Date of Award
Doctor of Philosophy (PhD)
Zhiqiang (John) Zhai
Michael J. Brandemuehl
Building façade contributes to the overall architectural aesthetic but can be utilized for heat storage when proper systems are incorporated. Latent heat storage such as using a phase change material (PCM) gains growing attentions recently due to its ability of storing significant thermal energy within a small volume, making it one of most promising technologies for developing energy efficient buildings.
This research is focused on modeling and simulation of PCM when integrated into advanced façade systems. The study first reviews the different mathematical modeling methods generally used for PCM's simulations. It categorizes the PCM's numerical models that are implemented for standalone facade systems. The study then evaluates the PCM's models that are integrated into whole building simulation tools such as EnergyPlus, TRNSYS, ESPr etc. It is revealed that the heat capacity method is mostly used in programs, despite its limitations on time and spatial resolutions. Therefore, alternative numerical models are investigated to overcome the above constrains and limitations in current PCM's simulation practice.
Eight potential computational models based on a fully implicit finite volume method are developed in MATLAB/SIMULINK environment, validated using experimental results from the literature and verified against well-known building simulation programs. A linearized enthalpy method with hybrid correction scheme is proposed and validated in this work as an improvement to the existing numerical schemes for implementation into building simulation tools. Through sensitivity analysis achieved by varying the PCM thermal properties, the models have been analyzed for their computational efficiency and prediction accuracy. Some models are found sensitive to melting range of PCM, for example heat capacity method, but less sensitive to the variations of latent heat. Among the correction schemes, the non-iterative scheme is inaccurate due to the significant temperature spikes when PCM changes a state. The iterative and the hybrid correction schemes are computationally efficient and less sensitive to variations of PCM's thermal properties. Hence, these two schemes can potentially be implemented for modeling PCM instead of existing slow and unstable numerical algorithms. Based on this conclusion, a library of modules capable of modeling Advanced Façade Systems, entitled "AdvFacSy" toolbox, is developed in SIMULINK GUI environment. The toolbox can be easily used to evaluate innovative advanced façade systems with and without PCM. Using this toolbox, two PCM-enhanced façade designs are evaluated and general conclusions have been drawn.
Using a novel coupling methodology, several modules from the toolbox are then fully integrated into TRNSYS; a whole-building simulation tool. In addition, a standard TRNSYS module, Type-285, is specifically developed under this research work for modeling multilayer wall with/without PCM. A typical residential building with PCM-embedded walls is analyzed under representative US climates. It is concluded that PCM poorly performs when it is exposed to natural environmental conditions. However, the performance of PCM has indeed been enhanced when activated using other passive strategies.
Al-Saadi, Saleh Nasser, "Modeling and Simulation of PCM-Enhanced Façade Systems" (2014). Civil Engineering Graduate Theses & Dissertations. 52.