In large commercial buildings the chilled water system is usually the largest single energy user. Two plants with identical chillers can perform very differently, and the difference is rarely the chillers themselves. It lies in how water is pumped, balanced and controlled.
Protect the design delta-T
Chillers and pumps are sized for a design temperature difference between supply and return water. When coils are oversized, valves leak through or bypasses stay open, return water comes back too cold. This "low delta-T syndrome" forces more chillers and pumps to run than the load requires.
Pumping strategy
Variable-speed pumping, whether variable primary flow or primary-secondary with variable secondary pumps, lets flow follow the load. The pressure set point should be as low as the critical circuit allows, and resetting it based on valve positions saves further energy.
Valves and balancing
Pressure-independent control valves keep flow stable as the system pressure changes and simplify balancing on large networks. Whatever valves are chosen, the system must be balanced, flushed and filtered properly before commissioning; dirt and air are among the most common causes of poor coil performance.
Controls and sequences
Good sequences stage chillers by load and efficiency, reset the supply water temperature when loads are low and avoid constant cycling. Trending the main values in the building automation system (supply and return temperatures, flows, valve positions, power) turns operation into something that can be measured and improved.
Quick wins on existing systems
- Check that coil control valves close fully and bypasses are not left open
- Review the pump pressure set point and enable reset if possible
- Re-balance after tenant fit-outs and layout changes
- Clean strainers and verify water treatment
- Use trend data to find chillers or pumps running without need
Lessons learned
The best-performing plants are commissioned as a complete system: chillers, pumps, valves, coils and controls together. Designing for maintainability and verifying performance at handover pays back every year the building operates.