Results are reported of full-scale experiments, carried out at Advantica Technologies Ltd in Loughborough under controlled conditions, aimed at determining the optimum ventilator configuration for a natural draught open-flued gas boiler operating within a compartment. Testing was conducted using different sizes of compartment and three different open-flued boilers to assess the effect of varying the ventilator arrangement on the process of vitiating the compartment volume following spillage of combustion products due to insufficient flue pull. The time taken for a boiler spilling combustion products at a consistent rate to cause a build-up of combustion products, and consequent reduction in oxygen, in the compartment was measured and taken to be an indication of how much the ventilation configuration delayed vitiation. Other parameters monitored included the carbon monoxide/carbon dioxide ratio and the temperature of the appliance casing. The specification recommended in BS 5440: part 2: 1989 (Specification for the installation of ventilation for gas appliances) for ventilating compartments naturally is compared with various ventilation regimes assessed during the programme. A major conclusion of the work has been that the ventilation specified in the British Standard probably represents the most effective means of delaying vitiation caused by a spilling installation. Greater ventilator areas did not significantly increase the time taken to vitiate and there was evidence to suggest that to deviate from the recommended split in area between low level and high level (2:1) can accelerate the vitiation process.
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