Hi,
1. The calculated heating load does not take into account any internal or solar gains. That means it will be lower.
yes, exactly. It is A09. According to the heating engineer, it just came out recently. There is nothing about it on the internet...
2. Unfortunately, I also cannot find any technical data online for this heat pump. The modulation range and performance at low temperatures would be essential. Maybe the heating engineer can provide you with the technical specifications and you can post them here. Then it would be easier to say whether it fits or not. Otherwise, one can only guess.
3. According to the annual performance factor calculator, the heat pump achieves an annual performance factor of 4.47 under your conditions (BAFA value 4.5). So it is just eligible for funding. Even if the value 4.47 is exceeded by others, it is still good. You probably will not really notice a 0.1 better annual performance factor in practice. More important is that the heating engineer and accordingly the design of the hydraulics and heating surfaces are good in order to achieve a good annual performance factor. See the following points.
4. Also avoid heating buffer tanks (and bypass valves). These only lower the annual performance factor and have no benefit except increasing costs for you and profits for the heating engineer. To ensure the volume flow, see 5.
5. No ERR. It only throttles the volume flow of a heat pump and forces it to run with higher flow temperatures (flow temperature) than actually necessary, which lowers the annual performance factor. The temperatures are set by hydraulic/thermal balancing. The idea that you can quickly (<8h) adjust room temperature with the thermostat in a low-temperature heating system is an illusion anyway. Possibly, you can install thermostats in individual rooms, for example. Personally, I would still prepare the wiring for thermostats. The next points are also important to keep the flow temperature in a heat pump-friendly range.
6. Design heating surfaces for low temperatures and high volume flows. That means the laying distance for underfloor heating should be around 10 cm and the length of each heating circuit roughly the same length at 60-80 m. The bathroom is problematic, however, as there is little space for underfloor heating and the desired high temperatures, which unnecessarily raises the entire flow temperature. Solution, see next point.
7. Wall heating in the bathroom! Definitely! This provides additional surface area, which increases the heating surface performance in the bathroom and lowers the flow temperature. Additionally, the higher comfort due to radiant heat lowers the actually required air temperature to 22°C, because the perceived temperature is higher due to the radiant heat.
8. Last but not least, BKA. BKA is concrete core activation. It is rarely possible in timber frame construction. In solid construction, it should be installed in every concrete ceiling. Cooling with heat pumps and climate change is becoming increasingly important. However, underfloor heating is only conditionally suitable for this. BKA significantly increases the cooling capacity so that the room temperature can be lowered by up to 5K. Combined with shading, even hot summers become pleasant. Another positive effect is that BKA allows the flow temperature of the heat pump to be pushed below 30°C even at a low outside temperature of -16°C. This increases efficiency and thus the annual performance factor of the heat pump further. Improving by 1K increases efficiency by approximately 2.5%. A 5K difference in flow temperature increases efficiency by over 10% and the annual performance factor by 0.2. With a controlled ventilation system with ventilation ducts in the concrete ceiling, BKA has a nice side effect: in winter the supply air is preheated and in summer precooled. What more could you want?
In my view, the costs for BKA are marginal compared to efficiency and comfort gains when compared to other investments in the house, such as nicer tiles. These are generally between 1,000-3,000€ depending on own labor as well as the flexibility and willingness to innovate of the heating engineer.
Regards, Nika