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Comment by etchalon

3 years ago

10000 x .9005 is 9,005. 10000 x .90005 is 9,000.5.

Meaning that the first filter left 5 particles vs the second filter leaving .5 particles.

A 10x difference.

The goal isn't to "play with numbers" but to understand why/if the relative effectiveness of a filter results in a substantive difference in air quality.

The data shows it does.

> The data shows it does

As I described above [1] the data show that the difference between 70% and 99.95% matters, not that the difference between 99.5% and 99.95% does. (And that's ignoring difference in flow rates, which is also very large.)

[1] https://news.ycombinator.com/item?id=31823047

  • The 70% and 99.95% difference is because of the 10x filtration efficiency difference, combined with the CADR difference.

    This is very straight-forward.

    • The "10x" you've been referring to is about the difference in how many particles make it through filters of 99.5% vs 99.95% efficacy [1], not 70% vs 99.95%, which would be 600x [2].

      [1] (1−.995)÷(1−.9995)

      [2] (1−.7)÷(1−.9995)

      1 reply →

Extraordinary claims require extraordinary evidence. The data shows a huge difference which cannot be explained by the difference between 5 particles and 0.5 particles.

As noted in the article, the Wirecutter does not explain its methodology or give particularly complete data, and what explanations they do give about filtration make no sense.

  • It's a 10x difference in filtration efficiency, combined with a CADR difference between the two units.

    I don't understand why you think more of an explanation is required?

    • There is a 10x difference between (1-efficiency) for the two filter media choices. Explanation needed as to why this is at all relevant.

      Your comment is like observing that car A burns 87 octane gasoline and another burns 89 octane gasoline and claiming, without explanation, that one of them accelerates faster because (90-octane) is 3x lower.

      hint: the bigger purifier wins because it has a more powerful, more power hungry fan pushing air through it. Its performance might be further improved (depending on the fan and motor characteristics) by putting a less efficient, lower pressure drop filter in because more air would go through it per unit time.

      Meanwhile, two IKEA filters will outperform it in every measure, including cost, noise, and power consumption. But their efficiency will still be lower.