ISO 18125:2017 PDF

Overview

ISO 18125:2017 specifies a standardized laboratory method for determining the calorific value of solid biofuels using a bomb calorimeter. The standard defines how to measure the gross calorific value (GCV) at constant volume and at the reference temperature 25 °C, with the calorimeter calibrated by combustion of certified benzoic acid. It also provides the formulae and procedures to convert measured results into net calorific values (NCV)-both at constant volume and at constant pressure-so results are directly applicable to real-world combustion conditions.

Key topics and technical requirements

• Measurement principle: Determination of GCV at constant volume in an oxygen-filled bomb calorimeter; products of combustion assumed to include liquid water for GCV.
• Calibration: Bomb calorimeter calibration using certified benzoic acid; calculation of the effective heat capacity (ε) of the calorimeter.
• Corrections and calculations: Procedures to correct observed temperature rise, reference-temperature adjustment to 25 °C, and conversion formulas to NCV at constant pressure or volume.
• Apparatus and reagents: Requirements for calorimeters and thermometers; list of required reagents and use of combustion aids when applicable.
• Sample handling: Links to sample preparation and moisture determination standards (normative references cover sample prep and moisture analysis).
• Instrument-specific guidance: Normative annexes for adiabatic, isoperibol/static-jacket and automated bomb calorimeters (Annexes A–C).
• Quality controls: Calibration checklists, examples and informative annexes (D–E), plus clauses on repeatability and reproducibility limits and test reporting (clauses 11 and 13).

Applications and who uses it

ISO 18125:2017 is essential for:

• Testing laboratories performing fuel characterization and reporting calorific values for solid biofuels (wood pellets, agricultural residues, torrefied biomass).
• Biofuel producers and quality control teams validating energy content for product specifications and trading.
• Research organizations studying combustion performance, emissions, and energy efficiency.
• Equipment manufacturers (bomb calorimeters, automated systems) using the standard’s annexes to ensure instrument compliance.
• Regulators and certification bodies requiring standardized energy-value data for compliance, labelling, and fuel standards.

Practical benefits include consistent, comparable calorific value data, traceable calibration using benzoic acid, clear guidance for instrument setup, and conversion of laboratory GCV measurements to operative NCV used in real combustion processes.

Related standards

Normative references in ISO 18125 include:

• ISO 14780 (sample preparation for solid biofuels)
• ISO 18134-3 (moisture determination - oven dry)
• ISO 18135 (sampling)
• ISO 16559 (terminology for solid biofuels)
• ISO thermometer standards (ISO 651/652/1770/1771)

These linked standards ensure harmonized sampling, moisture correction and terminology when reporting calorific values.