BS EN 779:2002 pdf download – Particulate air filters for general ventilation — Determination of the filtration performance
5 Requirements The filter shall be designed or marked so as to prevent incorrect mounting. The filter shall be designed so that when correctly mounted in the ventilation duct, no leak occurs at the sealing edge. The complete filter (filter and frame) shall be made of material suitable to withstand normal usage and exposures to those temperatures, humidities and corrosive environments that are likely to be encountered.
The complete filter shall be designed so that it will withstand mechanical constraints that are likely to be encoun- tered during normal use. Dust or fibres released from the filter media by air flow through the filter shall not consti- tute a hazard or nuisance for the people (or devices) exposed to filtered air.
6 Classification Filters are classified according to their efficiency (arrestance) under the following test conditions:
the air flow shall be 0,944 m 3 /s (3 400 m 3 /h) if the manufacturer does not specify any rated air flow rate;
250 Pa maximum final pressure drop for Coarse (G) filters;
450 Pa maximum final pressure drop for Fine (F) filters. If the filters are tested at 0,944 m 3 /s and at maximum final pressure drops, they are classified according to Table 1 . For instance G3, F7. Filters tested at airflows and final pressure drops different from those above shall be classified according to Table 1 . The classification shall be qualified by test conditions in parentheses, e.g. G4 (0,7 m 3 /s, 200 Pa), F7 (1 ,25 m 3 /s).
7 Test rig and equipment
7.1 Test conditions Room air or outdoor air may be used as the test air source. Relative humidity shall be less than 75 %. The exhaust flow may be discharged outdoors, indoors or recirculated. Requirements of certain measuring equipment may impose limits on the temperature of the test air. Filtration of the exhaust flow is recommended when test aerosol and loading dust may be present.
7.2 Test rig The test rig (see Figure 1 ) consists of several square duct sections with 61 0 mm × 61 0 mm nominal inner dimen- sions except for the section where the filter is installed. This section has nominal inner dimensions between 61 6 mm and 622 mm. The length of this duct section shall be at least 1 ,1 times the length of the filter, with a minimum length of 1 m. The duct material shall be electrically conductive and electrically grounded, have a smooth interior finish and be sufficiently rigid to maintain its shape at the operating pressure. Smaller parts of the test duct could be made in glass or plastic to see the filter and equipment. Provision of windows to allow monitoring of test progress is desir- able. HEPA filters may be placed upstream of section 1 , in which the aerosol for efficiency testing is dispersed and mixed to create a uniform concentration upstream the filter. Section 2 includes in the upstream section the mixing orifice (1 0) in the centre of which the dust feeder discharge nozzle is located. Downstream of the dust feeder is a perforated plate (1 1 ) intended to achieve a uniform dust dis- tribution. In the last third of this duct is the upstream aerosol sampling head. For arrestance tests, this sampling head shall be blanked off or removed.
To avoid turbulence, the mixing orifice and the perforated plate should be removed during the efficiency test. To avoid systematic error, removal of these items during pressure drop measurements is recommended. Section 5 may be used for both efficiency and arrestance measurements and is fitted with a final filter for the ar- restance test and with the downstream sampling head for the efficiency test. Section 5 could also be duplicated, allowing one part to be used for arrestance test and the other for the efficiency test. The test rig can be operated either in both negative or positive pressure. In the case of positive pressure operation (i.e. the fan upstream the test rig), the test aerosol and loading dust could leak into the laboratory, while at negative pressure particles could leak into the test system and affect the number of measured particles. The dimensions of the test rig and the position of the pressure taps are shown in Figure 2. The pressure drop of the tested filter shall be measured using static pressure taps located as shown in Figure 2. Pressure taps shall be provided at four points over the periphery of the duct and connected together by a ring line. Section 6 is fitted with a standardised air flow measuring device. If an alternative air flow measurement device is used, this section can be shortened.