scope:

This standard describes features of the state of the art for downstream control devices (also referred to as separators) collecting solid and/or liquid particles from small-sized solid fuel combustion systems falling within the scope of the First Federal Air Pollution Control Ordinance (1. BImSchV). For this purpose, a distinction is made between the types of combustion system listed in Table 1.

The prime objective of this standard is to define the efficiency (in this case the collection efficiency) for dust control devices installed downstream of single-room heaters burning solid fuels.

Note 1: For retrofits to single-room heaters, the 1. BImSchV allows the use of downstream dust control devices reflecting the state of the art. As the ordinance does not detail the state of the art any further, it will be described in this standard. In line with the intention of the legislator, the aim is to achieve a maximum possible reduction of dust emissions. This means that all existing dust control technologies suited for singleroom heaters are competing with one another. Only those technologies having an efficiency that is close to the maximum value of all measurement results, taking into account the principle of proportionality, can reflect the state of the art. Consequently, certain technologies may not qualify as state of the art in the application under review because of their insufficient efficiency.

For solid fuel-fired central heating systems in the above capacity ranges by contrast, the relevant factor determining the efficiency of the various dust control technologies is the clean gas dust content as a function of the different flue gas dust conditions (fuel and combustion system-specific level and composition of the aerosol load in the flue gas of the combustion system) defined in DIN SPEC 33999. On this basis, it would be possible to determine the clean gas dust levels achievable as a function of the flue gas dust condition and the type of installed dust control technology in terms of the state of the art applicable from time to time. This would allow a simple statement on whether the limit values laid down in the 1. BImSchV can be achieved by the individual installed configuration. For filtering dust Minderungseincontrol devices where the clean gas dust levels are largely independent of the raw gas dust levels (especially surface filters), this interdependence can be expected. For all other downstream dust control devices where the collection efficiency is a function of the raw gas dust concentration, the type of dust, etc., this interdependence does not hold. This is also the reason why the dust collection efficiency is indicated as a function of the specific tested flue gas dust condition in the case of central heating systems. This will provide the manufacturer of the central heating system, the operator, the chimney sweep, and the manufacturer of the dust control device with a basis for deciding which configuration is to be used for a specific application in order to ensure that the emission limit values prescribed by the 1. BImSchV are consistently complied with during the recurrent measurements.

Note 2: Unlike for single-room heaters, the 1. BImSchV sets specific clean gas dust levels for the practical operation of central heating systems. Therefore it must be left to the discretion of the users which dust control technology they want to use as long as the limit values are met during the recurrent measurements. This means that here all separator technologies must be described with regard to their efficiency. In addition, proven clean gas dust levels that a device based on a specific technology must achieve to reflect the state of the art of the devices available for this technology must be defined.

Note 3: Currently, efficiency data (collection efficiency and clean gas dust levels as a function of the flue gas dust condition) are mainly based on literature data and results from measurements performed so far by various institutions. These measurements were determined by different measurement methods as test results determined according to DIN SPEC 33999 are not yet available. The next revision of this standard will consider to a greater extent measurement results determined according to DIN SPEC 33999. In this way, the features of the state of the art described in this standard will be gradually updated to reflect efficiency levels determined by standardised methods. This approach is dictated in view of the schedule constraints. The uncertainties and weaknesses of this first version of VDI 3670 are to be compensated for within a short time frame through timely and routine revisions.

Not covered by this first version is the effectiveness of catalytic converters on gaseous emissions. As catalytic converters normally also have a filtering effect for dust, they will be considered as part of the filtering dust separators (depth filters) with regard to their dust control effect. For this purpose, the minimum flue gas inlet temperature required by the catalytic control device to attain the efficiency values set out in this standard must in each case be indicated in the description of the state of the art for catalytic converters.

Note 4: As part of the planned revision of VDI 3670, CO reduction effects will also be considered. Here, it should be noted that there are combustion systems regulated under the 1. BImSchV on the market that may have problems meeting the emission limit values for CO.

According to the building regulations of the German federal states, dust control retrofits are nonregulated construction products for the time being whose suitability for use must be demonstrated by a suitability certificate issued by the building inspectorate such as a national technical approval, for instance.

In Germany, issues regarding equipment safety and the control of construction products are regulated by Deutsches Institut für Bautechnik (DIBt; www.dibt.de), an agency of the German federal government and the federal states. Test methods to determine the efficiency of downstream dust control devices are described in DIN SPEC 33999. If alternative methods are used, care must be taken to ensure that the results are comparable.

Note 5: Once DIN SPEC 33999 has been adopted as a standard, the methods there described will be binding for the assessment of single-room heaters. For downstream dust control devices of central heating systems, only measurement results determined as per DIN SPEC 33999 or a method that has been proven to yield comparable results will be considered in VDI 3670. For dust control devices to be installed downstream of central heating systems, an efficiency test as per DIN SPEC 33999 is not mandatory as such systems are subject to recurrent measurements.

Note 6: Downstream dust control devices with a national technical approval (DIBt) https://www.dibt.de/de/zv/NAT_n/ zv_referat_III5/SVA_7.htm) reflect the state of the art from safety aspects. Under the building regulations of the German federal states, there is also the option of obtaining an approval on a case-by-case basis from the responsible building supervisory authority.