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Why don’t we just open the windows? Covid-19 prevention lost in translation

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Re: Why don’t we just open the windows? Covid-19 prevention lost in translation

#291

Post by _benedict »

willyt wrote: post #287
_benedict wrote: post #255

Earlier quoted context omitted.

> my understanding is that passive house is 3-4x better ACH than a typical recently built house in the UK Part L1A of UK building regulations stipulate an air permeability of no more than 10m3/hr/m2 of building envelope at 50pa of pressure. My home has approximately a 1:1 ratio of building envelope to volume, though this will vary a great deal. But for such a home this works out to 10ACH at 50pa. There are various st…

As built and as normally used measurements being the key here. Very small new build houses in the damper western parts of the uk often have problems with mould growth because of actual in everyday use ACH below building regulations design levels. It’s particularly an issue in new build social housing. People don’t open trickle vents, they turn down the extract fan timer because of fan noise and buildings are often mo…

So, firstly 88% of homes were built pre-2000[1] and the regulations that resulted in these improvements came into force in 2010. Assuming the regulations instantly had the desired impact (unlikely) we're discussing around 6% of UK houses. Those built earlier (on average) achieve significantly worse than 10m3/hr/m2 air permeability of the building envelope[2]. So the vast majority of UK homes have more ventilation than a Passivhaus building, and for the purposes of the initial discussion I think this is enough to demonstrate the inadequacy of this level of ventilation for the stated purpose, else Covid spread wouldn't be a problem in the UK within the home.

It appears that for new builds latest research[3] shows an average of around 4m3/hr/m2, which is better than I expected, however the research suggests this is in part due to temporary measures by builders to achieve higher ratings than they would otherwise, and this is born out by the distribution of ratings achieved with an unlikely precipitous drop at precisely 5m3/hr/m2.

However, for houses built to this standard some form of additional ventilation is a requirement of Part F[4]. It is possible to build a house with as low as 3m3/hr/m2 and provide no additional ventilation, but it must have been designed to > 5m3/hr/m2 so this should not be common. For social housing we can assume a single bedroom home will be around 40m2 with 2.6m between floors, and the required ventilation rate is 13l/s, or 47m3/hr/m2. This is around 0.45ACH.

In fact the legal minimum rate per m2 is 1.08m3/hr, so for a typical home with 2.6m between floors this works out to 0.42ACH. So any house built to modern standards and used correctly should achieve the Passivhaus level of ventilation, unless it has tall ceilings. Certainly any UK home built with continuous mechanical ventilation is pretty comparable to Passivhaus standards for airflow.

> People don’t open trickle vents, they turn down the extract fan timer because of fan noise

People can also turn off the MVHR in a Passivhaus. I'm not sure what purpose it serves to compare correct use of a Passivhaus to incorrect use of this small fraction of UK homes.

[1]https://www.statista.com/statistics/292252/age-of-housing-dw...

[2]https://www.researchgate.net/profile/Dominic-Miles-Shenton/p...

[3]https://discovery.ucl.ac.uk/id/eprint/1573697/1/1-s2.0-S0378...

[4]https://assets.publishing.service.gov.uk/government/uploads/...

Re: Why don’t we just open the windows? Covid-19 prevention lost in translation

#292

Post by mlyle »

dredmorbius wrote: post #290
mlyle wrote: post #277

Earlier quoted context omitted.

> I don't know, though I'd suspect that plans for increased air exchange are being considered. In general, newer buildings with sealed windows have pretty good air exchange ( with heat recovery ) and filtration. > For much of the state, through much of the year, open windows are a reasonably minor consideration. Yah, tell that to me languishing masked a 95 degree classroom between building heat gain and a temperature…

Much depends on just how open those windows are. "All windows wide open in every classroom" during very warm or very cold weather is excessive. A window cracked open for ventilation, and either at the top of the classroom (warm weather w/ cooling active) or bottom (with heating), and a fan within the room for vertical mixing ... might help. (Keep in mind that mixing air also mixes infectious particles.) A slight impr…

> Much depends on just how open those windows are. "All windows wide open in every classroom" during very warm or very cold weather is excessive

During a pandemic, it makes a lot of sense-- at least for the "extremes" of weather faced here.

> A window cracked open for ventilation, and either at the top of the classroom (warm weather w/ cooling active) or bottom (with heating), and a fan within the room for vertical mixing ... might help.

Might, but who knows how much? How does one weight the ordinary risk of sickness and infection (outside of a pandemic) with energy costs? (Especially when there are less energy-intensive ways to get the ventilation).

> A slight improvement is to have a single exit point (vented with a fan) and rely on structure permiability to introduce fresh air. That's effectively a negative-pressure system.

> From there, exhaust and intake with heat recovery is the next obvious step.

Yes, and pretty quickly from here you're ending up designing a structure without windows that open, so you can ensure that your fancy ventilation system does the right thing, filters don't get fouled, and you're not wasting heat.

> I mention older construction as replacing building stock is a long-term and expensive process.

Well, sure. But we were talking about it in the context of someone complaining a new building doesn't have windows. Older, smaller, poorly sealed buildings are a lot less likely to be retrofitted with no windows than new construction.

> It also recommends on exhaust fans rather than interior circulation fans to minimise strong internal air currents, with intake provide as I've indicated above.

Well, duh.

An otherwise well-sealed building, with a porous wall structure held at a small negative prssure, is effectively a very simple heat recovery ventilation system, too.

Re: Why don’t we just open the windows? Covid-19 prevention lost in translation

#293

Post by viraptor »

fulafel wrote: post #264
viraptor wrote: post #154

Earlier quoted context omitted.

