Study On Application Of Phase Change Thermal In Solar Energy Heating System

Along with the growing of environment issues in energy development, ithasbecome a new trend for modern buildings heating to use clean and renewable energyinstead of the traditional ones. The solar energy heating as an efficient, energy-savingand environmental technology emerges as the time requires. It cannotonly meet thedemand of heating in winter, but also provide sanitary hot water all year round, besides,with the development of solar energy heating technology more and more attention hasbeen paid to the study of phase change thermal storage in the solar energy heating syste.In this paper, a certain office building in Chongqing isas experimental platform. Inthe heating system, it adopts flat solar collector in combination with phase change heatstorage device for heating, and the fan coil and users of floor heating as the end part ofthe system. This experimental platform has carried on the theoretical analysis,numerical calculation and experimental research to all part of the heating system.And this paper aims to study method applied to the engineering in high latitude area byanalogy. It mainly studied the following aspects: the thermal storage characteristic ofthe solar system, thermal storage and discharge characteristics of phase change heatstorage device, coupled heat transfer characteristics of solar heating system and phasechange heat storage system. The text will focus on the influence of the flow of thermalfluid and temperature to the heat storage performance of device.First of all, based on the theory of phase change heat storage, this text establishedthe physical model and mathematical model of phase change energy storage tank. Thenumerical calculations are carried out by Fluent software, the law of phase change of asingle energy storage tank can be obtained,besides, under different working conditions,the model of the energy storage tank are carried on the numerical calculation, and stillthe paper analyses the factors, which affect the performance of heat storage device, suchas flow rate and temperature of hot media. From the numerical calculation results, theconclusion is got as follow: Improving the thermal fluid flow or temperature can shortenthe duration of phase change heat storage and enhance the accumulation of heateffect.Besides, the influence on the time of phase transformation by adjusting thespeed.to change flow is more effective than adjusting the inlet temperature of thermalfluid,which means that the influence of heat transfer fluid flowon the phase transitionprocess is bigger than the temperature of the heat transfer fluid. In order to verify the correctness of the numerical simulation results, a solar phasechange heat storage heating test bench is established. The heating system of test benchis composed of eightflat-plate collectors, phase change heat storage system consists ofsix phase change energy storage tank. As to this test bench, the experimenter need tomonitor the internal temperature of the energy storage tank in different solar radiationcondition, and system flow. The test results show that energy storage tank can quicklyenter the latent heat storage phase after the hot fluid temperature and flow rate increases,and latent heat storage duration is shortened before hot fluid temperature and flow rateincreases, then the mechanism of changes of regenerative heat release can be got, whichare consistent with the results of numerical calculation and verifies the correctness ofthe model.By testing the water temperature and the flow rate of solar collector’s main sidepipelne,as well as the water temperature and the flow rate of the inlets and outlets ofdifferent collectors of the loops. The different performance of different collectors arecompared and analyzed and how the heat-collecting capacity of single collector affectsthe total heat-collecting capacity of the whole system. Test results show that in the solarheat-collecting system, while the number of solar collectors is determined, meet thedemand of end users under the circumstances, the system should be tried to reduce thetotal set of heat in collection hot side, and the flow of each collector so the hot mediathrough the single block collector can get larger temperature rise. Thus improve thetemperature of total water in collection hot side as soon as possible to achieve phasetransition temperature, and enhance the accumulation of heat effect. In addition,although the experimental pipeline adopted with reversed return system, as theinfluence of some parts such as flow meter, thermometer makes the collector in differentline loss and some difference in flow rate to lead to set cause heat differences.By testing the solar radiation intensity, the temperature of supply and return waterin the heat storage device, the changes of the flow under different weather, anddifferent time in a day, the coupling trends of the heat-collector capacity and the heatstorage device capacity. The results demonstrate that, when the solar heat and heatstorage in weak coupling, and the number of run panels should be adjusted. When solarradiation is enough, the number of run panels can be reduced. Conversely, when solarradiation is poorer, the operation quantity of the panels should be increased. For thisexperiment platform, on the condition of sufficient sunlight, five flat collectors run withsix phase change heat storage tank can achieve a better coupling. Due to the phase transition temperature is higher (about52℃), and the solarenergy resources of chongqing, the phase change heat storage device in this study has abetter heat storage in the strong solar radiation in July and August. there are many daysthe intensity of solar radiation is above of600~800w/㎡, and daily radiation reachesmore than17MJ/㎡,Energy storage tank can quickly reach phase transition temperatureto store the latent heat. In June and September, even though it can the effects alsoachieve the phase-transition temperature the effect is not as good as that in July andAugust. It is difficult to achieve above phase transition temperature in other months, theeffect of heat accumulation is poor.It concluded that this topic experiment platform has great application potentialincold area,such as Lhasa.etc. where solar energy resources are rich, by comparing solarradiation in Lhasa with that in chongqing. For example, the applicable period for Phasechange heat storage of solar energy heating system is from February to November inLhasa.During this time, the heat reliability of storage can reach88.9%.