BS EN ISO 15971:2014

This InternationalStandard concerns the measurement of calorific value ofnaturalgas and natural gas substitutes by non-separative methods, i.e. methods that do not involve the determination of the gas composition nor calculation from it. It describes the principles of operation of a varietyof instruments in use forthis purpose, and providesguidelines for the selection, evaluation, performance assessment, installation andoperation of these.

Calorific values can be expressed on a mass basis, a molar basis or, more commonly,a volume basis. The working range for superior calorificvalue of natural gas, on the volume basis, is usuallybetween 30MJ/m³and 45 MJ/m³ at standard reference conditions (see ISO13443). The corresponding range for the Wobbeindex is usuallybetween 40 MJ/m³ and 60 MJ/m³.

This International Standard neitherendorses nor disputes the claims of any commercial manufacturer for theperformance of an instrument. Its central thesis is that fitness-for-purpose in anyparticular application (defined in terms of a set ofspecific operational requirements) can be assessed onlybymeans of a well-designed programme of experimental tests. Guidelines are provided for the proper content of these tests.