ᐅ Is the district heating consumption too high for a KW 55 house?
Created on: 21 Nov 2019 15:55
T
Tom1971Hello,
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
KfW-55 usually requires less than 30 kWh/m²*a. So, extrapolating for November, you nearly used up your annual energy consumption.
Were windows left open? Is the heat exchanger in the controlled ventilation system working properly?
Also: how warm was the building at handover? Heating 3.6 tons of sand-lime brick by 1° requires about 1 kWh. Screed, concrete, and bricks have roughly the same values. Assuming 180 tons (calculate yourself!) and a 6°C (11°F) difference would already amount to about 300 kWh.
Were windows left open? Is the heat exchanger in the controlled ventilation system working properly?
Also: how warm was the building at handover? Heating 3.6 tons of sand-lime brick by 1° requires about 1 kWh. Screed, concrete, and bricks have roughly the same values. Assuming 180 tons (calculate yourself!) and a 6°C (11°F) difference would already amount to about 300 kWh.
You think I’m just hyperventilating right now? I hope it really turns out to be just me panicking.
Regarding the questions:
1) The underfloor heating was running for 14 days before the handover, and the walls feel “normal,” definitely not cold.
2) We ventilate by fully opening the windows for five minutes 2-3 times a day to remove moisture. Can that really have such a big effect?
Regarding the questions:
1) The underfloor heating was running for 14 days before the handover, and the walls feel “normal,” definitely not cold.
2) We ventilate by fully opening the windows for five minutes 2-3 times a day to remove moisture. Can that really have such a big effect?
Hello Scout – yes, that’s also my concern: the annual consumption is practically used up by November.
Regarding the calculation: good idea, I’ll start doing the math. The walls are no longer cold (interior walls definitely not, but even the exterior walls feel normally warm).
Regarding the calculation: good idea, I’ll start doing the math. The walls are no longer cold (interior walls definitely not, but even the exterior walls feel normally warm).
Bonus question: Is it possible that the underfloor heating has a leak, causing the district heating to be continuously refilled? There are no visible signs anywhere in the house, and after at least 3 days of leakage, it should have been detected by now. I hope it’s not worse than it appears from the numbers alone...
Similar topics