Ventilation system in single-family house without effect = planning error?

Right - I hadn't considered the preheating register... But this makes me all the more certain that the ventilation system can definitely not save energy through electricity/gas consumption over the course of the year. On average, the system otherwise consumes a good 50-60W/h, which adds up to quite some costs over the year... (about €120-130 + plus what is added now during the cold days)

Yes, I connected Fritz.Dect sockets to each one - I find it interesting that the pattern of power consumption is almost identical and wonder if I made a user error in thinking

The gas boiler shouldn't actually consume more than usual, at most a couple of percent. In the controlled residential ventilation system, the preheating coil is certainly to blame.

Yes, that's what I thought too - I can well understand that gas consumption increases significantly at very low temperatures - but the electricity consumption!? I think I must have done something wrong - that’s illogical. Especially since the values are almost the same... I have a suspicion and will take a look in the attic right away ;-)

But that only makes me all the more certain that the ventilation system can by no means save energy through electricity/gas consumption over the year.

In general terms, controlled residential ventilation saves you 10-12% in losses due to shock ventilation. In other words, you save 10-12% on energy costs per year = roughly 1 month of gas payments... which you can then offset against the electricity costs for the controlled residential ventilation. But controlled residential ventilation is certainly not primarily a savings model, but purely a comfort gain with a small saving effect.

Constant fresh air and no unpleasant odors, as well as less dust and no need for constant manual ventilation. These are the main tasks of controlled residential ventilation.

Yes, that is - if it works properly - certainly the main task. But I do not understand why it should be sufficient as an "energy-saving" measure to meet, for example, the [Energieeinsparverordnung 2016] standards when it consumes more energy than it saves. For example, we no longer had to install solar thermal systems or similar, because it was apparently sufficient in the calculations with the [Kontrollierte-Wohnraumlüftung].

But okay - that should not be my biggest problem -> first of all, it should work properly. I could imagine that it would require much less electricity if it were properly sized and designed.

The problem for power consumption is your preheating coil. A large system can run at a lower level and save some electricity in the process. However, the purchase price is more expensive. Through heat recovery, you save energy, but as has already written, the biggest advantage is comfort. Especially in such a tight house, you can no longer keep up with manual ventilation. In very large systems, the preheating coil hardly ever runs because sufficiently warm air flows over the heat exchanger.

We have a very large system. The supply and exhaust air are located on the other side of the property. The air is guided approx. 35 meters at a depth of 5 meters through the ground. Our system has a special heat exchanger that is frost-resistant down to minus 20°. Currently, the outside air (-5°) arrives at +2° in the controlled residential ventilation. As a result, even in freezing temperatures, no additional heating has been activated so far. The system currently runs at the lowest level (1000m3) with approx. 250W. At full power and reheating, it's almost 8KW :p. Ventilation alone at full power is about 1.5kw.

I don’t understand why it should be sufficient as an "energy-saving" measure to meet, for example, Energy Saving Ordinance 2016 standards if it consumes more energy than it saves.

That’s often the case with "energy-saving" things. Electric cars only break even after several years. Cars with aluminum bodies are lighter and save fuel, but practically never reach the break-even point because the energy used in manufacturing exceeds what the car could ever save. Individual room control in many houses nowadays consumes more energy than it saves. And so on, etc. The list can go on for a long time. Controlled residential ventilation saves about 10% compared to manual ventilation. This justifies it. But it is of course assumed that it is properly sized, properly installed, and properly operated. However, if one or possibly all three of these points are not ideal, the calculation no longer works out. Driving a car always in second gear and wasting fuel unnecessarily is also not the manufacturer’s fault. Electric preheating coils, however, are a quick and easy way for manufacturers to get off the hook. These should actually be banned. There are better methods regarding the saving effect that are passive, but these increase the cost of the system and for that reason are rather rare. Because homebuyers/builders/general contractors always only look at the price.