ᐅ Excessive Electricity Consumption in Single-Family Home Construction – Experiences

dertill schrieb:

So you had construction activities exceeding the meter reading from 09/20 to 02/21, but only typical construction equipment (drills, mixers, lamps, etc.).
How was heating provided? Was there any heating at all?

In November 2021, the construction power box was connected to a meter by the local utility company. Until March/April, only rotary hammers were occasionally used; during the demolition phase, no heating was applied, etc.

dertill schrieb:

You mentioned it is not a new build. What energy standard does the house meet and what is its size? Was the underfloor heating properly insulated against the ground? In existing buildings, it is usually hard to change the build-up height.

The house was renovated to KfW 85 standard; KfW 70 was not possible because the slab-on-grade could not be insulated. Walls, including the parts below ground level, were insulated (16cm (6 inches) with insulation material rated WLG 0032). Under the screed, there is 4cm (1.5 inches) of insulation rated WLG 0035 covering nearly 370 square meters (3980 square feet).

dertill schrieb:


If you subtract 1,500 kWh for household electricity excluding heating (which is already quite high), you are left with 3,500 kWh.
Since the heating demand from April to September should be very low, mostly only in April, a large share of this is likely used for domestic hot water. 3,500 kWh corresponds to about 12,000 kWh of heat (with a high COP for heating in April and also a high COP for hot water in summer). Other new builds consume this amount over an entire year for heating and hot water, which is quite a lot for a single-family house of typical size.
Again: data on the house and its usage (number of occupants, special features, electric car?) are missing; without these details, it is impossible to evaluate properly.

Sorry, to add: 2 adults + 2 children (6 + 4 years old) and you are right, there is still a smaller electric car (not charged on construction power ;-))
The electric car consumes about 150 kWh per month.

NikSindi schrieb:

The house was renovated to KfW 85 standard; 70 wasn’t possible because the floor slab couldn’t be insulated. Walls, including those below ground level, were insulated (16cm WLG0032).
Under the screed, 4cm WLG035 on almost 370m² (3980 sq ft).

That’s still quite large.
Screed drying can require about 5,000 to 10,000 kWh depending on how the heat pump was used or if the electric heating element was frequently running. If it ran longer than planned, it might even be more.

KfW 85 with a 40% existing building surcharge (congratulations on the generous funding at the time) should result in around 100 kWh/m² (32 kBtu/sq ft) and a heating load of around 60 W/m² (6.2 W/sq ft). Multiplying by 370m² (3980 sq ft) gives a heating demand of 37,000 kWh and a heat load of 22 kW.

With a SCOP of 3, you would expect about 12,000 kWh of electricity usage; with a SCOP of 4, under 10,000 kWh.

Using 3,500–4,000 kWh for half a summer is quite a lot—too high to end up below 12,000 kWh annual consumption.
You should have a calculation for the KfW application. What values does it show for heat demand (final energy, useful energy, primary energy)?
Overall, you should closely monitor electricity consumption this winter and log it at least monthly, preferably weekly, along with outdoor temperatures. If the values seem too high, talk to your heating installer or the KfW consultant to have the heating system readjusted. Maybe it’s not running smoothly, cycling too often, running at too high temperatures, etc.

Assuming realistically about 15,000 kWh for construction phase heating and drying, that leaves 30,000 kWh of electricity for normal winter use. That cannot be right for a KfW 85 standard house.

dertill schrieb:

You should have a calculation for the KfW-related matters. What does it say about the energy demands (final energy, delivered energy, primary energy)?

Yes, I have an iSFP; it states the house’s primary energy demand as 37 kWh/(m2a) (37 kWh per square meter per year), which amounts to 13,690 kWh?

Expected final energy consumption is 9,350 kWh/year.
I don’t have data on delivered energy. ;-)
As mentioned before, I am very dissatisfied with the heating technician, partly because the system has not been properly handed over yet. I’m sure it still needs adjustments...

Thanks for your calculation.

If you say the system has not been properly handed over yet: it is already set up to a reasonable extent and is running in "normal mode," not on the electric heater for months?

Have the temporary construction power meter inspected. There are independent authorities that handle this.