Energy Storage And Release Theory Of Phase Change Material (PCM) And Its Application For Cooling In Telecommunications Base Station (TBS)

The quantity of telecommunications base stations (TBSs) have been increasing with the continuing development of communication technology and electronic industry. The requirement of continuously communicating consumes increasing energy. The energy consumption of air conditioning systems in TBSs accounts for46%of the total energy consumption of TBSs. This large energy consumption demonstrates the significant potential for energy savings. In recent years, the proposed energy savings technologies for space cooling in TBSs consisted of renewable energy, solar energy, wind energy, geothermal energy, et al. However, because of the periodic variation of solar radiation and outdoor air temperature as well as that the cold load in TBSs during nighttime is lower than it during daytime; there exists a mismatch between energy supply and demand. As a result, thermal energy storage technologies, which store and release energy, have drawn significant attention not only to assist in solving this mismatch but to save energy.This dissertation presents the research on energy storage and discharge of phase change materials (PCMs) and its application for cooling in TBSs. Both passive and positive energy storage technologies were studied. A TBS envelope outfitted with a phase change material board (PCMB) and a latent heat storage air handling unit was developed in this dissertation. Simulations of these two applications in one entire year were conducted in five different cities, which locate in different climatic regions. Simple payback period (SPP) and energy savings ratio (ESR) were developed to evaluate these two applications, respectively.A mathematical model based on the moving-source about the heat transfer during phase transition processes is presented and resolved. Dimensionless relationships were developed. The heat transfer rate is showing asq=(?)(|ste|0.5,(κ1/ks)0.5,Fo-0.5) This model is validated using experimental and published data and it was found that it accurately predict the heat transfer processes. When|Ste/(κl/κs)|>1, improving the thermal conductivity of PCMs is effective to enhance the heat transfer. Otherwise, heat transfer temperature difference should be enlarged.Experiments were carried out to verify the proposed mathematical model and figure out the influence of moving of liquid PCM on heat transfer processes. The influence was quantified by comparing the solidification process and melting process under same heat transfer temperature differences. A heat transfer enhancement factorwas proposed to illustrate the influence of the moving of liquid PCM on heat transfer,which was12%for vertical heat transfer and33%for horizontal heat transfer. LiquidPCM’s motion enlarged its melting temperature range, resulting in the extension ofmelting process. However, it did not affect solidification process.Based on the model that was proposed above, the application of passive energystorage technology was proposed through TBS enclosure outfitted with a PCMB.Considering the amount of outdoor natural cool source, the thickness of PCMB andthe coefficient of performance (COP) of air conditioning system, SPP was proposed toevaluate this application. SPP increased from Kunming to Zhengzhou, to Shenyang, toChangsha and to Guangzhou. It decreased with increasing phase transitiontemperature of PCM. When the phase transition temperature is higher than outdoormean air temperature plus5oC, SPP stays almost as a constant.To improve the heat transfer of passive energy storage, the application ofpositive energy storage technology in TBSs is realized by a latent heat energy storageair handling unit. Compared against existing air conditioning system in TBSs in fiveclimatic regions, the energy efficiency ratio (EER′), operating time during differentmodes and ESR were analyzed. The relationships between EER′and outdoor airtemperature as well as ESR and outdoor air temperature were developed. The EER′increased with decreasing outdoor air temperature and the annual mean EER′in thesefive cities was14.04. The ESR by using this unit was up to67%in Kunming with anannual mean value of50%.