How does Pack Flow work on the A320?
Source: FCOM A320 familly

From the flight crew operating manual (FCOM) about the pack flow selector (4):


  Permits the selection of pack valve flow, according to the number of
  passengers and ambient conditions (smoke removal, hot or wet
  conditions).
   LO (80 %)  - NORM (100 %) - Hl (120 %).
  
  Manual selection is irrelevant in single pack operation, or with APU 
  bleed supply. ln
  these cases, Hl is automatically selected.
  
  lf LO is selected, the
  pack flow can be automatically selected up to 100 % when the cooling
  demand cannot be satisfied.


So to answer your question directly:


The normal flow (100%) is when the selector is on position NORM.
Position HI adds 20% to the air flow, and LO removes 20%.


In addition:


In LO position, the flow can be increased by the controller up to 100% in case the temperature cannot be obtained with only 80%.
In case of single pack operation, the flow is automatically set by the controller to 120%.