Trane SYS-APM001-EN manual Chilled-Water Distribution System, Chilled-water pump

Primary System Components

pumped all the time; however, in systems with very small water pressure drops, this system arrangement may work economically.

Figure 8. Uncontrolled water flow with bypass damper

Bypass

Damper

Airflow

Face

Damper

Additional reference information on the components of a chilled-water distribution system is available in the 2008 ASHRAE HVAC Systems and Equipment Handbook, chapter 12, “Hydronic Heating and Cooling System Design.” 3

Chilled-Water Distribution System

Chilled water is circulated through fixed piping—most commonly steel, copper, or plastic—that connects the chiller with various load terminals. Piping is sized to meet pressure loss, water velocity, and construction cost parameters.

Chilled-water pump

The chilled-water pump creates pressure to circulate chilled water within the loop. Generally, the pump must overcome the frictional pressure losses caused by the piping, coils, and chiller and the pressure differential across open control valves in the system. The pump, while working at the system static pressure, does not need to overcome this static pressure. For example, in a forty-story building, the pump need not overcome the static pressure due to those forty stories.

The chilled-water pump is typically located upstream of the chiller; however, it may be anywhere in the system, provided that the pump:

•meets the minimum pump net positive suction-head requirements. That is, the system pressure at the pump inlet must be both positive and high enough to allow the pump to operate properly;

•maintains the minimum dynamic pressure head at critical system components (usually the chiller). If the dynamic pressure head is not high enough at these components, proper flow will not be established through them;

10 Chiller System Design and Control SYS-APM001-EN