Hello everyone,
We are currently starting to deal with the technical aspects of our single-family home.
I haven’t found a thread discussing whether a ventilation system generally makes sense or not. So here is a general discussion thread on the topic:
At first, we looked into various timber frame construction providers, which made us quite sensitive in this area. Naturally, a ventilation system is quite important due to the tighter building envelope, which I can completely understand. However, everything is also marketed accordingly...
Since we have now decided to go with a regional solid construction company, completely different questions arise:
I currently have a detailed offer from a solid construction company:
- $10,000 additional cost for thermal insulation measures
- $13,000 additional cost for a central ventilation system or $9,000 additional cost for a decentralized ventilation system
--> So the repayment subsidy of $18,000 is of little use to me; on the contrary, I am even paying extra for this (of course, I get a “better” house in return).
Key Data:
- Single-family home city villa, 150m² (1,615 ft²) with basement
- Air-to-water heat pump
- Building material: brick
The questions I am now asking myself:
1. Is a ventilation system even necessary to achieve KfW 55 standard?
2. If yes, would it maybe make more sense to go for KfW 70 and forget about the subsidy?
3. Is a ventilation system really that great? There are many reports about noise, high maintenance, etc.
4. If yes, in our building project would a decentralized or central system be better? I have read a lot of positive things about decentralized systems, so central ones might not be an option? Is that correct or not?
5. Is it even possible to reach KfW 55 standard otherwise? Do you really have to ventilate every 2 hours? Are there any experiences?
6. Is the additional $10,000 cost for KfW 55 without a ventilation system justified? Are the prices for the ventilation systems justified?
I know this is an endless debate and there are clearly two opinions here. However, we find it really difficult to make a decision. Maybe a few discussions and information here will help us make up our minds.
We are currently starting to deal with the technical aspects of our single-family home.
I haven’t found a thread discussing whether a ventilation system generally makes sense or not. So here is a general discussion thread on the topic:
At first, we looked into various timber frame construction providers, which made us quite sensitive in this area. Naturally, a ventilation system is quite important due to the tighter building envelope, which I can completely understand. However, everything is also marketed accordingly...
Since we have now decided to go with a regional solid construction company, completely different questions arise:
I currently have a detailed offer from a solid construction company:
- $10,000 additional cost for thermal insulation measures
- $13,000 additional cost for a central ventilation system or $9,000 additional cost for a decentralized ventilation system
--> So the repayment subsidy of $18,000 is of little use to me; on the contrary, I am even paying extra for this (of course, I get a “better” house in return).
Key Data:
- Single-family home city villa, 150m² (1,615 ft²) with basement
- Air-to-water heat pump
- Building material: brick
The questions I am now asking myself:
1. Is a ventilation system even necessary to achieve KfW 55 standard?
2. If yes, would it maybe make more sense to go for KfW 70 and forget about the subsidy?
3. Is a ventilation system really that great? There are many reports about noise, high maintenance, etc.
4. If yes, in our building project would a decentralized or central system be better? I have read a lot of positive things about decentralized systems, so central ones might not be an option? Is that correct or not?
5. Is it even possible to reach KfW 55 standard otherwise? Do you really have to ventilate every 2 hours? Are there any experiences?
6. Is the additional $10,000 cost for KfW 55 without a ventilation system justified? Are the prices for the ventilation systems justified?
I know this is an endless debate and there are clearly two opinions here. However, we find it really difficult to make a decision. Maybe a few discussions and information here will help us make up our minds.
Heat recovery works in both directions. This does not mean active cooling, which only an air conditioning system can provide.
A simplified example:
Indoor temperature 23°C (73°F) / outdoor temperature 30°C (86°F).
Exhaust air is 23°C (73°F) / supply air is 30°C (86°F).
Now the heat exchanger comes into play. It cools (actually exchanges) the temperature of the exhaust air with the supply air. However, this process is not 100% efficient. Therefore, the supply air temperature is not 23°C (73°F) but rather 24°C (75°F).
The numbers are made up; I cannot provide actual figures. They are intended to illustrate the function.
This means the house gradually warms up because it is not actively cooled. Just more slowly than if you were to open the windows at intervals and let 30°C (86°F) air inside. It is important not to keep windows closed all day, as with airtight building envelopes this would cause stuffiness.
The second effect is the summer bypass. This feature ensures that, under specific conditions, the mechanical ventilation system recognizes that during cool summer nights, the supply air should not be warmed by the exhaust air. Instead of reheating the night air from, for example, 18°C (64°F) to the usual 21°C (70°F), the air bypasses the heat exchanger so that the effect described above lasts longer.
Overall, this means that a house (with proper shading) heats up more slowly and stays within comfortable temperature ranges longer than a comparable house without mechanical ventilation with heat recovery.
Of course, there are limits. If there is a heatwave lasting more than three weeks with nighttime temperatures around 26°C (79°F), this system will no longer be effective.
A simplified example:
Indoor temperature 23°C (73°F) / outdoor temperature 30°C (86°F).
Exhaust air is 23°C (73°F) / supply air is 30°C (86°F).
Now the heat exchanger comes into play. It cools (actually exchanges) the temperature of the exhaust air with the supply air. However, this process is not 100% efficient. Therefore, the supply air temperature is not 23°C (73°F) but rather 24°C (75°F).
The numbers are made up; I cannot provide actual figures. They are intended to illustrate the function.
This means the house gradually warms up because it is not actively cooled. Just more slowly than if you were to open the windows at intervals and let 30°C (86°F) air inside. It is important not to keep windows closed all day, as with airtight building envelopes this would cause stuffiness.
The second effect is the summer bypass. This feature ensures that, under specific conditions, the mechanical ventilation system recognizes that during cool summer nights, the supply air should not be warmed by the exhaust air. Instead of reheating the night air from, for example, 18°C (64°F) to the usual 21°C (70°F), the air bypasses the heat exchanger so that the effect described above lasts longer.
Overall, this means that a house (with proper shading) heats up more slowly and stays within comfortable temperature ranges longer than a comparable house without mechanical ventilation with heat recovery.
Of course, there are limits. If there is a heatwave lasting more than three weeks with nighttime temperatures around 26°C (79°F), this system will no longer be effective.
Tarnari schrieb:
Yep, in my view, combined with the cooling function of the underfloor heating system, it's better than nothing.
I'm curious to see how it works. It works for us. However, the most important component is shading.
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