Discharge flow is the assumed flow from discharge units. Normally, it refers to the flow entering a pumping station. It is typically expressed in litres per second or cubic metres per hour.
EN 12056-2 gives some figures and rules on how to calculate discharge flow from buildings of different kinds. The calculation is also part of the sizing program in Grundfos WebCAPS and WinCAPS.
The discharge flow changes during the day depending on building usage. This is called the daily profile or discharge pattern. For dimensioning purposes, always use the peak flow in the daily profile. The graph shows the daily profile for a hotel.