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.
Mechanical ventilation with heat recovery (MVHR) typically exchanges the air volume about 0.6 times per hour. This means the entire air is replaced at least every 2 hours, which equals a minimum of 12 exchanges per day.
MVHR will only provide dry air compared to window ventilation if you rarely or never ventilate by opening windows. You can also reduce the MVHR exchange rate to 0.1 or 0.2 times per hour if desired. I would recommend having more plants instead.
There are MVHR systems with humidity recovery available if you want. These systems can even offer an advantage over window ventilation. Otherwise, the dryness of the air with MVHR matches that of window ventilation when exchanging the same amount of air. Feel free to experiment to see how low you can set the MVHR exchange rate before mold risk appears. However, I do not recommend this. It’s better to have more plants.
The point is, with MVHR you can actually regulate ventilation. Only with MVHR can you integrate humidity recovery. In the worst case, you can turn the MVHR off or even seal the outlets. Retrofitting is practically not possible. If you are sensitive to dryness, research humidity recovery and controllability, and consider combining MVHR with humidity sensors (KNX or other systems).
And with plants, you’re not creating a rainforest. You don’t need to buy hundreds of plants to increase humidity from 20% to 90%. This can be controlled as well... 1 plant too few, 2 plants too few, 3 to 10 plants ideal = perfect indoor climate with MVHR including heat recovery and humidity recovery, 11 to 20 plants too many, 300 plants = rainforest, and so on...
MVHR will only provide dry air compared to window ventilation if you rarely or never ventilate by opening windows. You can also reduce the MVHR exchange rate to 0.1 or 0.2 times per hour if desired. I would recommend having more plants instead.
There are MVHR systems with humidity recovery available if you want. These systems can even offer an advantage over window ventilation. Otherwise, the dryness of the air with MVHR matches that of window ventilation when exchanging the same amount of air. Feel free to experiment to see how low you can set the MVHR exchange rate before mold risk appears. However, I do not recommend this. It’s better to have more plants.
The point is, with MVHR you can actually regulate ventilation. Only with MVHR can you integrate humidity recovery. In the worst case, you can turn the MVHR off or even seal the outlets. Retrofitting is practically not possible. If you are sensitive to dryness, research humidity recovery and controllability, and consider combining MVHR with humidity sensors (KNX or other systems).
And with plants, you’re not creating a rainforest. You don’t need to buy hundreds of plants to increase humidity from 20% to 90%. This can be controlled as well... 1 plant too few, 2 plants too few, 3 to 10 plants ideal = perfect indoor climate with MVHR including heat recovery and humidity recovery, 11 to 20 plants too many, 300 plants = rainforest, and so on...
S
Sebastian794 Sep 2016 13:17Normally, 0.6 is not used because the system then runs quite high, which is unnecessary – moisture protection is significantly lower, and you can set something in between according to your preference.
Believe it or not, a controlled residential ventilation system with moisture recovery does make a difference – more counterproductive in summer, sufficient in winter. However, the winter needs to be cold for the drying effect to be significant.
Believe it or not, a controlled residential ventilation system with moisture recovery does make a difference – more counterproductive in summer, sufficient in winter. However, the winter needs to be cold for the drying effect to be significant.
And many systems nowadays no longer need to run constantly. It is often possible to use weekly or daily schedules that adjust the ventilation based on demand (for example, a bit more in the morning after waking up, or short intensive ventilation activated by a button in the bathrooms after showering, etc.). Over the last two years, I have also been satisfied with the moisture recovery. Even in summer, it works better than having none at all, since it functions in both directions (excessively humid air is also dried).
from away
from away
Yes, air is a poor conductor of heat. That is why, for example, solid clay bricks had to be replaced by perforated or hollow bricks.
Yes, without additional measures, many ventilation systems fail early during subzero temperatures because the 1000-watt (about 1.3 horsepower) preheater consumes a lot of electricity, but the heat output is comparable to that of a travel hairdryer.
And yes, enthalpy recovery units are beneficial for sensitive individuals. Standard ventilation systems produce condensate that needs to be drained, whereas with enthalpy units, the discharge is almost always dry.
Yes, without additional measures, many ventilation systems fail early during subzero temperatures because the 1000-watt (about 1.3 horsepower) preheater consumes a lot of electricity, but the heat output is comparable to that of a travel hairdryer.
And yes, enthalpy recovery units are beneficial for sensitive individuals. Standard ventilation systems produce condensate that needs to be drained, whereas with enthalpy units, the discharge is almost always dry.
Saruss schrieb:
In the past two years, I have also been satisfied with the humidity recovery system. Even in summer, it performs better than having none, since it works both ways (too humid air also becomes drier).What type of unit do you have?
P
Peanuts745 Sep 2016 13:48The installer also told us that after a hot, steamy shower, you should even open the window...
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