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comment by veen
veen  ·  52 days ago  ·  link  ·    ·  parent  ·  post: PSA: Why Is the Risk of Coronavirus Transmission so High Indoors?

If you dig deeper, you can find out why it does that: this Zeit article is based on this Max Planck Insitute model which points to this scientific article which has the ventilation assumptions in table 3. 'No ventilation' is replacing air 0.3 times per hour, 'Active ventilation' (windows open) is twice per hour, and 'Ventilation system' assumes nine times per hour.

kleinbl00's bitchin' medical-grade system does 11 per hour, so no, regular people don't have that system. I'm pretty sure that, since home ventilation systems are very rare in Germany, this is a lost-in-translation thing where ' ventilation system' means something else to you than to bratwursteaters.





kleinbl00  ·  52 days ago  ·  link  ·  

11 per hour if we leave the fart fans on. 8 if we don't. It wouldn't surprise me if european standards, due to cubic meters per minute, work out to 9 airchanges for hospitals while American standards, due to cubic feet per minute, work out to 8.

If this was a hospital-based study they may have just assumed "hospital ventilation" which, for basic-bitch exam rooms, emergency rooms and recovery rooms, is at 8 air changes per hour in the US.

user-inactivated  ·  52 days ago  ·  link  ·  

it's worth noting that .3 is actually below the minimum health recommendation (by an american org, again, no comment on europe) to even spend time in a room, never mind coronavirus. so uh. yeah. no.

user-inactivated  ·  52 days ago  ·  link  ·  

basing it around .3 replacements per hour is hilariously misleading

https://www.engineeringtoolbox.com/air-change-rate-room-d_867.html

https://www.contractingbusiness.com/service/article/20868246/use-the-air-changes-calculation-to-determine-room-cfm

etc

no comment, of course, on the differences between germany and the usa. but over here we do have extremely aggressive air conditioning systems just as a cultural thing

kleinbl00  ·  52 days ago  ·  link  ·  

ASHRAE 62.2 specifies a minimum of 0.35 airchanges per hour for residences built in 2008 or later.

    ASHRAE Standard 62-1973 required ventilation in most buildings of 20 cfm per person. In 1981, ASHRAE 62 reduced the rate to 5cfm per person in an effort to address the energy impact of ventilation. This was quickly found to be far too low a ventilation rate. ASHRAE 62 was updated in 1989 and set a residential ventilation rate of 15 cfm per person or 0.35 ACH, whichever was higher. However, this version of the Standard contained only a half-page on residential ventilation. In the early 1990s, ASHRAE began the process of updating Standard 62 and in 1997 separated the overall standard into two documents with two committees, SPC 62.1 that dealt with all the occupancies other than low-rise residential and SPC 62.2 that dealt with low-rise residential only.

Your certainty about the situation, however, is noted.