ᐅ New construction KfW55 energy standard with gas heating, solar panels, and controlled ventilation system with heat recovery
Created on: 22 Oct 2016 14:03
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XeNiA
Hello!
We are just starting the planning of our new build, and the big question we keep discussing is the heating system.
We are building a detached single-family house with 145 sq m (1560 sq ft) plus an expanded attic of about 40 sq m (430 sq ft) with underfloor heating (including in the attic).
We want to achieve KfW55 standard. The house will be built with solid masonry and brick veneer.
One thing we definitely want is a controlled ventilation system with heat recovery.
The most cost-effective option so far seems to be a combination of gas, solar thermal, and ventilation. The construction companies we are requesting quotes from are also offering a KfW55 package with improved insulation, as it might be difficult to meet the required standards otherwise.
An alternative (the second most affordable option) would be an air-to-air heat pump instead of gas.
What are the advantages and disadvantages of these two heating systems? What would the approximate expected monthly costs be?
Some heating installers have told us that achieving KfW55 with gas is not possible at all.
We are quite confused, and everyone says something different.
What are your experiences?
Thank you very much!
We are just starting the planning of our new build, and the big question we keep discussing is the heating system.
We are building a detached single-family house with 145 sq m (1560 sq ft) plus an expanded attic of about 40 sq m (430 sq ft) with underfloor heating (including in the attic).
We want to achieve KfW55 standard. The house will be built with solid masonry and brick veneer.
One thing we definitely want is a controlled ventilation system with heat recovery.
The most cost-effective option so far seems to be a combination of gas, solar thermal, and ventilation. The construction companies we are requesting quotes from are also offering a KfW55 package with improved insulation, as it might be difficult to meet the required standards otherwise.
An alternative (the second most affordable option) would be an air-to-air heat pump instead of gas.
What are the advantages and disadvantages of these two heating systems? What would the approximate expected monthly costs be?
Some heating installers have told us that achieving KfW55 with gas is not possible at all.
We are quite confused, and everyone says something different.
What are your experiences?
Thank you very much!
Alex85 schrieb:
I currently live in a house built in the mid-1970s with a very new gas condensing boiler. I record consumption at least monthly. With four people, we used about 350 kWh of gas per month in summer – that is, without heating operation and only for hot water. This corresponds to energy costs of around €21. For comparison, in November during the heating period, we used about 3300 kWh, which is just under ten times as much.
Conclusion? Hot water with gas heating is a negligible byproduct of the heating operation.
How expensive was the solar thermal system again?
It will never pay off. Solar thermal is installed to meet the renewable energy requirement of the Energy Saving Ordinance. As little as possible.
I think it’s great that XeNiA managed to achieve KfW 55 solely with controlled mechanical ventilation with heat recovery. The investment is probably higher than installing solar thermal, but at least it offers real added value in terms of comfort through improved air quality and mold prevention. Solar thermal is dead capital.That’s exactly our view as well!
The solar thermal system with heating support and hot water would have cost €9,000. Without heating support, only for hot water about €4,500.
Clearly, the controlled mechanical ventilation is expensive, but it’s the only thing we were not willing to give up.
Alex85 schrieb:
I currently live in a house built in the mid-1970s with a very new gas condensing boiler. I record the consumption at least monthly. With four people, we used about 350 kWh of gas per month in summer—meaning no heating operation, only hot water. That corresponds to consumption costs of roughly €21. For comparison, in November during heating operation, we used about 3,300 kWh, which is just under ten times as much.
Conclusion? Hot water with a gas heating system is a negligible byproduct of the heating operation.
How expensive is the solar thermal system again?
It will never pay off. Solar thermal is installed to fulfill the renewable energy requirements of the Energy Saving Ordinance—doing as little as possible.
I think it’s great that XeNiA manages to achieve KfW 55 standard solely with controlled residential ventilation and heat recovery. The investment is probably higher than installing solar thermal, but at least it has real added value in terms of comfort gains through air quality and mold prevention. Solar thermal is dead capital.Hi,
I think you can’t compare a house from the ’70s with a current KfW 55-standard building under today’s Energy Saving Ordinance. The difference is that the ratio between heating operation and hot water demand in a modern house will certainly not be that close to tenfold consumption.
