Trane SYS-APM001-EN System Configurations, Bypass flow, Chiller sequencing, Plant configuration

System Configurations

•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 ΔT 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

SYS-APM001-EN Chiller System Design and Control 69