Hongxia Zhou

For the design of sustainable buildings, it is crucial with accurate methods to evaluate how alternative constructions will influence thermal comfort, as well as energy efficiency. This study introduces a model to investigate how the use of phase change materials (PCM)in building envelopes can influence the temperature stratification, which also influences the indoor thermal comfort. PCM is characterized by large latent heat in the melting/solidifying process during phase transition. Applications with PCM have been recognized as possible alternatives in building envelopes to improve thermal comfort as well as energy efficiency. The selection of the properties of the PCM, as well as how and where the PCM was installed in the building envelope, are crucial factors to be considered before application in practice.In this study, a simplified experimental set-up including a hot-box was used. The PCM material Climsel28 with different layers thicknesses was installed in the sidewall of a hot-box. Extruded polystyrene (XPS) foam boards were used as wall insulation material in the study. XPS was installed as a reference case and in different layer combinations with the PCM. The sequence of the XPS and PCM was varied. Temperature and heat flux were measured in different positions of the hot-box and on the tested walls. A 3D COMSOL model was developed to study the thermal performance of the system. The model was validated in the study using the collected experimental data. The results indicated that the developed COMSOL model can reasonably predict the performance of the system, both with and without the incorporation of PCM. Additionally, the measured temperature stratification were theoretically validated by the COMSOL model. The study gives indicative guidance of how PCMs can be installed in building constructions elements to reduce temperature peak loads and thus also contributing to an improvement of the indoor thermal comfort.

The thermal performance of building envelopes is essential for building thermal comfort and the reduction of building energy requirements. Phase change materials (PCMs) implemented in building envelopes can improve thermal performance. An explicit finite element method (ex-FEM) has been developed based on a previous study to investigate the heat transfer performance through building walls with installed PCMs. For verification, we introduce an electrical circuit analogy (ECA) method. For model validation, at first, COMSOL is used. For comparison, data were collected from experiments using a small hotbox, part of the sides are covered by PCMs with different configurations. This work shows how the ex-FEM model can predict the wall’s temperature profile with and without incorporated PCM. With the implementation of PCMs, the work problematizes unpredictable influences for modeling. In addition, the study introduces results from simulations of sequencing of PCM layers in wall construction.

To understand the influence of PCM wall configurations on the thermal performance of building envelopes, an explicit finite element model of heat transfer from indoor to outdoor (or vice versa) is developed. The accuracy of this model is first validated against the electrical circuit analogy model, and then compared with the experimental data measured in a Hot-Box device. A good agreement between the simulation results and experimental results is obtained. The results of this study show that the PCM configuration layer sequence significantly will affect the thermal performance of building envelopes and that the FEM model developed is a promising tool, which after some more development may be used for optimising PCM wall configurations.