period four
Chiller-Plant Control
notes
System Optimization
▲Chiller
◆Decrease condenser-water temperature
◆Increase chilled-water temperature
▲Chilled-water pump (variable-flow system)
◆Increase chilled-water ∆T
▲Cooling tower
◆Increase condenser-water temperature
▲Condenser-water pump (variable-flow system)
◆Increase condenser-water ∆T
Figure 104
System Optimization
The chiller-plant control system can also be used for system optimization. For the purposes of this discussion, we will define optimization as minimizing the energy used by the chiller plant (including chillers, chilled-water pumps, condenser-water pumps, and cooling tower) while still maintaining comfort or satisfying process loads.
The first step is to examine the energy use of the major components of the chiller plant, to see what can be done to minimize each component individually.
The chiller energy usage can be reduced by lowering the condenser-water temperature or by raising the chilled-water temperature.
In a variable-flow system, chilled-water pumping energy can be reduced by lowering the chilled-water temperature while increasing the system ∆T. With the lower water temperature and increased ∆T, the coil requires less water flow to handle the same load.
Cooling-tower energy can be reduced by increasing the condenser-water temperature. This allows the tower fans to cycle or slow down. Condenser- water pumping energy can be reduced by increasing the ∆T through the condenser side of the system, thereby pumping less water. This is achieved by reducing the water flow through the condenser.
Obviously, looking at only a single component presents a conflicting picture for energy reduction, and a change in one component has an impact on other components. To truly optimize the chiller plant, all components must be analyzed together.
