How do I size a chilled water expansion vessel for a closed circuit system?

The expansion vessel should prevent the built-up of high pressure in case the chiller stops and the water takes the temperature of the surrounding air.You have to calculate the water mass entrapped in the system,and multiply this by the difference in specific volume.
E.g the specific volume of water @ 0°C is 1.000 liter/kg, at 50°C it is 1.012 liter/kg.

Differents parts of HVAC Chilled Water System