We are planning a new build as an energy-efficient house according to the Energy Saving Ordinance, KfW70 standard. The developer claims that with very good insulation, solar thermal systems, and a condensing boiler, etc., this can be achieved without mechanical ventilation. A new build is sealed quite tightly as verified by a blower door test. The developer says we do not need to worry about moisture problems.
We are also used to regular manual ventilation from living in our old house... However, there the cold, fogged-up window was a reliable indicator...
The additional costs for a ventilation system would be significant...
What do the experts here think? Is it better not to forgo such a system, or does it not matter? I do not want to suffocate at night or discover mold after two years...
We are also used to regular manual ventilation from living in our old house... However, there the cold, fogged-up window was a reliable indicator...
The additional costs for a ventilation system would be significant...
What do the experts here think? Is it better not to forgo such a system, or does it not matter? I do not want to suffocate at night or discover mold after two years...
Basically, we could calculate that, but it requires a lot of information.
I’m not sure if it helps the person asking the question in a forum to just list calculations, abbreviations, and formulas. Technical knowledge is good, but a forum visitor wants their question answered. That’s why, in my opinion, it is also unhelpful to pick apart the answers of other participants. The questioner can judge for themselves and certainly does not need assistance with that.
Still, my opinion:
Physically, that is unfortunately not possible. In practice, at best 60 to 70% of exhaust air energy is actually recoverable!
Incorrect: current systems have an efficiency of 92%!
Every building component exposed to solar radiation, including opaque ones, fundamentally uses part of the solar energy! No ventilation is required for this!
Opaque? I don’t know that term. Correct: every component uses solar energy, but here it’s about the mechanical ventilation system. In the case of window ventilation, the solar energy leaves the house unused. In summer, that’s not a problem; in the transition periods and winter, it is uneconomical. We should return to the question: This is about a low-energy house!
Correct:
For buildings close to the passive house standard, however, a controlled mechanical ventilation system with heat recovery is essential.
I’m not sure if it helps the person asking the question in a forum to just list calculations, abbreviations, and formulas. Technical knowledge is good, but a forum visitor wants their question answered. That’s why, in my opinion, it is also unhelpful to pick apart the answers of other participants. The questioner can judge for themselves and certainly does not need assistance with that.
Still, my opinion:
Physically, that is unfortunately not possible. In practice, at best 60 to 70% of exhaust air energy is actually recoverable!
Incorrect: current systems have an efficiency of 92%!
Every building component exposed to solar radiation, including opaque ones, fundamentally uses part of the solar energy! No ventilation is required for this!
Opaque? I don’t know that term. Correct: every component uses solar energy, but here it’s about the mechanical ventilation system. In the case of window ventilation, the solar energy leaves the house unused. In summer, that’s not a problem; in the transition periods and winter, it is uneconomical. We should return to the question: This is about a low-energy house!
Correct:
For buildings close to the passive house standard, however, a controlled mechanical ventilation system with heat recovery is essential.
R
ralph1234513 May 2010 21:16The low-energy house is primarily mandatory due to energy-saving regulations, and the KfW70 standard house is common among most developers, often supported by low-interest loans from KfW. So, it is not necessarily just a preference of the homeowner, even though many do appreciate energy-efficient living and reduced energy costs. It should not be treated as a dogma.
The controlled ventilation system is intended to maintain a healthy indoor climate and prevent mold. If that can be achieved through regular ventilation, all the better. Without heat recovery, controlled ventilation essentially only provides air exchange. Filtering is a plus. In the end, controlled ventilation without heat recovery is mainly a matter of comfort.
With controlled ventilation systems that include heat recovery, it’s a different matter, and in terms of energy savings, this is certainly top of the line. The question of cost-effectiveness can go either way; whether the efficiency is 70 or 90% is secondary. In any case, such a system requires an initial investment of around 10,000 € (approximately $10,900), which is simply not feasible financially for many, even if it saves about 20,000 € (approximately $21,800) over 30 years of occupancy.
The controlled ventilation system is intended to maintain a healthy indoor climate and prevent mold. If that can be achieved through regular ventilation, all the better. Without heat recovery, controlled ventilation essentially only provides air exchange. Filtering is a plus. In the end, controlled ventilation without heat recovery is mainly a matter of comfort.
With controlled ventilation systems that include heat recovery, it’s a different matter, and in terms of energy savings, this is certainly top of the line. The question of cost-effectiveness can go either way; whether the efficiency is 70 or 90% is secondary. In any case, such a system requires an initial investment of around 10,000 € (approximately $10,900), which is simply not feasible financially for many, even if it saves about 20,000 € (approximately $21,800) over 30 years of occupancy.
Hello,
Who is “we” and how would you calculate it? I do this kind of thing almost every day!
This is not about “dissecting”, but about objectivity!
Where do you get this claim from? Brochure or advertising? Are those 92% part of the contract for your balanced mechanical ventilation with heat recovery system? In all my measurements, I have never seen this so far. But I am willing to learn.
Currently, there is no industry as inventive in defining the efficiency of heat recovery systems. We have already reached the 12th definition!
By the way, at low outdoor temperatures, the drying potential is greatest, as can be seen in the Mollier h-x diagram. This shortens the ventilation time and thus the related heat loss through ventilation!
In conclusion:
First clarify and verify the necessity and requirement. Then have the cost-effectiveness calculated.
Those with enough money can plan this in for comfort reasons without any verification whatsoever.
