ᐅ Reliability of an energy calculation for KfW 55 – is it too high?

Hello everyone,

For our new build with 2 full floors and a basement, we have now received a calculation for the entire KfW application. However, it seems to me that the numbers are being calculated quite high or may even be incorrect.

Some data about the house:

• Architect’s plan shows living area: ground floor 75m² (807 ft²) & upper floor 70m² (753 ft²) (difference due to open space)
• Clear ceiling height: ground floor 2.7m (8 ft 10 in) & upper floor 2.5m (8 ft 2 in)
• Basement is unheated, air-water heat pump located in the basement
• Attic is not developed
• Air-water heat pump with ventilation system including heat recovery
• The expert assessor calculates a usable floor area of 277m² (2,982 ft²), which seems very high to me! He then uses this to estimate electricity consumption and arrives at a final energy demand of 4,860 kWh/year

Is that the electricity consumption I should expect, or am I misunderstanding something? That seems very high!

Thank you in advance.

4860 kW/a!? Do you mean 4860 kWh per year heating demand, primary energy demand, or final energy demand?
Heating demand would be very low, primary energy very high. Final energy would mean about 90 € per month at 22 cents per kWh – not unreasonable for domestic hot water and heating, including the basement.
Could you possibly anonymize the report and upload it? There is a lot of guesswork without more details.

Hello,
this topic is very complex and difficult to explain for a non-expert.

However, purely theoretically and based on the given assumptions, you need around 4,900 kWh of heating energy, more or less.

It does not specify where this heating energy comes from or how it is generated.

If you calculate with a COP of 3, you would need about 1,600 kWh of electricity, or 1,500, or 1,800, or something close to that. Initially, it would likely be higher anyway.

This consideration is very theoretical and does not reflect the actual situation.

But I think it is not entirely unrealistic given the size of the house.

As already mentioned, I am referring to a final energy demand of 4860 kWh/year.

The basement is neither heated nor occupied.

The calculated annual primary energy demand Q according to the energy saving ordinance for the new building is 31.6 kWh/m² (3.0 kWh/ft²).

The built-up area is 11 x 9 m (36 x 30 ft)!

Solid construction method.

All data can be found in the attachment. I do not understand the calculation of the usable floor area; the basement is not heated after all!!!

The heating system must be located within the insulated envelope; is that the case?

Is the basement ceiling insulated, or is it the basement floor? What about the basement walls?

Overall: What is included in the thermal envelope?

The heating system is located in the basement, which is insulated to KfW55 standard. Is the basement counted as living space for energy consumption, even though there are no radiators or underfloor heating installed there? The usable floor area just seems very high to me!