Hello everyone,
We are building a semi-detached house with a total heated area of approximately 460 sqm (4,951 sq ft). The building will be constructed to KFW 55 standard. Both units will have a central ventilation system from Zehnder with heat recovery. According to our energy certificate, one half of the house has a heating demand of 10 kW and the other 7 kW.
The heated area includes the two basements, which are not occupied but only moderately heated (partly used for storage).
We are producing everything separately except for the boiler, specifically:
A shared Fröling PE1 boiler without a particle filter
and for each unit:
A solar collector with vacuum tubes and a gross surface area of 10 sqm (108 sq ft)
A 1000-liter (264-gallon) hygienic storage tank with two solar coils, one at the top and one at the bottom.
The system will be set up so that the solar collectors heat the respective buffer tanks of each half, and the boiler will only activate when one of the buffer tanks gets too cold and then heat both to the target temperature.
Now the big question is: Which PE1 boiler should we choose? We want to avoid being cold, but at the same time, not oversize the boiler given pellet consumption and wear from frequent cycling.
I am not sure how much emphasis we can put on the figures in the energy certificate and how the domestic hot water consumption needs to be factored in here.
I look forward to your ideas and hope I haven’t forgotten any details. Otherwise, I’m happy to provide more information.
We are building a semi-detached house with a total heated area of approximately 460 sqm (4,951 sq ft). The building will be constructed to KFW 55 standard. Both units will have a central ventilation system from Zehnder with heat recovery. According to our energy certificate, one half of the house has a heating demand of 10 kW and the other 7 kW.
The heated area includes the two basements, which are not occupied but only moderately heated (partly used for storage).
We are producing everything separately except for the boiler, specifically:
A shared Fröling PE1 boiler without a particle filter
and for each unit:
A solar collector with vacuum tubes and a gross surface area of 10 sqm (108 sq ft)
A 1000-liter (264-gallon) hygienic storage tank with two solar coils, one at the top and one at the bottom.
The system will be set up so that the solar collectors heat the respective buffer tanks of each half, and the boiler will only activate when one of the buffer tanks gets too cold and then heat both to the target temperature.
Now the big question is: Which PE1 boiler should we choose? We want to avoid being cold, but at the same time, not oversize the boiler given pellet consumption and wear from frequent cycling.
I am not sure how much emphasis we can put on the figures in the energy certificate and how the domestic hot water consumption needs to be factored in here.
I look forward to your ideas and hope I haven’t forgotten any details. Otherwise, I’m happy to provide more information.
O
Oetzberger2 Oct 2021 16:46I took a look at the brochure, and the 15 kW and 20 kW models appear to be essentially the same in construction, with a minimum output of 4.5 kW for both. The 15 kW model should be more than sufficient, but the 20 kW is technically just as suitable. For probably irrational psychological reasons, I would choose the 20 kW model for a small additional cost, but that is rather an unnecessary oversizing. The 25 kW model, on the other hand, has too high a minimum output and would be a major mistake.
P.S.: In practice, the 10 kW model would probably be enough and might even be a better fit, but first, the heating installer is unlikely to agree, and second, there’s no need to overdo it. A well-balanced underfloor heating system paired with the 15 or 20 kW unit will work best.
P.S.: In practice, the 10 kW model would probably be enough and might even be a better fit, but first, the heating installer is unlikely to agree, and second, there’s no need to overdo it. A well-balanced underfloor heating system paired with the 15 or 20 kW unit will work best.
konibar schrieb:
Consider your usage scenario:
We were often away for two weeks in winter and set the heating to frost protection mode (around 4°C (39°F)).
As a result, after returning, warming up the cooled-down building was time-consuming and took more than one day.
The heating system was sized according to the standard (here winter-low at -13°C (9°F)).
If you often experience similar situations, I would recommend choosing the larger boiler. I don’t think it makes much sense to let a house cool down that much.
But aside from that, the question is whether the one-day warm-up really takes that long because the heating system lacks enough power. The flow temperature usually depends on the outside temperature. This results in a slow heat transfer to the rooms.
The heating output only needs to be sufficient to maintain the flow temperature. More power would not make the rooms heat up faster.
Schimi17912 Oct 2021 21:04guckuck2 schrieb:
…
More power would not lead to faster heating of the rooms.It sounds like the analogy to a car. More horsepower (power) first has to be transferred from the wheels to the road. Here, it’s probably about the heating system’s power being transferred to the heating surface(s).Hi! We built a semi-detached house in 2018 with about 400 sqm (4,300 sq ft) of heated floor area, also meeting the KfW55 standard. We have an Ökofen 18 kW condensing pellet boiler, which is completely underutilized. The heating technician already reduced its maximum output to 13 kW (I can’t recall the exact value, but it was around 13) because it allows for better modulation. So, based on my experience, it’s better to choose a lower kW rating.
haraldv schrieb:
also kfw55. We have an Ökofen 18kWAnd so, there was no heating load calculation here either. 😕 However, the original poster can still do everything correctly.
driver55 schrieb:
And here, apparently, there was no heat load calculation either. 😕
But the original poster can still do everything correctly. That is probably the case, but the idea of using pellets in a new build is simply not very wise. For example, Ökofen only starts at 10 kW (34,000 BTU/h). No matter how you calculate it, that is much too oversized. Nothing will run efficiently, and the wear and tear will be correspondingly higher. All of this comes with very high initial costs.
It is simply not a sensible heating method for new builds, at least not for single- or two-family houses. For a multi-family building, the situation can be viewed differently.
Ökofen website:
The new generation for the low power range
With the Pellematic Compact, the name says it all. Besides its extremely space-saving design, it is available in output sizes of 10, 12, 14, 16, and 18 kW (34,000, 41,000, 48,000, 55,000, and 61,000 BTU/h), making it suitable for virtually any single-family home.
You can hardly tell bolder lies than that. This is consumer deception at the highest level.
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