A chiller reaching 20–25 years of service is a prompt for investigation, not an automatic like-for-like replacement. Start with condition, refrigerant leakage, maintenance history and an actual cooling-load profile. Trend electrical demand, chilled-water supply and return temperatures, condenser-water temperatures and flow over a representative cooling season, then compare current selections at full and part load.
The load profile can expose faults that replacement alone would not fix. On one monitored site, several years of operating data showed unusually low chilled-water return temperatures during peak operation. Investigation traced this to excessive pumping and low delta-T syndrome. The flow problem had to be corrected before a new chiller could be sized with confidence.
Plant-room access and changeover planning belong in early design. Confirm removal and delivery paths, lifting points, equipment weights, pipe connections, pump duty and available electrical capacity. An efficient selection can still become an expensive project if it cannot be rigged into place or requires an unplanned switchboard upgrade.
Handover should demonstrate performance rather than simply record that the chiller starts. Commission staging, minimum-flow protection, pump control, temperature reset and alarms. Capture final setpoints, trends, test sheets and the controls narrative in the as-built and O&M documentation so future operators understand the intended sequence.
The replacement business case should compare the cost of retaining and maintaining the existing machine with the capital, energy and maintenance implications of new plant. The original TPCE study notes that HVAC can account for 50–70% of base-building energy use, with chillers responsible for 25–40% of HVAC energy. Indicative modern efficiencies near 0.15 kWe/kWr can materially outperform older machines around 0.25 kWe/kWr, but savings must be calculated against the site's load profile.
A simulated load test can be completed in one or two days by manipulating water temperature and observing operation from higher to lower load, but it may not represent the building's seasonal behaviour. Longer monitoring through the full cooling season is more informative. Use BMS trends where reliable or temporary data loggers where needed, and clean the heat-exchanger tubes before testing so fouling does not distort the efficiency assessment.
