GCV, NCV and Fuel Test Basis: How to Compare Fuel Results
In brief
Start a fuel comparison by recording the GCV or NCV convention, unit, moisture basis and sample reference. This guide explains the source-backed definitions and offers a practical report-review checklist.
Start with the heat-content convention
Gross calorific value (GCV) and net calorific value (NCV) use different conventions for water after combustion. The U.S. Energy Information Administration also calls these higher and lower heating value. Its distinction concerns whether heat content includes the energy associated with vaporising water. EIA heat-content glossary.
For solid biofuels, ISO 18125 specifies a bomb-calorimeter method for gross calorific value. Its public abstract describes the result with combustion water in liquid form and explains the relationship to net calorific value, where water can leave as vapour. ISO 18125:2017 public summary.
| Convention | Water convention | Our suggested comparison check |
|---|---|---|
| GCV / higher heating value | Combustion water is treated as liquid. | Record GCV explicitly beside the value and unit. |
| NCV / lower heating value | Excludes heat associated with water remaining as vapour. | Ask for the reported calculation basis and inputs. |
Keep the moisture record with the result
ISO 18134-3 describes oven-drying measurement of moisture in a general analysis sample of solid biofuel. Its abstract explains that small-particle biofuels are hygroscopic, so moisture is determined alongside properties such as calorific value. It also describes as-received moisture reporting on a wet basis. ISO 18134-3:2023 public summary.
Our recommendation is to copy the laboratory’s exact basis wording into a comparison sheet. Keep dry-basis and as-received results separately identified. If a conversion is proposed, ask the laboratory or responsible technical adviser to document the equation and inputs before using the converted figure.
Connect the report to a sampling plan
ISO 18135 covers sampling plans and collection of solid-biofuel samples from production, deliveries and stocks. Its scope includes samples used to examine moisture, ash, calorific value and other properties. These references concern solid biofuels; ask the laboratory to establish the applicable method for an RDF or mixed-waste fuel. ISO 18135:2017 public summary.
The following is our suggested report-review checklist. It is practical editorial guidance, not a reproduction of an ISO procedure or an acceptance specification.
| Suggested record | Question to resolve |
|---|---|
| Sample identity, location and date | Which delivery, stock or sampling event does this report describe? |
| Sampling and preparation reference | Can the laboratory portion be traced to the sampling plan? |
| GCV or NCV, unit and moisture basis | Are the compared results stated on the same basis? |
| Laboratory method and report | Is the method suitable for this fuel, and is the full report available? |
| Conversions and unresolved fields | Who will verify each conversion or missing entry? |
Use the comparison to frame the next discussion
We recommend leaving unknown fields marked “not provided” instead of filling them with assumed values. Ask the receiving plant which additional tests and review steps it wants before considering a fuel trial. Keep laboratory findings, calculated estimates and proposed supply terms in separate fields for the technical and commercial teams to review.
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Questions
What is the difference between GCV and NCV?
Gross calorific value treats the water produced by combustion as liquid. Net calorific value excludes the heat associated with that water remaining as vapour. ISO 18125 explains these conventions for solid biofuels.
Why record the moisture basis?
ISO 18134-3 explains that moisture is determined alongside properties such as calorific value because small-particle solid biofuels are hygroscopic. We recommend keeping the exact moisture-basis wording beside every result being compared.
Which sampling reference applies to solid biofuels?
ISO 18135 covers sampling plans and samples from solid-biofuel production, deliveries and stocks. Ask the laboratory to confirm the applicable method and scope for the particular fuel.
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