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
PeterXYZ schrieb:
... does anyone have knowledge about calculating the air exchange rate? DIN 1946-6! PeterXYZ schrieb:
... Humidity and poor air quality mostly occur when people are present, right? It seems illogical to me that the house should be ventilated just as often when unoccupied or on vacation as when people are at home. Are there any opinions on this? Again, DIN 1946-6 applies here with its different ventilation levels. This can result in significantly different air exchange rates compared to the mentioned 0.5/h. Best regards.
€uro schrieb:
Of course! That’s why the thermally effective airflow rates, for example in heating load calculations, must be taken into account. The better a building is insulated, the more noticeable and sustainable the impact of heat recovery will be.
RegardsSorry for the silly question, but would installing a controlled ventilation system with heat recovery reduce a KfW 70 house to KfW 55 standard, or does it not make a difference? As mentioned before, the location uses district heating with a primary energy factor of 0.11.
Best regards
B
Bauexperte8 Apr 2012 11:38Hello,
DIN and technical HVAC information can be better provided by €uro than anyone here; I tend to rely more on practical experience.
Have you ever been in a house that was left empty for a long time? Hmm... it smells quite musty... recently I had the “pleasure” of inspecting one where a water pipe had burst for some reason.
With a new build, there is always water involved; even in prefabricated houses. This moisture needs to be removed, which is extremely important during the first 2 years. Later on, even with regular quick ventilation, it’s not so easy to remove the moisture produced by people’s breathing, cooking, or bathing—especially before going on holiday. That’s why a key is often left with family or neighbors; plants can also survive longer without care thanks to hydroponic systems.
Kind regards
PeterXYZ schrieb:
Humidity and poor air quality almost only occur when people are present, right? It seems illogical to me that you should ventilate the house as often during absences or holidays as when people are home! Are there any opinions on this?
DIN and technical HVAC information can be better provided by €uro than anyone here; I tend to rely more on practical experience.
Have you ever been in a house that was left empty for a long time? Hmm... it smells quite musty... recently I had the “pleasure” of inspecting one where a water pipe had burst for some reason.
With a new build, there is always water involved; even in prefabricated houses. This moisture needs to be removed, which is extremely important during the first 2 years. Later on, even with regular quick ventilation, it’s not so easy to remove the moisture produced by people’s breathing, cooking, or bathing—especially before going on holiday. That’s why a key is often left with family or neighbors; plants can also survive longer without care thanks to hydroponic systems.
Kind regards
B
Bauexperte8 Apr 2012 12:00Hello €uro,
You know I really appreciate your answers and would like to see more of them.
I agree with you 100%.
Unfortunately, it’s not as small as you suggest here; however, when measured against the overall volume of new construction, it is negligible.
I agree with you for a Passive House; however, the vast majority of builders do not go for a Passive House.
For most houses today, although buildings are tighter than ever before, heat recovery is not truly cost-effective; except for engineers on paper, whose approach I still consider a kind of marketing trick. Also, not every location allows for a heat pump, let alone a ground-source heat pump! It is not that easy to warm 22°C (72°F) room air from outside air—say 0°C (32°F). This requires additional technology, which leads to more costs; it is an endless spiral that the people in Brussels seem happy to push. Whether all this is reasonable is another question.
I would be satisfied if every building project were considered individually and analyzed based on its specific parameters, with corresponding recommendations provided. Imposing energy-saving regulations, targeted misinformation from selling industries, or even scaremongering tends to achieve the opposite.
Kind regards
You know I really appreciate your answers and would like to see more of them.
€uro schrieb:
The real value of a mechanical ventilation with heat recovery is measured by comfort
I agree with you 100%.
€uro schrieb:
and by the controlled ventilation. The cost difference between central mechanical ventilation without heat recovery and with heat recovery is not as significant as often assumed.
Unfortunately, it’s not as small as you suggest here; however, when measured against the overall volume of new construction, it is negligible.
€uro schrieb:
The “cooler” the climatic location, the more effective the mechanical ventilation with heat recovery. Also, it always makes sense to consider the mechanical ventilation in connection with the rest of the building services. Mechanical ventilation with heat recovery partially and significantly reduces heating loads, meaning that with, for example, a heat pump as the heat source, often a smaller capacity unit can be chosen. This saves several thousand euros, especially with ground-source heat pumps, since not only the unit but also the heat source becomes more affordable. This often offsets the additional cost of heat recovery and results in not only an investment saving.
I agree with you for a Passive House; however, the vast majority of builders do not go for a Passive House.
For most houses today, although buildings are tighter than ever before, heat recovery is not truly cost-effective; except for engineers on paper, whose approach I still consider a kind of marketing trick. Also, not every location allows for a heat pump, let alone a ground-source heat pump! It is not that easy to warm 22°C (72°F) room air from outside air—say 0°C (32°F). This requires additional technology, which leads to more costs; it is an endless spiral that the people in Brussels seem happy to push. Whether all this is reasonable is another question.
I would be satisfied if every building project were considered individually and analyzed based on its specific parameters, with corresponding recommendations provided. Imposing energy-saving regulations, targeted misinformation from selling industries, or even scaremongering tends to achieve the opposite.
Kind regards
Hello Bauexperte,
Best regards.
Bauexperte schrieb:I always try to consider the overall context, because in my opinion, overemphasizing individual details rarely leads to an overall satisfactory solution.
...It’s not as small as you suggest here; however, compared to the total volume of the new build, it is again negligible.
Bauexperte schrieb:I see this a bit differently, but we don’t always have to agree. Whether a passive house makes sense is another matter altogether.
...I agree with you regarding a passive house; however, the vast majority of builders do not have a passive house.
Bauexperte schrieb:As I said, I have a slightly different view, although here too, each case must be considered individually. Generalizations rarely help.
...heat recovery doesn’t really pay off; ...
Bauexperte schrieb:Here I agree with you again. Sometimes what you get handed is more than questionable.
...apart from the structural engineer on paper, which I still consider a sham approach.
Bauexperte schrieb:This is basically possible, but it is often not used, probably because it is less convenient.
...I would be satisfied if each building project were considered individually based on its specific parameters and recommendations made accordingly.
Bauexperte schrieb:This mostly doesn’t help the builder, and can even be harmful — though sellers have little cause to complain.
...Imposing energy saving regulation requirements, targeted misinformation by selling industries, or even scaremongering usually produces the opposite effect.
Best regards.
mirage schrieb:
Sorry for the possibly silly question, but would installing a controlled residential ventilation system with heat recovery help reduce the rating of a KfW 70 house down to KfW 55, or does it not make a difference? As mentioned before, we will use district heating at the location with a primary energy factor of 0.11.
Best regardsHi €uro,
could you possibly add some input on this as well?
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