When the primary pumps (headered or dedicated) are constant speed, then a secondary pump arrangement can be selected. The secondary pumps are always headered and can be only variable speed to be able to efficiently control the building chilled water dP. A dP setpoint reset algorithm using valve positions of the main chilled water coils in the building is an option of the selection tree.
Primary Headered with Secondary Chilled Water System
The following figure shows a system consisting of chillers with primary headered pumps (must be constant speed) and secondary variable speed pumps.
The constant speed primary chilled water pumps are sequenced to supply the required chilled water flow for the active chillers. The secondary chilled water pumps are sequenced and modulated to maintain chilled water pressure differential to the building in the most efficient way possible. Check valves are used with each pump to prevent back flow when a pump is off. The isolation valves are piped to the chillers in a dedicated configuration to prevent water from flowing through an inactive chiller.
Primary Dedicated with Secondary Chilled Water System
The Primary Dedicated with Secondary Chilled Water System shown in the following figure consists of chillers with primary constant speed chilled water pumps and variable speed secondary chilled water pumps. The primary chilled water pumps are piped in a dedicated configuration.
The constant speed primary chilled water pumps are interlocked on/off with the chillers. The secondary chilled water pumps are sequenced and modulated to maintain a chilled water pressure differential to the building in the most efficient way possible. Check valves are piped with each secondary pump to prevent back flow when a pump is off.
