improve indoor ventilation air purifier combat covid 19 coronavirus

Three Ways to Improve Indoor Ventilation to Combat COVID-19

Data compiled by the world health organization (WHO) shows that poor ventilation can lead to an increase in virus transmission. As such, improving ventilation indoors should be considered an important step in reducing the spread of viruses such as COVID-19. This article covers three simple steps to improve indoor ventilation … Read more

Can You Clean a Car Air Filter With Compressed Air?

Working on DIY air purifiers for over 6 years, I’ve heard from a lot of people who have strong intuitions about cleaning car air filter. People tell me they wash their vehicle’s air filter, vacuum it, or bang it really hard. Opinions are plenty, but what about real, hard data? … Read more

Does AC Bring in Air Pollution Test

Does AC Bring in Outdoor Air Pollution?

It’s that time of year when Beijing is starting to sizzle, if this person roasting fish on her car is any indication. We’ve just turned our air conditioner on, and that got some in the Smart Air office wondering: does our AC suck in outdoor air pollution?     Although … Read more

Q&A: Do ACs Bring in More Dirty Air?

tmthyliu 提问: Just built a DIY air filter, pretty excited to have clean air in the house! I was wondering though, how does this work when the air conditioner is on? Does it make a difference at all? I don’t know how ACs work but it seems they pump more … Read more

Does the Air Conditioner Bring in Dirty Air From Outside?

A question that I get asked often (and that I have always wondered about) is whether my wall-mounted air conditioner is bringing in dirty air from outside. If so, it’d be safer not to use it, especially on really bad days.

air conditioner

My short answer is no. To explain why, I’ve got three points of evidence:

 

1. How air conditioners work

Regular wall-mounted air conditioners in China do have a unit outside connected with tubes to the inside, but that tube is not bringing in outside air. It’s passing coolant, and letting heat escape outside.

So where does the air it’s blowing come from? If you look around your air conditioner, you’ll probably discover that it works like mine: it brings air from the top, runs it over the cooling coils, and blows it out the front. It’s recycling indoor air, not bringing in outdoor air.

 

2. Tests of the air coming out of the air conditioner.

I’ve held my particle counter up into the air coming out of my AC unit, and it’s no different from the ambient room air (See a live test here). I’ve also compared that air to outside air on very dirty days, and the air coming out of the AC is nowhere near as dirty as outside air.

(I did this test when I had just turned on my AC. If the AC were bringing in dirty air and I were to test the exhaust after I had been running the AC for a long time, then my whole room would be dirty, not just the exhaust.)

 

3. Tests of the ambient room air before and after turning the AC on

Results? AC makes basically no difference.

Here’s what happened in one test after turning the AC on:

And here is the average effect over 7 different tests in my bedroom.

In each test, I ran my particle counter for 30 minutes to get a baseline. Then I turned on the AC for 30 minutes. Here I’m comparing the numbers just before I turned the AC on and 30 minutes later. As you can see, there’s basically no effect. If anything, the larger 2.5 micron particles go down slightly. My guess is this is because the coarse plastic filter in the AC unit captures up some large particles.

 

Conclusion: If it’s hot outside, don’t sweat it. Use your AC.

Central AC: I should note that these tests are of wall-mounted AC units in China. Central air conditioning may work differently.

For those interested, I’m pasting the detailed data below.

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Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.