# The Difference between Gross Heating Value, High Heating Value, Net Heating Value, and Low Heating Value

One day I found a nice and short article about the difference between terminology used to express heating values: Gross Heating Value (GHV), High Heating Value (HHV), Net Heating Value (NHV), and Low Heating Value (LHV).

As mentioned in my previous post about how to convert high heating value (HHV) to low heating value (LHV), the difference between those terms is if energy used to vaporize water include in the value.

During combustion, fuel react with oxygen molecules to form carbon dioxide, water, and to release heat. The heat released is called heat of combustion. Some of the heat released are used to vaporize existing moisture in the fuel and the water product.

Because all combustion reactions occur at temperatures above water boiling point, both existing water in fuel and water product are in vapor state after combustion. In a bomb calorimeter, the water in vapor state (existing as fuel moisture and water product) is cooled and condensed to room temperature. Therefore, the heat of condensation is recovered. All the heat of combustion are measured by the bomb calorimeter. The total heat of combustion measured by a bomb calorimeter per unit mass is called “high heating value” (HHV) or “gross heating value” (GHV).

Contrastingly, if the water in vapor state is not condensed, the heat of condensation is lost as the flue gases, together with water vapor, and flows out the atmosphere. These cases can be found in traditional boiler or dryer. This heat of combustion, less heat of condensation of water per unit mass is called “low heating value” (LHV) or “net heating value” (NHV).

# Difference Between the Different Terms

I do not remember if I studied these topics during college back in 2005-2009. But there are differences between HHV and GHV, and LHV and NHV.

HHV is defined as the heat of combustion per unit oven dry mass, expressed in the unit J/dry gram, whereas, GHV is defined as the heat of combustion per unit wet mass, expressed in the unit J/wet gram. Oven dry mass refer to the mass of fuel without any moisture (moisture content = 0); wet mass refers to the mass of fuel, which contains moisture content above zero.

The same goes for LHV and NHV. LHV is defined in the basis of oven dry mas, whereas NHV is defined in the basis of wet mass.

# How about Gross Calorific Value (GCV) and Net Calorific Value (NCV)?

Gross calorific value (GCV) is equivalent to high heating value (HHV), whereas net calorific value (NCV) is equivalent to net heating value (NHV).

The terms “Gross Calorific Value” and “Net Calorific Value” are more commonly used in European countries, while the terms “Gross Heating Value” and “Low Heating Value” are more commonly used in North America.

In my experience, I usually use Gross Heating Value term, especially in gas project.

Table below summarize the differences between the terms.

 Terms End State of Water Basis Notes Gross Heating Value (GHV) Liquid Wet Measurable from bomb calorimeter using the sample as is. High Heating Value (HHV) or Gross Calorific Value (GHV) Liquid Dry Measurable from bomb calorimeter if the sample is oven dried. Net Heating Value (NHV) or Net Calorific Value (NCV) Vapor Wet Calculated from HHV Low Heating Value (LHV) Vapor Dry Calculated from HHV

Reference:

Clarifying the Uses of Heating Values by Jun Sian Lee, edited by Professor Anthony K. Lau.