What is primary/secondary pumping in a chiller plant used for?

• A. A single pump with variable speed to manage flow
• B. A two-pump configuration that decouples systems to maintain stable flow and head, improving efficiency and control
• C. A bypass loop that has no effect on system performance
• D. A pump that only serves the cooling tower

Answer: (B)

Primary/secondary pumping is about decoupling the chiller plant from the building distribution so each loop can be controlled independently. The primary loop, which includes the chillers, is kept at a stable flow and head by its own pumps, while the secondary loop, which feeds the building, has its own pumps to meet varying demand. This separation lets the chillers operate at their optimal flow regardless of building load, enables proper sequencing and staging of multiple chillers, and allows each loop to run with appropriate variable-speed pumping. The result is better efficiency, more precise temperature and pressure control, and smoother operation overall.

The other options don’t fit because a single pump cannot decouple the chiller and building loops, a bypass that does nothing to the system’s flow and head won’t improve performance, and a pump that only serves the cooling tower ignores the crucial distribution side of the system and its impact on building loads.