In addition to the above, BSRIA is also now able to offer DEFRA smoke emissions tests on appliances seeking exemption for burning unauthorized fuel in smoke control areas within the UK (section 21 of the Clean Air Act 1993). The state of the art test facility uses the dilution tunnel approach with isokinetic sampling of the flue gases, an approach which is also used by some European test houses. Tests are conducted in accordance with PD 6434, BS 3841 Parts 1 & 2 and the Richardo -AEA Test Protocol issue 3.0. Because of the variation in the smoke emission between tests, multiple tests are conducted at high heat output as well as reduced heat output. As the smoke emission rate is dependent on the size of the stove (volume of its firebox), its air controls which affects its combustion performance and the fuel used, the measured heat output at each load must also be reported. If appliances are fundamentally different in their designs, then individual smoke tests are also required. The exception to this are appliances with cosmetic changes to the exterior.
The smoke emission rate can also be affected by the manner in which the appliance is refuelled. If the firebed is not established i.e. if there is insufficient burning material to cause the new fuel charge to ignite within a reasonable period or if the appliance is overloaded with a new fuel charge, excessive smoke can occur. Care has to be therefore taken during the tests to avoid such adverse operating conditions that can cause the stove to unnecessary fail the smoke emission tests.
The iso-kinetic method of sampling the smoke emission within the dilution tunnel used by BSRIA is an accurate and representative method of determining the smoke emission rate from appliances burning wood and mineral fuels. In this technique, the velocity of the sampled gases within the sampling nozzle is maintained the same as that of the mainstream flue gases within the dilution tunnel. The specialist instrumentation used for sampling is an automatic gravimetric sampler which continually adjusts the sample volume flow rate and hence the flue gas velocity in the smoke sampling nozzle.
In tests conducted at BSRIA, iso-kinetic sampling has been consistently maintained during the tests. The maximum isokinetic deviation on the velocity is around 0.8% compared to 2.5% which is required in the test standard.
BSRIA’s smoke emission test results are expressed in grams/hour to enable comparison with the permitted smoke emission rate given in BS PD 6463 and represent the average smoke emission rate taken over the test cycle which is typically 45 minutes to an hour. Alternatively the smoke emission rate can be expressed in mg/m3 at a reference oxygen content of 13% in the undiluted flue.
Opacity measurements are also taken during the tests to detect the peaks in the smoke emissions during refuelling and de-ashing.
Further information on testing of stoves and other types of solid fuel appliances can be obtained by contacting Dr Arnold Teekaram, Head of Combustion at BSRIA, tel +44 (0)1344 465538, email firstname.lastname@example.org or read more about BSRIA's testing of solid fuel appliances.