> Open windows when it's above 50F / 10C (to give a healthy safety margin to the water pipes) and tell people to wear sweaters. Yeah, please don't. There's a comfortable level somewhere above that, but at 10C I wouldn't be able to function in context of work / school. With worse circulation you just end up with your hands / feet feeling like they're constantly freezing. Some teachers thought that's a good idea, but I…

If you open windows when weather starts to warm up past 10c, you won't get a cooling to 10c indoors.

The context here is heating to comfortable temperatures. If the inside is Locally for example: "Optimum comfort for sedentary work is between 20°C and 26°C, depending on the time of year and clothing worn."

Re: Why don’t we just open the windows? Covid-19 prevention lost in translation

#294

Post by jhugo »

newaccount74 wrote: post #247
jhugo wrote: post #126

Earlier quoted context omitted.

> Air purifiers are very loud and mostly effective at removing particulates. If you want to remove VOCs, formaldehyde and CO2 then ventilation is a lot more effective. Modern air purifiers are basically silent in normal operation, and there are models that remove VOCs and formaldehyde. CO2 is still best removed with ventilation.

> Modern air purifiers are basically silent in normal operation Maybe on the lowest setting, but I doubt you'll actually have clean air on the lowest setting. Especially if you want to filter VOCs.

> Maybe on the lowest setting, but I doubt you'll actually have clean air on the lowest setting. Especially if you want to filter VOCs.

Have you actually used a decent air purifier or are you just guessing? There are plenty of models that do a good job filtering VOCs (as measured by a separate VOC sensor) and are almost silent in normal operation. A lot of the innovation in this space seems to be happening in Asian brands, I remember when I lived in London it was very hard to find good air purifiers.

Re: Why don’t we just open the windows? Covid-19 prevention lost in translation

#295

Post by jhugo »

hanniabu wrote: post #183
jhugo wrote: post #125

Earlier quoted context omitted.

Washing your hands properly with soap and water is much more effective than hand sanitiser in typical use. Hand sanitiser is most useful when you don't have convenient access to soap and hot water. Since you're arriving home anyway, you might as well wash your hands properly — the skin on your hands will thank you for one less exposure to hand sanitiser, too.

Hand sanitizer is more effective than your average person's hand washing practices, which is pretty poor

That statement could only be true if you are comparing perfect-use hand sanitiser to typical-use hand washing, which isn't reasonable. If someone can't wash their hands properly, why assume they can use hand sanitiser perfectly?

Re: Why don’t we just open the windows? Covid-19 prevention lost in translation

#296

Post by newaccount74 »

jhugo wrote: post #294
newaccount74 wrote: post #247

Earlier quoted context omitted.

> Modern air purifiers are basically silent in normal operation Maybe on the lowest setting, but I doubt you'll actually have clean air on the lowest setting. Especially if you want to filter VOCs.

> Maybe on the lowest setting, but I doubt you'll actually have clean air on the lowest setting. Especially if you want to filter VOCs. Have you actually used a decent air purifier or are you just guessing? There are plenty of models that do a good job filtering VOCs (as measured by a separate VOC sensor) and are almost silent in normal operation. A lot of the innovation in this space seems to be happening in Asian b…

I don't have an air purifier myself, but I've talked to people who own air purifiers and read lots of online reviews.

All I've heard is that on the lowest setting they are very silent, but on "auto" mode they start up regularly and are not silent at all, and if your room is anywhere close to the recommended size the lowest setting doesn't do much at all.

I was mostly researching about the Mi brand air purifiers, since they are readily available in Europe and a lot cheaper than European brands, but if you have suggestions for a brand that makes purifiers that are actually silent AND effective I'd be curious to hear about them.

Re: Why don’t we just open the windows? Covid-19 prevention lost in translation

#297

Post by jhugo »

newaccount74 wrote: post #296
jhugo wrote: post #294

Earlier quoted context omitted.

> Maybe on the lowest setting, but I doubt you'll actually have clean air on the lowest setting. Especially if you want to filter VOCs. Have you actually used a decent air purifier or are you just guessing? There are plenty of models that do a good job filtering VOCs (as measured by a separate VOC sensor) and are almost silent in normal operation. A lot of the innovation in this space seems to be happening in Asian b…

I don't have an air purifier myself, but I've talked to people who own air purifiers and read lots of online reviews. All I've heard is that on the lowest setting they are very silent, but on "auto" mode they start up regularly and are not silent at all, and if your room is anywhere close to the recommended size the lowest setting doesn't do much at all. I was mostly researching about the Mi brand air purifiers, sinc…

The Mi 3H is a decent model (fairly significant improvement on the earlier models). I have one in my bedroom, and it really only cranks up the volume if I fry something in the kitchen and forget to run the extractor.

VOC levels (as measured by a separate sensor) were up around 400 μg/m^3 when we moved in — somewhat high, probably because the apartment was new — and after a week, during which the Mi 3H was on auto mode and always silent, I tested again and they were down around 120 μg/m^3. It also deals with moderate spikes in PM — like someone smoking on the balcony outside, or opening a dusty moving box in the room — without increasing the noise levels noticeably.

Re: Why don’t we just open the windows? Covid-19 prevention lost in translation

#298

Post by chillwaves »

PeterisP wrote: post #87
Madmallard wrote: post #32

Earlier quoted context omitted.

? If your windows are open you will trend toward outside weather. If you’re in a dry climate then yeah it’ll be dryer but the reverse is also true. Outside air is far better than inside nearly everywhere in the world

For humidity, the key issue is that relative humidity matters for us and that is temperature dependent. For example, if outside air has 100% humidity, then it effectively can't absorb more (e.g. evaporation of sweat) and would make things moist, but at -5 degrees Celsius, which I have now outside my window, that's only 2.46 g of water per kg of air - and if that exact air flows inside and gets heated to room temperat…

I appreciate your detailed rundown. This kind of stuff is not intuitive to me.
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