What is the Difference Between HCV and LCV

The main difference between HCV and LCV is that in HCV, byproducts of the reaction are allowed to cool down to the room temperature whereas, in LCV, byproducts are allowed to escape. Therefore, some amount of heat which is going to be lost with the byproducts can be recovered in HCV while a specific amount of heat is carried away by the steam in LCV. Moreover, LCV is equal to the value obtained by the subtraction of the heat carried away by the steam from HCV. 

HCV (higher calorific value) and LCV (lower calorific value) are two measurements of heat liberated from the combustion of a unit mass of fuel. Also, HCV is also known as the gross calorific value while LCV is known as the net calorific value. 

Key Areas Covered 

1. What is HCV
     – Definition, Facts, Importance
2. What is LCV
     – Definition, Facts, Importance
3. What are the Similarities Between HCV and LCV
     – Outline of Common Features
4. What is the Difference Between HCV and LCV
     – Comparison of Key Differences

Key Terms 

Combustion of Fuel, Condensation, HCV, Latent Heat of Vaporization, LCV, Net Calorific Value, Water Vapor 

What is HCV 

HCV (higher calorific value) or HHV (higher heating value) is the amount of heat or energy liberated from the combustion of a particular fuel when its byproducts are allowed to condense. Here, the combustion of some hydrogen fuels releases water vapor, which subsequently evaporates from the system. The process of water evaporation is said to soak up some of the heat liberated during the combustion reaction. And, this heat is known as the latent heat of vaporization. However, it does not contribute to the work done by the energy produced by the system. That means; the formation and the release of water vapor reduce the amount of thermal energy available in the system.  

Figure 1: Combustion of Methane

Therefore, some systems are capable of undergoing a secondary condensation process, condensing water vapor. Thus, this method helps to recover some amount of heat liberated from the system, allowing it to use the latent heat to do some work. Therefore, the value of HCV is equal to the sum of the amount of energy retained in the system; in other words, to the LCV and the amount of heat recovered by the secondary condensation process. On that account, the HCV is also known as gross calorific value.

What is LCV 

The LCV (lower calorific value) or LHV (lower heating value) is the amount of heat or energy liberated from the combustion of a particular fuel when the byproducts freely escape from the system. Therefore, the value of LCV is equal to the value obtained by the subtraction of the heat carried away by the steam from the HCV of the system. Thus, LCV is also known as the net calorific value. 

Figure 2: Relationship Between HCV and LCV

Also, the LCV value becomes the calorific value for the fuel when the combustion unit does not have a secondary condensation process. However, this reduces the efficiency or the productivity of the fuel. 

Similarities Between HCV and LCV 

• HCV and LCV are two measurements of heat liberated from the combustion of a unit mass of fuel. 
• Therefore, both of them represent the amount of heat or energy in a given mass or volume of fuel. 
• Also, the units of measurement of both are MJ/kg for solid fuels and MJ/nm3 for gases.  
• Besides, the LCV value is equal to the value obtained by subtracting the heat carried away by the stem from the HCV value. 

Difference Between HCV and LCV 

Definition 

HCV (higher calorific value) refers to the amount of heat evolved when a unit weight (or volume in the case of gaseous fuels) of the fuel is completely burnt and the products of combustion cooled to the normal conditions (with water vapor condensed as a result). LCV (lower calorific value) refers to the amount of heat evolved when a unit weight (or volume in the case of gaseous fuels) of the fuel is completely burnt and water vapor leaves with the combustion products without being condensed.  These definitions explain the main difference between HCV and LCV. 

Other Names 

HCV is also known as higher heating value (HHV) or gross calorific value while LCV is also known as lower heating value (HHV) or net calorific value. 

Correspondence 

Another difference between HCV and LCV is that HCV is the total energy released when products have cooled down to the room temperature and water condensed out while LCV is the energy released when products are hot.  

Byproducts 

The byproducts are allowed to condense in HCV while the byproducts are allowed to escape in LCV. This is another difference between HCV and LCV. 

Heat or Energy in Byproducts 

Moreover, some of the heat or energy in byproducts can be recovered in HCV through condensation while the heat or energy in byproducts escapes the system. 

Value 

Value is another difference between HCV and LCV. HCV is high while LCV is low. 

Conclusion 

HCV is the amount of heat or energy liberated from the combustion of a fuel when its byproducts are condensed to recover some of the energy released from the combustion. In comparison, LCV is the amount of energy liberated from the combustion of a fuel when its byproducts freely escape from the system. Therefore, the main difference between HCV and LCV is the type of heat considered in each system. 

References:

 1. “What Is Lower Calorific Value and Higher Calorific Value.” Mechanical Engineering, 24 May 2016, Available Here