ᐅ Mechanical ventilation with heat recovery: no – explanation provided in the text.
Created on: 15 Jul 2015 00:00
G
Grym
For a long time, I was very much in favor of controlled residential ventilation, but I have now revised my opinion. First, some basic considerations:
- Modern houses are built so tightly that additional mechanical ventilation is necessary; otherwise, windows must be opened several times a day, summer and winter, for airing out
- Whether this ventilation is manual or automatic is a matter of comfort
- Whether this ventilation includes heat recovery or not is a question of economic efficiency
When considering economic efficiency, cleaning costs must be included. A reputable provider who only sells controlled residential ventilation estimated these costs at 700 EUR, with a recommended cleaning interval of at least every 5 years. However, in the demonstration house, the first cleaning was done after only 2 years because a microbial test detected contamination in the supply air exceeding the limit values (I don’t know the exact limits, but if the seller says cleaning after 2 years was necessary, I take their word for it—the company does not sell a house without controlled residential ventilation).
Depending on whether you divide the 700 EUR over 5 years or 2 years, the annual maintenance costs come to between 140 and 350 EUR.
The unit itself consumes electrical energy, approximately 250–400 kWh_el per year, which costs between 63 and 100 EUR annually.
The controlled residential ventilation system is a technical device; assuming a service life of 15 years, removal and disposal of the old unit, a new unit, and commissioning are estimated at around 5,000 EUR. This results in an annual depreciation of 333 EUR. If the ventilation system is expected to last 20 years, with disposal, new unit, and commissioning costs totaling 4,000 EUR, then depreciation is 200 EUR per year.
For new filters, maintenance, and minor repairs, I estimate a flat rate of 100 EUR.
Total annual costs in the best case scenario: 140 + 63 + 200 + 100 = 503 EUR
Total annual costs in the worst case scenario: 350 + 100 + 333 + 100 = 883 EUR
The savings effect is roughly estimated at about 2,000 kWh_thermal up to over 3,000 kWh_thermal. 2,000 kWh_thermal equate to 2,000 kWh of gas at 5.5 cents or 400–500 kWh_el at 20 cents (heat pump tariff) or 25 cents (household electricity). This results in savings of about 110 EUR (gas), 125 EUR (air-source heat pump with household electricity), or 80 EUR (ground-source heat pump with heat pump electricity).
At 3,500 EUR savings, this corresponds to 193 EUR (gas), 219 EUR (worst-case heat pump), or 140 EUR (best-case heat pump).
If you compare the best-case controlled ventilation with the worst-case heat pump, you get 503 EUR - 219 EUR = 284 EUR. The other way around is 883 EUR - 140 EUR = 743 EUR.
No matter how you look at it, controlled ventilation with heat recovery cannot even save the running costs. Therefore, in my opinion, the best system—especially to avoid hygienic problems in the house—is exhaust air modules in wet rooms combined with window rebate ventilation or an external wall air inlet. Decentralized controlled ventilation systems with heat recovery do not have such high cleaning costs, but even they would never recoup the additional cost of heat recovery. Additionally, these devices must be placed in bedrooms and living areas, which creates noise. Pure exhaust air systems without heat recovery are suitable in rooms where quiet noises are less disturbing (kitchens, toilets, utility rooms, bathrooms) and can even be switched off for hours (bathroom). Modern window rebates work without drafts and reduce sound insulation by only 1 to 2 dB. Anyone living in a quiet residential area probably doesn’t mind.
I look forward to the discussion, but please keep it relevant to the topic. I am not questioning the necessity of non-user-dependent mechanical ventilation; my focus is only on central heat recovery. Central heat recovery requires the duct system, which incurs high cleaning costs, as well as a complex technical device with limited service life and high costs (unlike a standard exhaust air module without heat recovery). Controlled ventilation without heat recovery operates without the duct system.
- Modern houses are built so tightly that additional mechanical ventilation is necessary; otherwise, windows must be opened several times a day, summer and winter, for airing out
- Whether this ventilation is manual or automatic is a matter of comfort
- Whether this ventilation includes heat recovery or not is a question of economic efficiency
When considering economic efficiency, cleaning costs must be included. A reputable provider who only sells controlled residential ventilation estimated these costs at 700 EUR, with a recommended cleaning interval of at least every 5 years. However, in the demonstration house, the first cleaning was done after only 2 years because a microbial test detected contamination in the supply air exceeding the limit values (I don’t know the exact limits, but if the seller says cleaning after 2 years was necessary, I take their word for it—the company does not sell a house without controlled residential ventilation).
