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.
I have read the text, and in the post by the colleague, it says that constant air volume controls work with a membrane.
I have now read all the posts again, but in my opinion, my questions are still not answered.
Also, you are confusing me a bit.
You wrote:
"Otherwise, just get one without constant air volume control, then you can easily open the window."
-> To me, this means that constant air volume control is what I need if I want to be able to open the window.
Later, referring to opening a window, you wrote:
"With constant air volume control, it works against it, without it doesn’t care."
-> This is a bit unclear, but I think you mean that constant air volume control works against an open window, so it is not good for window opening after all?!
Then you added:
"There are controlled residential ventilation systems that can control the airflow by adjusting the fan motor speed – and then you have a constant increase and decrease of speed. An open window (of course) disrupts the airflow...."
-> You had mentioned constant air volume control as opposed to dynamic control; here, dynamic control is bad for opening windows, so as the opposite, constant control is good for windows?!
-> My thought then: maybe your comment was just expressed poorly.
Now you say again:
"Without this technology, you don’t have problems – as I already said – because the ventilation is dumb and just blows continuously."
So it’s different again?
I think there are many communication issues here; it seems to annoy you a bit as well, judging by your choice of words.
I think the problem is that you know the subject, already have one installed, and have experience with it.
People like me don’t have any and come to the forum for that reason.
But maybe you could explain again (for beginners) what different techniques there are regarding air volume control (none, constant control, dynamic control, others) and how each reacts to a window being left open overnight.
That would be very helpful and kind.
I have now read all the posts again, but in my opinion, my questions are still not answered.
Also, you are confusing me a bit.
You wrote:
"Otherwise, just get one without constant air volume control, then you can easily open the window."
-> To me, this means that constant air volume control is what I need if I want to be able to open the window.
Later, referring to opening a window, you wrote:
"With constant air volume control, it works against it, without it doesn’t care."
-> This is a bit unclear, but I think you mean that constant air volume control works against an open window, so it is not good for window opening after all?!
Then you added:
"There are controlled residential ventilation systems that can control the airflow by adjusting the fan motor speed – and then you have a constant increase and decrease of speed. An open window (of course) disrupts the airflow...."
-> You had mentioned constant air volume control as opposed to dynamic control; here, dynamic control is bad for opening windows, so as the opposite, constant control is good for windows?!
-> My thought then: maybe your comment was just expressed poorly.
Now you say again:
"Without this technology, you don’t have problems – as I already said – because the ventilation is dumb and just blows continuously."
So it’s different again?
I think there are many communication issues here; it seems to annoy you a bit as well, judging by your choice of words.
I think the problem is that you know the subject, already have one installed, and have experience with it.
People like me don’t have any and come to the forum for that reason.
But maybe you could explain again (for beginners) what different techniques there are regarding air volume control (none, constant control, dynamic control, others) and how each reacts to a window being left open overnight.
That would be very helpful and kind.
I would take a very pragmatic approach. If the ventilation system has a problem with an open window, then it simply gets switched off. In my case, it’s easy: window open detection via KNX switches the system off.
You would just turn the system off in the evening and back on in the morning, and that’s it. Then it can exchange the air all day, and if you open the window in the evening, it just switches off again.
With manual ventilation, you won’t achieve the necessary air exchange rates with today’s building standards anyway.
If you need a draft to sleep, just put a fan in the bedroom.
I don’t think the air quality will change significantly with an open window compared to the ventilation system.
A ventilation system is usually specified with an air exchange rate of 0.6 to 0.7. This means it replaces 60% to 70% of the room air per hour. I don’t believe you can achieve that manually in any way.
You would just turn the system off in the evening and back on in the morning, and that’s it. Then it can exchange the air all day, and if you open the window in the evening, it just switches off again.
With manual ventilation, you won’t achieve the necessary air exchange rates with today’s building standards anyway.
If you need a draft to sleep, just put a fan in the bedroom.
I don’t think the air quality will change significantly with an open window compared to the ventilation system.
A ventilation system is usually specified with an air exchange rate of 0.6 to 0.7. This means it replaces 60% to 70% of the room air per hour. I don’t believe you can achieve that manually in any way.
S
Sebastian7931 Aug 2016 10:59Yes, I also see this as a communication issue.
“The colleague,” meaning Bieber0815, mentioned something that does exist but is not necessary for a typical modern single-family house. So just forget about all that, okay?
When I say you should NOT get a system with constant air volume control so that you can easily leave windows open, why do you interpret that as advice to get exactly that kind of system?
You brought up this dynamic control—I'm not familiar with it, but I would equate it with constant air volume control.
There are roughly two types of systems: those that just blow air and need to be balanced accordingly (for each stage and then again for individual rooms), and systems capable of constant air volume control, which (in my opinion) only require initial room balancing.
I still think the issue of overloading the system is exaggerated here, but the fact remains that a system with this kind of control always has to compensate.
EDIT: And again, KNX... It would be unwise for the system to switch off based on that, because opening a window in one room does not ventilate an entire house.
And an open window certainly provides a much higher air exchange rate for that room than any system can.
“The colleague,” meaning Bieber0815, mentioned something that does exist but is not necessary for a typical modern single-family house. So just forget about all that, okay?
When I say you should NOT get a system with constant air volume control so that you can easily leave windows open, why do you interpret that as advice to get exactly that kind of system?
You brought up this dynamic control—I'm not familiar with it, but I would equate it with constant air volume control.
There are roughly two types of systems: those that just blow air and need to be balanced accordingly (for each stage and then again for individual rooms), and systems capable of constant air volume control, which (in my opinion) only require initial room balancing.
I still think the issue of overloading the system is exaggerated here, but the fact remains that a system with this kind of control always has to compensate.
EDIT: And again, KNX... It would be unwise for the system to switch off based on that, because opening a window in one room does not ventilate an entire house.
And an open window certainly provides a much higher air exchange rate for that room than any system can.
Why not turn off the mechanical ventilation system completely in summer? During the day, it only brings in warm air (even though the mechanical ventilation system might cool the outside air slightly), and at night, a fully opened window on the upper floor is simply more effective.
S
Sebastian7931 Aug 2016 11:10Because ventilation is necessary even in summer.
And in our home, the mechanical ventilation system does not cause any warming – just as it cannot cool, it cannot really heat either. However, I would always run the system at a minimal level during the day...
And in our home, the mechanical ventilation system does not cause any warming – just as it cannot cool, it cannot really heat either. However, I would always run the system at a minimal level during the day...
Sebastian79 schrieb:
Because ventilation is necessary even in summer. Yes, of course you ventilate, but not during the day, rather at night.
Sebastian79 schrieb:
And in our case, the mechanical ventilation system does not make it warmer – just as it cannot cool, it also cannot really heat. Certainly, the mechanical ventilation system does not heat the air, but it draws in warm outside air.
It always seems like, with you, a house cannot function without mechanical ventilation. I also have a mold-free house without mechanical ventilation. This also works by ventilating in the early morning and evening.
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