ᐅ Mechanical ventilation with heat recovery and still keeping windows open at night
Created on: 30 Aug 2016 14:23
K
Kaspatoo
Hi,
I would like to have a mechanical ventilation with heat recovery system in our newly built house, but we always sleep with the window open at night (mainly because of the cool, fresh-feeling air; warm air doesn’t feel fresh to me).
Here in the forum, I’ve read several times that many people just do this “without any issues.”
I’ve also often read that this could interfere with the mechanical ventilation system (it might "malfunction"). It was mentioned that this leads to increased wear and tear, but I couldn’t clearly identify exactly how and on which components this higher wear would occur. Apparently, this only happens if the system uses some kind of dynamic pressure control and doesn’t operate with a constant static pressure.
I have also read that this not only cools down the bedroom with the open window but, in the worst case, could cool the entire house because the ventilation system causes a temperature equalization. So either the heating has to compensate or the other rooms get colder.
For me as a layperson and reader, this means:
- If you have a mechanical ventilation system, make sure it does not have dynamic pressure control to avoid the “malfunction” problem.
- When planning the ventilation, ensure that at least the attic and the ground floor have separate circuits for the mechanical ventilation and are not connected “in series.”
Regarding the latter: As far as I understood correctly from a planner, the pipe layout would look like this: assuming you have four rooms in the attic (bathroom, 3 bedrooms), two rooms would get supply air ducts, and two rooms would get exhaust air ducts (one of those definitely the bathroom). The airflow then passes under the door.
1) If I open the window in an exhaust room, I would expect the following:
- At most, only my room cools significantly due to colder outside air coming in through the open window.
- It might be that little happens (almost no fresh air in the room), except that the outside air flows quite directly into the exhaust.
- Other rooms lose their air exhaust; the air might stagnate there, causing the air pressure to rise and the pressure increase to reach the supply air fan. This results in more resistance and could lead to higher wear (it’s like a freight train with locomotives at front and rear: if there’s no locomotive pulling at the front, the one at the back has it harder, although it won’t supply more power than set). In the extreme case, this would be like holding the supply air fan in place, which I believe is not good for the component in the long run.
- The question is: how serious is this or am I overthinking?
2) If I open the window in a supply air room, I would expect:
- In the worst case, the supply air flows directly outside, and I get nothing from the open window.
- The “pushing” locomotive has more load because the “pulling” locomotive is absent.
If the answer is: yes, opening windows is a bad idea with mechanical ventilation with heat recovery, then my follow-up question is: how do I prevent mold if I can’t regularly manage to open windows?
In summary, it seems to me there are only four possible options:
- Spend a lot of money on individual controls.
- Forget mechanical ventilation with heat recovery, ventilate manually and, if you ventilate too rarely, just skip the insulation and build a house like in the 1970s.
- Install mechanical ventilation with heat recovery and live without opening windows.
- Install mechanical ventilation with heat recovery, ventilate anyway, and accept the consequences (energy loss, system wear, disturbed indoor climate).
What do you think?
Which of my statements are correct, which are not?
Thanks a lot for your answers.
I would like to have a mechanical ventilation with heat recovery system in our newly built house, but we always sleep with the window open at night (mainly because of the cool, fresh-feeling air; warm air doesn’t feel fresh to me).
Here in the forum, I’ve read several times that many people just do this “without any issues.”
I’ve also often read that this could interfere with the mechanical ventilation system (it might "malfunction"). It was mentioned that this leads to increased wear and tear, but I couldn’t clearly identify exactly how and on which components this higher wear would occur. Apparently, this only happens if the system uses some kind of dynamic pressure control and doesn’t operate with a constant static pressure.
I have also read that this not only cools down the bedroom with the open window but, in the worst case, could cool the entire house because the ventilation system causes a temperature equalization. So either the heating has to compensate or the other rooms get colder.
For me as a layperson and reader, this means:
- If you have a mechanical ventilation system, make sure it does not have dynamic pressure control to avoid the “malfunction” problem.
- When planning the ventilation, ensure that at least the attic and the ground floor have separate circuits for the mechanical ventilation and are not connected “in series.”
Regarding the latter: As far as I understood correctly from a planner, the pipe layout would look like this: assuming you have four rooms in the attic (bathroom, 3 bedrooms), two rooms would get supply air ducts, and two rooms would get exhaust air ducts (one of those definitely the bathroom). The airflow then passes under the door.
1) If I open the window in an exhaust room, I would expect the following:
- At most, only my room cools significantly due to colder outside air coming in through the open window.
- It might be that little happens (almost no fresh air in the room), except that the outside air flows quite directly into the exhaust.
- Other rooms lose their air exhaust; the air might stagnate there, causing the air pressure to rise and the pressure increase to reach the supply air fan. This results in more resistance and could lead to higher wear (it’s like a freight train with locomotives at front and rear: if there’s no locomotive pulling at the front, the one at the back has it harder, although it won’t supply more power than set). In the extreme case, this would be like holding the supply air fan in place, which I believe is not good for the component in the long run.
- The question is: how serious is this or am I overthinking?
2) If I open the window in a supply air room, I would expect:
- In the worst case, the supply air flows directly outside, and I get nothing from the open window.
- The “pushing” locomotive has more load because the “pulling” locomotive is absent.
If the answer is: yes, opening windows is a bad idea with mechanical ventilation with heat recovery, then my follow-up question is: how do I prevent mold if I can’t regularly manage to open windows?
