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.
nordanney schrieb:
- Regular filter cleaning (if I have to breathe in everything trapped in the filters, I feel sick) you can do yourself
- new coarse filter: costs just cents if you buy it by the roll and cut the filter to sizeTell me— I still have an unused filter from a former range hood (not a carbon filter). At first glance, it looks like the coarse filters used in my decentralized ventilation units. I’ve been considering whether I could cut it to size and use it as a replacement during the next cleaning.
Even though you have a mechanical ventilation with heat recovery system and I have a decentralized one— what do you think, would this potentially work? That way, the filter would at least have a useful purpose, since the range hood has long been out of service.
What about the heat exchanger? A heat exchanger with humidity recovery must also transfer some particulate organic material from the exhaust air to the supply air, right? From a hygiene perspective, that is often not acceptable. How is it with conventional heat exchangers— is any contact inside the heat exchanger categorically and technically 100 percent excluded?
Are there really no bacteria or germs worldwide that can survive even at low humidity?
But now I get it: What happens in summer? Warm and yet saturated air is drawn in and cooled in the heat exchanger. The humidity is at 100 percent, and on the way to the supply air outlet, the 25-35°C (77-95°F) warm air cools further toward the temperature of the building structure. Continuous condensate forms as long as the outside temperature is higher than the inside temperature.
This is not visible dirt; that was never the point. The concern is about germs, bacteria, fungi...
Are there really no bacteria or germs worldwide that can survive even at low humidity?
But now I get it: What happens in summer? Warm and yet saturated air is drawn in and cooled in the heat exchanger. The humidity is at 100 percent, and on the way to the supply air outlet, the 25-35°C (77-95°F) warm air cools further toward the temperature of the building structure. Continuous condensate forms as long as the outside temperature is higher than the inside temperature.
This is not visible dirt; that was never the point. The concern is about germs, bacteria, fungi...
S
Sebastian7915 Jul 2015 15:12Every mechanical ventilation system with heat recovery includes a drain to remove condensate – and condensate only forms when the dew point is reached. However, this practically never happens in mechanical ventilation systems (which is why there is also a dry trap, since it is used so infrequently).
A heat exchanger with moisture recovery (like the one I have) is made from a material that does not allow bacteria or germs to grow – the key here is bound salt.
In conventional (crossflow) heat exchangers, there is no contact at all between supply and exhaust air...
So, you haven’t quite got it yet.
A heat exchanger with moisture recovery (like the one I have) is made from a material that does not allow bacteria or germs to grow – the key here is bound salt.
In conventional (crossflow) heat exchangers, there is no contact at all between supply and exhaust air...
So, you haven’t quite got it yet.
Yes, the mystery is solved. Almost throughout the entire summer, moisture condenses inside the pipes. Not only does the air cool down in the heat recovery unit, but afterwards, the warm and fully saturated air also adjusts to the ambient temperature. As a result, water condenses inside the pipes during the summer. It is therefore logical that the pipes gradually develop microbial growth even without any construction defects.
And this is likely what happened in the mentioned model house. After two summers, the critical threshold was simply exceeded. An ozone treatment of all pipes lasting several hours eliminated the microbes. Now, the system can provide sellers, visitors, architects, and others with more hygienic, microbe-free air for another two years.
And this is likely what happened in the mentioned model house. After two summers, the critical threshold was simply exceeded. An ozone treatment of all pipes lasting several hours eliminated the microbes. Now, the system can provide sellers, visitors, architects, and others with more hygienic, microbe-free air for another two years.
S
Sebastian7915 Jul 2015 15:31No, it isn’t, because there is no mystery.
Again: dew point is the key term... You simply have no idea what you keep insisting on.
Especially since, according to the theory, the pipes would be recontaminated after one day of ozone treatment – you don’t understand your own arguments...
Again: dew point is the key term... You simply have no idea what you keep insisting on.
Especially since, according to the theory, the pipes would be recontaminated after one day of ozone treatment – you don’t understand your own arguments...
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