ᐅ KfW70 standard with a gas condensing boiler and solar panels is definitely not feasible.
Created on: 6 Aug 2014 15:56
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TeuPhilHello 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
Hi,
I am definitely not an expert in these matters. There are others here in the forum who know much more about this.
When I looked into heating technology in the past, a consultant mentioned the zeolite gas heat pump as a particularly energy-efficient gas heating system. However, it also depends on your budget, as this costs quite a bit more than a standard gas condensing boiler.
You can surely get more information from search engines and, of course, from the experts here in the forum.
I am definitely not an expert in these matters. There are others here in the forum who know much more about this.
When I looked into heating technology in the past, a consultant mentioned the zeolite gas heat pump as a particularly energy-efficient gas heating system. However, it also depends on your budget, as this costs quite a bit more than a standard gas condensing boiler.
You can surely get more information from search engines and, of course, from the experts here in the forum.
Hello f-pNo,
thank you for your response. I had actually already looked into the zeolite gas heat pump. It’s definitely an impressive piece of technology. However, the disadvantages are significant enough that this technology is only suitable for builders who don’t need to worry about costs and who can strictly follow a purely eco-friendly conscience.
Such a system would be more than twice as expensive as a conventional gas condensing boiler. My heating contractor quoted me additional costs of about €14,000. Amortization is probably just a dream in this case.
Surely it should be possible to meet the KfW 70 standard with a conventional modern gas condensing boiler, a controlled residential ventilation system with heat recovery, and (the unfortunately almost essential) solar thermal system for domestic hot water and heating support.
By the way, my already approved building permit / planning permission is still based on the 2009 Energy Saving Ordinance, if that is relevant here at all. According to my building planner, I can almost be glad to have received a building permit at all despite using gas as the primary energy source. …Oh really?!
thank you for your response. I had actually already looked into the zeolite gas heat pump. It’s definitely an impressive piece of technology. However, the disadvantages are significant enough that this technology is only suitable for builders who don’t need to worry about costs and who can strictly follow a purely eco-friendly conscience.
Such a system would be more than twice as expensive as a conventional gas condensing boiler. My heating contractor quoted me additional costs of about €14,000. Amortization is probably just a dream in this case.
Surely it should be possible to meet the KfW 70 standard with a conventional modern gas condensing boiler, a controlled residential ventilation system with heat recovery, and (the unfortunately almost essential) solar thermal system for domestic hot water and heating support.
By the way, my already approved building permit / planning permission is still based on the 2009 Energy Saving Ordinance, if that is relevant here at all. According to my building planner, I can almost be glad to have received a building permit at all despite using gas as the primary energy source. …Oh really?!
...allegedly no significant improvement in primary energy consumption either. In this case, it would mainly further reduce the heat loss through the building envelope. However, my current values for the transmission heat loss are already within the desired range. The problem still lies in the too high primary energy consumption.
Perhaps someone in this forum has already built a solid wall house with a single-shell construction and a gas condensing boiler system, achieving the KfW70 standard... How did it go for you?
Perhaps someone in this forum has already built a solid wall house with a single-shell construction and a gas condensing boiler system, achieving the KfW70 standard... How did it go for you?
I know this isn’t the answer you’re looking for, but nonetheless: we decided to skip all that KfW stuff. Financially, the loan terms don’t offer much advantage, but it does restrict your options in the building services and even forces you into certain requirements that I consider pointless.
We are simply building according to the 2009 Energy Saving Ordinance with a gas condensing boiler and insulating in a way that allows us to take advantage of the 15% rule.
Just question everything.
We are simply building according to the 2009 Energy Saving Ordinance with a gas condensing boiler and insulating in a way that allows us to take advantage of the 15% rule.
Just question everything.
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