Contents
Introduction
Heating value is a fundamental property of fuels, representing the amount of energy released during combustion. For hydrogen, two values are commonly used: Lower Heating Value (LHV) and Higher Heating Value (HHV). Understanding the difference between these values is essential for accurate energy calculations, project feasibility studies, and comparing hydrogen to other fuels.
What is Heating Value?
The heating value of a fuel is the amount of heat released when a specified amount of the fuel is combusted completely with oxygen. It is typically expressed in units of energy per mass (e.g., kWh/kg, MJ/kg) or per volume (e.g., kWh/Nm³).
Heating values are crucial for:
- Calculating fuel consumption
- Designing energy systems
- Comparing different fuels
Hydrogen LHV and HHV: Definitions
Lower Heating Value (LHV)
The LHV of hydrogen is the amount of heat released when hydrogen is combusted and the water produced remains in vapor form. The latent heat of vaporization of water is not recovered. For hydrogen, the typical LHV is 33.33 kWh/kg (or 120 MJ/kg).
Higher Heating Value (HHV)
The HHV of hydrogen is the amount of heat released when hydrogen is combusted and the water produced is condensed back to liquid, recovering the latent heat of vaporization. For hydrogen, the typical HHV is 39.44 kWh/kg (or 142 MJ/kg).
Key Differences Between LHV and HHV
- Water State: LHV assumes water remains as vapor; HHV assumes water is condensed to liquid.
- Energy Value: HHV is always higher than LHV for the same fuel.
- Application: LHV is commonly used in Europe and for fuel cell/electrolyser efficiency; HHV is often used in the US and for combustion systems.
- Reporting: Always check whether efficiency or energy content is reported as LHV or HHV, as this can significantly affect calculations and comparisons.
Why Does It Matter?
The choice between LHV and HHV affects:
- Efficiency calculations for electrolysers, fuel cells, and combustion systems
- Project feasibility and cost estimates
- Comparisons between hydrogen and other fuels
Example: Electrolyser Efficiency
If an electrolyser uses 50 kWh of electricity to produce 1 kg of hydrogen:
- Efficiency (LHV basis) = 33.33 / 50 = 66.7%
- Efficiency (HHV basis) = 39.44 / 50 = 78.9%
Always check which basis is used when comparing technologies or reporting results.
Conversion Example
To convert between LHV and HHV for hydrogen:
HHV = LHV × 1.183
LHV = HHV ÷ 1.183
For example, if you have an LHV-based value of 1000 kWh, the equivalent HHV-based value is 1183 kWh.
Related Calculators
Need Help with Hydrogen Calculations?
Understanding LHV and HHV is essential for accurate hydrogen project design and reporting. If you have questions or need support, our team is here to help.