Furthermore, the solar thermal system also supports the heating, not just the hot water. Controlled residential ventilation must be installed anyway, and the mentioned quality is part of that.
I have to admit, though, that I’m not 100% sure whether it’s financially worthwhile. We’ll see.
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Bieber08151 Dec 2016 21:06XeNiA schrieb:
The energy consultant calculated everything, and we will now build with gas plus a controlled residential ventilation system with heat recovery. In addition, extra insulation will be added to the foundation slab and roof. This is still cheaper than the solar thermal system we wanted to skip and now will. Great! That’s what I would have preferred, actually. With the developer, it would have been more expensive than an air-to-water heat pump. So that was the deciding factor. I think you have the ideal solution. Keep investment low, insulation high. Controlled residential ventilation is a matter of comfort for me.
If you haven’t considered this option yet: How would the costs look with an air-to-water heat pump instead of gas? I mean, not the energy saving regulation calculation, but the investment costs assuming everything else (insulation, controlled residential ventilation) stays the same.
Bieber0815 schrieb:
Great! That’s actually what I would have preferred. However, with the property developer it would have been more expensive than the air-to-water heat pump. So we stayed with our choice. I think you have the ideal solution. Keeping the investment low, insulation high. Mechanical ventilation with heat recovery is a comfort feature for me.
If you haven’t considered this option yet: What would the calculation look like with an air-to-water heat pump instead of gas? I mean not the energy saving regulation calculation, but the investment costs, assuming everything else (insulation, mechanical ventilation with heat recovery) stays the same.From a cost perspective, it looks almost the same as with gas now. Unfortunately, the gas connection also costs quite a bit, and there is a €1500 (about $1600) subsidy from Bafa for the air-to-water heat pump.
For us, we quickly ruled out the air-to-water heat pump. We have heard and read too many negative things.
At the moment, we heat and cook with gas and are completely happy with the system. That’s why we wanted to stick with it.
andi-2000 schrieb:
Hi,
I think you can’t compare a house from the 1970s to a current KfW55 standard house under the latest energy-saving regulations. The difference is that the ratio of heating operation to hot water consumption in a modern house definitely won’t be ten times as high.
Moreover, the solar thermal system also supports the heating, not just the domestic hot water. Controlled mechanical ventilation is required anyway, and the quality mentioned applies to that as well.
I have to admit, though, that I’m not 100% sure if it’s cost-effective. We’ll see. Of course it’s not cost-effective!
If you take the 350 kWh per month for hot water (which I consider very, very high, unless I have a mental typo), that would be about 270 € per year at 6.5 cents per kWh.
Assuming the solar thermal system covers roughly 60% of that demand, you save about 160 € per year.
On the other hand, the investment for the solar thermal system is about 4,500 €.
You can calculate the payback period yourself now. However, I doubt it will be shorter than the system’s lifespan...
XeNiA schrieb:
We feel the same way! The solar thermal system with heating support and domestic hot water would have cost 9,000€ (approximately $9,900). Without heating support, only for domestic hot water, about 4,500€ (approximately $4,950).
It’s clear that controlled mechanical ventilation is expensive, but that’s the only element we didn’t want to do without.What I don’t understand—and please don’t take this the wrong way, as I’m still new to this—is that every builder I’ve spoken with, whether for solid construction or prefab, as well as every architect and planner, has told me that reaching KfW55 standard is only possible if the building materials have the right thermal conductivity AND the technology is appropriate.
Regarding the technology, that means for gas heating: the condensing boiler, solar thermal system, and controlled mechanical ventilation with heat recovery. This information was given to me from various sources, and I’ve come to accept it.
Has your energy consultant calculated such a good primary energy demand that achieving KfW55 is actually possible without these three technical components?
Our appointment with the energy consultant is coming up soon, so hopefully I’ll be better informed then.
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