Developing a TRNSYS model for radiant cooling floor with a pipe-embedded PCM layer and parametric study on system thermal performance

Abstract

The design of the radiant cooling floor with a pipe-embedded PCM layer (RCF-PEPCML) lacks a relevant reference basis. Simulation is the best way to determine the optimal design of the system. The simulation research of PCM radiant terminals has been developed, but there is still a need to establish a convenient transient simulation method for RCF-PEPCML, in order to conduct various optimization studies on system design. In order to meet this simulation requirement, a two-dimensional heat transfer model for a pipe-embedded PCM layer (PEPCML) was established. The numerical model was written in FORTRAN language and integrated into TRNSYS to create a new module (TYPE207) for simulating a PEPCML. The accuracy of the new module was verified by experiments conducted in a scaled experiment room with radiant floor cooling. Then, using the newly-built module and TRNSYS, a case study was conducted to explore the effect of several key parameters on the thermal performance of the RCF-PEPCML. The influencing parameters considered include the PCM's phase change temperature, phase change latent heat, and the PCM layer thickness. The results of univariate sensitivity analysis show that these three parameters all greatly affect the thermal performance of RCF-PEPCML. The recommended optimal phase change temperature should meet this condition where the lower limit of the phase change temperature interval is higher than the water supply temperature by 0–1 °C. The optimal phase change latent heat and optimal PCM layer thickness depend on the specific design conditions of the cooling terminal. It is suggested to perform optimization design analysis for specific cases through simulation. The orthogonal test analysis of multiple parameters shows that the optimal design parameters combination for the case study is the combination of a phase change temperature of 20 °C, a phase change latent heat of 160 kJ/kg, and a PCM layer thickness of 15 mm. Among the three influencing factors, the phase change temperature should be given priority.