ᐅ Is the district heating consumption too high for a KW 55 house?
Created on: 21 Nov 2019 15:55
T
Tom1971
Hello,
We have just taken over our house from the developer. It is a detached KfW Efficiency House 55, the blower door test was passed with flying colors, so the house is airtight. We have underfloor heating, and the heating system is connected to a district heating network (heated area 230 square meters (2475 square feet)). But now we have the following problem:
1. Within the first three days after handover, the calibrated meter recorded 470 kilowatt-hours of district heating consumption. Keep in mind that at the moment only the underfloor heating is running at 21 degrees (70°F), bathrooms and showers are not in use yet (we are moving in next month). So this consumption is exclusively from the underfloor heating.
2. When I extrapolate this to 30 days in November, this results in about 4700 kilowatt-hours of heating energy. Historically, November accounts for about 11.4% of the annual heating energy (source: Munich utility company averaged over all their district heating customers). Based on this, the annual consumption would be nearly 43,000 kilowatt-hours, or 185 kilowatt-hours per heated square meter per year.
3. According to the 2018 heating cost index for district heating, the average value is 133 kilowatt-hours per heated square meter per year, and this includes tens of thousands of buildings from the 1970s, 80s, and 90s with poor insulation. We are therefore nearly 40% above the average, which probably means 70–80% above the value expected for KfW 55 houses if compared.
Does this sound strange to you as well?
A technician for the heating system will visit tomorrow, but if they don’t find anything to explain the discrepancy, I will have to file a complaint immediately.
What do you think?
Many thanks in advance for your replies!
Best regards,
Thomas
We have just taken over our house from the developer. It is a detached KfW Efficiency House 55, the blower door test was passed with flying colors, so the house is airtight. We have underfloor heating, and the heating system is connected to a district heating network (heated area 230 square meters (2475 square feet)). But now we have the following problem:
1. Within the first three days after handover, the calibrated meter recorded 470 kilowatt-hours of district heating consumption. Keep in mind that at the moment only the underfloor heating is running at 21 degrees (70°F), bathrooms and showers are not in use yet (we are moving in next month). So this consumption is exclusively from the underfloor heating.
2. When I extrapolate this to 30 days in November, this results in about 4700 kilowatt-hours of heating energy. Historically, November accounts for about 11.4% of the annual heating energy (source: Munich utility company averaged over all their district heating customers). Based on this, the annual consumption would be nearly 43,000 kilowatt-hours, or 185 kilowatt-hours per heated square meter per year.
3. According to the 2018 heating cost index for district heating, the average value is 133 kilowatt-hours per heated square meter per year, and this includes tens of thousands of buildings from the 1970s, 80s, and 90s with poor insulation. We are therefore nearly 40% above the average, which probably means 70–80% above the value expected for KfW 55 houses if compared.
Does this sound strange to you as well?
A technician for the heating system will visit tomorrow, but if they don’t find anything to explain the discrepancy, I will have to file a complaint immediately.
What do you think?
Many thanks in advance for your replies!
Best regards,
Thomas
You seem to enjoy calculations. With a bit of effort, you can easily estimate how much energy—ignoring any losses—is required to raise the temperature of your building structure by a certain number of degrees.
Just as a rough example:
The floor slab and ceiling weigh about 120,000 kg (265,000 lbs) of concrete. Concrete has a specific heat capacity of 0.88 kJ/kg·K.
Assuming the house is initially at 12°C (54°F) and needs to be heated to 20°C (68°F), this results in a temperature difference (ΔT) of 8 K.
Energy = 0.88 × 120,000 × 8 = 850 MJ, which converts to approximately 250 kWh.
Now do the same calculation for masonry, screed, plaster...
And finally, subtract the heat losses linearly over time.
It all adds up.
Just as a rough example:
The floor slab and ceiling weigh about 120,000 kg (265,000 lbs) of concrete. Concrete has a specific heat capacity of 0.88 kJ/kg·K.
Assuming the house is initially at 12°C (54°F) and needs to be heated to 20°C (68°F), this results in a temperature difference (ΔT) of 8 K.
Energy = 0.88 × 120,000 × 8 = 850 MJ, which converts to approximately 250 kWh.
Now do the same calculation for masonry, screed, plaster...
And finally, subtract the heat losses linearly over time.
It all adds up.
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