• Energy Research

Abstract To alleviate the shortage of natural gas resource and ease carbon emissions, a novel solar-driven combined cooling, heating and power (CCHP) system is designed and optimized using the genetic algorithm in the work. Different from the process of direct combustion in a conventional CCHP system, natural gas is firstly converted into syngas by a solar-driven natural gas reforming step, which is consumed in an efficient tri-generation system. Energy, economic and environmental evaluations on five office buildings in different climate zones in China are implemented to validate the advantages of the proposed system. Results show that the annual maximum primary energy saving, total cost saving, and CO2 emission reduction are 69.76%, 49.80%, and 71.55%, respectively. The system located in severe cold zones, where solar energy is abundant and building requires more heat load in whole year, achieves the highest benefits in comparison with separate systems. Furthermore, the sensitivities on the price fluctuations of electricity, natural gas and solar field to the system profits are investigated, which indicates that the influence of electricity price on the system performance is the most significant. Thus, a promising method for reducing the natural gas consumption and improving the utilization efficiency of solar energy is provided.

Abstract A solar chemical energy storage system with photochemical process and thermochemical process is proposed to convert full-spectrum solar energy into chemical energy. The ultraviolet and part of visible sunlight are firstly absorbed by norbornadiene derivatives, and the norbornadiene derivatives are converted into the related quadricyclane derivatives. When the quadricyclane derivatives are catalyzed, they are converted back to the norbornadiene derivatives for next cycle. The storage and releasing cycle are eco-friendly without CO2 emission. The rest of solar energy, which cannot be used in the solar photochemical process, are exploited by solar thermochemical process, providing heat for methanol decomposition. It is demonstrated that solar photochemical efficiency increases firstly and then it decreases with the increase of cut-off wavelength, while the solar thermochemical efficiency declines with the cut-off wavelength rising. In the hybrid system, the decrease of the solar thermochemical efficiency is balanced by an increase of the solar photochemical efficiency, and the maximum solar-to-chemical efficiency of the hybrid system reaches 68.7%.

Mobilized thermal energy storage (M-TES) system is considered as an attractive alternative to supply heat to distributed heat users, especially when the waste heat from industries is used as a heat ...

Abstract To solve the blocking issue of direct contact thermal storage and further improve the heat exchange efficiency, a novel method that ejecting the molten phase change material (PCM) into the heat transfer fluid (HTF) was proposed in this paper. The experiments were carried out to understand the ejection and breakup behaviors of PCM and investigate the feasibility of this concept. Two properties about ejection and breakup, i.e. jet breakup length (LP) and angle (β), were discussed. The relationship between operation parameters, including ejection velocity, nozzle size, ejection temperature, and particle diameters were quantificationally analyzed. The results shown that there exist four obvious stages of ejection and breakup behaviors: i) 0-40 mm: an approximate horizontal liquid column with smooth surface; ii) 40-110 mm: a slight curvulate liquid column with unstable and fluctuate surface; iii) 110-210 mm: peel-off and superficial breakage; iv) From 210 mm: deposition of PCM droplets. The two properties LP and β shows negative and positive correlation with ejection velocity, respectively. The LP varies from 72.2 mm to 30.2 mm, the β varies from 17.5 ° to 21.0 °. However, the correlation between above two properties and nozzle size and also ejection temperature is on the contrary. The diameter of most PCM particle is in the range of 0-8 mm. The higher ejection velocity, smaller nozzle size, and lower ejection temperature results in smaller particle diameters in breakup processes. Compared with the traditional direct contact thermal storage, the novel method can not only solve the blocking issue but also dramatically enlarge heat transfer area by dispersing molten PCM, which can provide an insight of development of new direct contact thermal storage.

A mobilized thermal energy storage (TES) system has been proposed to recover and use industrial waste or excess heat for distributed users. In this paper, lab-scale test facilities have been built ...

In this paper, the melting and solidification behaviours of the PCM in an indirect contact mobilized thermal energy storage (ICM-TES) container were numerically investigated to facilitate the furth ...

Abstract Based on the thermal response test, a 3-D unsteady-state numerical model for vertical borehole heat exchangers (BHE) was established using the computational fluid dynamics software FLUENT. The unbalanced thermal short-circuiting coefficient was introduced as an index to evaluate the thermal short-circuiting. The factors impacting on short-circuiting, i.e. the grout thermal conductivity, the flow velocity and the operation model were analyzed. The following results could be drawn: first, the thermal conductivity of grout and the borehole depth is proportional to the unbalanced thermal short-circuiting coefficient. Second, the flow velocity is inversely proportional to the unbalanced thermal short-circuiting coefficient and has the greatest impact on thermal short-circuiting. Third, the heat transfer efficiency of the system can be enhanced with the intermittent operation. Additionally, a reasonable range of the grout thermal conductivity and flow velocity were proposed according to the simulation results.

Abstract The displacement ventilation and chilled ceiling (DVCC) is a promising technique for the design of comfortable and energy saving ventilation and air conditioning system. However, dew condensation on the chilled ceiling is a main disadvantage for the application of DVCC system. In this paper, the variation of temperature and humidity in the room with DVCC system is numerically studied. A two-step approach is proposed to solve the issue of dew condensation. The independent operation time of displacement ventilation before running the chilled ceiling is discussed. The results will provide an insight for solving the issue of dew condensation on the chiller ceiling of DVCC system.