Characterizing phase change materials using the T-History method: On the factors influencing the accuracy and precision of the enthalpy-temperature curve

While research on using the latent heat of so called phase change materials (PCMs) for thermal energy storage has gained increasing interest in the last decade, the measurement of its thermal properties are still subject to research. The T-History method has been frequently used by researchers to measure the enthalpy–temperature curve of PCMs but the factors influencing its accuracy and precision have rarely been discussed. This work provides a systematic experimental study of an organic PCM based on different insulated sample holders. It is first shown that the data evaluation method has to be adjusted against noise to improve both accuracy and precision for all experimental setups. The results moreover show that neglecting the insulation thermal mass in the experimental setup leads to systematic errors in the enthalpy results due to oversimplification of the mathematical model. This confirms a previous numerical study by the authors. It is recommended that either the mathematical model or the experimental setup are adjusted in future work to decrease this error. Until then it is generally recommended to use sample holders with a high ratio between the thermal mass of the PCM to the insulated sample holder. This is further supported by a measurement uncertainty analysis via Monte Carlo simulations

Numerical and experimental investigation of an insulation layer with phase change materials (PCMs)

Phase change materials (PCMs) are used in novel thermal insulating materials in order to exploit their high apparent thermal capacity, which is particularly interesting for buildings with moderate thermal inertia because PCMs have a high potential for CO2 reduction in lightweight buildings and their energy consumption as well as for increasing the thermal comfort of the inhabitants. In addition, one of the most promising applications of PCMs is embedding them directly in the insulation layers of a lightweight wall. In fact, due to their apparent thermal capacity, light insulators with embedded PCM particles have good performances in smoothing and shaving of thermal peak loads. Furthermore, in some climatic conditions, they can act as thermal storages by reducing thermal loads in buildings. Many sectors of evidence in the literature indicate that it is necessary to use a hysteresis model with two different curves of specific heat versus melting and solidification to assess the transient thermal performance of PCMs embedded precisely in an insulation layer. The main aim of this research is to develop a detailed dynamic model in order to calculate the effects of PCMs in insulation layers of lightweight walls. In this paper, the results of some actions, used to improve the effectiveness of the models, are investigated. In particular they are the adoption of two distinct cp curves, which improves the accuracy of dynamic simulations and, hence, allows the development of the model using a smaller number of points and a larger time step. Several experimental tests validate the numerical model. Furthermore, this paper presents the way in which the position of the PCM insulation layer, in a typical wallboard, affects the temperature and heat flux, inside each layer, in transient conditions. The results show that, in the case evaluated, the maximum reduction of heat consumption, of about 15%, was obtained when PCMs are located in positions three and four, which are approximately in the middle of the wall. In addition, this specific kind of insulation layer generates a delay of the maximum heat flux that is of about two hours