Low Chilled Water Delta-T Halved Chiller Capacity in One Building

A chilled water system's delta-T, the gap between warm return water and cold supply water, determines how much cooling a chiller delivers, and a drop in that gap can sharply reduce output even at full compressor speed. In one example, a 300-ton chiller running at 600 GPM fell from a 12°F design delta-T to 5°F, cutting its capacity to about 125 tons. Causes included three-way bypass valves on air handling coils, fouled coil surfaces, and pump speeds set too high, which forced a second chiller to run on peak days. Converting to two-way valves and chemically cleaning the coils restored the delta-T to 10°F, letting one chiller handle the load and saving an estimated $47,000 a year. The article advises measuring supply and return temperatures and comparing the result to design values to diagnose similar problems.