New construction - assessment of energy efficiency

Good morning,

first of all, thank you for your answers. I will try to address the points you mentioned. Once again, we are still in the early phase of our planning and definitely open to advice.

Basically, yes, we are pursuing idealistic goals with our house building project and also certain self-sufficiency aspirations, as long as this can be reconciled with our ideas. We are not economically driven, i.e. ROIs or payback periods do not interest us as long as we do not pay (noticeably) more over our lifetime than, for example, with the minimum Energy Saving Ordinance standard with a simple gas heating system. However, this definitely does not mean that we have unlimited financial resources for the new build! Our idea is simply this: If it costs exactly the same over a lifetime but saves fossil fuels, is "good for the environment," or whatever one wants to call it, then we will do it.

[*]Achieving the KfW-40 standard is a goal but not an absolute dogma. If no realistic solution can be found within our ideas, we will also accept the KfW-55 standard. But we definitely want to try it, also because we want to know what is possible "outside of common practice" (heat pumps) to achieve the KfW-40 standard.

[*]Radiators in the bedrooms(!) - since the other half of the house is to be heated with underfloor heating! - we want so that, if necessary, we can quickly heat the children's rooms, for example. According to our research, underfloor heating of whatever type is too slow for this and wall heating is too expensive or too complicated for us. Apart from electric radiators, we have not come across any other alternatives. Ideas and suggestions for other possibilities are very welcome!

[*]According to our research, low-temperature radiators are precisely well-suited for room heating in well-insulated new buildings. Our idea would also be to use 1/0 panel radiators to maximize the radiant heat portion. The size of the bedrooms is between 14 and 16 m², so the corresponding radiators should not have to be too large.

[*]We want to avoid the topic of solar thermal energy. The roof area in question (30° pitch) will probably be oriented OSO (west-southwest), so it is no longer optimally suited. Also, there is the known problem of the performance peak in summer and the minimal effect in winter. Last but not least, the construction site is in northern Germany. Taken together, we have serious doubts that solar thermal energy will provide a meaningful — here, indeed economically viable — benefit for us.

[*]To address the topic of geothermal energy at once: For our plot, only a ground probe would be possible, i.e. we would need a deep borehole. This is too expensive for us, with the simultaneous uncertainty as to whether the heating capacity in winter would be sufficient (without gas as backup).

[*]We want the fuel cell out of conviction and enthusiasm for technology and, as mentioned at the beginning, to have a constant electricity production throughout the year. (Photovoltaics would in principle be possible, absolutely yes, but do not provide constant electricity over the year.) From the 0.6 kW heating power, we expect a noticeable contribution to hot water preparation (this was also "confirmed" above), but one that is constant over all months and not just in summer. Regarding the system and the company I mentioned, we are quite confident after our research that it is not a "one-hit wonder." In case of doubt, it would have been expensive tuition, but then there is still the gas condensing boiler. Simply avoiding new technology because it may appear risky (subjectively, objectively?) is not a solution from our point of view.

I hope I was able to explain some of our reasons more closely so far. We will now consult an energy advisor soon. However, we are still happy if there are any assessments of our planning as outlined above.

Best regards
Hans

Houses are no longer quickly heated on demand today... especially KFW40 means a sluggish system that retains heat for a long time.

Underfloor heating of any kind is too slow for that

There are renovation systems that are quite fast (e.g. heating pipes directly in the top cm of Wediplates, which serve as screed and tiles are laid directly on them. But this only works with tiles and I would avoid it in new buildings.

You can also install underfloor heating everywhere and additionally hang small radiators under the windows. Then you have both.

With the planned use of a gas boiler + fuel cell, the supply temperature is not so critical, the system does not become less efficient if you have 40-45°C in the supply line. This is much more important for heat pumps.

With the recently greatly increased subsidies for fuel cells, this is no longer only suitable for enthusiasts. However, it is not cheaper than gas + solar thermal. OSO as an orientation, together with only 30° tilt, is really not good for solar thermal or photovoltaics.

Radiators in the bedrooms(!) - the other half of the house is supposed to be heated with underfloor heating! - we want them so that we can quickly(!) heat up, for example, the children's rooms if needed. According to our research, underfloor heating of any kind is too slow for this purpose and wall heating is too expensive or complicated for us.

KfW 40 houses are very slow; there are no major temperature fluctuations anyway.

It also isn't easy to make it cold enough that heating afterwards would be necessary.

Hi, please think about and inform yourself again about the topic of fuel cells. Our neighbor is a professor of environmental engineering and researches on and with fuel cells. He also has a fuel cell but far outside the house because these explode more often than you think. I would not want something like that in the house, especially not in the utility room where your gas connection is located.

So radiators with low temperature, to heat up a room quickly, are mutually exclusive. And running the system with two flow temperatures (for underfloor heating and radiators) would be even more pointless. In such a well-insulated building, you first have to manage to keep one room significantly cooler than the others.

KfW40 purely for sportiness is easier to achieve by using a pellet heating system instead of gas. As for solar thermal energy, I agree with you. That is the crazy idea of misguided energy policy, but what can you do.