Hydraulic configuration analysis of chiller-based cooling systems

Abstract

Hydraulic imbalance in chilled water systems remains one of the most underestimated causes of reduced cooling capacity, degraded part-load efficiency, and excessive energy consumption in commercial buildings. Although modern chillers, variable-speed drives, and advanced control algorithms have significantly improved nominal equipment efficiency, real plant performance is frequently constrained by improper flow distribution, uncontrolled mixing, and degradation of the system temperature difference (ΔT) under partial load operation. This study applies a comparative analytical methodology to investigate the relationship between hydraulic configuration, return water temperature, and chiller efficiency in three commonly used chilled water system concepts: constant primary and secondary flow, constant primary and variable secondary flow (primary–secondary), and variable primary flow systems. The analysis focuses on hydraulic interaction between production and distribution circuits, ΔT behavior, flow stability, and chiller loading under full-load and part-load conditions. Using a representative annual cooling load duration profile and a 500 kW chiller as a reference case, seasonal energy consumption and efficiency trends are quantified. The results demonstrate that constant-flow systems are inherently prone to low-ΔT syndrome, while primary–secondary systems remain sensitive to hydraulic decoupler mixing. Variable primary flow systems consistently maintain higher return temperatures, enable effective hydraulic unloading, and achieve the lowest annual electricity consumption. The findings confirm that hydraulic design and flow control strategy are decisive factors for seasonal chiller efficiency, exceeding the influence of nominal chiller performance ratings.