at this point, you’ll probably need to add a buffer tank (one of the standard solutions to reduce cycling).
Best regards,
Thorsten
I just looked up the heating system online.
It’s a very powerful system. In my opinion, it’s way oversized.
It can heat >>250 sqm (2700 sq ft) of living space……Power to the People! A 22 kW heater for 140 sqm (1500 sq ft)! Wow. Who did the calculations here? Unbelievable!
We have a usable area of 135 sqm (1450 sq ft), KfW 70 standard (Q_p and H_t trending towards KfW 55). Our (very small) condensing boiler has a nominal output of 14 kW (11 kW for heating, 14 kW for domestic hot water); and even that is far too large and doesn’t modulate down enough. Even at 23% (minimum modulating output of about 3 kW), you’re often still using too much power. It took me many weeks with numerous adjustments to stop the unit from cycling so often. Less than 10 burner starts per operating hour.
In your heating system documentation, I didn’t see where the minimum modulating output is specified. I probably missed it, but I’d estimate about 4-5 kW.
That’s too much for a modern house of your size.
The heating curve also needs to be significantly lowered. 45°C (113°F) supply temperature for underfloor heating? I run my panel radiators at 40-45°C (104-113°F) and it feels comfortably warm; but that’s definitely not underfloor heating.
That raises alarm bells for me. 28-32°C (82-90°F) is okay. But usually, no more is needed.
Your heating operation definitely needs a serious review. As it is now, it simply won’t work properly! Since you’re unlikely to replace the heating system at this point, you’ll probably need to add a buffer tank (one of the standard solutions to reduce cycling).
Best regards,
Thorsten
Has a heat load calculation ever been done? I have a 5 kW wood stove on the upper floor (about 85 sqm (900 sq ft)) that overheats the entire floor. It also provides some heat downstairs, where we currently don’t have a stove or any other heating system (we do have a heating system installed, but no underfloor heating, so the heating is not used). So 20 kW would be about double what our house—an old building being renovated but still losing a lot of heat unnecessarily, for example upwards through the moderately insulated roof—actually needs. We also had a heating technician come once who tried to sell us a 25 kW heater, saying that’s the usual rule of thumb instead of doing a heat load calculation. That calculation later showed that only about 6 kW would be needed after renovation!
If you can’t replace the gas boiler, how about installing a buffer tank? Then the boiler could run at full capacity to heat the tank and then stay off for the rest of the day—or even longer. This could at least prevent short cycling.
If you can’t replace the gas boiler, how about installing a buffer tank? Then the boiler could run at full capacity to heat the tank and then stay off for the rest of the day—or even longer. This could at least prevent short cycling.
We have 5.3 kW for 190 m² (2,045 sq ft) … although I’m still worried that this might be too little.
22 kW, in my opinion, is way too much… it’s annoying, but pure heating costs with gas aren’t that high (at least if it ever breaks down…)
Check out the pink forum – maybe you’ll find some ideas there for optimizing the controls.
22 kW, in my opinion, is way too much… it’s annoying, but pure heating costs with gas aren’t that high (at least if it ever breaks down…)
Check out the pink forum – maybe you’ll find some ideas there for optimizing the controls.
BeHaElJa schrieb:
We have 5.3 kW on 190 m² (2045 sq ft) ... although I’m still worried that it might be too little.
In my opinion, 22 kW is way too much... it’s annoying, but heating alone isn’t that expensive with gas (at least if it ever breaks down...).
Check out the pink forum – maybe you’ll get some tips on optimizing the control system.I calculated my heating load at 3.6 kW; 160 m² (1722 sq ft) above ground, 85 m² (915 sq ft) in the basement (it doesn’t get that cold there in winter, usually the floor remains above 0°C (32°F) except for the first few centimeters). But that’s only for the design temperature. Most of the time it’s much warmer, so at 0°C (32°F) I have at most about 2 kW, and so on.
I assume the 22 kW is to allow unlimited hot water usage, like long showers or something similar. That’s what an inexperienced heating engineer would install, just thinking “as long as it’s warm” (water).
Similar topics