The temperature difference of chilled water supply and return (can be 10, 12, 14, 16, 18, and 20).
The chilled water flow in chillers varies at different temperature differences ( T):
Delta T gpm/ton
10 2.4
12 2
14 1.7
16 1.5
18 1.33
20 1.2
Higher T makes the pipe sizes smaller.