Hello,
to my surprise, we managed to hit the target exactly with our house planning for KfW 55. Since the repayment subsidies became more attractive from 04/01/16, I also took a look at KfW 40/40+.
Roughly about the house:
Single-family house with approximately 138 sqm (1,485 sq ft), basement for utility rooms, ground floor, and attic. Gable roof with 18°. Monolithic construction with controlled residential ventilation and an air-to-water heat pump.
The KfW 40+ information sheet states:
- A renewable energy-based power generation system
- A stationary battery storage system (electricity storage)
- A ventilation system with heat recovery
- A visualization of power generation and consumption via an appropriate user interface
So, would a photovoltaic system with battery storage possibly be enough to qualify for KfW 40+?
With a 15,000 € grant, that wouldn’t be a significant additional cost.
Best regards,
dsin8788
to my surprise, we managed to hit the target exactly with our house planning for KfW 55. Since the repayment subsidies became more attractive from 04/01/16, I also took a look at KfW 40/40+.
Roughly about the house:
Single-family house with approximately 138 sqm (1,485 sq ft), basement for utility rooms, ground floor, and attic. Gable roof with 18°. Monolithic construction with controlled residential ventilation and an air-to-water heat pump.
The KfW 40+ information sheet states:
- A renewable energy-based power generation system
- A stationary battery storage system (electricity storage)
- A ventilation system with heat recovery
- A visualization of power generation and consumption via an appropriate user interface
So, would a photovoltaic system with battery storage possibly be enough to qualify for KfW 40+?
With a 15,000 € grant, that wouldn’t be a significant additional cost.
Best regards,
dsin8788
Building expert, one more question (because I’m curious). The 55 model has different values...
You mean: HT doesn’t matter and I might be able to reduce Q_p enough with the solar system plus buffer?
Because the 40 Plus has a different HT value, which is not affected by the photovoltaic system.
Best regards, Thorsten
You mean: HT doesn’t matter and I might be able to reduce Q_p enough with the solar system plus buffer?
Because the 40 Plus has a different HT value, which is not affected by the photovoltaic system.
Best regards, Thorsten
However, Ht plays a significant role. To be precise, I even believe that Qp with a heat pump (thanks to the political primary energy factor) and controlled residential ventilation is already met, but Ht is probably the critical target, and that makes it extremely challenging with a monolithic construction method.
Normally, the wall should have a U-value of 0.15, which requires a T7 or an equivalent aerated concrete block with a lambda value of 0.07. A 0.08 block with 49cm (19 inches) achieves 0.16 — meaning that other components would need to compensate for this, which is difficult since they are also weighted down by factors, and the roof, with a calculated KfW 40 U-value of 0.11, already offers hardly any savings potential.
I have done numerous calculations, and by now, I think that with monolithic construction, a KfW 55 standard is just still economically feasible to achieve according to the reference values in the technical datasheet because the general thermal bridge approach already ruins everything. The required 0.035 thermal bridge allowance can also be simply demonstrated WITHOUT detailed thermal bridge calculations using Form D (KfW short thermal bridge method). All valid from 01.04.2016.
Calculations:
U-value Energy Saving Ordinance 2016: 0.28
KfW 55: 0.28 x 0.70 = 0.196; 0.20 according to reference values
KfW 40: 0.28 x 0.55 = 0.154; poorer values here must be compensated elsewhere
Thermal bridge allowance KfW 40: 0.05 x 0.55 = 0.0275; In my opinion, this is achievable with monolithic construction; the locally based brick manufacturer advertises 0.025 with precise calculation
Normally, the wall should have a U-value of 0.15, which requires a T7 or an equivalent aerated concrete block with a lambda value of 0.07. A 0.08 block with 49cm (19 inches) achieves 0.16 — meaning that other components would need to compensate for this, which is difficult since they are also weighted down by factors, and the roof, with a calculated KfW 40 U-value of 0.11, already offers hardly any savings potential.
I have done numerous calculations, and by now, I think that with monolithic construction, a KfW 55 standard is just still economically feasible to achieve according to the reference values in the technical datasheet because the general thermal bridge approach already ruins everything. The required 0.035 thermal bridge allowance can also be simply demonstrated WITHOUT detailed thermal bridge calculations using Form D (KfW short thermal bridge method). All valid from 01.04.2016.
Calculations:
U-value Energy Saving Ordinance 2016: 0.28
KfW 55: 0.28 x 0.70 = 0.196; 0.20 according to reference values
KfW 40: 0.28 x 0.55 = 0.154; poorer values here must be compensated elsewhere
Thermal bridge allowance KfW 40: 0.05 x 0.55 = 0.0275; In my opinion, this is achievable with monolithic construction; the locally based brick manufacturer advertises 0.025 with precise calculation
@Grym, a very valuable contribution in my personal opinion.
I’m not yet fully familiar with the topic. I’m currently considering whether I could bring my KfW70 (which has better performance values, somewhere between 70 and 55) down to KfW55 with photovoltaic systems plus buffer storage (long-term house value). Now: most likely not, the small amount of auxiliary energy simply won’t make the difference. “Politically declining primary energy factor of electricity,” yes or no. I can achieve Q_p, but not the rest (unless I redo the insulation, make the foundation slab thicker and insulated, etc.). That’s not really feasible; the existing structure as built is difficult to positively influence afterward in terms of KfW criteria, I believe.
