ᐅ KfW70 standard with a gas condensing boiler and solar panels is definitely not feasible.
Created on: 6 Aug 2014 15:56
T
TeuPhil
Hello everyone!
Yes, this is the statement from my architect that has been on my mind for quite some time now, and given that houses exactly like these exist—with the certificate I want—I am not quite satisfied with it.
But first, a brief overview of the key data for our planned single-family house, hopefully including the values relevant here:
- 2 full stories with a converted and habitable attic (35-degree pitched roof) with a total heated area of 220 sqm (2370 sq ft) without a basement
- heated building volume: 828 cubic meters (29,240 cubic feet)
- usable area according to energy saving regulations: 265 sqm (2852 sq ft)
- primary energy demand QP: 61.02
- transmission heat loss HT: 0.337
- ventilation heat loss HV: 128.35 W/K
The whole thing will be realized with the following technology and insulation:
- gas condensing boiler with solar thermal for domestic hot water (and heating support option)
- controlled ventilation system with heat recovery
- house orientation: SSW/NNE
- exterior masonry: 365 mm (14 inches) aerated concrete, thermal conductivity 0.035, U-value = 0.229
- pitched roof U-value = 0.19 (currently 20 cm (8 inches) insulation between rafters)
- ground floor slab U-value = 0.298
- aluminum front door U-value = 1.3
- triple-glazed windows U-value = 0.84
As a result, the KfW70 standard is met in terms of transmission heat loss. However, the annual primary energy demand is still problematic.
When I asked how the remaining approximately 11 kWh could be saved in a (also economically) reasonable way, I received the rather general answer: “with a heat pump or a pellet boiler.” But I deliberately chose conventional gas and do not want to deviate from that decision. Also, I suspect that these are hardly the only possible solutions but rather the simplest ones.
Before I take the (already planned) step to consult an energy advisor, I would like to ask the experts here in the forum whether my prospects are really that bleak if I stick with gas as my primary energy source.
Oh, one more thing... the house is not being built by a developer or general contractor. So I’m relatively flexible with purchasing. The cost-benefit factor should just be kept reasonable.
As a final note, here’s the answer in advance to the question: “Why KfW70 in particular?”
I am aware that a KfW85 house can have a lower energy demand than a KfW70 house. Much can be calculated advantageously here (keyword: heat pumps). But ultimately, it’s the “good feeling” of having proof at any time with a certificate that I own a particularly energy-efficient house. How paradoxical that sounds... In the end, I simply want to achieve the best possible energy standard for my budget.
Best regards
TeuPhil
Yes, this is the statement from my architect that has been on my mind for quite some time now, and given that houses exactly like these exist—with the certificate I want—I am not quite satisfied with it.
But first, a brief overview of the key data for our planned single-family house, hopefully including the values relevant here:
- 2 full stories with a converted and habitable attic (35-degree pitched roof) with a total heated area of 220 sqm (2370 sq ft) without a basement
- heated building volume: 828 cubic meters (29,240 cubic feet)
- usable area according to energy saving regulations: 265 sqm (2852 sq ft)
- primary energy demand QP: 61.02
- transmission heat loss HT: 0.337
- ventilation heat loss HV: 128.35 W/K
The whole thing will be realized with the following technology and insulation:
- gas condensing boiler with solar thermal for domestic hot water (and heating support option)
- controlled ventilation system with heat recovery
- house orientation: SSW/NNE
- exterior masonry: 365 mm (14 inches) aerated concrete, thermal conductivity 0.035, U-value = 0.229
- pitched roof U-value = 0.19 (currently 20 cm (8 inches) insulation between rafters)
- ground floor slab U-value = 0.298
- aluminum front door U-value = 1.3
- triple-glazed windows U-value = 0.84
As a result, the KfW70 standard is met in terms of transmission heat loss. However, the annual primary energy demand is still problematic.
When I asked how the remaining approximately 11 kWh could be saved in a (also economically) reasonable way, I received the rather general answer: “with a heat pump or a pellet boiler.” But I deliberately chose conventional gas and do not want to deviate from that decision. Also, I suspect that these are hardly the only possible solutions but rather the simplest ones.
Before I take the (already planned) step to consult an energy advisor, I would like to ask the experts here in the forum whether my prospects are really that bleak if I stick with gas as my primary energy source.
Oh, one more thing... the house is not being built by a developer or general contractor. So I’m relatively flexible with purchasing. The cost-benefit factor should just be kept reasonable.
As a final note, here’s the answer in advance to the question: “Why KfW70 in particular?”
I am aware that a KfW85 house can have a lower energy demand than a KfW70 house. Much can be calculated advantageously here (keyword: heat pumps). But ultimately, it’s the “good feeling” of having proof at any time with a certificate that I own a particularly energy-efficient house. How paradoxical that sounds... In the end, I simply want to achieve the best possible energy standard for my budget.
Best regards
TeuPhil
In short: achieving KfW 70 is possible with relatively little effort, while reaching KfW 55 requires disproportionately more. Therefore, in my view, you really have to be quite environmentally committed for KfW 55, whereas KfW 70 can be justified more from a practical standpoint. Just my opinion.
J
Julemming14 Oct 2014 00:31Hi
I have to admit that I don’t know myself as well as I would like yet, but today I received the approval for KFW funding.
Building plan:
30 cm (12 inch) aerated concrete blocks
Gas heating system with solar support for hot water
Ventilation system with heat recovery
2 full floors
150 m² (1,615 sq ft)
No basement
Hope this helps, otherwise sorry.
If it helps, I can also check the documents for primary energy demand, etc.
Best regards
I have to admit that I don’t know myself as well as I would like yet, but today I received the approval for KFW funding.
Building plan:
30 cm (12 inch) aerated concrete blocks
Gas heating system with solar support for hot water
Ventilation system with heat recovery
2 full floors
150 m² (1,615 sq ft)
No basement
Hope this helps, otherwise sorry.
If it helps, I can also check the documents for primary energy demand, etc.
Best regards
KFW 70 with 30 cm (12 inches) aerated concrete?? I can hardly believe that; without external thermal insulation composite systems (ETICS), you will never meet the requirements. With a simple 30 cm (12 inches) aerated concrete wall, you can at best achieve a U-value of 0.28.
However, I don’t understand why a KFW standard wouldn’t be possible based on the original poster’s specifications. In principle, solar panels are not even necessary. We plan to build with controlled mechanical ventilation and a gas boiler, so we can do without solar.
However, I don’t understand why a KFW standard wouldn’t be possible based on the original poster’s specifications. In principle, solar panels are not even necessary. We plan to build with controlled mechanical ventilation and a gas boiler, so we can do without solar.
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