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 11:46My mechanical ventilation with heat recovery does not warm the house, but it is still located within the insulated area. And you don’t really believe that it significantly heats the surroundings.
Furthermore: The mechanical ventilation with heat recovery does not actually warm the house – its purpose is to bring in fresh air and remove moisture.
Furthermore: The mechanical ventilation with heat recovery does not actually warm the house – its purpose is to bring in fresh air and remove moisture.
Musketier schrieb:
The statement referred to your previous comment that a mechanical ventilation system with heat recovery cannot cool or heat. This is logical because such a system is neither an air conditioner nor a heater. The heat exchanger only tries to transfer as much energy as possible from the outgoing air to the incoming air (or vice versa in summer). However, this will never be 100%. Therefore, with every air exchange, the indoor air temperature rises.
Additionally, every electrical device produces energy. For this reason, in summer, mechanical ventilation can even be counterproductive (unless it is located outside the building’s thermal envelope).
So I wonder why energy (electricity) is consumed to warm a house when I want it cooler. I completely agree, except regarding “fresh air” (this argument is something each person must weigh individually).
Humidity in summer is probably less of an issue.
S
Sebastian7931 Aug 2016 12:04Moisture is a major problem in summer.
Manufacturers of ventilation units offer various options with their models.
Many units already include an integrated bypass, which can be activated either directly or via programming based on conditions such as:
- Outdoor temperature being higher/lower than x°C (x°F)
- Outdoor temperature being higher/lower than indoor temperature by y°C (y°F)
- Indoor temperature being higher/lower by z°C (z°F) than the set temperature
or providing fresh air at night bypassing the heat exchanger.
Additionally, many units feature an integrated electric preheater to prevent the ventilation system from cooling down the warmed indoor air during winter. This can be mitigated, for example, by reducing the ventilation level.
As an accessory, many manufacturers offer retrofit electric reheaters.
Some models even have the option for a hydronic reheater.
Certain units are available with enthalpy heat exchangers (humidity recovery).
Some models can be upgraded with sensors for air quality, humidity, and CO2.
And, of course, options such as pollen filters, wireless remote controls, and more.
Many models have Passive House certification.
Approvals from the German Institute for Construction Technology (DIBt) are often applied for by manufacturers; for this, contacting the manufacturer is necessary.
The two fans are usually controlled separately.
A 4 Pa pressure sensor is required when a fireplace is installed in the house.
In some ventilation units, it is possible to configure the control parameters so that both fans run completely synchronized, and if one fan fails, the other stops as well.
This is the method some providers advertise to avoid the cost of the 4 Pa pressure sensor.
However, the final decision lies with the local chimney sweep authority. Usually, they only want to verify the system’s settings. For them, the combination of both units (ventilation system and fireplace) is crucial. A self-closing door on the fireplace is often the minimum requirement, regardless of the configuration.
Tip: Regional fireplace dealers are familiar with the local chimney sweep authorities and their preferences. Before purchasing a fireplace, arrange a meeting with the chimney sweep to avoid issues during inspection.
By increasing the ventilation level overnight, the building can cool down more strongly, or you can have more fresh air while sleeping.
Alternatively, if possible, when building a house with a basement, incorporate a ground heat exchanger into the foundation pit. This helps prevent the indoor air from warming up excessively during the day. Position the supply air intake on the north side of the building. Without a ground heat exchanger, reduce the ventilation level during hot weather.
Many units already include an integrated bypass, which can be activated either directly or via programming based on conditions such as:
- Outdoor temperature being higher/lower than x°C (x°F)
- Outdoor temperature being higher/lower than indoor temperature by y°C (y°F)
- Indoor temperature being higher/lower by z°C (z°F) than the set temperature
or providing fresh air at night bypassing the heat exchanger.
Additionally, many units feature an integrated electric preheater to prevent the ventilation system from cooling down the warmed indoor air during winter. This can be mitigated, for example, by reducing the ventilation level.
As an accessory, many manufacturers offer retrofit electric reheaters.
Some models even have the option for a hydronic reheater.
Certain units are available with enthalpy heat exchangers (humidity recovery).
Some models can be upgraded with sensors for air quality, humidity, and CO2.
And, of course, options such as pollen filters, wireless remote controls, and more.
Many models have Passive House certification.
Approvals from the German Institute for Construction Technology (DIBt) are often applied for by manufacturers; for this, contacting the manufacturer is necessary.
The two fans are usually controlled separately.
A 4 Pa pressure sensor is required when a fireplace is installed in the house.
In some ventilation units, it is possible to configure the control parameters so that both fans run completely synchronized, and if one fan fails, the other stops as well.
This is the method some providers advertise to avoid the cost of the 4 Pa pressure sensor.
However, the final decision lies with the local chimney sweep authority. Usually, they only want to verify the system’s settings. For them, the combination of both units (ventilation system and fireplace) is crucial. A self-closing door on the fireplace is often the minimum requirement, regardless of the configuration.
Tip: Regional fireplace dealers are familiar with the local chimney sweep authorities and their preferences. Before purchasing a fireplace, arrange a meeting with the chimney sweep to avoid issues during inspection.
By increasing the ventilation level overnight, the building can cool down more strongly, or you can have more fresh air while sleeping.
Alternatively, if possible, when building a house with a basement, incorporate a ground heat exchanger into the foundation pit. This helps prevent the indoor air from warming up excessively during the day. Position the supply air intake on the north side of the building. Without a ground heat exchanger, reduce the ventilation level during hot weather.
B
Bieber081531 Aug 2016 23:16Sebastian79 schrieb:
An open window naturally disrupts the air flow rate....But why exactly?Similar topics