Most people are not immediately aware that this entire primary energy calculation according to KfW depends on many factors (including those mentioned above), but also on the “fuel type” of the heating system.
What, in my personal view, is very relevant for the people living in the house is the annual heating energy demand (energy carrier) = annual costs. The primary energy demand is a derived, calculative (partly quasi-static) value, usually depending on the energy carrier ... (and its future price development).
Of course, one can invest in KfW class upgrades that may not pay off financially but do make ecological sense and can be enjoyable. You just have to be able to afford that. Here, too, the calculation is not that simple ... when do I invest in ecology, not in my personal business case?
Still, the topic of energy and living is fascinating, enjoyable, and exciting for me.
Best regards,
Thorsten
I’m not yet fully familiar with the topic. I’m currently considering whether I could bring my KfW70 (which has better performance values, somewhere between 70 and 55) down to KfW55 with photovoltaic systems plus buffer storage (long-term house value). Now: most likely not, the small amount of auxiliary energy simply won’t make the difference. “Politically declining primary energy factor of electricity,” yes or no. I can achieve Q_p, but not the rest (unless I redo the insulation, make the foundation slab thicker and insulated, etc.). That’s not really feasible; the existing structure as built is difficult to positively influence afterward in terms of KfW criteria, I believe.
Most people are not immediately aware that this entire primary energy calculation according to KfW depends on many factors (including those mentioned above), but also on the “fuel type” of the heating system.
What, in my personal view, is very relevant for the people living in the house is the annual heating energy demand (energy carrier) = annual costs. The primary energy demand is a derived, calculative (partly quasi-static) value, usually depending on the energy carrier ... (and its future price development).
Of course, one can invest in KfW class upgrades that may not pay off financially but do make ecological sense and can be enjoyable. You just have to be able to afford that. Here, too, the calculation is not that simple ... when do I invest in ecology, not in my personal business case?
Still, the topic of energy and living is fascinating, enjoyable, and exciting for me.
Best regards,
Thorsten
B
Bauexperte16 Dec 2015 23:00Good evening Thorsten,
To be honest, I’m not interested in those number games, so I probably won’t remember them and could only give you incomplete information—which I definitely won’t do. If one of our interested parties wants to go into detail on this, the appropriate specialist will attend the next appointment.
I know someone who is knowledgeable about this; that’s all that matters to me.
Regards, Bauexperte
T21150 schrieb:
Bauexperte, one more question (because I'm curious). The 55 model has different values...
You mean: HT doesn't matter and I might be able to lower Q_p enough with the solar system plus buffer?
Because the 40 Plus has a different HT value, which is not affected by the photovoltaic system
To be honest, I’m not interested in those number games, so I probably won’t remember them and could only give you incomplete information—which I definitely won’t do. If one of our interested parties wants to go into detail on this, the appropriate specialist will attend the next appointment.
I know someone who is knowledgeable about this; that’s all that matters to me.
Regards, Bauexperte
B
Bauexperte16 Dec 2015 23:16Good evening,
this is the issue with professionals and laypersons.
There have been Passive House standards achieved with monolithic construction using 36.5cm (14.5 inches) blocks for years; even for multi-storey apartment buildings. By the way, if someone builds a multi-family building as an investment, the primary decision is based on their yield calculations; it can hardly be as uneconomical for the builders as you suggest. It is understood that a significant part is driven by environmental conscience as well as political will.
Ask Google if you don’t want to believe me
Regards, Bauexperte
this is the issue with professionals and laypersons.
Grym schrieb:Aerated concrete is best suited because, due to its uniform porosity, it has consistent thermal conductivity and a high heat storage capacity. It also ensures a high airtightness of the building envelope, which helps to prevent significant energy losses.
Normally, the wall should have a U-value of 0.15, which requires either a T7 or the corresponding aerated concrete block with a lambda value of 0.07.
Grym schrieb:Anything from KfW 55 onwards certainly raises justified questions about payback periods. However, it does not matter whether KfW 55 is achieved using external wall insulation systems (EWIS) or monolithic construction. The additional costs for both methods are almost identical.
I have done calculations back and forth, and by now I believe that with monolithic construction, KfW55 is just still economically feasible.
There have been Passive House standards achieved with monolithic construction using 36.5cm (14.5 inches) blocks for years; even for multi-storey apartment buildings. By the way, if someone builds a multi-family building as an investment, the primary decision is based on their yield calculations; it can hardly be as uneconomical for the builders as you suggest. It is understood that a significant part is driven by environmental conscience as well as political will.
Ask Google if you don’t want to believe me
Regards, Bauexperte
dsin8788 schrieb:
So, a photovoltaic system with battery storage might be enough to reach KfW 40+ standard?
In that case, with a €15,000 subsidy, there wouldn’t be a significant additional cost.
Best regards,
dsin8788 What exactly is meant by that, or what is the reasoning behind it?
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