I would suggest using QVDs. I checked the help and this topic is a little better covered in the QlikView help which still applies in qlik sense because its the same load script language. (just replace QVW with QVF)
I've attached the help for this topic in PDF here. I would suggest looking at option 2 (insert) which will load only the new records from the QVD file.
i'm going to see if we can get an equivalent level of help available in Sense.
QVD_Incremental_Load.pdf 445.4 K