Enter the total water volume of the heating/cooling system this separator will serve, before the simulation starts. It sets how often the water passes through the separator, and with it how fast air and dirt are removed. The results depend strongly on it.
Include the boiler or chiller, all piping on both the primary and secondary side, emitters (radiators, fan coils, in-floor loops), buffer tanks and heat exchangers.
You can change it later under “Air and dirt removal”.