Any idea how to estimate the proper system water volume for a dry cooler to take care of 500kW with water as warm as 50C?

Current estimated system water volume around 4000 liters. Question would be if 'artificially' getting higher (say double) would be beneficial or is even required. Target would be to create a small buffer on fluctuations of outside weather (ie. sun shining on dry cooler etc).

I may be using the wrong keywords, but Google and the search function on RE didn't give me anything :/