Developing a Practical Thermal Performance Index for Radiant Terminals-Structural Thermal Resistance

Radiant terminals have been widely applied in heating and cooling systems. However, few existing thermal performance evaluation indices can reflect the influence of structural forms on heat transfer performance. This study introduces the structural thermal resistance (Rs) to rapidly evaluate the structure form's effects. First, theoretical analysis and experimental tests were introduced. Three types of terminals, including the copper conduit graphite plate (CCGP), plastic tube-embedded metal plate (PTMP), and capillary network-embedded structural plate (CNSP) were tested in the laboratory. Then, the CNSP terminals were taken as validation examples. The results show that the Rs values of the same type of radiant terminal tend to be stable and constant. The variations in Rs within the same type of radiant terminals were small both under cooling and heating conditions. Only when the terminal structure changed, the Rs would change. This suggests that the Rs can reflect the complex heat transfer processes inside the radiant terminals while distinguishing different terminal types. The validation analysis showed an average relative error of 3.4% and 2.9% for cooling and heating, respectively. Lastly, the potential application of Rs in practical applications was discussed, and a Python-based online tool was developed to help design, operate, and evaluate radiant terminals.