Ventilation och luftkonditionering

This International Standard specifies the sampling method of fabric filter media from filter system in operation and test method thereof to evaluate the degradation of filter media for dry type filtering dust collector (hereafter referred to as "bag filters") used in thermal power plants, municipal waste incineration facility, etc.

Bag filters are one of the most widely used dust collectors in industries such as municipal garbage incinerators, coal fired boilers, iron makings, cement factories, power plants, etc. Since filter media are used under various gas and dust circumstances for a long time, its physical and chemical properties change (deteriorate) with operation time due to various causes[1]-[9]. Especially, in the municipal garbage incinerator, bag filter has been used very popularly to overcome dioxin emission[10],[11]. Since users of bag filter system usually evaluated the necessary items for the change in the filter properties with each method by themselves, obtained results were not compatible with each other. For this reason, the establishment of the standard operation management and maintenance of filter system is an important issue to predict the timing of replacement and/or service life time of filter media.

It is usually desirable to remove dust from the filter element before sampling. However, it may be sampled with dust when it is difficult. In any case, special care shall be paid not to scatter too much dust accompanying sampling work and not to bring out extra dust outside the factory.

Since measured physical and chemical properties of the filter media may differ depending on whether or not dust adheres to the media, it is recommended to measure with and without attached dust on the filter media. When dust removal from the filter media is necessary, it shall be carried out using a brush and a vacuum being careful not to damage the filter media.

Sampled filter media may be contaminated with potential hazardous substances so it shall be handled with special care.

This document specifies a laboratory substitution method to determine the insertion loss without flow of ducted, mainly absorbent, circular and rectangular silencers, as well as other duct elements for use in ventilating and air-conditioning systems.

NOTE 1 Laboratory measurement procedures for ducted silencers with superimposed flow are described in ISO 7235.

This document is applicable to silencers where the design velocity does not exceed 15 m/s. As the method does not include self-generated flow noise, this document is not suitable for tests on silencers where this type of noise is of great importance for the evaluation of the silencer performance. As most silencers, particularly in offices and dwelling, have design velocities below 15 m/s this document can often be a cost efficient alternative to ISO 7235.

The insertion loss determined according to this document in a laboratory will not necessarily be the same as the insertion loss that will be obtained in an installation in the field. Different sound and flow fields in the duct will yield different results. In this document the sound field will be dominated by plane wave modes. As this document requires regular test ducts, the results may include some flanking transmission via structural vibrations in the duct walls, that sets an upper limit to the insertion loss that can be determined.

NOTE 2 ISO 7235 gives methods for determining this limit.

This document is intended to be used for circular silencers with diameters of 80 mm to 2000 mm or rectangular silencers with cross-sectional areas within the same range.