A big part of why this works so well in German homes is that they have a high thermal mass. Even single family homes are built with concrete floors and plastered over brick walls (brick as in square building block, I think the currently popular form is expanded concrete?).
In these buildings, you can replace all air with outside air at once, and once you close the windows the thermal mass of the building will quickly heat it up again.
New buildings tend to move away from it though, instead using automatic fans for ventilation
Mechanical ventilation refers to just using fans. The comment you’re replying to is suggesting that heat recovery ventilators (HRV) be used to transfer heat from the warm exhausted to the incoming outside air via a heat exchanger (or cools incoming outside air in hot climates). It reduces the need for heating or cooling while still getting fresh air into the building.
No. It usually takes the form of extractors in the most humid locations of the house (kitchen, bathroom, laundry) that are connected to a central unit that vents air to the outside. Fresh air comes in through ventilation grills around the house, normally located above windows by means of the resulting pressure. No air conditioning is involved, or recirculating, though more modern (and much more expensive) units have heat recovery systems and air filters that will also bring fresh air back in.
One way or the other you have to heat up the air again. The main reason this works is because air has very low thermal mass. Something like a thousand times less than typical solid materials. Even a small amount of solid mass is not going to cool down that much in such a short period of time.
I think there is one single factor why it is done and it is more energy efficient in comparison to keeping windows slightly open all the time for constant ventilation.
Rooms are mainly heated by water radiators in Germany. These radiators are most likely under windows to compensate for the radiated cold and draft from the windows that may create discomfort. As the heat moves up then it will create (mainly) closed circulation in the room when the windows are closed.
Now when the windows are open then the heat from the radiators will instead escape from the windows. On top of this the radiators are most likely locally regulated (with thermal valves) and will heat up because of the cold air from the outside while increasing the energy loss even more.
This is the main reason why the heating must be closed during the shock ventilation and why it is less energy efficient to keep the windows slightly open for constant ventilation.
This is of course a compromise between good air quality and energy efficiency and the correct answer is to build a proper mechanical ventilation with an heat exchange.
In modern buildings the heat recovery system in the ventilation transfers the heat from the outgoing warm air to the incoming cold air, which saves a lot of energy. The savings are big especially in colder climates.
(As a bit of trivia, the specific heat capacity of air is pretty close, +- 50%, to common building materials. Explained by the rather low density of air at normal pressure and temperature compared to those.)
This is used in Norway as well (and I suspect many other places).
The term uses the same structure "sjokklufting", which like the German means shock ventilation.
A quick search in the Norwegian National Library dates the Norwegian use of this specific term pretty firmly to ~1974 or so.
Interestingly all the uses of the term in writing in Norwegian media in 1970's seem to either be or echo the text in an ad from Jøtul, one of the largest manufacturers of cast-iron fireplaces as a negative (making it too cold), while many later mentions are positive, though also with a tinge of "we're only doing this as a fallback because our ventilation isn't good enough" in quite a few articles.
A somewhat more common Norwegian variant describing much the same is utlufting ("out-ventilation") or storutlufting ("big out-ventilation"), which is found in print at least back to the 1850's, and which tends to imply much the same, though perhaps with a less negative slant.
At some point around the 1980's, the viewpoint seems to have changed from promoting this as a good thing to describing the need for it as evidence of poor ventilation systems.
My mum would often do this, and I do it myself too, - open several windows at least a couple of times a day during winter to rapidly clear out stale air. The benefit vs. less ventilation all the time being that while you're cooling the air, it's short enough that you don't lose much heat, and neither does the building mass. It's overall much more pleasant when it's really cold outside than having a window open a crack on an ongoing basis.
A lot of newer (last 15 years or so) apartments in Oslo have a mixture of ‘natural’ ventilation through vents that let in cold air and mechanical ventilation in wet rooms, and even newer builds are starting to use ‘balanced’ ventilation that heats up cold outside air using heat from air that is being blown out https://www.byggmakker.no/rad-og-guider/kjokken-og-bad/vet-d...
Yeah, it's obviously a lot more energy-efficient to have proper ventilation.
(Then again, having recently flown back from Norway to the UK one of the things that strikes me every winter is how floodlit Norway looks from the air at night compared to the UK despite far lower population density - Norway is still riding high on the past low energy prices...)
Yes, heated pavements outside the shops, wind turbines on the hills, hydro, gravel roads and the sovereign wealth fund saving the money from oil for the future (check out https://www.nbim.no/, it's about 10Nok to the dollar).
This might be due to road standards where major roads and highways usually have road lights when it’s dark. Most of Oslo’s internal roads are lit up too, as it makes them safer in terms of traffic safety and crime suppression. But this does have a cost which became even more obvious with the wartime energy price spikes.
I'm french and I don't think there is a specific word to describe this.
