Name: 通风是对抗Covid的关键这就是为什么（Ventilation Is Key to Battling Covid. Here’s Why | WSJ）
Uploaded: 2021-05-31T06:07:19.000Z
Duration: 5 min 53 s
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And as the weather gets colder and people had back indoors,

- As we get through the fall and into the winter

- [Reporter] Experts warn that many buildings,

are not equipped with the ventilation and filtration systems

but fewer people are aware that ventilation

- [Reporter] It's now clear that the coronavirus

which is why indoor gatherings can be so deadly.

- That virus is never naked in the air, is what we say.

It's always floating in respiratory droplets

- [Reporter] Indoors, those particles can add up,

is to pump in fresh air with a ventilation system.

- We have to think about the thermal conditions

but also just how much outdoor air is moving in.

For me, the priority is to increase the air exchange rate.

but experts say that three to six exchanges per hour

But good flow of fresh air is only one part

of preventing the indoor spread of the coronavirus.

and experts recommend using one called HEPA.

It can remove more than 99% of airborne particles,

including those carrying viruses like the coronavirus.

can effectively capture airborne coronavirus.

That's because these filters are rated for particles

that are 0.3 microns in size, larger than the coronavirus.

People assume that they don't catch anything smaller,

- Filters are rated for the particle size

they perform worst at, and that's 0.3 microns.

As you get to bigger particles, and even smaller particles,

the HEPA filter will capture closer to 100%.

- [Reporter] Because the coronavirus tends to travel

in droplets that are larger than 0.3 microns,

HEPA filters can capture almost all of them.

The virus also travels in droplets that are smaller,

- Filters work not by straining out things

but they actually work by trapping particles in the air

as the air flows around the different fibers in the filter.

bump into gas particles, they move in a random pattern.

- Kind of like a drunk person stumbling around in the dark.

- [Reporter] The harder it is for particles

carrying viruses to pass through a filter,

the lower the chance of viral transmission.

But the problem is that not every building

through the building, and then it runs through a filter,

you can imagine that a higher-efficiency filter

is going to be harder to push air through.

Very few systems can push air through a HEPA filter

because HEPA is the most efficient filter we have.

- [Reporter] That is why experts recommend

use a different type of lower-efficiency filter called MERV.

- If you can get up to something called MERV-13,

- [Reporter] This is important because this type of filter

can be installed in standard ventilation systems,

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通风是对抗Covid的关键这就是为什么（Ventilation Is Key to Battling Covid. Here’s Why | WSJ）

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