If the centrifugal chiller is vsd then do we need to have primary pump also vsd? Or can it be constant speed also?

Sorrry , i dono t have any experience on chillers.

First of all apologies for the late reply, I have been travelling and so couldn't respond earlier.

Normally, I like to explain the issue but not a lot of information is available on the type of chiller system you are using. Some information would have been helpful.

In the absence of essential data, let me ask you a question, if your chiller flow is reduced, does the flow of primary fluid needs to be regulated? If no, then you don't need vsd primary pump. But in case you answered yes, in that case, you have two options:

1- use a flow regulating device (valve) - Low capital cost, high running cost in comparison to option 2.

2 - install a vfd for variable speed. - high capital cost, energy savings on low loads.