TABLE OF CONTENTS "A theory may be so rich in descriptive possibilities that it can be made to fit any data. "
- Phillip Johnson-Laird, The Computer and the Mind
Although most commercial chillers are designed and installed to operate at constant coolant flow rates, the power consumption of their compressors can be altered by modifying the design to incorporate variable coolant flow rates. The issue addressed in this chapter is how to model that explicit flow-rate dependence within the analytic chiller model of the preceding chapters. We'll show how the model is easily expanded to account explicitly for the influence of coolant flow rate. Then we'll validate model predictions against an extensive set of experimental measurements from a large commercial centrifugal chiller [Gordon et al 2000].
Coolant flow rate, in particular at the condenser, could be an additional control variable. Although one incurs the complication and expense of a variable-speed coolant pump, chiller efficiency can be improved. For example, in the centrifugal chiller reported below, the power consumption of the compressor at a given cooling rate and fixed coolant temperatures can change by as much as 10% over a range of realistically implementable condenser coolant flow rates.
Before embarking upon model development, we should address the perceived value of this type of information for the chiller installer and consumer. The simple chiller model adopted here accounts for the power consumption of the compressor only. This also accounts for pressure drops on the refrigerant side of the heat...