In summary, it seems to me there are only four possible options:
- Spend a lot of money on individual controls.
- Forget mechanical ventilation with heat recovery, ventilate manually and, if you ventilate too rarely, just skip the insulation and build a house like in the 1970s.
- Install mechanical ventilation with heat recovery and live without opening windows.
- Install mechanical ventilation with heat recovery, ventilate anyway, and accept the consequences (energy loss, system wear, disturbed indoor climate).
What do you think?
Which of my statements are correct, which are not?
Thanks a lot for your answers.
S
Sebastian7931 Aug 2016 11:19From a purely technical standpoint, this can hardly work if everything is truly airtight.
And I can’t just quickly ventilate a house over three floors in the morning or evening—especially not the basement. It’s also not guaranteed that mold will form immediately, but the risk is significantly higher—and often you only notice the mold once it’s too late. Right now, after the construction phase, I am enjoying the comfort of the system—there was no way I could have ventilated that much.
Explain this statement to me:
- and still: The heat exchanger works both ways.
And I can’t just quickly ventilate a house over three floors in the morning or evening—especially not the basement. It’s also not guaranteed that mold will form immediately, but the risk is significantly higher—and often you only notice the mold once it’s too late. Right now, after the construction phase, I am enjoying the comfort of the system—there was no way I could have ventilated that much.
Explain this statement to me:
Musketier schrieb:
Of course, a mechanical ventilation system with heat recovery does not heat the air, but it draws in warm outside air.
- and still: The heat exchanger works both ways.
because you wrote "get one" and not "don’t get one"
ok, then I think I understand now:
make sure that it only blows air and doesn’t have any control technology, so you can open windows without any problems
higher wear and tear might occur, or maybe not
I would possibly explain the wear like this:
the fans are powered by an electric voltage, and normally the airflow is created as set by the heater
if I open a window or a door, the airflow might encounter more or less resistance (depending on whether and how overpressure or underpressure develops through the window)
so it becomes either easier or harder for the fan to spin. The fan then either spins faster (which could lead to more wear on bearings, etc.) or spins slower (which might cause stress in the drive system, etc.).
overall, in my opinion this doesn’t really matter, because if the system were set stronger or weaker, you would have this “undesired” mode all the time anyway. I think it balances out.
you might think that problems could arise from the short-term changes, but then you really wouldn’t be able to get through the front door anymore.
on the other hand, ventilating a room by opening a window for several hours would be similar to operating the controlled ventilation system continuously at just a different level.
whether this is true or not, who knows, I’m not an expert, but that’s how I imagine it.
ok, then I think I understand now:
make sure that it only blows air and doesn’t have any control technology, so you can open windows without any problems
higher wear and tear might occur, or maybe not
I would possibly explain the wear like this:
the fans are powered by an electric voltage, and normally the airflow is created as set by the heater
if I open a window or a door, the airflow might encounter more or less resistance (depending on whether and how overpressure or underpressure develops through the window)
so it becomes either easier or harder for the fan to spin. The fan then either spins faster (which could lead to more wear on bearings, etc.) or spins slower (which might cause stress in the drive system, etc.).
overall, in my opinion this doesn’t really matter, because if the system were set stronger or weaker, you would have this “undesired” mode all the time anyway. I think it balances out.
you might think that problems could arise from the short-term changes, but then you really wouldn’t be able to get through the front door anymore.
on the other hand, ventilating a room by opening a window for several hours would be similar to operating the controlled ventilation system continuously at just a different level.
whether this is true or not, who knows, I’m not an expert, but that’s how I imagine it.
S
Sebastian7931 Aug 2016 11:29Well, I agree with you that this is somewhat overemphasized.
Musketier schrieb:
Why not turn off the mechanical ventilation system completely in summer? During the day, it only brings in warm air (even if the system can cool the outside air slightly), and at night, fully open windows upstairs are simply more effective.I would immediately answer that with "fresh air," nothing else.
As far as I have read, however, many people do switch the system off.
The statement referred to your earlier comment that a mechanical ventilation system with heat recovery cannot cool or heat. This is logical since the mechanical ventilation system is neither an air conditioner nor a heater. The heat exchanger only tries to transfer as much energy as possible from the extracted air to the incoming air (or vice versa in summer). However, this will never reach 100%. Therefore, with each air exchange, the air inside the house warms up.
Additionally, every electrical device generates energy. In this respect, the mechanical ventilation system is counterproductive in summer as well (unless it is located outside the thermal envelope).
Thus, I wonder why energy (electricity) is used to heat a house when I want it to be cooler.
Additionally, every electrical device generates energy. In this respect, the mechanical ventilation system is counterproductive in summer as well (unless it is located outside the thermal envelope).
Thus, I wonder why energy (electricity) is used to heat a house when I want it to be cooler.
However, I do need to make one caveat.
As I recently learned here in the forum, there are people who require complete darkness at night.
So, if you have the roller shutters fully closed, you obviously cannot ventilate at the same time.
PS:
I always speak from my own experience. Even if a bomb went off next to me and the sun was shining in my face, I would still keep sleeping. My wife is similar, and our child has inherited this from us.
As I recently learned here in the forum, there are people who require complete darkness at night.
So, if you have the roller shutters fully closed, you obviously cannot ventilate at the same time.
PS:
I always speak from my own experience. Even if a bomb went off next to me and the sun was shining in my face, I would still keep sleeping. My wife is similar, and our child has inherited this from us.
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