ᐅ KfW 70 standard is not met, reference values for gas condensing boiler heating
Created on: 10 Apr 2014 22:35
R
rebenstorf
Hi everyone,
I need some advice from you. Our new single-family home is currently being calculated, and the person doing the calculations called me to say that the house doesn’t meet KfW 70 standards, which shocked me because I actually thought we would almost reach KfW 55.
Here are the house details:
186m² (2000 sq ft) living area
Basement floor insulation: 8cm (3 inches) XPS, 0.04 WLG (thermal conductivity)
Exterior wall structure: 1.5cm (0.6 inches) gypsum plaster, 24cm (9.5 inches) Poroton T16 bricks, 18cm (7 inches) mineral wool insulation with 0.035 WLG, 2cm (0.8 inches) air gap, 11.5cm (4.5 inches) clinker brick facade
Windows: triple-glazed, Ug 0.7
Roof insulation: 6cm (2.4 inches) continuous insulation above rafters, 24cm (9.5 inches) mineral wool between rafters at 0.035 WLG, 6cm (2.4 inches) insulation below rafters also 0.035 WLG
Heating system: Buderus GBH172 T75S 14kW gas condensing boiler with a 750L (198 gallons) buffer storage, five SKS 4.0 solar collectors at a 45° roof pitch, south orientation, no shading
Underfloor heating on ground and upper floors
I hope I haven’t forgotten anything. Based on the transmission heat losses alone, this should almost be KfW 55, but the heating system is also taken into account. Although it’s a gas condensing boiler, it should still meet KfW 70.
Since I’ve collected quotes from several home builders and construction companies, I know what they typically do to reach KfW 70—and none of them even included a ventilation system, usually only gas condensing boilers with domestic hot water production. Regarding insulation, none of the houses even matched our planned specs.
My question to the experts: Is the person doing the calculations correct? That would basically mean almost all house providers are exaggerating their numbers... or did she make a calculation error? I understand that no opinion here replaces an official calculation, but a rough assessment should be possible.
Thanks in advance!
I need some advice from you. Our new single-family home is currently being calculated, and the person doing the calculations called me to say that the house doesn’t meet KfW 70 standards, which shocked me because I actually thought we would almost reach KfW 55.
Here are the house details:
186m² (2000 sq ft) living area
Basement floor insulation: 8cm (3 inches) XPS, 0.04 WLG (thermal conductivity)
Exterior wall structure: 1.5cm (0.6 inches) gypsum plaster, 24cm (9.5 inches) Poroton T16 bricks, 18cm (7 inches) mineral wool insulation with 0.035 WLG, 2cm (0.8 inches) air gap, 11.5cm (4.5 inches) clinker brick facade
Windows: triple-glazed, Ug 0.7
Roof insulation: 6cm (2.4 inches) continuous insulation above rafters, 24cm (9.5 inches) mineral wool between rafters at 0.035 WLG, 6cm (2.4 inches) insulation below rafters also 0.035 WLG
Heating system: Buderus GBH172 T75S 14kW gas condensing boiler with a 750L (198 gallons) buffer storage, five SKS 4.0 solar collectors at a 45° roof pitch, south orientation, no shading
Underfloor heating on ground and upper floors
I hope I haven’t forgotten anything. Based on the transmission heat losses alone, this should almost be KfW 55, but the heating system is also taken into account. Although it’s a gas condensing boiler, it should still meet KfW 70.
Since I’ve collected quotes from several home builders and construction companies, I know what they typically do to reach KfW 70—and none of them even included a ventilation system, usually only gas condensing boilers with domestic hot water production. Regarding insulation, none of the houses even matched our planned specs.
My question to the experts: Is the person doing the calculations correct? That would basically mean almost all house providers are exaggerating their numbers... or did she make a calculation error? I understand that no opinion here replaces an official calculation, but a rough assessment should be possible.
Thanks in advance!
B
Bauexperte12 Apr 2014 14:45Hello,
In that respect, emer’s comparison is not really accurate.
Regards, Bauexperte
rebenstorf schrieb:I am almost certain that the person you visited and where you took the measurements would have achieved the same effect, even if they had only installed an exterior (above-rafter) insulation.
There is no mixed stuff there, and no comparing apples and oranges.
In that respect, emer’s comparison is not really accurate.
Regards, Bauexperte
I know this might not help you now, but maybe it will be useful for others reading this: I made sure by contract that our house would achieve the desired KFW level without any additional costs for us compared to the original planning basis. By the way, I really like your roof structure; because of our "open" roof frame and summer heat protection, I have also extensively worked with the U-value calculator.
We decided to skip the KfW stuff because it is a political, lobby-driven mess that unnecessarily complicates the good idea of ecological building and leads it in the wrong direction. (A very simplified, subjective summary on my part.)
With KfW, you initially get a somewhat better 10-year loan, which isn’t that great considering current interest rates. However, the entire planning and energy calculation process is time-consuming and complex. This complexity often leads to mistakes, and the range within which a house with the chosen technology can later be operated energy-efficiently is rather narrow.
We are now building according to the 2009 Energy Saving Ordinance with 42.5cm (17 inches) aerated concrete blocks and a gas condensing boiler. Underfloor heating. We can skip solar stuff because the 15% rule applies.
With KfW, you initially get a somewhat better 10-year loan, which isn’t that great considering current interest rates. However, the entire planning and energy calculation process is time-consuming and complex. This complexity often leads to mistakes, and the range within which a house with the chosen technology can later be operated energy-efficiently is rather narrow.
We are now building according to the 2009 Energy Saving Ordinance with 42.5cm (17 inches) aerated concrete blocks and a gas condensing boiler. Underfloor heating. We can skip solar stuff because the 15% rule applies.
One00 schrieb:
..... and also extensively dealt with summer heat protection using the U-value calculator. Have you also read the liability and warranty disclaimers? Anyone who thinks that free online tools actually offer real help should take a closer look at the disclaimers and general terms and conditions! Those who believe that economically valuable, practical knowledge is distributed for free probably live in a socialist mindset. The results of such "guides" are not legally reliable and therefore essentially worthless! These free guides and tools are funded by Google AdSense, not by professionally or legally usable content.Best regards
Yes, of course. I should have hired an HVAC engineer, and by chance, you happen to be one. I understand.
With my modest background in mechanical engineering, I think I can at least interpret this page and its results to the extent that it gives me a simple understanding of how temperature profiles change within the building component when the roofing system parameters are also altered. Nothing more. It should be clear to the user that the author does not guarantee these results. Anyone who doesn’t understand this is probably not capable of using the calculator correctly anyway.
With my modest background in mechanical engineering, I think I can at least interpret this page and its results to the extent that it gives me a simple understanding of how temperature profiles change within the building component when the roofing system parameters are also altered. Nothing more. It should be clear to the user that the author does not guarantee these results. Anyone who doesn’t understand this is probably not capable of using the calculator correctly anyway.