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.
S
Sebastian7915 Jul 2015 15:43No, because the moisture already condenses on the heat exchanger and drains there.
Also, you rarely or never have 30°C (86°F) warm air with 75% humidity at these latitudes – typically it is more than 10% lower.
Do you really believe you have discovered something that apparently all manufacturers, buyers, distributors, and institutions have overlooked? Do you really think there would be a building approval if this component were a breeding ground (which, according to you, it definitely is)?
Also, you rarely or never have 30°C (86°F) warm air with 75% humidity at these latitudes – typically it is more than 10% lower.
Do you really believe you have discovered something that apparently all manufacturers, buyers, distributors, and institutions have overlooked? Do you really think there would be a building approval if this component were a breeding ground (which, according to you, it definitely is)?
The moisture condenses on the heat exchanger (HX), so what happens next? Then you have air at temperature X after the HX with a relative humidity of 100 percent. What likely happens next in the ducts if condensate has already formed on the HX?
No, I certainly haven’t discovered anything completely new. The hygienic issues of ventilation systems are well known. They are often deliberately ignored or not mentioned by controlled residential ventilation salespeople.
No, I certainly haven’t discovered anything completely new. The hygienic issues of ventilation systems are well known. They are often deliberately ignored or not mentioned by controlled residential ventilation salespeople.
f-pNo schrieb:
Tell me – I have an unused filter from a former range hood (not an activated carbon filter). At first glance, it looks like the coarse filter used in my decentralized ventilation units. I’ve been thinking about cutting it to size and using 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 be potentially possible? (At least the filter would still serve a useful purpose since the range hood has long been discarded.) Good question. If the filter has the same specifications as the one in the mechanical ventilation with heat recovery system, why not.
For example, I bought my coarse filter from a filter supplier – they are all identical, whether for mechanical ventilation systems with heat recovery, range hoods, etc. (for me: G4, 20mm (0.8 inch) thick, exactly as installed by the manufacturer in the mechanical ventilation system with heat recovery ==> 2m² (21.5 ft²) = €16.99 ==> lasts half the lifetime of a mechanical ventilation system with heat recovery).
Grym schrieb:
The moisture condenses at the heat exchanger, so what happens next? Then you have air at temperature X after the heat exchanger with 100 percent relative humidity. What do you think happens afterward in the ducts when condensate has already formed in the heat exchanger?
No, I certainly haven’t discovered anything completely new. The hygiene issues related to ventilation systems are well known. They are often conveniently ignored or downplayed by controlled residential ventilation sellers. So why have my ducts been completely dry for 14 months, including the condensate drain during summer? Why are the hygiene problems of ventilation systems known yet ignored?
S
Sebastian7915 Jul 2015 16:20Because you, me, and all of us simply have no idea – just accept that already, nordanney
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