Study On Thermal Performance Of Phase Change Materials In Energy Saving Buildings

Energy conservation becomes more and more important nowadays all over the world. The phase change materials play important roles in solar energy system, energy saving buildings and heating or air conditioning systems that absorb and release latent heat during the phase change processes. The phase change materials help to overcome the mismatch between energy demand and supply by latent heat storage and releasing when needed. If phase change materials are applied to the exterior-protected construction, it could absorb and store heat that enter the room during the day and release it at night to keep the room temperature in a comfortable range. Thus the heating and cooling energy consumptions of the building would be lowered to achieve the purpose of energy saving.Sodium sulfate hydrated salt is chosen in this paper as it's a byproduct of many chemical processes and a cheap phase change materials with appropriate phase change temperature. It has relatively high latent heat and high thermal conductivity. But it has the problems of phase segregation and supercooling during the phase change process. Thickening agents and nucleating agents added in sodium sulfate hydrated mixture are effective to diminishing phase segregation and supercooling.Different kinds of thickening agents, such as attapulgite, carboxymethyl cellulose sodium, diatomite, were experimented in this paper. Attapulgite is chosen as the optimal thickening agent based on experiments. Different nucleating agents were tested, such as adding borax and nano-silicon dioxide can overcome the supercooling problem, and the phase change temperature of the mixture still remains at 31℃. The phase change temperature of the mixture decreased gradually with the increasing of sodium chloride. Thermal storage materials with different phase change temperature could be prepared via the controlling of the content of sodium chloride. The influences of different types of additives to the latent heat of mixtures with Differential Scanning Calorimetry are investigated which draw a conclusion that the mixture with nano-silicon dioxide has the maximum latent heat.The numerical analysis of the effects of the phase change materials applied in the wall of building is done at last with a simplified model of wall and compared with normal wall without any phase change materials inside. The experimental study and the theoretical analysis are valuable for farther study and applications.