Dedicated Primary CHW Pumps
The primary dedicated chilled water system shown in the following figure consists of chillers with dedicated chilled water pumps and check valves, and a bypass valve. The chillers are enabled or disabled to match cooling capacity to the building load. While active, a chiller controls the chilled water temperature to the chilled water temperature setpoint. When a chiller needs to be brought on line, its dedicated pump is started first. The pumps have check valves to prevent back flow when a pump is disabled. Finally, the system is equipped with a bypass valve which modulates open as the building flow decreases below the chilled water minimum flow setpoint. When the chilled water pump speed is variable speed, the bypass valve is available for chilled water minimum flow control. When the chilled water pump is single speed, the bypass valve is available for dP control.
Parallel Primary CHW Pumps
The primary headered chilled water system shown in the following figure consists of chillers, primary chilled water pumps, proportional isolation valves, check valves, and a bypass valve. Chillers are enabled or disabled to match cooling capacity to the building load. Proportional isolation valves are connected to the chillers to prevent water from flowing through a disabled chiller. The pumps are piped in a parallel or headered configuration and are sequenced to match the chiller’s chilled water flow requirement. The bypass valve (constant speed pumps) or the pump speed (variable speed pumps) is modulated to control the building dP to the dP setpoint (building dP applies only if there is not a secondary system). The pumps have check valves, which prevent back flow when a pump is disabled. Finally, if variable speed chilled water pumps are selected, this system is equipped with a bypass valve that modulates open as the building flow decreases below the chilled water minimum flow setpoint.
