Intermediate Air Filters for General Ventilation Applications: An Experimental Evaluation of Various Filtration Efficiency Expressions

Figures & data

TABLE 1 Tested full-scale bag filters and their properties. Pressure drops were measured at 0.944 m³/s

	Filter class
	European	US standard		Nr. of	Fiber
Filter	standard	ANSI/ASHRAE	Size, L·H·D	filter	diameter	Thickness	Packing	Pressure
code*	EN 779	52.2	(mm)	bags	(μm)	(mm)	density	drop (Pa)
#1-CS	M5	MERV 9–10	592 × 592 × 500	4	5 –10	1.3	0.013	64
#2-CS	M6	MERV 11–12	592 × 592 × 635	8	5 –10	1.8	0.035	75
#3-GF	M6	MERV 11–12	592 × 592 × 500	10	5 –10	4.1	0.01	118
#4-CS	F7	MERV 13	592 × 592 × 635	8	1–5	3.8	0.026	98
#5-GF	F7	MERV 13	592 × 592 × 500	10	1–5	4.4	0.01	125
#6-CS	F8	MERV 14	592 × 592 × 635	8	1–5	2.6	0.011	152
#7-GF	F8	MERV 14	592 × 592 × 450	8	1–5	4.3	0.011	204
#8-CS	F9	MERV 15	592 × 592 × 635	8	1–5	1.5	0.015	180
*GF: glass fiber; CS: charged synthetic fiber.

TABLE 2 Tested filter samples and their properties. Pressure drops were calculated for an air velocity of 12.3 cm/s through the filter medium

	Filter class
Filter code*	European standard EN779	US standard ANSI/ASHRAE 52.2	Effective fiber diameter (μm)	Thickness (mm)	Calculated packing density	Calculated pressure drop (Pa)
#1-GF	M5	MERV 9–10	6.2	3.7	0.010	14
#2-CS	M5	MERV 9–10	6.5	1.3	0.013	37
#3-GF	M6	MERV 11–12	5	4.1	0.010	24
#4-US	M6	MERV 11–12	2.5	0.2	0.044	51
#5-GF	M6	MERV 11–12	2.5	1.8	0.010	41
#6-CS	M6	MERV 11–12	2.5	0.6	0.025	41
#7-CS	M6	MERV 11–12	3.5	0.5	0.040	51
#8-CS	M6	MERV 11–12	2.5	0.6	0.030	75
#9-GF	F7	MERV 13	2.2	4.3	0.010	126
#10-US	F7	MERV 13	2	0.4	0.054	59
#11-US	F7	MERV 13	2	0.6	0.030	116
#12-GF	F7	MERV 13	2.2	3.5	0.010	103
#13-CS	F7	MERV 13	2	0.7	0.014	42
#14-CS	F7	MERV 13	2.5	0.6	0.026	64
#15-CS	F7	MERV 13	2	0.6	0.018	77
#16-GF	F8	MERV 14	2	4.3	0.012	199
#17-US	F8	MERV 14	1.5	1.2	0.020	219
#18-GF	F8	MERV 14	1.4	2.0	0.010	146
#19-US	F8	MERV 14	1.6	0.8	0.023	128
#20-CS	F8	MERV 14	1.5	0.9	0.010	57
#21-CS	F8	MERV 14	2.3	1.4	0.011	44
#22-GF	F9	MERV 15	2	4.3	0.011	178
#23-CS	F9	MERV 15	2	1.4	0.015	93
*GF: glass fiber; CS: charged synthetic fiber; US: uncharged synthetic fiber.

FIG. 1 SEM images of the simulated filter media: #9 glass fiber; #10 uncharged synthetic fiber; #14 charged synthetic fiber.

FIG. 2 Sketches of the full-scale (a) and small-scale (b) filter test rigs. (Color figure available online.)

TABLE 3 Summary of filter efficiencies obtained using the neutralized DEHS aerosol in the full-scale test rig at an air velocity of 0.16 m/s through the filter medium; the uncertainties are expressed as the standard deviation (efficiency percentage units)

		EFMPPS		EF0.4μm		EFUFPs
Filter class and type		Ave.	SD	Ave.	SD	Ave.	SD
M5	GF	—	—	—	—	—	—
	CS	3%	0%	9%	3%	3%	2%
M6	GF	15%	2%	23%	1%	21%	1%
	CS	23%	3%	35%	4%	31%	1%
F7	GF	46%	2%	57%	2%	54%	3%
	CS	32%	2%	44%	2%	35%	3%
F8	GF	55%	1%	68%	2%	58%	1%
	CS	37%	2%	51%	3%	38%	1%
F9	GF	—	—	—	—	—	—
	CS	49%	1%	62%	2%	50%	2%
GF: glass fiber; CS: charged synthetic.

FIG. 3 MPPS observed at three different air velocities through the filter medium. The data were obtained for both glass fiber filters and charged synthetic filters of various classes. The measurements were made using the neutralized DEHS aerosol in the full-scale test rig.

FIG. 4 Reduction of filtration efficiency at 0.22 m/s compared to that observed at 0.08 m/s. The data comprise M6-F8 glass fiber filters and charged synthetic filters tested with the neutralized DEHS aerosol in the full-scale test rig. GF: glass fiber filters; CS: charged synthetic filters.

FIG. 5 Results from the full-scale filter tests using the neutralized DEHS aerosol. Filtration efficiency values based on MPPS plotted against values based on 0.4 μm particles, for glass fiber filters (a) and charged synthetic filters (b). The average efficiency and the standard deviation are taken from repeated measurements in a full-scale filter test.

FIG. 6 Fractional filtration efficiency observed for one glass fiber filter (GF) and one charged synthetic filter (CS), both of class F7. The measurements were made in the full-scale test rig at 0.22 m/s using the DEHS test aerosol. For each filter, one measurement was made with, and one without neutralization of the aerosol.

FIG. 7 Comparison of the measured efficiency and the simulated efficiency for glass fiber filters. The simulated efficiency in the range 0%–100% was obtained through theory simulation on the #9-GF filter medium with varied packing density. Low air velocity: 0.08 m/s; high velocity: 0.22 m/s.