Gross Calorific Value (High Heating Value) refers to the total heating value of a fuel. Usually in the fuel. The water is mixed with. And when it burns This part of the water is combined with Water that is produced by the burning of Hydrogen, which is partially heated, is used as a latent heat of vaporization. This latent heat. Can not be used in practice. For Gross Calorific Value this does not deduct this latent heat.
Net Calorific Value (Low Heating Value) refers to the heat value that can be used in practice. Which is equal to the Gross Calorific Value minus (the latent heat of condensation X weight of water per unit weight of fuel)
the difference between the Gross Calorific Value and Net Calorific Value for low quality coal. It depends on the moisture content. And the amount of hydrogen produced by the organic matter in the coal.