ᐅ New Construction KfW 70 House and Your Feedback on Our Project
Created on: 9 Sep 2015 20:49
S
stiff80
Hello,
We are currently planning a new build for our family.
The plan is for a bungalow with an attic space for storage (wood-beam ceiling).
This week, the energy consultant came and presented the calculation for the planned KfW 70 house.
I will upload the documents from the energy consultant later or add them to this thread.
One of my first questions was how to improve from KfW 70 to KfW 55 and what the cost implications would be.
Now I would like to hear your opinions on the documents and then ask my questions.
So far, these are the facts:
- Single-layer wall construction 36.5 cm (14.4 inches) Bisotherm Bisoplan 0.09
- Air-to-water heat pump
- Underfloor heating
- No mechanical ventilation with heat recovery
- 5 cm (2 inches) insulation below and 8 cm (3 inches) insulation above the foundation slab
These are my questions:
- Are the additional costs for a Bisotherm block with integrated insulation worthwhile or wasted money?
- Should I rather increase the insulation in other areas such as below and above the foundation slab or in the ceiling?
- ..........
We are currently planning a new build for our family.
The plan is for a bungalow with an attic space for storage (wood-beam ceiling).
This week, the energy consultant came and presented the calculation for the planned KfW 70 house.
I will upload the documents from the energy consultant later or add them to this thread.
One of my first questions was how to improve from KfW 70 to KfW 55 and what the cost implications would be.
Now I would like to hear your opinions on the documents and then ask my questions.
So far, these are the facts:
- Single-layer wall construction 36.5 cm (14.4 inches) Bisotherm Bisoplan 0.09
- Air-to-water heat pump
- Underfloor heating
- No mechanical ventilation with heat recovery
- 5 cm (2 inches) insulation below and 8 cm (3 inches) insulation above the foundation slab
These are my questions:
- Are the additional costs for a Bisotherm block with integrated insulation worthwhile or wasted money?
- Should I rather increase the insulation in other areas such as below and above the foundation slab or in the ceiling?
- ..........
Actually, everything on this topic has already been said... Building without a mechanical ventilation system with heat recovery basically means, to me, that someone always has to be home to heat and ventilate.
In my opinion, working people cannot maintain the required ventilation intervals... at least we and our friends and family cannot.
And if there is no mold yet... it will appear eventually... nowadays, people basically live in a plastic bag... moisture simply cannot escape easily, unless you can stick to the heating and ventilation intervals mentioned above, or the house was built so poorly that there are drafts everywhere...
In my opinion, working people cannot maintain the required ventilation intervals... at least we and our friends and family cannot.
And if there is no mold yet... it will appear eventually... nowadays, people basically live in a plastic bag... moisture simply cannot escape easily, unless you can stick to the heating and ventilation intervals mentioned above, or the house was built so poorly that there are drafts everywhere...
Thank you all for the many responses. I have now spoken with the heating company, and they are offering me a system from Viessmann. I believe it is the Vitovent 300.
Now to my main question.
How did you decide where to use additional insulation?
This question, of course, is something everyone has answered differently for their own build.
In the second post, you can see the current facts.
Best regards
Now to my main question.
How did you decide where to use additional insulation?
This question, of course, is something everyone has answered differently for their own build.
In the second post, you can see the current facts.
Best regards
From my heating load calculation for our kitchen:
Floor slab: 28.52 m² (307 sq ft) * 0.17 W/m²K * 20 K = 96 W (assumed 0°C (32°F) outdoor temperature)
Exterior wall: 19.84 m² (213 sq ft) * 0.186 W/m²K * 32 K = 118 W
Windows: 10.48 m² (113 sq ft) * 0.78 W/m²K * 32 K = 262 W
Thermal bridges: 58.84 * 0.05 W/m²K * 32 K = 95 W
Ventilation losses: 90 W (600 W total / 190 m² (2045 sq ft) living area * 28.5 m² (307 sq ft) room area)
________
661 W
Rafters / top floor ceiling have a U-value of 0.156 W/m²K.
Your heat transfer coefficient (HT) is still better than mine (0.234 vs. 0.246), but that is probably due to your larger window area of 18.5 m² (199 sq ft).
My primary energy demand is lower at 31 kWh compared to yours, but that is only due to the heating system. We calculate monthly costs for hot water and heating at about €55 (11,400 kWh and an annual performance factor of 4.5).
What would I take away from this? You will have low heating costs - whether adding more insulation to your building is worthwhile is unclear - what might be beneficial would be having more window area.
What heating demand do you have for your project? Then you can calculate how much you would pay now and what you would need to do to pay less. Improving roof insulation is relatively cost-effective to achieve, depending of course on the planned rafter thickness.
Floor slab: 28.52 m² (307 sq ft) * 0.17 W/m²K * 20 K = 96 W (assumed 0°C (32°F) outdoor temperature)
Exterior wall: 19.84 m² (213 sq ft) * 0.186 W/m²K * 32 K = 118 W
Windows: 10.48 m² (113 sq ft) * 0.78 W/m²K * 32 K = 262 W
Thermal bridges: 58.84 * 0.05 W/m²K * 32 K = 95 W
Ventilation losses: 90 W (600 W total / 190 m² (2045 sq ft) living area * 28.5 m² (307 sq ft) room area)
________
661 W
Rafters / top floor ceiling have a U-value of 0.156 W/m²K.
Your heat transfer coefficient (HT) is still better than mine (0.234 vs. 0.246), but that is probably due to your larger window area of 18.5 m² (199 sq ft).
My primary energy demand is lower at 31 kWh compared to yours, but that is only due to the heating system. We calculate monthly costs for hot water and heating at about €55 (11,400 kWh and an annual performance factor of 4.5).
What would I take away from this? You will have low heating costs - whether adding more insulation to your building is worthwhile is unclear - what might be beneficial would be having more window area.
What heating demand do you have for your project? Then you can calculate how much you would pay now and what you would need to do to pay less. Improving roof insulation is relatively cost-effective to achieve, depending of course on the planned rafter thickness.
Hello and thank you for your reply.
I do not have a figure for the heating demand. The only documents from the energy consultant are already attached in the second post. The heating demand should therefore be lower than my annual primary energy demand, or have I misunderstood something? Why would having more windows be beneficial? That would worsen the heat transfer coefficient (U-value), wouldn’t it? The architect has, of course, taken the building’s location and orientation into account when calculating the window area.
I do not have a figure for the heating demand. The only documents from the energy consultant are already attached in the second post. The heating demand should therefore be lower than my annual primary energy demand, or have I misunderstood something? Why would having more windows be beneficial? That would worsen the heat transfer coefficient (U-value), wouldn’t it? The architect has, of course, taken the building’s location and orientation into account when calculating the window area.
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