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.
B
Bieber08155 Sep 2016 23:08AOLNCM schrieb:
A ventilation system is designed to bring fresh, unused, oxygen-rich air into the house. ... with heat recovery and preferably also moisture recovery. The rest of your post, in my opinion, compares apples and oranges (ventilation via controlled residential ventilation vs. not ventilating at all?) using a very unusual example (-20°C (‑4°F)); I find this not very meaningful, although I appreciate many of your other posts.AOLNCM schrieb:
Yes, air is a poor conductor of heat. Nitpicking mode: This was reasonably about heat capacity, not heat conduction. I prefer not to comment on the rest of the calculation, as I did not follow it (it may be correct, but it doesn't have to be; was moisture considered?).Kaspatoo schrieb:
My thoughts:
- From the perspective of dryness, a controlled residential ventilation system seems mercilessly oversized.
- Would lowering the ventilation rate not improve the situation?
- But 2 air changes per day are not that much. Opening windows twice a day also exchanges air twice but retains more moisture?!
- I’m afraid that manual ventilation might be insufficient and is sometimes skipped due to time constraints, but controlled ventilation seems to go too far in the opposite direction; something reasonable in between would be needed (for KfW5)1. Moisture recovery or humidifier or no ventilation (dry air during the heating period is unrelated to whether a controlled residential ventilation system is installed, but only whether ventilation occurs at all). Possibly, running the controlled ventilation system at a lower setting may help (higher humidity, higher CO2 levels).2. Yes, regarding moisture, not regarding "good" air.
3. It depends.
4. You can run the controlled ventilation at any setting of your choice. Generally, the rated capacity is appropriate; the standards are not unreasonable.
Peanuts74 schrieb:
Our installer said that after a hot, steamy shower you should even open a window... We skip opening the window (not the showering); apparently, it is not necessary with our controlled residential ventilation system. Disclaimer: Of course, anyone who wishes may and is allowed to open the window!S
Sebastian795 Sep 2016 23:10When I shower in the basement bathroom without a window, the humidity returns to normal relatively quickly.
If necessary, operate the humidistat.
If necessary, operate the humidistat.
We have exhaust air in the bathrooms and kitchen, and supply air in the other rooms. This means that in these exhaust areas, the airflow rate (due to smaller surface area compared to the other rooms) is proportionally much higher, resulting in fewer problems with moisture or odors.
P
Peanuts746 Sep 2016 06:53So when Madame runs about 150 liters (40 gallons) of water, which feels boiling hot to me, through the showerhead in winter, you can’t see anything in the bathroom anymore. Surely the ventilation would manage it eventually, but I prefer to open the window instead...
S
Sebastian796 Sep 2016 07:03Correctly Sizing and/or Adjusting Ventilation
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