Evaluation of terminal coupling and its effect on the total delta-T of chilled water systems with fan coil units

• Published in: Energy and buildings Vol. 72; pp. 390 - 397
• Main Authors: Chang, Cheng, Jiang, Yi, Wei, Qingpeng
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 01-04-2014; Elsevier
• Subjects: Applied sciences; Building technical equipments; Buildings; Buildings. Public works; Chilled water system; Computation methods. Tables. Charts; Dynamic simulation; Environmental engineering; Exact sciences and technology; Fan coil units; Hydraulic balance; Low delta-T syndrome; Structural analysis. Stresses; System coupling factor; Ventilation. Air conditioning; Hydraulic balance; Chilled water system; Dynamic simulation; System coupling factor; Low delta-T syndrome; Fan coil units; System evaluation; Chiller; Modeling; Coil; Fan; Hydraulic balancing; Numerical simulation; Coupling; Dynamic model; Application
• ISSN: 0378-7788
• DOI: 10.1016/j.enbuild.2013.11.016

•A dynamic simulation platform for chilled water system is constructed.•System coupling factor is defined to evaluate the coupling degree in FCU system.•Increasing system coupling factor will increase system delta-T loss.•Adding resistance on non-terminal branches should be avoided.
Most chilled water circulation systems with fan coil units suffer from a low temperature differential between the supplied and returned water. On-site investigation shows that the relationship between total cooling consumption and total water flow rate of real systems is different from that of single coil units mainly as a result of the interaction of the terminals. When certain terminals close their water valves, the other terminals have higher water flow rates and lower water delta-T values. This study presents a quantitative analysis of terminal coupling and its effect on system characteristics. System coupling factor is used as an indicator to describe the total degree of fan coil unit coupling in a system. To observe the effect of the system coupling factor, a dynamic simulation platform is constructed and simulation tests are performed. The results show that the higher the system coupling factor is, the larger is the total delta-T loss under partial load conditions. Based on this indicator, certain problems of system design can be reviewed from the perspective of terminal coupling.