period two
Chilled-Water System Design
notes
Production Loop
production pumps
supply tee
return tee
Figure 49
The production pumps circulate water only from the return tee, through a chiller, to the supply tee, and through the bypass pipe. This represents a relatively-small pressure loss and, therefore, relatively-low pump energy. In addition, each pump only operates when its respective chiller is operating.
A primary-secondary system provides a high degree of flexibility in the production loop. Not only are the individual chiller “loops” decoupled from the distribution loop, they are also decoupled from each another. In this configuration, the production loop consists of independent pairs of chillers and pumps. Each pump is turned on and off with its respective chiller. Supply water temperature is maintained by the controls supplied with the chiller. Because the bypass pipe prevents flow interaction between chillers, there is little worry of flow disturbances. In addition, the chillers can be of any type, size, or age, or even from different manufacturers. Because each chiller has a dedicated pump, the chillers can have different evaporator pressure drops.