Depending on whether you divide the 700 EUR over 5 years or 2 years, the annual maintenance costs come to between 140 and 350 EUR.
The unit itself consumes electrical energy, approximately 250–400 kWh_el per year, which costs between 63 and 100 EUR annually.
The controlled residential ventilation system is a technical device; assuming a service life of 15 years, removal and disposal of the old unit, a new unit, and commissioning are estimated at around 5,000 EUR. This results in an annual depreciation of 333 EUR. If the ventilation system is expected to last 20 years, with disposal, new unit, and commissioning costs totaling 4,000 EUR, then depreciation is 200 EUR per year.
For new filters, maintenance, and minor repairs, I estimate a flat rate of 100 EUR.
Total annual costs in the best case scenario: 140 + 63 + 200 + 100 = 503 EUR
Total annual costs in the worst case scenario: 350 + 100 + 333 + 100 = 883 EUR
The savings effect is roughly estimated at about 2,000 kWh_thermal up to over 3,000 kWh_thermal. 2,000 kWh_thermal equate to 2,000 kWh of gas at 5.5 cents or 400–500 kWh_el at 20 cents (heat pump tariff) or 25 cents (household electricity). This results in savings of about 110 EUR (gas), 125 EUR (air-source heat pump with household electricity), or 80 EUR (ground-source heat pump with heat pump electricity).
At 3,500 EUR savings, this corresponds to 193 EUR (gas), 219 EUR (worst-case heat pump), or 140 EUR (best-case heat pump).
If you compare the best-case controlled ventilation with the worst-case heat pump, you get 503 EUR - 219 EUR = 284 EUR. The other way around is 883 EUR - 140 EUR = 743 EUR.
No matter how you look at it, controlled ventilation with heat recovery cannot even save the running costs. Therefore, in my opinion, the best system—especially to avoid hygienic problems in the house—is exhaust air modules in wet rooms combined with window rebate ventilation or an external wall air inlet. Decentralized controlled ventilation systems with heat recovery do not have such high cleaning costs, but even they would never recoup the additional cost of heat recovery. Additionally, these devices must be placed in bedrooms and living areas, which creates noise. Pure exhaust air systems without heat recovery are suitable in rooms where quiet noises are less disturbing (kitchens, toilets, utility rooms, bathrooms) and can even be switched off for hours (bathroom). Modern window rebates work without drafts and reduce sound insulation by only 1 to 2 dB. Anyone living in a quiet residential area probably doesn’t mind.
I look forward to the discussion, but please keep it relevant to the topic. I am not questioning the necessity of non-user-dependent mechanical ventilation; my focus is only on central heat recovery. Central heat recovery requires the duct system, which incurs high cleaning costs, as well as a complex technical device with limited service life and high costs (unlike a standard exhaust air module without heat recovery). Controlled ventilation without heat recovery operates without the duct system.
merlin83 schrieb:
So the air conditioning doesn't have to compete with the controlled mechanical ventilation?On the contrary, the controlled mechanical ventilation cools the incoming air using the heat exchanger (if it is cooler inside than outside), so you are not bringing warm outdoor air into the house. Therefore, the condensate drain of the controlled mechanical ventilation should definitely be connected; it is also important that the bypass, which some controlled mechanical ventilation systems have, is then deactivated (bypass = air bypasses the heat exchanger).
Grym schrieb:
We will probably install a mechanical ventilation system with heat recovery.
Retrofitting is not really an option, and controlled ventilation should definitely be included. In the worst case, the mechanical ventilation could be converted into an exhaust-only system, but I’m just hoping everything works as promised. I would never opt for purely manual ventilation in a new house. For me, the choice was between a central exhaust system with decentralized supply air or a central supply and exhaust system with heat recovery.Thanks for your response. However, I will likely decide against it—not because of one central reason, but due to several factors. Since I plan to build with brick and mineral plaster both inside and outside, there shouldn’t be any moisture problems even without a ventilation system. The situation is different with diffusion-tight systems such as sand-lime brick plus styrofoam or airtight prefabricated houses.
Your bricks and plaster basically act as a barrier to moisture just like other building materials. Try blowing through a brick. It’s not possible, even if you put your mouth very close to it. They are just as airtight as other building materials (fortunately, since that’s required). The vapor resistance is many times too high to transport moisture out of the house. Otherwise, it would get quite damp during rain (and this works both ways!).