We commonly use the verb "aérer" which translates to "to ventilate". But when someone uses this term, I think it designates implicitly a short ventilation as described by this German word or your Norwegian one. At least that's what I noticed around me. I don't know of anybody keeping a window open all day long to ventilate when it's cold outside.
Interestingly, Norwegian has both "luft" (air)/"lufte" (to air) and "lukt"/"lukte" (smell, to smell), and it turns out they share the same proto-Germanic origin as Dutch "luchten" as well as the equivalent German terms, and English "to lift" and Norwegian "å løfte", all centering around air with different angles.
Germanic languages are very well suited to these kinds of compound words because you can pretty much keep adding words - hence the many jokes about ridiculously long German ones - where in many other languages if you want to add precision you use a phrase instead, or rely on context...
You can do that in Norwegian too, but we tend to be a bit more shy about it than the Germans...
I'm German and this was drilled into my head since I was a child. My dad insisted on doing this. Every landlord I had so far required doing this to avoid mold. I do it before I go to sleep, because some fresher/cooler air also helps me sleep better.
It is also done in offices and schools.
Seems to be the best way to get rid of stale air (while conserving energy) in a country that prides itself of its tightly sealed windows.
> Asked by the tabloid BILD-Zeitung what feelings Germany awakes in her, Angela Merkel once famously replied, 'I think of well-sealed windows! No other country can make such well-sealed and nice windows [dichte und schöne Fenster].'
It really doesn't matter how fast you replace the air. If you let in the cold air then you need to warm it up.
What you actually do is a compromise between energy conservation and properly ventilated room as for the morning the room will be filled with high concentration of CO2 and humidity (from your breathing and sweating) and you more than often end up with bad sleep and headache.
Constant proper mechanical ventilation is the key for better sleep and health when windows are goods as German windows (some other European countries make good windows too).
> It really doesn't matter how fast you replace the air. If you let in the cold air then you need to warm it up.
Ventilating quickly is preferable to ventilating slowly.
Heat transfer through materials is comparatively slow. That means that exchanging the air in an instant retains the heat in the walls, furniture,… exchanging the air slowly allows heat from materials to „leak out“ as well.
If you ventilate through a heat exchanger when inside and outside are different temperatures, you can have more fresh air more of the time while saving energy.
energy consumption wise, yes, I guess. though mechanical ventilation requires electricity to be used, so it costs energy too. the heat exchangers are max 90% efficient as far as I know from my own research on what's available on a reasonable budget and size.
there are some potential issues if outside temp is higher and it's humid tough. these systems can cause mold.
> there are some potential issues if outside temp is higher and it's humid tough. these systems can cause mold.
Moreso than the shock ventilation method?
If there's worrying amounts of moisture, we could go ahead and say we'll do the same amount of air with the heat exchanger. Is that worse for mold potential than the alternative?
It was one of the most stunning finds for me when I moved to England to discover that my tenancy agreement, and later my flat's lease, stipulated to dry my clothing inside. Because using the garden or balcony is "unsightly". To this day it amazes me how one can, at the same time, complain about mould in the flat while refusing to air it. And yet this is a totally common attitude around here ...
This “Stoßlüften” is just opening a couple of windows for several minutes to create a draft.
There’s a nice booklet about ventilation for regular Joes called “Richtiges Lüften in Wohnungen” (Proper ventilation in apartments) published by the Fraunhofer IRB (i.e. information centre for inner spaces and construction).
This booklet explains the role of material and air humidity, how ventilation became important as buildings became more airtight, how relative humidity works, etc.
A key observation is that the main purpose of such intense ventilation is refreshing the air, i.e. removing unpleasant smells and CO2.
Landlords, experts and courts of law have nevertheless settled on the idea that 2-3x intensive ventilations per day are necessary to avoid mould.
The booklet claims that dehumidification is ideally achieved through “Spaltlüften”, which is keeping a window partly open for a longer period of time: the cool outside air enters the room in small quantities which can be quickly heated, thereby drying said air and enabling it to absorb additional humidity. Due to the longer ventilation period, materials which absorb humidity such as drapes, carpets, wallpaper or plaster can release said humidity which shall be absorbed by the dry air and ultimately exchanged with outside air.
The heater must stay permanently on so that the cool air can be heated.
Some apartments have passive mechanical ventilation such as openings in the rubber seals of the windows or ventilation slots in the window frames which follow this principle.
My landlord here in Austria put that in the flat "manual". It's the main technique to avoid high humidity in Winter.
Because high humidity means you won't feel warm and it fosters mold.
In Germany as a tenant it is usually your duty to ventilate properly. If you do not do that and this results in mold you as a tenant are responsible, not the landlord. This is of course much more complex in practice, as mold is often not caused by poor ventilation but by bad construction. So the blame can lie with the landlord, or the tenant or both depending on the specific case.
