why the HHV number overestimates the actual heat value 1. the presence of metals temperature maybe not sufficiently high to force the reaction, like the oxidation of aluminum 2. the incomplete combustion of organics while all organic material will oxidize in a calorimeter,this will not occur in a full-scale combustor. The amount of unburned organics can vary from 2 to 25%, depending on the effectiveness of the operation Q龙 UNEP 1. the presence of metals 2. the incomplete combustion of organics temperature maybe not sufficiently high to force the reaction， like the oxidation of aluminum while all organic material will oxidize in a calorimeter, this will not occur in a full-scale combustor. The amount of unburned organics can vary from 2 to 25%, depending on the effectiveness of the operation why the HHV number overestimates the actual heat value