A New Method to Determine Thermal Properties of the Mixture of PCM and Concrete

Integration of phase change materials in building envelopes is a technology that with high potential to decrease the building energy consumption and improve indoor thermal comfort. Accurate measurement of thermal physical properties of PCM-concretes is very important for simulation and evaluation of its energy saving performance. However, there isn’t an effective way to measure thermal physical properties of PCM-concretes accurately. The shortcomings of using traditional testing methods to measure thermal physical properties of PCM-concretes were firstly analyzed. Then a new method based on the inverse problem was proposed to deal with the measurements of thermal conductivity and specific heat of PCM-concretes during the phase change process. This method transforms the determination process to an optimization problem, which regarded the difference between the measured and calculated heat flux and temperature as the objective function, and the thermal conductivity and specific heat distribution with temperature will be automatically adjusted through the Sequential Quadratic Programming (SQP) algorithm. The equivalent specific heat of 4 wt% and 6 wt% PCM concretes were determined using the proposed methods. The accuracy (the maximum error is less than 2%) is acceptable for engineering use. The influences of temperature segments and optimization algorithms were analyzed. The results showed that, SQP method is with the highest accuracy and least complexity compared with the Particle Swarm Optimization and Genetic Optimization methods. Finally, some suggestions to apply this method to other similar problems were proposed to extend its application scope.