Testing times for ever more complex chimney systems
Ensuring safety, reliability and CE compliance as well as enabling continuous development of prefabricated chimney and exhaust systems requires comprehensive test facilities like those employed by SFL Flues & Chimneys
In a world where harmonised European standards for manufacture and design are increasingly stringent and safety is paramount, test facilities are becoming as important as new product development itself. Some products also carry specialist approvals such as those given by Lloyds Register for off-shore and shipping applications and these, too, demand sophisticated test facilities.
Any test facility worth its salt will be able to perform pressure and stress testing - prefabricated chimney manufacturer SFL's test facility, for example, can simulate wind loads of up to 110mph using pneumatic pistons and calibrated load cells to create a uniform loading over the test system.
It also has also a compression rig capable of exerting up to 10 tonnes of pressure on a component or combination of parts in either a tensile or compressive loading. Regular pressure tests are carried out for development and during production for quality purposes at up to 5,000Pa (H1), although most products are specified at P1 (200Pa) or N1 (40Pa).
British Standard 'BS EN 1859-2009 - chimneys - metal chimneys - test methods' provides details of test methods covering compressive, tensile and lateral strength, gas tightness, thermal performance, thermal resistance, water vapour diffusion, condensate resistance, rainwater resistance, thermal flow resistance. It also examines aerodynamic behaviour of terminals under wind conditions and flow resistance of fittings.
Move away from heat flow values
Publication of this standard saw a move away from the traditional heat flow values used for the thermal assessment of chimneys and towards velocity rates based on pressure classification and temperature rating.
Generating and maintaining the required flue gas temperature and velocity within the tight tolerance required by the standard is a real challenge and requires specialist expertise.
In the case of SFL, the company sought the help of Heatsol Technology, a supplier and installer of commercial and industrial gas oil and dual fuel burners and associated products. Senior R&D engineer Peter Ryan explains: 'We used to use an atmosphere gas-wand burner which was lit, then inserted into a combustion chamber, but getting a constant output at a high enough temperature was very difficult to control and costly.'
A working temperature range of up to 1,000 deg C and accurate temperature control were critical, as were ease of set-up and fast heat-up time. The answer for SFL was a bespoke Dreisler burner with a thermal cut-out set at 1,150 deg C, supplied by mains-feed natural gas capable of firing exhaust gas at up to 15m/s to the top of a 15m high test-rig designed to simulate the floors of a habitable building.
A unique specification
'Heatsol have worked in total partnership with us to produce a flue gas generator to our unique specification and this may well be the only burner in Europe capable of such extremes.' says Mr Ryan. 'While the burner operates, we monitor 74 thermocouples, placed throughout the test-rig via a computer which records a reading every minute.'
The amount of information that must be digested is immense. Comparisons have to be made every minute with readings that were taken 30 minutes earlier, analysing the difference in performance of both the chimney liner and the insulation that protects the surrounding building materials to ensure temperatures don't reach combustion point. Mr Ryan again: 'We use a basic plywood surround, but current building regulations stipulate that all enclosures be made from half-hour fire-rated materials.'
He adds: 'Years ago, we would have to record our thermocouple readings by hand and then analyse them using complicated formulae and by drawing graphs. Now it is so much easier to see exactly what is going on within a system, to identify hot-spots and ensure a thorough test.'
Even the exhaust terminal to the test facility is as bespoke as the burner because the high temperature gas from the trials cannot simply be vented to the atmosphere. A large secondary hot-gas collector is employed to vent gases to the outside of the building.
10 December 2012