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.
P
Peanuts746 Sep 2016 08:05I'm not saying it's impossible. It's just that, in my opinion, there is no harm in opening the window for 5 minutes instead of constantly adjusting the ventilation up and down...
S
Sebastian796 Sep 2016 08:07No, there’s nothing wrong with that – I just find it uncomfortable in winter when it’s done that way.
As I said, in case of emergency, press the button and the ventilation will run at a high setting for a predefined period, then return to automatic mode.
As I said, in case of emergency, press the button and the ventilation will run at a high setting for a predefined period, then return to automatic mode.
I was at my brother-in-law’s place yesterday. He has an LWZ303.
As far as I know, the device operates with constant volume flow.
He said the device has a “summer mode.” It detects when the outside temperature exceeds a certain threshold during the day and then falls below a certain temperature in the evening or at night. In that case, the device automatically switches to reduced or off supply air and possibly increased exhaust air.
You then have to open the windows manually to let in cool air.
I don’t know exactly how it works 100% or in detail, and I might have misunderstood something.
What I want to say is that such functions may exist and probably vary from device to device.
A bypass might achieve a similar effect.
But this feature supports my assumption that opening windows is not harmful to these systems.
As far as I know, the device operates with constant volume flow.
He said the device has a “summer mode.” It detects when the outside temperature exceeds a certain threshold during the day and then falls below a certain temperature in the evening or at night. In that case, the device automatically switches to reduced or off supply air and possibly increased exhaust air.
You then have to open the windows manually to let in cool air.
I don’t know exactly how it works 100% or in detail, and I might have misunderstood something.
What I want to say is that such functions may exist and probably vary from device to device.
A bypass might achieve a similar effect.
But this feature supports my assumption that opening windows is not harmful to these systems.
P
Peanuts749 Sep 2016 11:50The ventilation system reduces the supply air so that no warm air is drawn in, while at the same time, the windows should be opened to let in "COOL" air??? How is that supposed to work? If it’s warm outside, cool air won’t come in through the windows either...
USING ALL CAPS AND QUESTION MARKS USUALLY DOES NOT HELP IN INTERPERSONAL COMMUNICATION.
I wrote "[...] and the dropping below a certain temperature then at night/ in the evening."
So, it is about cool air. And this air comes directly through the window into my bedroom instead of through the duct system. Admittedly, I cannot say for sure if this really has an advantage over the bypass. In any case, there is this option available there, and it is used quite often and the user is satisfied with it.
As I said, I only wanted to point out that there are functions that support/allow opening a window. This, in turn, relates to the main topic of this thread. I did not want to discuss whether it makes sense or not. Although the people at Stiebel Eltron probably had a reason for it, even if I have not fully understood it myself yet.
I wrote "[...] and the dropping below a certain temperature then at night/ in the evening."
So, it is about cool air. And this air comes directly through the window into my bedroom instead of through the duct system. Admittedly, I cannot say for sure if this really has an advantage over the bypass. In any case, there is this option available there, and it is used quite often and the user is satisfied with it.
As I said, I only wanted to point out that there are functions that support/allow opening a window. This, in turn, relates to the main topic of this thread. I did not want to discuss whether it makes sense or not. Although the people at Stiebel Eltron probably had a reason for it, even if I have not fully understood it myself yet.
P
Peanuts749 Sep 2016 12:48This is not meant negatively, but just as an emphasis.
To me, it sounded like cool air would flow in through the windows during the day.
Sorry if that was misunderstood...
To me, it sounded like cool air would flow in through the windows during the day.
Sorry if that was misunderstood...
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