Understanding Low Delta-T Syndrome in Chilled-Water Systems

nexoradesign.net
Jul 31
2 min read

Chilled-water systems are designed to transport cooling energy from a central chiller plant to air-handling units, fan-coil units, heat exchangers, and other cooling loads throughout a building.

One of the most common performance problems encountered in large chilled-water systems is Low Delta-T Syndrome.

The problem may initially appear simple: the chilled-water return temperature is lower than expected. In reality, however, low ΔT can affect almost every part of the chilled-water system, including:

Chilled-water flow rates
Pumping energy
Chiller staging
Available plant capacity
Differential-pressure control
Cooling-coil performance
District-cooling performance
Plant expansion capability
Overall HVAC energy efficiency

ASHRAE literature specifically identifies maximizing the difference between chilled-water return and supply temperatures as an important chilled-water plant control objective because excessive water flow increases pumping requirements and can negatively affect overall plant performance. (Understanding Low Delta-T Syndrome in Chilled-Water Systems)

Understanding why ΔT deteriorates—and identifying where the deterioration originates—is therefore essential for HVAC designers, commissioning engineers, and facility operators.