Heat exchangers are devices used to transfer heat energy from one fluid to another that is hot fluid to cold fluid. The fluids are separated by a solid wall to prevent mixing.

Chillers are devices used to transfer cold fluid to another liquid medium.

The easiest way to answer this question is to ask a few more; Do you have a facility water supply available? If no, you need a chiller. If yes, then ask another question, will my process temperature be above my facility water temperature? If no, you need a chiller. If yes, a heat exchanger may suit your application. It is generally less expensive than a chiller and more reliable as it has less mechanical components to fail, and if water consumption is not an issue it is more energy efficient as well.

A chiller is always required for temperatures below the normal water temperature or whenever the temperature required is much lesser than ambient temperature.