| Latent heat storage systems have been applied in many fields such as energy efficient buildings, solar energy systems and industrial waste heat recovery, due to their high energy storage density and small temperature variation from storage to retrieval. In a latent heat storage system, energy is stored during melting and recovered during freezing of phase change materials (PCM). It plays an important role in solving the energy imbalance, improving the energy efficiency and protecting environment. But latent heat storage technology exist two problems: liquid leakage in the solid - liquid phase change process and low thermal conductivities of PCM. In order to overcome the mobility of liquid, in recent years, microencapsulated PCM and shape-stabilized PCM (SSPCM) have been studied to solve the liquid leakage problems. However, the thermal conductivities of these PCM tend to be lower than desired, which may decrease heat storing and releasing rates during melting and crystallization processes, which in turn limits their utility areas. To solve above problems, This paper studied to prepare a new type of heat conduction enhanced SSPCM, Moreover, this paper also applied the SSPCM to radiant floor heating system, and the effect of this new type of radiant floor heating system with heat conduction enhanced SSPCM plates was discussed.This paper firstly proposed to improve the thermal conductivity of SSPCM by addition of expanded graphite (EG), and the new heat conduction enhanced shape-stabilized paraffin/high density polyethylene (HDPE) composite SSPCM were prepared by self-established experimental device. The thermal properties of the new SSPCM were measured by Hot Disk thermal constant analyzer, differential scanning calorimetry (DSC) and scanning electron microscope (SEM).The experimental results showed that when the addition of EG was in the ration of 4.6 wt%, the thermal conductivity of the SSPCM was up to 1.30W.m-1.K-1, more than 4 times of that without any additives, which was far greater than that by addition of other thermal conductivity enhanced additives. The latent heats of these new SSPCM decreased little due to small amount of EG, and the melting temperatures were still constant. In addition, the good uniformity structure was confirmed by SEM.By adjusting the mixture ratio of the solid paraffin and liquid paraffin, a new type of PCM with suitable melting temperature was obtained to use as the energy storage medium of radiant floor heating system. Based on the preparation method in the laboratory, the pilot production process of the heat condution enhanced SSPCM was introduced, and finished 2 tons pilot scale, which demonstrated that the mass production of the heat condution enhanced SSPCM could be implemented by this pilot production process.Finally, a new type of radiant floor heating (RFH) system with heat conduction enhanced SSPCM was presented and discussed. To analyze the effect of this new heating system better, this paper not only built the RFH system with heat conduction enhanced SSPCM plates, but also set up an RFH system without heat storage and an air condition heating (ACH) system for comparison. The experimental results showed that that this new heating system could utilize the nighttime electricity fully to meet the heating demand all day, and the average indoor temperature was about 16℃with small temperature, which demonstrated high thermal comfort degree. Guaranteeing the same indoor temperature for rooms, the running costs of this new heating system was much lower than that of electric floor heating system without energy storage and air condition heating system, with the peak/valley electricity price ratio increased, this new heating system was more economy and energy-saving. |
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