Hi boonchong91,
The "Direct impacts" tab only provides you with the impacts of this particular process (https://greendelta.github.io/openLCA2-manual/processes/tab_direct_impacts.html?highlight=direct%20impacts#direct-impacts). In a unit process database, some processes just don't have direct emissions and the emissions are shown upstream. E.g. heating water with a gas-heated boiler has direct emissions while heating water with electricity has barely direct emissions but upstream the generation of the electricity has.
Hope this helps.
