Germany's inefficient love affair with open windows (2021)
politico.eu
politico.eu
-Indeed be 'airtight', in the sense that limited air (and noise, as a bonus) will enter or leave the building except via defined ventilation routes.
-Offer primary 24/7 ventilation (mostly for CO2 management) via ingress/egress vents as part of a balanced ventilation system, which performs 'comfort' regulation of incoming air temperature using heat recovered from outgoing air.
-Heat or cool the building via under-floor convection connected to a reversible heat pump. This will slowly but surely bring most of the building mass to a comfortable temperature regardless of season.
-In addition to basic ventilation and heating/cooling offer very-well-insulated yet securely operable windows for additional temporary ventilation. Window openings are very much defined ventilation routes as part of the 'airtight' plan.
The important things to keep in mind here are that the balanced ventilation system prevents things like mold already, and that opening windows for brief periods of time (as in: measured in hours) for (perceived) comfort won't impact energy efficiency very much at all.
The most relevant criticism here is that retrofitting existing buildings for the above scheme is a significant challenge, but that doesn't quite seem to be the point the article wants to be making...
I've never assumed anyone to actually do all of this excess ventilation, though...I've always been too lazy to "open all windows three times a day for five minutes each" (where the heck do people find the time to do that each and every day?), and the "solution" of just opening the window a little over a long period is so obviously expensive in terms of heating costs that I rather keep most windows closed most of the time (except bathroom after showers for obvious reasons).
Something about that rubs me the wrong way. Doesn't it matter that the task is menial and doesn't seem all that effectual?
Yes, water vapor in the air causes mold, but here is the thing: the water only sticks to cold walls.
It is the combination of a cold wall plus water in the air that is the problem. Ventilation alone cannot make your wall warmer, in fact, excessive ventilation may cool your walls down even faster. As expensive as it might sound, the only reliable solution is to properly insulate the wall and keep it warm.
But is really true „Lüften“ is something we do in every room every morning here.
Luckily modern Bauhaus architecture style homes have windows down to the floor so that opening them is always possible because there is no sideboard with plants on top in front of the window.
The irony is that the windows that Germans insist on leaving open at night put our crank casement things to shame. Double gasketed? No, triple gasketed! Guaranteed airtight to god-knows-how-many psi, and without even a center post. And open horizontally or tilt vertically depending on which way you turn the handle.
It's super efficient and improves air quality a lot when your building is highly insulated. The enthalpy part is important because winter air is pretty dry after heat exchange. Bonus points when you can fit good air filters (ePM1 50%+). Also, some systems offer a summer bypass for cooling in summer without AC as well as "smart functions" like orchestration of multiple devices or automatic control via CO2/humidity sensor.
Central ventilation is unfortunately very hard to retrofit...
If there’s actual poor air quality (smoke, etc), this is inadequate. 50% is fine for a recirculating system — fine particles will be reduced by half on each pass. For for a single pass system, if you have 50 μg/m3 outdoors (quite common in a lot of places, sadly) you get 25 μg/m3 coming in through your fancy ventilation system, which is not great.
What you want is a great honking filter, 95% or better, with a prefilter. You’ll pay several hundred dollars for that big filter, but you’ll be running it at low velocity (maybe 150cfm of flow in a 24”x24” filter housing), so it will have minimal pressure drop and will last a long time. Even an actual HEPA filter wouldn’t be out of place here.
But even the really fancy European ERV/HRV brands use those inadequate ePM1 50% filters. I’ve even measured them with a handheld particle counter — they work every bit as poorly as one would expect from the specs. And those filters are small, and they gunk up quickly.
Got any suggestions how I could retrofit a better filter solution for my device (Zehnder ComfoSpot50). It has "slotted" filters like these https://cleanfilter.eu/en/product/zehnder-comfospot-50-filte.... Maybe something to chain outside in front of the intake or inside after the outlet (though I'm afraid I could run the Comfospot out of specs..)?
Or I guess I could kind of suboptimally get a standalone one.
These handheld particle counters look intriguing. Unfortunately a bit on the expensive side... Maybe I can borrow one, might give me some hard data for contacting my municipality about this.
https://www.hvacquick.com/products/residential/Air-Filters/P...
Haven’t actually finished connecting it yet. It’s nicely constructed, though.
I'll look around a bit but I'll probably get a standalone indoor one.
IQAir Atem X and Allermed devices, that I've read good things about, are too expensive right now (and too large as well, considering the ~20m^2 room is relatively crammed).
Hope the device is a sane choice. As usual I needed to prevent myself from overanalyzing while battling spam blogs and broken corporate sites.
The IKEA things apparently are "only" EPA12, but totally ok for my case... Might still evaluate one if the Levoit doesn't perform well for some reason.
For a given amount of power consumption, you end up with (concentration of contaminants) · (flow rate) · (filter efficiency) / (power), which is (at fixed contaminant level and a fixed quality of fan) roughly proportional to (filter efficiency) / (pressure drop at design flow rate) and this is where IKEA is making the right tradeoff: those non-HEPA filters have considerably less pressure drop and only fail to filter a percent or so of the air going through.
You still get your HEPA filtering, because that's on your HVAC system.
> The key may be to have less insulation, because the current system seems to be too airtight to accomodate for residents' differing preferences
Why not change the windows to open outward/upward?
Yeah, that's an absurd suggestion.
Insulation against heat transfer and insulation against mass transfer are also two different things. Although in a trivial setup the latter inevitably leads to the former, that doesn't need to be the case: Counterflow heat exchangers are a thing.
> Why not change the windows to open outward/upward?
Opening outward is much harder to handle (as it requires something to pull the window back in to close it); upward would need a robust mechanism that prevents the window from violently smashing down due to gravity.
Sliding windows have neither downside, but are much, much worse at noise and thermal insulation.