Yearbook 2013/2014 - ehedg

Performance testing of air filters for hygienic environments: Standards and guidelines in the 21st century 51
Similar to EN 1822, the new international standard ISO 29463
defines the scan test method as the reference method, where
the local and the integral particle collection efficiencies are
measured for the most penetrating particle size (MPPS).
Table 1 defines the ISO filter classes and the related collection
efficiencies and penetrations, respectively. In total, the test
and classification procedure consists of four individual steps:
(1) Determination of the MPPS by measuring the fractional
collection efficiency curve as a function of the particle size on
flat sheet media samples (see part 3 of the standard); (2) leakproof
testing of the filter element (see part 4 of the standard);
(3) determination of the integral efficiency of the filter element
(see part 5 of the standard); and (4) classification according to
Table 1 (see part 1 of the standard). In part 3 of the standard,
the required statistical methods are described.
General ventilation air filters
Coarse and fine dust filters ensure sufficient indoor air
quality in less critical production areas and in general
building and office ventilation. In high care production areas,
cleanrooms and associated controlled environments, these
filters are used as pre-filters to the EPA, HEPA and ULPA
filters. Coarse and fine dust filters are tested and classified
in Europe according to EN 779. In contrast to the testing
of HEPA and ULPA filters, the procedure in EN 779 is a
destructive test method, where the tested element is loaded
with a synthetic test dust known as ASHRAE dust. The filter
classes are determined from the average arrestance and
the average efficiency as averaged over the dust loading.
This standard has recently been revised and published as
EN 779:2012. The main modification in this revision is the
introduction of requirements for the minimum efficiencies to
the filter classes F7 to F9, which gives higher operational
safety to the end users with regard to the particle collection
efficiency of filter elements (Table 2).
Table 2. Class definitions to EN 779:2012.
Group
Coarse filter
Fine filter
G
M
Class
G1
Final test
pressure
drop
Average
arrestance A m
to ASHRAE
dust in %
50 ≤ A m
< 65
G2
250 Pa
65 ≤ A m
< 80
G3 80 ≤ A m
< 90
G4
M5
90 ≤ A m
Average
efficiency E m
to 0.4 µm in %
Minimum
efficiency to
0.4 µm in %
— —
40 ≤ E m
< 60
M6 60 ≤ E m
< 80
F F7 450 Pa — 80 ≤ E m
< 90 ≥ 35
F8 90 ≤ E m
< 95 ≥ 55
F9 95 ≤ E m
≥ 70
To ensure a high confidence level of end users with regard
to the quality and design specifications of fine air filters,
the European Committee of Air Handling & Refrigeration
Equipment Manufacturers (Eurovent) introduced some years
ago a certification program, wherein the main performance
characteristics of the products offered by the participants are
verified by regular and independent checks (www.euroventcertification.com).
On an annual base, the initial pressure
—
drop, the initial and minimum particle collection efficiency, the
filter class, and the energy efficiency class of four randomly
chosen fine filters from the participants’ product range are
verified by independent laboratories.
Figure 1. Eurovent certification mark.
Energy efficient operation of air filters
In the context of increasing energy prices and the imperative
of reducing CO 2
emissions, the energy consumption caused
by air handling units has become the focus of attention. In
an average industrial plant approximately 10-20% of the total
energy is consumed by fans in heating, ventilation and air
conditioning (HVAC) systems. In high care production areas
and in cleanrooms and associated controlled environments,
this percentage is even higher. Approximately one-third is
related to the flow resistance (pressure loss) of air filters,
depending on the size and the design of the HVAC units.
Besides investments in energy-efficient fans and variable
speed drives, for example, the optimisation of the filter
efficiencies used and the use of high quality, energy efficient
air filters is a comparably easy possibility to achieve significant
energy savings. Hence, a reduction of the pressure loss of air
filter systems can make a significant contribution to energy
savings and reduction of carbon dioxide emissions when
used in conjunction with variable speed drives. At the same
time, the air quality targets have to be considered, which
means that ultimately the individual optimum of sufficient
filter efficiency with lowest possible energy consumption
must be found.
To guide the end user to the most energy efficient filter
selection, Eurovent published a new document, Eurovent
4/11, which defines an energy efficiency classification
system for air filters.
Under the assumption that the volume flow rate supplied
by the fan is constant, and hence, does not depend on the
filters‘ pressure drop, the energy consumption of air filters
can be calculated by Equation 1 (Goodfellow, 2001).
⎯
q V ⋅ Δp ⋅ t
W = ⎯⎯⎯
η ⋅ 1000 (1)
The abovementioned assumption is valid if the fan is
controlled by a frequency inverter to operate at constant
volume flow rate q V
(in m³/s). In Eq. (1) W (in kWh) is the
energy consumed in the time t (in h). Since the pressure loss
of an air filter increases with the dust collected during the time
of operation, in Eq. (1) the pressure loss Δp (in Pa) has to be
introduced as integral average value over the time interval t.
The overall electromechanical fan efficiency η depends on
the design and the operating conditions of the fan. Modern
fans can have an efficiency of 70%; while for older models
or when utilised in disadvantageous operating conditions,
realised efficiencies might be just 25% or even lower.