Regards
PenK schrieb:
Basically, we could calculate that, but it requires a lot of information.
Who is “we” and how would you calculate it? I do this kind of thing almost every day!
PenK schrieb:
... That is why, in my opinion, it is unhelpful when other participants’ answers are being dissected. The person asking the question can judge for themselves and certainly does not need assistance there.
This is not about “dissecting”, but about objectivity!
PenK schrieb:
...
Incorrect: current systems have an efficiency of 92%!
Where do you get this claim from? Brochure or advertising? Are those 92% part of the contract for your balanced mechanical ventilation with heat recovery system? In all my measurements, I have never seen this so far. But I am willing to learn.
Currently, there is no industry as inventive in defining the efficiency of heat recovery systems. We have already reached the 12th definition!
PenK schrieb:What would be economical then? Investing 9,000 € to save annually x..600..y kWh?
...
... uneconomical during transitional periods and winter.
By the way, at low outdoor temperatures, the drying potential is greatest, as can be seen in the Mollier h-x diagram. This shortens the ventilation time and thus the related heat loss through ventilation!
In conclusion:
First clarify and verify the necessity and requirement. Then have the cost-effectiveness calculated.
Those with enough money can plan this in for comfort reasons without any verification whatsoever.
Regards
€uro schrieb:
Hello,
Who is “we” and how would you calculate that? I do this kind of thing almost every day!
This is not about "taking apart" – it’s about objectivity!
RegardsA specialist planner from the manufacturer’s company will do the calculation. But that’s enough now. I understand you: you are right and everyone else is wrong. Please avoid posting when you’re having a bad day. And don’t act like an expert here.
--> I will not respond to any further posts from you on this topic!
Hello,
The goal of the energy saving regulations and the KfW subsidy is to reduce primary energy consumption! This approach is basically positive, as it aims to lower environmental impact through CO2 reduction.
Future energy costs can primarily only be offset by investment costs! To mitigate this additional investment effort, the MAP (Market Incentive Program) was established! Therefore, no economic efficiency is necessarily guaranteed for the homeowner.
The legislator, with §25 of the Energy Saving Ordinance and §9 of the EEWG, has given both homeowners and planners full scope to find an overall economical solution.
The fact that this flexibility is mostly not utilized in owner-occupied residential buildings is probably due to a lack of expertise.
Commercial clients behave quite differently, as economic efficiency is their main focus. They examine whether the investment subsidy actually has an economic effect.
Unfortunately, this is not always generally or universally possible! The necessity and requirements need to be examined. Afterwards, a decision "for" or "against" can be made.
Best regards.
Gartenbau schrieb:
The low-energy house is initially mandated by the energy saving regulations, and the KfW70 house is standard for most developers and furthermore subsidized by KfW with favorable loans. So it is not necessarily a pure wish of the homeowner.
The goal of the energy saving regulations and the KfW subsidy is to reduce primary energy consumption! This approach is basically positive, as it aims to lower environmental impact through CO2 reduction.
Future energy costs can primarily only be offset by investment costs! To mitigate this additional investment effort, the MAP (Market Incentive Program) was established! Therefore, no economic efficiency is necessarily guaranteed for the homeowner.
The legislator, with §25 of the Energy Saving Ordinance and §9 of the EEWG, has given both homeowners and planners full scope to find an overall economical solution.
The fact that this flexibility is mostly not utilized in owner-occupied residential buildings is probably due to a lack of expertise.
Commercial clients behave quite differently, as economic efficiency is their main focus. They examine whether the investment subsidy actually has an economic effect.
Gartenbau schrieb:
If normal ventilation is sufficient, great.
Unfortunately, this is not always generally or universally possible! The necessity and requirements need to be examined. Afterwards, a decision "for" or "against" can be made.
Best regards.
R
ralph1234514 May 2010 13:01€uro schrieb:
The reason these options are mostly not used in owner-occupied residential buildings is probably due to a lack of expertise. Commercial clients behave very differently because profitability is the main focus. They examine whether subsidizing the investment actually has an economic benefit. I frequently work professionally on calculating the profitability of investments—expenses, income, savings, return on investment… This is not a mystery to me. I am an engineer and understand enough thermodynamics to know that heat recovery ventilation makes sense. But all of that is pointless if there is no budget for the measure. So my main question is what is really necessary.
I also read in another forum where many users share their experiences. The general consensus about mechanical ventilation with heat recovery: very comfortable, but if you don’t have it, ventilation works fine too—provided you’re not too lazy to open the windows.
Unfortunately, this is not always true in a general sense! The necessity and requirements need to be evaluated. How? Could you please mention some factors for and against it? As I said, we live as a family of four, we shower and wash regularly, we dry clothes outdoors in summer and indoors in winter; a dryer is a possibility. The climate is typical for northern Germany—not a dry desert climate, no constantly humid tropics, no permafrost; it rains regularly here. The house has no basement, is well insulated, and built to KfW70 standard. What other factors should be considered?
And the second question: If I can remove moisture effectively by ventilating regularly, why would a mechanical ventilation system still be absolutely necessary? Heat loss through warm air during ventilation is the same whether done by regular airing or mechanical ventilation without heat recovery, as long as you avoid cooling down the walls when airing.
To avoid misunderstandings: I am not fixed on “no mechanical ventilation” or biased, but I would like to understand why some say it simply can’t be done without it. So far, I haven’t read a convincing argument for that.
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