The idea that walls “breathe” is more of a myth. If any air exchange happens, it is through gaps or holes. The truth lies somewhere in between, but not in the way you suggested.
The idea that walls “breathe” is more of a myth. If any air exchange happens, it is through gaps or holes. The truth lies somewhere in between, but not in the way you suggested.
Brick and lime plaster won’t help much with today’s new builds. They also don’t provide the 30–40 m3 (1,060–1,410 ft3) of fresh air per person per hour that everyone needs. A brick house is just as airtight as a prefabricated timber house.
An older building has a natural air exchange rate of over 1, so there are no issues (gaps, windows, etc.). Such older buildings reach values above 10 in blower door tests, as I have read. Modern new builds, depending on the wind, sometimes have a natural air exchange rate below 0.1 (blower door test results usually under 1.0).
If you build without any kind of ventilation, be prepared to air out the house by opening windows or cross-ventilating at least five times a day. That is barely enough to prevent mold, but good air quality will disappear within an hour after the last airing.
At least install a central exhaust system with outdoor air inlets. From there, it’s only a small step to a mechanical ventilation system with heat recovery.
An older building has a natural air exchange rate of over 1, so there are no issues (gaps, windows, etc.). Such older buildings reach values above 10 in blower door tests, as I have read. Modern new builds, depending on the wind, sometimes have a natural air exchange rate below 0.1 (blower door test results usually under 1.0).
If you build without any kind of ventilation, be prepared to air out the house by opening windows or cross-ventilating at least five times a day. That is barely enough to prevent mold, but good air quality will disappear within an hour after the last airing.
At least install a central exhaust system with outdoor air inlets. From there, it’s only a small step to a mechanical ventilation system with heat recovery.
Saruss schrieb:
Your bricks and plaster essentially act as barriers to moisture in the same way as other building materials. Try blowing air through bricks—it’s impossible, even if you put your mouth very close. They are just as airtight as other construction materials (fortunately, since that is required by building regulations). The vapor resistance is orders of magnitude too high to transport moisture out of the house. Otherwise, during rain, it would also get quite damp (this works both ways!). The idea that walls “breathe” is more of a myth. If any breathing occurs, it’s through gaps or holes. The truth lies somewhere in between, but not where you suggested.Of course, that alone is not enough, but combined with proper cross-ventilation, moisture-related problems should not occur at all. Also, around 80% of builders here use this method (yes, I know that doesn’t necessarily prove anything).
I might also add a decentralized system like BluMartin later on.
Grym schrieb:
Bricks and lime plaster don’t help much in modern new builds. Plus, they don’t provide the 30–40 m³ (1,060–1,400 ft³) of fresh air per person per hour that each occupant needs. A brick house is just as airtight as a timber frame house.
An older building has a natural air exchange rate of over 1, so there are no issues (due to joints, windows, etc.). Such old buildings score over 10 on blower door tests, as I have read. Modern new builds often have natural air exchange rates below 0.1, depending on the wind (blower door tests usually show values under 1.0).
If you build without any kind of ventilation system, be prepared to open windows for cross- or shock-ventilation at least five times a day, and even then it will only barely prevent mold. Good air quality disappears about an hour after the last ventilation.
At minimum, use a central exhaust system with outdoor air inlets. From there, upgrading to a controlled mechanical ventilation system is just a small step.I’m not even in the planning phase yet; I’m just researching. My opinion will probably change—we’ll see. My statements referred only to moisture. I understand that the recommended air exchange rate is hardly achievable by manual ventilation alone. However, in my opinion, even 0.3 is sufficient. Controlled mechanical ventilation systems roughly achieve this value when operated on level 1, which many users actually do.
B
Bauexperte5 Jan 2016 00:18Good evening,
Happy New Year!
jaeger schrieb:3 to sometimes 5 times per day – every day – for the first two years?
..., but together with proper cross-ventilation, there really shouldn’t be any moisture-related issues at all.
jaeger schrieb:Because many homeowners save in the wrong places; sometimes it doesn’t have a big impact though, especially if a partner is on parental leave and inevitably moves around the house several times a day.
Also, an estimated 80% build like this here (yes, I know that doesn’t necessarily mean anything)
jaeger schrieb:Good choice; although I would describe it more as a hybrid system rather than a purely decentralized one.
I might also add a decentralized system like BluMartin.
Happy New Year!
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