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SYS-APM001-EN Chiller System Design and Control 69
• Understand the specific loading/unloading characteristics of the chiller
controller
Bypass flow
• Select a high-quality control valve with linear-flow characteristics
• Select flow-sensing devices that deliver precise, repeatable
measurements
• Minimize control lag by hard-wiring the controls or by selecting devices
that communicate directly
Chiller sequencing
• Temporarily unload the operating chillers before starting the next
• Open chiller isolation valves slowly to encourage stable operation
• Let the operating chiller(s) load almost fully before starting another
• Prevent short-cycling by devising a “stop” strategy based on the power
draw of the operating chillers
Plant configuration
• Consider a series arrangement for small VPF applications to avoid
transient flows
• Assess the economic feasibility of variable primary flow for single-chiller
plants
• Moderate “low T syndrome” by manifolding multiple chilled-water
pumps or slightly oversizing a single chilled-water pump
• Take care to properly manage transient flows regardless of the number of
chillers in the plant
Airside control
• Select slow-acting valves to control the chilled-water coils
• Use more than one air handler and stagger their start/stop times