ᐅ Decentralized vs. Centralized Controlled Residential Ventilation: Considerations for KfW House Calculations
Created on: 6 Apr 2012 09:22
M
mirage
Good morning everyone,
we, 30LJ and 27LJ, are currently planning our two-story house as a KfW 70 standard with approximately 140 sqm (1,507 sq ft). From the forum and various sales discussions, we have become aware that new houses, especially those built to KfW standards, tend to be quite airtight.
Now we have the question about ventilation. The seller offered us an inverter-controlled mechanical ventilation system for about 7,730.00 EUR. After some research here in the forum as guests and also via Google, I found that there are also central controlled mechanical ventilation systems. This seems to be the better option to us, since you don’t have noisy fans in every room as is the case with decentralized systems. Furthermore, you don’t have holes in every insulated wall.
In advance, I looked at the Zehnder ComfoAir 350 system as a central controlled mechanical ventilation. There seem to be good opinions about it, and compared to the Hoval HomeVent RS 250, it is more affordable. Now my question is whether this is the right choice, or if it might be possible to do without a controlled mechanical ventilation system in a KfW 70 house at all? Also, I am unsure whether, if a ventilation system is necessary, a decentralized or central controlled mechanical ventilation system would be better. There are so many factors to consider, and the salespeople tend to just tell you what you want to hear, partly trying to sell their own products.
In addition, I wonder whether a controlled mechanical ventilation system with heat recovery could improve the rating of a KfW house. In other words, without controlled mechanical ventilation with heat recovery, it would be KfW 70; with controlled mechanical ventilation plus heat recovery, could it become KfW 55?
For primary energy, we are using district heating, which the city produces with a primary energy factor of 0.11. No solar, no geothermal, etc.
I would appreciate many responses.
Best regards
mirage
we, 30LJ and 27LJ, are currently planning our two-story house as a KfW 70 standard with approximately 140 sqm (1,507 sq ft). From the forum and various sales discussions, we have become aware that new houses, especially those built to KfW standards, tend to be quite airtight.
Now we have the question about ventilation. The seller offered us an inverter-controlled mechanical ventilation system for about 7,730.00 EUR. After some research here in the forum as guests and also via Google, I found that there are also central controlled mechanical ventilation systems. This seems to be the better option to us, since you don’t have noisy fans in every room as is the case with decentralized systems. Furthermore, you don’t have holes in every insulated wall.
In advance, I looked at the Zehnder ComfoAir 350 system as a central controlled mechanical ventilation. There seem to be good opinions about it, and compared to the Hoval HomeVent RS 250, it is more affordable. Now my question is whether this is the right choice, or if it might be possible to do without a controlled mechanical ventilation system in a KfW 70 house at all? Also, I am unsure whether, if a ventilation system is necessary, a decentralized or central controlled mechanical ventilation system would be better. There are so many factors to consider, and the salespeople tend to just tell you what you want to hear, partly trying to sell their own products.
In addition, I wonder whether a controlled mechanical ventilation system with heat recovery could improve the rating of a KfW house. In other words, without controlled mechanical ventilation with heat recovery, it would be KfW 70; with controlled mechanical ventilation plus heat recovery, could it become KfW 55?
For primary energy, we are using district heating, which the city produces with a primary energy factor of 0.11. No solar, no geothermal, etc.
I would appreciate many responses.
Best regards
mirage
mirage schrieb:
...but would I move down from a KfW 70 house to a KfW 55 by using a controlled ventilation system with heat recovery, or does it not matter in this case? The efficiency rating is defined by two mandatory parameters: HT´ (W/m²K) – representing the maximum allowable transmission heat losses through the building envelope, and qp´´ (kWh/m²a) – the allowable specific primary energy demand. Both values must be met! The qp´´ parameter is influenced by both heat losses and gains as well as the building services systems. The controlled ventilation system with heat recovery has no effect on HT´ but does improve qp´´. In individual cases, it must be checked which of the two values, or whether both, are insufficient to meet KfW energy house 55 (EH 55) standards. In this particular case, it is likely that qp´´ will not be the limiting factor.
Usually, depending on the chosen building services technology, the HT´ value is the “problem area.” Meeting this requirement often involves significant effort.
An efficiency rating according to KfW standards only describes the building’s primary energy status qualitatively (building envelope and building services). However, it does not provide any statement or evaluation regarding economic viability.
A KfW EH 70 can overall be more economical than a certified passive house.
Purely chasing so-called “gifts” often leads to the wrong overall result.
Ah,
got it, thanks for your explanations. That helps me understand it a bit better. My main concern is to avoid paying twice for the same thing.
What I mean is, paying around 5,500 euros for the KfW 70 standard and then another roughly 9,000 euros for the mechanical ventilation with heat recovery. In hindsight, with the mechanical ventilation plus heat recovery and, for example, triple glazing, I could have achieved the KfW 70 standard and only paid about 11,500 euros instead of 14,500 euros.
Happy Easter to everyone.
got it, thanks for your explanations. That helps me understand it a bit better. My main concern is to avoid paying twice for the same thing.
What I mean is, paying around 5,500 euros for the KfW 70 standard and then another roughly 9,000 euros for the mechanical ventilation with heat recovery. In hindsight, with the mechanical ventilation plus heat recovery and, for example, triple glazing, I could have achieved the KfW 70 standard and only paid about 11,500 euros instead of 14,500 euros.
Happy Easter to everyone.
B
Bauexperte9 Apr 2012 11:36Hello €uro,
I suppose we both, along with a handful of others, see it that way; from 2021 on, this question unfortunately won’t even arise anymore. I am already curious about the different approaches that will be taken since not every plot of land can accommodate a Passive House.
Certainly, this option basically exists; but you—as well as I—know that it is rarely taken advantage of compared to the number of new builds statistically. To a layperson, a house seller is often seen like a white coat figure, especially if they are rhetorically well trained; accordingly, the houses are planned and sold. In my opinion, that is the first problem. The next would be the internet, which—as a reaction to trained sellers—turns a layperson into an unpleasant interlocutor. Not because they are well informed—that would be desirable—but because half-knowledge mixes with hearsay. And ultimately, every service costs money, while the new kitchen still matters more to the builder than proper consultation or mechanical, electrical, and plumbing (MEP) planning.
Most sellers won’t complain either; I’d bet that the majority of them wouldn’t even know what we are discussing here.
Happy Easter
€uro schrieb:
Whether a Passive House makes sense is a different matter.
I suppose we both, along with a handful of others, see it that way; from 2021 on, this question unfortunately won’t even arise anymore. I am already curious about the different approaches that will be taken since not every plot of land can accommodate a Passive House.
€uro schrieb:
This option basically exists, it’s just not used, probably because it’s not as convenient. It helps the builder less or might even be detrimental, but sellers have no reason to complain.
Certainly, this option basically exists; but you—as well as I—know that it is rarely taken advantage of compared to the number of new builds statistically. To a layperson, a house seller is often seen like a white coat figure, especially if they are rhetorically well trained; accordingly, the houses are planned and sold. In my opinion, that is the first problem. The next would be the internet, which—as a reaction to trained sellers—turns a layperson into an unpleasant interlocutor. Not because they are well informed—that would be desirable—but because half-knowledge mixes with hearsay. And ultimately, every service costs money, while the new kitchen still matters more to the builder than proper consultation or mechanical, electrical, and plumbing (MEP) planning.
Most sellers won’t complain either; I’d bet that the majority of them wouldn’t even know what we are discussing here.
Happy Easter
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