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 deltaT loss under partial load conditions. Based on this indicator, certain problems of system design can be reviewed from the perspective of terminal coupling. (C) 2013 Elsevier B.V. All rights reserved.