New building KfW55 with gas, solar, and controlled residential ventilation with heat recovery

I currently live in a house built in the mid-70s with a very new gas condensing boiler. I record the consumption at least monthly. With four people, we used about 350 kWh of gas per month in summer – that is, without heating operation and only for hot water. This corresponds to consumption costs of about €21. For comparison, in November during heating operation we used about 3300 kWh, so not quite ten times as much.
Conclusion? Hot water with a gas heater is a negligible byproduct of the heating operation.

How expensive was the PV system again?

It will never be profitable. PV is done to meet the renewable mandatory share according to the Energy Saving Ordinance. As little as possible.
I think it’s great that XeNiA manages to achieve KFW 55 standard purely with controlled residential ventilation/heat recovery. Presumably the investment is higher than installing PV, but at least it has a real return in the form of comfort gain through air quality and mold prevention. PV is dead capital.

I currently live in a house built in the mid-70s with a very new gas condensing boiler. I record consumption at least monthly. With four people, we used about 350 kWh of gas per month in summer – that is, without heating operation and only hot water. This corresponds to consumption costs of around €21. For comparison, in November during the heating period, we used about 3300 kWh, so not quite ten times as much.
Conclusion? Hot water with gas heating is a negligible byproduct of heating operation.

How expensive is the solar thermal system again?

It will never pay off. Solar thermal is done to meet the renewable mandatory part according to the Energy Saving Ordinance. As little as possible.
I think it's great that XeNiA manages to achieve KFW 55 purely with controlled residential ventilation/heat recovery. The investment is probably higher than installing solar thermal, but at least it has a real return in the form of comfort gained through air quality and mold prevention. Solar thermal is dead capital.

The energy consultant has calculated, and we will now build with gas + controlled residential ventilation with heat recovery. Additionally, extra insulation will be added to the base plate and the roof. However, this is still cheaper than the photovoltaic system, which we wanted to do without and now will.

Great! I would have liked that, actually. But with the developer, it would have been more expensive than the air-to-water heat pump. So it stayed that way. I think you have the ideal solution. Keep investment low, insulation high. Controlled residential ventilation is comfort for me.

If you haven’t considered this option yet: What would the calculation look like with an air-to-water heat pump instead of gas? Not the energy saving ordinance calculation, but the investment costs if everything else (insulation, controlled residential ventilation) remains the same.

Hi,

I don't think you can compare a house from the 70s to a current KfW55 according to the current energy saving regulations. The difference is that the ratio of heating operation to hot water in a modern house will certainly not be at ten times the consumption.

Furthermore, the ST also supports the heating, not just the hot water. Controlled residential ventilation must be done anyway, the mentioned quality is part of that.

However, I must admit that I'm not 100% sure if it pays off. We'll see

That's exactly how we see it too! The solar thermal system with heating support and hot water would have cost €9000. Without heating support, just for hot water, about €4500.

Of course, the controlled residential ventilation is expensive, but that's the only thing we did not want to do without.