Characterizing the performance of a do-it-yourself (DIY) box fan air filter

Figures & data

Figure 1. (a) Example number-weighted (left axis, blue) and volume weighted (right axis, gold) particle size distributions measured with the APS and shown for averages during the fill period with active particle production (solid line) period, near the end of the natural decay period (dashed line), and near the end of the active air filtration period (dotted line) for the home office. Number-weighted distributions are normalized to a diameter of 1.2 microns and volume weighted to 2.8 microns, corresponding to the number-weighted and volume-weighted median diameters, respectively. (b) Example results for one experiment in the home office showing the number-weighted median diameter (black solid line) and the particle number concentration (blue dashed line) across the fill period, natural decay period, and active air filtration period.

Figure 2. Example particle number decays measured in the home office for the natural ventilation + particle deposition (at t < 0) and with the filter-based air cleaners on (t > 0) shown on a (a) log scale and (b) linear scale. Particle concentrations have been normalized to unity at t = 0.

Figure 3. (left axis) The number-weighted clean air delivery rate for the various filter-based air cleaners (left axis, bars) as measured in the home office (left hash marks) and classroom (right hash marks). (right axis) The price normalized CADR (black circles), sound level (dark gray triangles), and power (light gray squares).

Table 1. Measured equivalent air changes per hour and clean air delivery rates.

Air Filter	ACHF+V+D ^# (h^-1)	CADRNp* (ft^3 min^-1)	ACHF+V+D^# (h^-1)	CADRNp* (ft^3 min^-1)	CADRVp* (ft^3 min^-1)	Noise level (dB)	Power Draw (W)	$ per CADR
	Classroom		Home office
None	3.5	--	1.3 ± 0.14	--		40
CR Box (low)	9.8 ± 0.4	614 ± 36	29.6 ± 1.5	599 ± 27	614 ± 26	58 ± 2	67	0.11
CR Box (med)	11.4	780°	38.0 ± 0.1	780 ± 32	824 ± 32	63 ± 2	84	0.08
CR Box (high)	11.9	823°	41.5 ± 1.7	852 ± 50	903 ± 49	67 ± 1	98	0.08
HEPA #1	6.8 ± 0.4	323 ± 44	15.4 ± 0.5	285 ± 2	300 ± 2	59 ± 1	89	0.86
HEPA #2	4.7 ± 0.3	114 ± 24	7.9 ± 0.2	129 ± 8	118 ± 3	54 ± 1	43	0.74

^# Based on number concentration measurement; not adjusted for additional turbulence.

* Calculated from individual pairs of ACH_V+D and adjusted ACH_F+V+D and so may not match with the CADR determined from the average ACH_F+V+D.

° Only one measurement was made.

Figure 4. (a) Size-dependent equivalent air changes per hour with the various filter-based air cleaners operating (solid lines) and for the natural room ventilation + particle deposition alone (dashed line), as measured in the home office. (b) The corresponding clean air delivery rates for the various filter-based air cleaners. Results for the classroom are similar (not shown).

Data and materials availability

All data needed to evaluate the conclusions in the article are present in the article and/or the supplementary materials.