Environmental Engineering Reference
In-Depth Information
in higher optical density readings than similar concentrations of lighter
colored particles.
The dust spot test was designed to measure an objectionable character-
istic (ability to soil interior building surfaces) caused by relatively small
diameter (<10
m) particles. It was developed in response to limitations of
the arrestance testing method. Because arrestance and dust spot testing
measure different performance characteristics, values derived from these
tests cannot be used interchangeably. However, filters with medium to high
dust spot efficiencies also have high arrestance values.
µ
3
Minimum efficiency reporting values
ASHRAE, under its recently published standard 52.2-1999, established a test
protocol to test filter performance based on measuring fractional collection
efficiencies. These efficiencies are determined by conducting particle counts
both upstream and downstream of filters challenged by exposure to labora-
tory-generated potassium chloride aerosols in 12 different size ranges (small-
est 0.3-0.4
m).
In addition to measuring the performance of clean filters, particle size
fractional efficiency curves are developed at incremental dust loadings.
These curves are used to develop composite curves that identify minimum
efficiency in each particle size range. Minimum efficiency composite values
are averaged in three size ranges (0.3-1.0 [E1], 1.0-3.0 [E2], and 3.0-10.0 [E3]
µ
m; largest 7-10
µ
µ
m) to determine minimum efficiency reporting values (MERVs). Filters with
MERV values of 1 to 4 are very low efficiency; they would be used as furnace
filters. Pleated filters would have MERV values of 5 to 8; box/bag filters, 9
to 12; box/bag filters, 13 to 16; and HEPA filters, 17 to 20.
4.
DOP smoke penetration tests
Measurements of particle collection efficiencies >98% are made using the
DOP (dioctyl phthalate) smoke penetration method. It is typically used to
test the performance of HEPA filters.
In this method, an aerosol of DOP is produced with a uniform particle
diameter of 0.3
m, the size range of minimal collection efficiency for most
HEPA filters. DOP particles that pass (penetrate) through the filter or leak
around filter-sealing gaskets are determined downstream by means of a
photometer that measures light scattering. Their concentration is compared
to that measured upstream of the filter. Filter penetration is calculated by
using the following equation:
µ
100
C
2
C
1
P
=
------
(12.2)
where P
= % penetration
C
= upstream concentration
1
C
= downstream concentration
2
