TWO RESEARCH QUESTIONS: What difference does it make to use a 2"-thick hospital-grade (MERV-13) air filter in our DIY filtration units, versus a 1"-thick filter? And is it indeed practical to place these filtration units in series, creating continual air movement around a room, so as to induce the thorough mixing of air?
This brief post continues an ongoing discussion that’s been tagged as “ventilation.” (See index.)
As a proxy for volumetric flow rate (which is proportional to air velocity), I measured the maximum distance from a box fan’s front that I could perceive air movement on my face and my hand. (This distance, too, is proportional to velocity.) Here is what I found:
- No filter: 12 feet
- 2" filter (Nordic Pure): 3 feet
- 1" filter (3M): 2 feet
This implies that a 2" filter cuts the flow rate by 75%; a 1" filter cuts it by another 33%.
Thus, replacing a 1" filter with a 2" filter increases the flow rate by half; conversely, the delivery rate of a 1" filter is 2/3 that of a 2" filter. This finding confirms the estimate used in my earlier calculations.
Another important implication is that it is not practical to chain DIY filtration units together to achieve whole-room ventilation in a large hall (like the Social Hall). In order for a given fan to pick up the output of the one behind it in the chain, they would need to be placed every 3' around the room’s perimeter! An expensive, noisy, and awkward proposition!
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