Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

A paradigm shift to combat indoor respiratory infection

drive.google.com

Post reply on HN
Print view View original

61–70 of 149 posts

Re: A paradigm shift to combat indoor respiratory infection

#61

Post by yosito »

daniellarusso wrote: post #41
prof-dr-ir wrote: post #7

From the article: "It is not known exactly what fraction of infections could be prevented if all building and transport ventilation systems on the planet were ideal (in terms of controlling airborne infections), or the cost of design and retrofitting to make them ideal." I think this is the key question. Surely better ventilation would have prevented some infections in the covid pandemic. But how many? And to decide…

This is the Ben Franklin / John Adams debate when they shared a small room together overnight with one window. “When Adams explained that he didn’t want to catch an illness from the cold night air, Franklin countered that the air in their room was even worse.” https://www.mentalfloss.com/article/54169/time-ben-franklin-...

This reminds me of an argument I had with a friend in October. When the weather got cold, I only wanted to socialize with our small group of friends outside because the open air was safer, but she only wanted to socialize inside because she thought being outside in the cold would make her catch COVID.

Re: A paradigm shift to combat indoor respiratory infection

#62

Post by rightbyte »

ddxxdd wrote: post #42
rightbyte wrote: post #39

Earlier quoted context omitted.

> It's fascinating to see how 2 pipes of air current switch temperatures when they're in contact and moving in opposite directions. Shouldn't the air ideally move in the same direction?

Nope, because they will both end up at the same temperature, namely, the average temperature halfway between the two previous temperatures. In a countercurrent heat exchanger, the hot air will get colder and colder until it is at the same temperature as the cold air, and the cold air will get hotter and hotter until it is the same temperature as the hot air. This is because the hot air is not warming up the same air…

Ah ye thank you makes sense.

Re: A paradigm shift to combat indoor respiratory infection

#63

Post by ddxxdd »

londons_explore wrote: post #58
ddxxdd wrote: post #32

Earlier quoted context omitted.

>Of course, that flies in the face of all efforts to make things green…which involve better insulation, sealing windows against leaks, more air filtration systems and etc. If anyone has a half-hour of time to waste, you can look into the science of "countercurrent heat exchangers". It's fascinating to see how 2 pipes of air current switch temperatures when they're in contact and moving in opposite directions. So if y…

Wikipedia claims "Heat recovery systems typically recover about 60–95% of the heat in exhaust air". But even recovering 95% of heat isn't exactly great. If you live in Canada and have a 2600 sq ft house with 8 ft ceilings and 10 changes of air per hour, and the indoors is 70F and outdoors is 0F, thats 2600 8 10 cubic feet of air/ per hour, or 12000 BTU/hr. That means you are more than doubling your heating costs comp…

10 air changes per hour is a lot; I believe the current recommendations for average climates is 3.

And we're looking at the margins; 1 air change per hour can do wonders for preventing the spread of disease and improving air quality, compared to 0 air changes per hour.

Nevertheless, I redid your math, and found that your hypothetical home has 26,728 more BTUs of energy in its air, compared to the outside air[-1][0][1], and that the recommended furnace for such a climate should be 160,000 BTU/hr [2].

Using those numbers as a base, I find that, with an efficiency of 95%, it would require 120 (that's one hundred and twenty) air changes per hour to double heating costs.

With 60% efficiency, it would require 15 air changes per hour to double heating costs.

And it only takes a few air changes per hour to increase comfort and prevent illness.

[-1] I suddenly realized that the google search links that I used for these calculations are messy and unwieldy, so I'll summarize my calculations: (2600 ft^2) * (8 ft) represent the volume of the house; (1.225 kg / m^3) represents the density of air, (1.005 kJ/(kg * Kelvin)) represents the specific heat of air, (70 * (5/9)) represents the temperature difference you gave me, in Kelvin. Multiplying everything together, and letting Google automatically take care of unit conversions, gives me 28.2 MegaJoules of energy in the house.

[0] https://www.google.com/search?q=%282600+ft%5E2%29*%288+ft%29...

[1] https://www.google.com/search?q=convert+28199142.9+joules+to...

[2] https://www.pickhvac.com/calculator/heating-btu/

Re: A paradigm shift to combat indoor respiratory infection

#64

Post by londons_explore »

ddxxdd wrote: post #63
londons_explore wrote: post #58

Earlier quoted context omitted.

Wikipedia claims "Heat recovery systems typically recover about 60–95% of the heat in exhaust air". But even recovering 95% of heat isn't exactly great. If you live in Canada and have a 2600 sq ft house with 8 ft ceilings and 10 changes of air per hour, and the indoors is 70F and outdoors is 0F, thats 2600 8 10 cubic feet of air/ per hour, or 12000 BTU/hr. That means you are more than doubling your heating costs comp…

10 air changes per hour is a lot; I believe the current recommendations for average climates is 3. And we're looking at the margins; 1 air change per hour can do wonders for preventing the spread of disease and improving air quality, compared to 0 air changes per hour. Nevertheless, I redid your math, and found that your hypothetical home has 26,728 more BTUs of energy in its air, compared to the outside air[-1][0][1…

My first calculation using entirely imperial units didn't go well... I think I'll stick to metric!

