不同蓄能材料的太阳能热泵系统性能对比

太阳能热泵系统与太阳能集热蓄能技术结合起来,能够很好地克服系统对太阳辐射的依赖性,该文设计了一种蓄能型太阳能热泵热水器系统。对蓄能材料分别为石蜡和癸酸时系统瞬时集热效率和2种材料的体积膨胀率进行了试验研究;在南京地区春季典型工况下,对分别采用癸酸和石蜡为蓄能材料的蓄能型太阳能热泵热水器系统性能系数进行了对比研究。研究结果表明:虽然石蜡体积膨胀率较大,系统的真空管有涨裂的危险,但在不同工况下,采用石蜡为蓄能材料的系统性能系数和瞬时性能系数均高于采用癸酸的系统,且系统稳定性好。

Performance comparison of solar heat pump system with different phase change materials

Abstract: The solar-assisted heat pump system combining with solar energy collection and storage can overcome the reliability on solar energy. A novel solar heat pump water heater integrated with collector, storage and evaporation is presented. The system consists of compressor, water-cooled condenser, solar storage/evaporation/collector, thermal expansion valve and hot water tank. The collection/storage/evaporator integrates the solar collectors, storage tank and evaporator together. The evaporator of the heat pump system is arranged in the solar vacuum tube in the form of a U-shaped evaporator, phase change materials filled in each vacuum evaporation tube. The system separately chooses the paraffin and decanoate as phase change material under the consideration of their capacity, phase change temperature and latent heat of phase change. The experiments were conducted on instantaneous collection efficiency, coefficient of performance, instaneous coefficient of performance and specific volumetric dilatation of decanoate and paraffin. The comparative studies were made on instantaneous collection efficiency, coefficient of performance, instaneous coefficient of performance and time of heating cycling water of the system with decanoate and paraffin under the typical weather conditions in spring in Nanjing. The results show that the instaneous collection efficiency has a negative correlation with the solar energy. In rainy days, the instaneous collection efficiency is higher than that in sunny days because the phase change material store lower energy in the rainy days than in sunny days. The instaneous collection efficiency of the paraffins is higher than that of the decanoate because the capacity and latent heat of paraffin are both higher than that of decanoate. Under different conditions, the coefficient of performance and the instantaneous coefficient of performance of the system filling with paraffin are both higher than the system filling with decanoate, because the paraffin has higher phase change temperature and higher latent heat of phase change. Moreover, the system filling with paraffin has a better stability, its maximum amplitude change is 53.78% while decanoate maximum amplitude changes is 57.17%. However, the vacuum tubes have the danger of splitting up because the the specific volumetric dilatation of the paraffin is 17.17%, while the specific volumetric dilatation of the decanoates is 3.27%. The system arranges brushes outside the evaporation tubes in ranges to solve the problem of splitting up of vacuum tubes. Moreover, the relationship between instantaneous collection efficiency and instantaneous coefficient of performance of the system was studied, the results show that instantaneous collection efficiency changes against the solar energy, it decreases as the solar energy increases, while instantaneous coefficient of performance changes with the solar energy. Under the same solar radiation intensity, through computation the change of instantaneous collection efficiency with solar energy is higher than the change of instantaneous coefficient of performance with solar energy. The water temperature changes with different energy storage materials were also studied. The results show that the system filling with paraffin and decanoate takes 240 and 280 min respectively to heat water. Through linear fitting, the results show that the paraffin has higher temperature increasing slope and higher heating rate.