Is any problem if whole chiller plant elevation changes?

If the elevations of the water piping was unchanged, you may have increase pressure head which will reduce the pump flow rate. If this is the case, some options are 1. install a higher capacity pump, 2. increase piping size to reduce system pressure losses, or 3. install a parallel water system loop to reduce pressure drop to increase flow rate.

What were pump suction and discharge pressure before change, and what are pump pressures after change?

I would guess larger pump might be least expensive, but you will need to determine.

The standard rule for flow rate is 2-2.5 gallons per minute per ton of refrigeraton effect. 160 Ton would of course be 320-400 gallons per minute. The elevation measured in height along with drag & flow coefficients of the pipe result in the "head' output of the pump.

That is .00757 to .00946 cubic meters per minute per ton. For the 160 ton unit it would be 1.21 to 1.51 cubic meters per minute.

From what you are writing it sounds like you should be able to run a 400 ton chiller.

http://www.hydro-zoneinc.com/ftp@hydro-zoneinc.com/Water%20Treatment%20Information/Engineering%20Formulas.doc

http://www1.eere.energy.gov/industry/bestpractices/software.html#psat

Look down the list here for the PSAT-Pumping System Assessment Tool. It is a great tool for checking your pump sizing, valves, fittings, pump impeller trim & motor sizing.

What are the chiller's Make & Model (ex. if Trane CVHE, RTHB)? Are they equipped with Building/Equipment Automation (ex. UCM, UCP2..)

Ur absolutely right about proportionality of its operation..

What are the inital steps you have taken? (i.e)

Tiil then

Rather then changing your pumps or redesigning your system, go back to your original mfg'r pump flow charts. The chart will show various models @ various heads and GPM and more often then not the Pump Manufacturer can cut you a new impeller to accomodate the additional head. Then your done and you can move on to the next project.

IF there is sufficient room in the pump casing for a new impeller, and IF the motor has sufficient rating to handle a larger power requirement, this is an excellent idea. If either the pump casing or pump motor are too small, this will not work.