Chilled Water Buffer Vessel Sizing

Apologies if this has been covered before but I couldn't find the answer I was looking for on the forums:

I have a supermarket application using direct secondary cabinets and water chillers. The total chiller capacity is 380kW. There wil be two chillers (190kW each), each with 4 compressors. The fluid is 30% prop glycol with flow and return temps of -6°/0°C.
The shop floor cabinets (around 60 in number) will each have a bypass valve arrangment when cooling is not required.

My first question is do I need a buffer vessel and secondly how do I size it if I do?

Any help would be very much appreciated.

Thanks

Rule of thumb.

Capacity of refrigeration, 380kw, multiply by magic number 6 equals 2280 litres of storage.