Upgrading chiller systems. Upgrading chiller systems Choosing the right control logic is an important step when adding new chiller capacity. Using a hastily designed chiller expansion for illustrative purposes, this article describes the many pitfalls that can undermine a project that's not designed right from the outset. Upgrading an existing chiller facility often turns out to be trickier than expected. Adding incremental capacity may induce conflicts in control logic. This article offers guidance for managing chiller-system ugrades.