Exorbitant power consumption house construction single-family house experiences

That means you had construction activities over the meter from 09/20 - 02/21, but only usual construction machines (driller, mixer, lamps, etc.). How was heating done? Was there any heating at all?

In Nov. 21 the construction power box was put into operation with a meter by the municipal utilities. Until March/April only rotary hammer drills were used; the demolition period was also not heated, etc.

You write it is not a new building. What is the house’s energy standard and how large is it? Was the underfloor heating well insulated against the ground? In existing buildings the installation height cannot be easily changed.

The house was renovated to Kfw 85 standard; 70 was not possible because the floor slab could not be insulated. Walls, including those below ground level, were insulated (16cm WLG0032). Under the screed 4cm WLG035 on just under 370 sqm.

If you deduct 1,500 kWh for household electricity excluding heating (which is already a lot), 3,500 kWh remain. Since the heating portion should be very low from April to September, at most still present in April, most of this will have been used for hot water. 3,500 kWh corresponds to about 12,000 kWh of heat (high COP for heating in April and also high COP for hot water in summer). That is what other new buildings consume in an entire year for heating and hot water, which is also way too much for a single-family house of normal size. The same applies here: data on the house and usage (people, special equipment, electric car?) are missing, otherwise this cannot be evaluated.

Sorry, as an addition: 2 adults + 2 children (6+4) and you are right, there is also a smaller electric car (not on the construction electricity ;-))
The electric car consumes about 150 kWh/month

The house was renovated to KFW 85 standard, 70 was not possible because the floor slab could not be insulated. Walls, including those in the earth, were insulated (16cm WLG0032).
Under the screed, 4cm WLG035 over nearly 370sqm.

So, quite large after all.
Screed drying then amounts to rather 5-10,000 kWh, depending on how the heat pump was used there, or whether the heating element was often on.
If it ran unexpectedly longer, maybe even a bit more.

KfW 85 with 40% existing building surcharge (congratulations on the quite generous funding back then) should then land at about 100 kWh / m² and heating load technically at 60 W/m². Multiplying that by 370m² results in 37,000 kWh heating demand or 22 kW heating load.

With a SCOP of 3, you should thus end up at about 12,000 kWh electricity, and with SCOP = 4 under 10,000 kWh.

The 3,500-4,000 kWh for the half summer year is already quite a lot, too much to end up below 12,000 kWh per year.
You should have a calculation for the KfW matter. What does it say there about heating demands (final energy, useful energy, primary energy)?
Overall, you should keep a close eye on the electricity consumption this winter and log it at least monthly, better weekly along with outdoor temperature. If that seems too high, talk to the heating technician or the KfW consultant so that something can be readjusted on the heating system. Maybe it simply isn’t running smoothly, cycling, temperatures too high, etc.

If you realistically assume 15,000 kWh for the construction phase including heating up, 30,000 kWh electricity remains for living through one winter. That can’t be correct for KFW 85.

You should have a calculation for the KfW matter. What does it say as heat demands (final energy, useful energy, primary energy)?

yes, I have an iSFP, it states for the house primary energy demand: 37 kWh/(m2a), which is then 13690 kWh? expected final energy consumption 9,350 kWh/a I don't have useful energy ;-) As described before, I am very dissatisfied with the "Heizi", because among other things the system has not yet been properly handed over. I am sure it still needs adjustment... Thanks for your calculation

If you write that the system has not been properly handed over yet: However, it is already set up to some extent and is running in "normal mode" and not on the heating element for months?

Have the meter checked for the construction power. There are independent agencies for this.