Chiller Pump Capacity and Chilled Water Pressure.

Not really sure what your asking. Are you designing a chiller system for water or are you just trying to figure out how it is done? So many things go into the design of any pumping system such as head, GPM, pipe sizing, layout and flow of materials, it it hard to answer a generic question. Sorry!

Your second question is beautifully answered by PWSlack. I try for the first one.

Chilled water system consists of chillers, pumps, storage tanks and load (like AHU).

Small chilled water system have only one tank & only supply pumps which take the chilled water from tank, circulate it through evaporator of chillers and supply to various load points and return back to tank. Chilled water pump discharge pressure depends on the over all pressure drop in the cycle, flow rate and pipe size.

Large chilled water system have two tanks, 'warm water tank' which collects return water from various loads and 'chilled water tank' from where it is sent to loads through supply pumps. Another set of pumps called circulation pumps are used in this system for pumping return water from 'warm water tank' through chillers and discharging to 'chilled water tank' . Discharge pressure of circulation pumps is much lower compared to supply pumps. This second set of pumps are employed to reduce pressure of supply pumps as well as to enhance operational flexibility.