Approach temperature (chillers)

Approach temperature is the gap between the refrigerant's temperature and the water it's exchanging heat with inside a chiller's heat exchangers. At the condenser it's the difference between the condensing refrigerant and the cooling water leaving to the cooling tower; at the evaporator it's the difference between the leaving chilled water and the evaporating refrigerant. It's one of the most useful efficiency diagnostics a chiller has: a small, stable approach means the heat exchanger is clean and transferring heat well, while a growing approach is an early warning that tubes are fouling or scaling, or that flow is off — the machine now has to run at a higher lift (and burn more energy) to deliver the same cooling. On a district-cooling or building plant, a creeping approach temperature quietly adds to the energy bill long before anything 'breaks', which is why it's tracked alongside the system's delta-T as part of routine performance monitoring by Al Ghubaiba's chiller team. Catch it early and a tube clean restores efficiency; ignore it and you pay for the loss every month.