House construction, KfW Efficiency House 55

Good morning,
We are planning to build a house for 5 people. Until now, we didn’t have to deal with it at all and have been happily living in our already 40-year-old single-family house.
Now we have to move again due to work.
But we have time, as we are still commuting at the moment (almost 3 hours every day).
Financing is basically secured since we can sell our house. The rest is almost covered by the saved car costs.
We already have 3 offers, 2 of them solid construction and one prefabricated house manufacturer.
The best in terms of costs is now the following

Increased thermal insulation of the base plate, highly insulating brick masonry, increased thermal insulation of the facade as well as in the roof area of the upper floor as required.

Efficient heat pump (Tecalor THZ 304/404 SOL including three-year manufacturer warranty) with 235-liter hot water storage and preparation for cooling and connection of a solar system. Controlled ventilation with cross heat exchanger for up to 90% heat recovery as well as pollen and fine dust filter. WEB module (Internet Service Gateway) including remote diagnosis and remote maintenance. Underfloor heating on the ground floor (except utility room) and upper floor, including room thermostats integrated into the switch program. Climate protection windows triple glazed (Ug 0.7-0.9) - mushroom head locking, security olives.

As a KFW 55 house. However, as read in construction blogs, only with 17.5 cm Poroton brick and then external insulation with Styrofoam.

Now I come to the question. How to approach the whole thing. Does it make sense to build like this? The many contributions confuse us completely.
Maybe you can first push us in the right direction.
Best regards Xinette

We are also currently planning to build (the floor plan is missing)
"enhanced thermal insulation of the facade" <–– what is that supposed to mean anyway? Compared to what?
"efficient heat pump" - that is an air-to-water heat pump... generally rather critical to consider - it somewhat depends on where you want to build... the warmer the better.
"However, as read in construction blogs, only with 17.5 cm Poroton brick and then exterior insulation with Styrofoam." ... would not be my choice, without the thickness of the Styrofoam it is not really helpful.
The worse the insulation, the more critical the air-to-water heat pump.
Generally, that sounds very much packaged in an advertising-friendly way.

Again about the air-to-water heat pump:
tecalor GmbH THZ 404 SOL 2.82 3.46 4.19 1 6.38 kW EN 14511 5.0 K
Your pump has a COP of 2.82 at -7°C - what does that mean? It produces 2.82 kWh of heat from 1 kWh of electricity. What does that mean? Assuming your house eventually has a heating demand of about 20,000 kWh, you would consume 7,100 kWh of electricity here, which means around €150 monthly heating costs. If you heated with gas, it would be €109. (I used the website of the local supplier). That is roughly the worst case. If you read around, some people have already had a consumption of up to 7,000 kWh electricity for their air-to-water heat pump... that is obviously rubbish at first and does not mean you have low operating costs, but rather that the house suppliers quickly meet the KFW standards (heat pumps are calculated much more favorably than gas).
That of course changes if you build a passive house or something similar (very good insulation) - then these things can be worthwhile, especially because they also handle ventilation. If it is about the ideal, ground-source heat pumps would probably be preferable - they cost significantly more but have COPs of about 5.

Does this mean, conversely, that with a better wall and a possible gas heating system we can also achieve the Kfw55 standard? Does the cross heat exchanger make sense in addition? We plan to install a wood stove. It can also provide additional heating during cold winters. Could you also tell me something about a geothermal heat pump? Does it make sense? What geological conditions do we need to consider? Thanks in advance

Geothermal heat pumps are expensive... about €20,000 more compared to gas - it only pays off after 12-15 years (at least for deep drilling). If you have a large plot of land, you can also bury surface collectors - that is then cheaper. But I would consult heating engineers for that - one who specializes in gas and one in geothermal, then you might get a better feeling for it. Yes, [KfW 55] is also possible with gas - but somewhat more difficult. You can read on Wikipedia what it actually means. It is definitely more sensible to focus on proper insulation instead of just the "KfW55" badge. The subsidy is partially at least eaten up again by the whole inspection process. A fireplace in the living room is, in my opinion, not a substitute for heating - if anything, it should also be connected to the heating system, but that gets a bit more expensive - and always remember, if you don’t get the wood cheaply, it no longer really makes sense. I believe cross heat exchangers are just one type - without a heat exchanger the heating won't work - that is the principle of heat pumps. You extract heat from a medium and thereby generate energy, which you then supply back to the house, for example.

A fireplace in the living room is, in my opinion, not a heating replacement ...

We have a fireplace - and in current times (the outside temperature in the evening is not enough for the heating to kick in so that you can call it cozy) it is enough to warm the house by 3 degrees.

What more do you want? Or: what more do you expect from a fireplace?

Unfortunately, I can’t say anything about the heat pump, but basically nowadays Kfw55 is not worthwhile/profitable, unless you have money to spare or do it out of conviction. But there are many hints about this here in the forum.

Best regards Yvonne

The heat pump is not exactly a top model in terms of efficiency; there are much better ones. According to the BAFA heat pump list, the COP values of the Tecalor 304 are 2.72 / 3.4 / 4.14. Good or efficient values would rather be >3 / >4 / >5. There are plenty of models that achieve these values as well. Therefore, I recommend taking a close look at the BAFA list. Top models come, for example, from Heliotherm, Weider, or Ochsner. Or if it absolutely has to be Tecalor, then at least the significantly more efficient model TTL 15 IS-2. As said: compare values! Nothing is worse than sinking into operating costs with an inefficient heat pump that was expensive to purchase.

A geothermal heat pump can be more efficient, but it greatly depends on where in Germany you live. Over volcanically active areas, such as the Eifel, or the Upper Rhine Graben, where the continent is pulling apart, temperatures are significantly higher.