Re: A paradigm shift to combat indoor respiratory infection

#65

Post by richardw »

londons_explore wrote: post #58
ddxxdd wrote: post #32

Earlier quoted context omitted.

>Of course, that flies in the face of all efforts to make things green…which involve better insulation, sealing windows against leaks, more air filtration systems and etc. If anyone has a half-hour of time to waste, you can look into the science of "countercurrent heat exchangers". It's fascinating to see how 2 pipes of air current switch temperatures when they're in contact and moving in opposite directions. So if y…

Wikipedia claims "Heat recovery systems typically recover about 60–95% of the heat in exhaust air". But even recovering 95% of heat isn't exactly great. If you live in Canada and have a 2600 sq ft house with 8 ft ceilings and 10 changes of air per hour, and the indoors is 70F and outdoors is 0F, thats 2600 8 10 cubic feet of air/ per hour, or 12000 BTU/hr. That means you are more than doubling your heating costs comp…

It can’t be that hard to focus on the rooms with people in them, reduce the other rooms to eg one change an hour.

Re: A paradigm shift to combat indoor respiratory infection

#66

Post by inanutshellus »

newsbinator wrote: post #19
zargon wrote: post #9

Earlier quoted context omitted.

The WHO and CDC have had their head in the sand for 60 years when it comes to airborne pathogens. They have only acknowledged aerosol transmission of covid in the last couple weeks. It was physicists who had to figure out why they were domatically denying reality. https://www.wired.com/story/the-teeny-tiny-scientific-screwu...

> EARLY ONE MORNING, Linsey Marr tiptoed to her dining room table, slipped on a headset, and fired up Zoom. On her computer screen, dozens of familiar faces began to appear. She also saw a few people she didn’t know It’s really hard for me to read a WIRED article for information. I mean I realize that’s not what it’s there for but it takes forever to get into the content of the article.

Wait, is this a Wired link? The URL seems to go to drive.google.com and... that weirded me out so I didn't click on it but figured I'd check out the comments to see what folk had learnt.

Re: A paradigm shift to combat indoor respiratory infection

#67

Post by ddxxdd »

londons_explore wrote: post #64
ddxxdd wrote: post #63

Earlier quoted context omitted.

10 air changes per hour is a lot; I believe the current recommendations for average climates is 3. And we're looking at the margins; 1 air change per hour can do wonders for preventing the spread of disease and improving air quality, compared to 0 air changes per hour. Nevertheless, I redid your math, and found that your hypothetical home has 26,728 more BTUs of energy in its air, compared to the outside air[-1][0][1…

My first calculation using entirely imperial units didn't go well... I think I'll stick to metric!

It's unavoidable when discussing residential heating. Just use google for automatic unit conversions, and be grateful that we didn't need to invoke the cumbersome unit of "R-value" to measure insulation!

Re: A paradigm shift to combat indoor respiratory infection

#68

Post by pbronez »

dorfsmay wrote: post #54
Reason077 wrote: post #31

Earlier quoted context omitted.

> "it takes forever to get into the content of the article." I've found this is the style of American long-format journalism in general. Just look at something like The New Yorker: not to dispute the quality of their writing, but the word counts certainly skew high. Articles in comparable British publications tend to be a lot more succinct.

I know this is going to sound crazy, but give it a try sometime. When I lose track while reading an article, or find difficult to understand it, I stop and reading it bottom up, one paragraph at a time. First the last paragraph, then the one before that, etc... This cuts through directly to the conclusion, then the detailed explanations form particular to general (which works better for me) and I can skip the "excite…

man... this is exactly the opposite of how news articles are supposed to be written.

Good news articles should tell you everything in the headline. Then tell you everything again in the first body sentence. Then tell you everything again in the first paragraph. and the first page. And so on.

It's supposed to be a fractal that unfolds additional detail as you press forward, while ensuring that even a casual reader comes away with a mostly complete and accurate understanding of the issue.

More of THAT please.

Re: A paradigm shift to combat indoor respiratory infection

#69

Post by svantana »

techdragon wrote: post #55
ddxxdd wrote: post #29

Earlier quoted context omitted.

Apparently the CDC has yet to catch up to 19th century physics. The physics of small particles moving in the air ("Brownian motion") was completely figured out by Einstein back in 1905. Given a virus' size and weight, it should be trivial for a physics graduate student to simulate how long it will be airborne.

The thing about medicine is they like to test. Theory and simulation are nice but it’s just not medicine and therefore not suitable for a doctor to tell to someone as “medical advice” with all of the legal burden of malpractice that the term entails. “What if I’m wrong?” is a question that keeps good doctors awake at night and bad doctors have forgotten to ask themselves… when this kind of question weighs on you, it’…

I can see your point, but isn't the WHO tweeting “FACT: #COVID19 is NOT airborne.” an example of the opposite? They made a hard assertion without any clear proof to back it up.
Post reply on HN