What is the Difference Between HHV and LHV?

The difference between Higher Heating Value (HHV) and Lower Heating Value (LHV) lies in the way they account for the energy released during the combustion process. Specifically, HHV and LHV differ in how they treat the latent heat of vaporization of water formed during combustion:

• Higher Heating Value (HHV): This value assumes that all the water formed during the combustion process is in liquid form and includes the energy released during the vaporization process. As a result, HHV represents the total energy released during combustion, including the latent heat of vaporization.
• Lower Heating Value (LHV): This value assumes that the water formed during the combustion process is in vapor form and does not include the energy required for vaporization. Therefore, LHV represents the net energy released during combustion, excluding the latent heat of vaporization.

The numerical difference between LHV and HHV of a fuel is roughly equivalent to the amount of latent heat of vaporization that can be recovered. When designing internal-combustion engines or boilers with no secondary condenser, the appropriate fuel value to use is the LHV, which assumes that the water vapor generated when the fuel is burned goes out in the exhaust stream. On the other hand, when designing advanced combustion units with secondary or tertiary condensers, the appropriate fuel value to use is the HHV.

Comparative Table: HHV vs LHV

The main difference between Higher Heating Value (HHV) and Lower Heating Value (LHV) lies in the treatment of water vapor produced during combustion. Here is a table summarizing the key differences between HHV and LHV:

In summary, HHV includes the heat recovered by condensing water vapor, while LHV does not include this heat. The choice between HHV and LHV depends on the specific system and its ability to condense water vapor during combustion.