Shock ventilation is a habit of Swiss housewives which is diametrically opposed to the new "Minergie" standard for green homes, which provides for air exchange via a super expensive heat exchanger system which extracts heat from stale air before sending it out.
Of course everyone who lives in Minergie homes opens the windows each morning while hanging out the duvets, and/or complains that the enormous windows are too big to open, or don't open at all.
It's like all the Minergie engineers were so busy at work they didn't notice what their wives were doing at home. (I assume the original engineering for these hear exchangers was in the 70's when that gendered statement was not controversial!)
This is a small segment of a weekly program that is broadcast on the french-german tv station "arte". The program is called "karambolage" and highlights interesting peculiarities in French or German culture or funny anecdotes about etymiology, history. It's quite fun.
They had this piece about a french exchange student that discovered
a requirement to regular "stoßlüften" in the rent-contract.
> Let’s start with the translation. Literally, Stoß means “shock, impact or thrust” and lüften means “ventilating.” Stoßlüften therefore translates to “shock ventilation.”
I’d say the connotation is more of a quick blowing out, ejection or (im)pulse, not a shock. Compare also “ausstoßen” and “Stoßatmung”. The main feature is the short duration.
I’ve started doing this in my home office after buying a CO2 monitor. It’s worked out pretty well. I don’t trade much room temperature at all to get back close to 400PPM.
This is the first German word I taught my (American) partner and it is, to this day, likely our most used German word. Such a core concept to our entire culture!
My Velux roof windows do this automatically for me every day. Works great as they won't open if it is raining or too cold. Sucks that the radiators don't turn off at the same time, so some wasted energy there.
Do you have any control of the radiators? I have Velux GGU windows too and plan on doing Home Assistant integration for precisely the reasons you mention plus some automatic shading based on sun position or light sensors. For this I understand you need a KLF200 interface [1] and of course HA integration [2], then the integration possibilities are pretty much endless.
I have Tado TRVs and do have a HA instance. I’m stuck though, as I like the functionality from Tado like home/away, and VELUX like the automations. I’m not sure I could get as good a result by coding that all up in HA.
AFAIK it's more typically known simply as "Luft" ("air). And the idea is great. Flush the room of aerial crud as quickly as possible so that objects in the room retain their heat.
Indeed, i was on a US keyboard. The ü has since been corrected. (Or it's been edited, but this client is still showing the typo. Perhaps i waited too long to edit it.)
Sounds like building codes haven’t forced old buildings to be retrofitted with decent ventilation. If that’s not possible then it shouldn’t be a school.
Also, not really necessary. It's more of an Old Wives Tale than an effective practice.
The only place I have trouble with mold is in the bathroom, and that's because so many homes built before the 80s were built without ventilation fans in the bathroom. The places I've lived with proper ventilation have not had mold problems.
While it’s true germans are plagued with all sort of holistic medicine and homeopathy mind virus, this one is true. With covid wave there was explosion of co2 meters and tons of people realised they live in stuffy air all the time.
What’s depressing is that neither rental rules do not require HRVs yo be installed nor little public places have started to upgrade.
Since forced-air heating is uncommon in Europe the impact is not that high. The radiators or under floor heating stays warm and will re-heat the air very quickly.
Yes, to a certain degree it undermines the point of having good insulation (as in, really good - when the thermal mass of the air starts to matter). Modern "nearly zero-heating" houses have long heat exchangers in the vents to avoid the waste.
uBlock Origin blocks the entire article. The article also seems to be sponsored content, though I'm not sure what for exactly. The whole page seems a bit fishy and/or slightly broken.
I was just joking about this today. For years I have heard all kinds of dismissive attitude to this concept yet the last few months tech Twitter has been full of people buying really expensive CO2 meters, presumably because they were unaware of CO2 in rooms?
When you buy a Window here, or you rent a flat it usually comes with a manual that asks you to ventilate regularly and how.
If you ventilate properly, a CO2 meter is entirely pointless. CO2 levels are very predictable and you can also usually tell when the air quality drops through your senses.
> you can also usually tell when the air quality drops through your senses
Only when you're paying attention. If I'm not paying attention, I end up in a sufficiently depressed state that I can't notice, which is extremely self-perpetuating.
If you are ventilating regularly your CO2 levels are not raising to ridiculous levels in the first place. I'm pretty sure for most people the novelty of the CO2 measurement device wears of quickly.
I really find this hard to believe. 2000 is already at the higher threshold of where people report bad air quality and drowsiness. In practical terms it doesn't matter much because if you are ventilating properly, your CO2 levels don't stay elevated for long and you really do not need to measure or observe.
We have a CO2 level at home, so I can validate my personal observations and those of others. But I don't even need to go to personal anecdotes, everything you can read on CO2 levels indicates that people notice.
https://archive.ph/KW0ZC